agronomy Article Abebe Zerihun 1, * and Deressa Haile 2

Transcription

1 agronomy Article The Effect Organic Inorganic Fertilizers on Yield Two Contrasting Soybean Varieties Residual Nutrient Effects on a Subsequent Finger Millet Crop Abebe Zerihun 1, * Deressa Haile 2 1 Bako Agricultural Research Center, P.O. Box 03, West Shoa, Ethiopia 2 Deutsche Gesellschaft fur Internationale Zusammenarbeit (GIZ) GmbH, P.O. Box , Addis Ababa, Ethiopia; haile.deressa@giz.de * Correspondence: baatiree@gmail.com; Tel.: Academic Editor: Francesco Montemurro Received: 5 April 2017; Accepted: 17 May 2017; Published: 12 June 2017 Abstract: The problems low soil fertility resulting from continuous monocropping, crop residue removal limited fertilizer use represent key challenges to produce surplus food for ever increasing population Ethiopia. However, practices crop rotation integrated sources fertilizer uses could potentially improve soil fertility productivity. In , soybean with different trials consisting two soybean varieties (Boshe Ethio-ugozilavia), three levels farm yard manure (FYM) (3, 6 9 t/ha) three phosphorus levels (8, kg P ha 1 ) were combined in factorial arrangements. Two soybean varieties receiving no fertilizer application followed by finger millet receiving a recommended rate (20 kg P/ha) were included. The experiment was laid out in a romized complete block design with three replications. In , finger millet was planted on each soybean plot as per previous treatment arrangements to evaluate effect precursor crop (soybean) integrated fertilizer application on yield performance subsequent finger millet. Soil ph, organic carbon, total nitrogen available phosphorus before planting after crop harvest soybean in each year showed treatment differences. Both precursor crop fertilizer application had a positive effect on soil fertility status, hence, improved performance subsequent finger millet. On or h, since rainfall amount distribution were different in seasons, response soybean varieties to applied fertilizers was significantly affected, correlation between soybean yield annual rainfall was strongly positive. Use an early maturing soybean variety (Boshe) with lowest rates organic inorganic fertilizers gave significantly higher yield in 2012 (short rainy season) compared with or treatment combinations. In 2014 cropping season, however, Ethio-ugozilavia showed greater yield performance with combined application 3 t FYM/ha 1616 kg PP/ha followed by 3 t FYM 88 kg P/ha. Hence, it is recommended to use Boshe variety under a short rainy season under a low soil fertility status, while variety Ethio-ugozilavia can be used under good rainy soil fertility management conditions. Considering residual effects, use early maturing soybean variety as a precursor with 3 t FYM/ha 8 16,816 kg P/ha during short rainy season could enhance yield subsequent finger millet. On or h, use late maturing soybean variety as a precursor with higher organic fertilizer rates (6 9 t FYM/ha) resulted in a significant yield increase subsequent finger millet. The use a late maturing variety soybean with lower rates organic manure resulted in a finger millet yield comparable to farmers practice, indicating that this option can be adopted by smallholder farmers who cannot produce sufficient organic manure. This study showed that planting finger millet after a soybean precursor crop even without fertilizer application could give better yield economic benefits as it saves 70 85% chemical fertilizer costs compared to farmers practice. Agronomy 2017, 7, 42; doi: /agronomy

2 Agronomy 2017, 7, Keywords: soybean; finger millet; crop rotation; FYM; phosphorus; rainfall 1. Introduction Declining soil fertility is a main reason for slow growth in food production in Sub-Saharan Africa [1]. Low soil fertility due to monoculture cereal production systems is recognized as one major causes for declining per capita food production). A declining soil fertility is also an important bottleneck for smallholder cereal producers in central western parts Ethiopia [2]. Continuous monocultures cereals also result in reduction yields soil nutrients, particularly nitrogen [3,4]. Declining yield soil fertility as a result continuous mono-cropping have also been reported for finger millet [5 7]. Crop rotation is considered to be a key cultural practice to avert problem mono-cropping by enhancing soil fertility crop productivity. Legume-based crop rotations have positive effects on soil fertility because legumes fix N contribute nutrients carbon in addition to litter fall residue decomposition [8,9]. According to Zerihun et al. [2], a 9 35% yield advantage was gained due to crop rotation practices compared to yield mono-cropped maize. Anor study showed that effect inoculated soybean as precursor crop resulted in a 15 21% yield increase maize over mono-cropped one [10]. However, application fertilizer to soybean significantly enhanced grain yield while at same time increasing biomass that drops as litterfall contributes to soil organic build up fertility improvement [3]). Studies show that rainfall soil fertility variability are main factors influencing response crops to applied nutrient sources. Tropical sub-tropical soils are variable in terms both physical chemical properties, which affect crop responses to different fertilizer inputs. For instance, spatial variability soil organic carbon, total or available nitrogen, available phosphorus soil ph are some factors [11]. The significant role spatial variability nitrogen phosphorus highly affected crop responses [6]. In addition, appropriate rainfall amount distribution not only enhance yield, but also reduce year to year variability [12]. Soybean is a pulse crop with multiple food economic advantages for small-scale farmers. It is used as food for home consumption, raw materials for local factories feed for animal dairy or fattening farms [13]. In addition, soybean has capacity to fix atmospheric nitrogen from air through symbiosis with rhizobium bacteria thus contributes to improved soil fertility when grown in rotation with cereals [13,14]. It also contributes to increased soil organic N carbon through its fallen senescent leaves below ground parts [15]. As a result, it has an additional advantage reducing N fertilizer requirement for subsequent crops in a rotation. Therefore, soybean is an important crop with multiple benefits, which can be grown in rotation with cereals like maize, finger millet sorghum. Despite se advantages, productivity soybean is limited due to lack improved varieties poor soil crop management practices. As a result, smallholder farmer yield for crop is far below potential production. For instance, national average yield soybean varied from 1.8 t ha 1 in 2012 to 2.0 t ha 1 in 2013 while potential yield obtained from on-station on-farm research fields was t ha 1, respectively [16]). Low soil nitrogen phosphorus are among major factors limiting production productivity legume crops. Legume plants that depend on biological N 2 fixation for ir N supply require more P than plants receiving fertilizer N since reduction atmospheric N by nitrogenous system is a very energy-consuming process. Hence, plants require more P or nutrients for symbiotic N fixation than for general plant metabolism [17,18]. Nitrogen is most important nutrient for crop production, its deficiency occurs in most countries world [18]. Evidence shows that use organic fertilizers combined with inorganic sources enhances nutrient availability, optimizes soil environment improves crop productivity [1]. To this end,

3 Agronomy 2017, 7, appropriate combination organic inorganic fertilizers sources for specific soil type is Agronomy 2017, 7, needed to improve soil fertility productivity crops. The objective this study was, refore, to evaluate refore, to effect evaluate combined effect usecombined improved use soybean improved varieties, soybean organic varieties, fertilizer organic (farm fertilizer yard manure) (farm yard inorganic manure) phosphorus inorganic on phosphorus yield on soybean yield under soybean variable under rainfall variable rainfall soil fertility conditions soil fertility conditions to furr evaluate to furr residual evaluate effect residual soybean effect assoybean a precursor as a precursor with combined with fertilizer combined application fertilizer yield application performance yield performance a subsequent a subsequent finger millet finger crop. millet crop Materials Methods The The experiment was was conducted at at Bako main research site for four ( ) consecutive years. years. The The experimental site site is located is located in in sub-humid sub humid areas central Western Ethiopia, it lies at a latitude a latitude 9 6 N, 9 6 longitude N, longitude E E mm above sea sea level. It It is a warm sub humid sub-humidclimate with with annual annual mean mean minimum minimum maximum air airtemperatures C C 29.7 C, 29.7respectively. C, respectively. The The area received received average average annual annual rainfall rainfall mm mm (2012), (2012), mm mm (2013), (2013), mm (2014) mm (2014) mm mm 994 mm (2015) with maximum precipitation recorded in months May August (Figure 1). 994 mm (2015) with maximum precipitation recorded in months May August (Figure 1). Figure 1. Mean monthly rainfall at Bako Agricultural Research Center, Ethiopia, Figure 1. Mean monthly rainfall at Bako Agricultural Research Center, Ethiopia, The The soil soil experimental site site is reddish-brown, reddish brown, nitosol. It is an acidic soil witha a ph range The The area area is a mixed is a mixed farming farming zone zone is oneis one most important most important maize (Zea maize mays (Zea L.) mays growing L.) beltsgrowing Ethiopia, belts in Ethiopia, cultivations cultivations tef (Eragrostis tef (Eragrostis tef(zucc.) Trotter, tef(zucc.) finger Trotter, millet finger (Eleusine millet (Eleusine coronata) common coronata) bean common (Phaseolus bean vulgaris (Phaseolus L.), sorghum vulgaris (Sorghum L.), sorghum bicolor (Sorghum L.), noug bicolor (Guizotia L.), abyssinica noug (Guizotia Lf.) soybean abyssinica (Glycine Lf.) max L.) soybean are common. (Glycine The max cropping L.) are system common. The area cropping is predominantly system maize-based area is predominantly maize based mono cropping with low soil fertility, which directly influences mono-cropping with low soil fertility, which directly influences production productivity production productivity cultivated crops. cultivated crops Soil Sampling 2.1. Soil Sampling Initial composite soil samples were collected from a depth 0 30 cm before planting Initial composite soil samples were collected from a depth 0 30 cm before planting soybean soybean trial in Soil samples were also taken from each plot after soybean was trial in Soil samples were also taken from each plot after soybean was harvested harvested to assess changes in soil fertility status due to effect soybean precursor crop to assess changes in soil fertility status due to effect soybean precursor crop integrated integrated application organic inorganic fertilizers. Soil ph was measured using a digital ph application (H2O) meter. organic The Walkley Black inorganic [19] fertilizers. method was Soil followed ph was for measured determination using a digital soil ph organic (H 2 O) meter. carbon The (%OC), Walkley Black whereas [19] method cation exchange was followed capacity for(cec, determination centimol (cmol)/100 soil organic g soil) carbon was (%OC), analyzed whereas using ammonium cation exchange acetate. capacity Total (CEC, nitrogen in centimol (%N) (cmol)/100 available phosphorus g soil) was analyzed (mg kg 1 soil) using ammonium were analyzed acetate. by Total Kjeldahl nitrogen (Jackson, (%N) 1958) available phosphorus Bray II ([20] methods, (mg kg 1 respectively. soil) were analyzed by Kjeldahl The (Jackson, result initial 1958) soil analysis Bray showed II ([20] that methods, ph respectively). was in strongly acidic range as per stard The result classification initial soil procedure analysisby showed [21] (2008). that Total phnitrogen was in strongly sites was acidic highly range variable as per stard found classification in low (2012) procedure to medium by [21] (2014) (2008). range. Total The nitrogen available phosphorus sites was content highly variable soil was found categorized in low under (2012) moderate to medium range (2014) for both range. cropping The available seasons. Similar phosphorus to soil content nitrogen, organic soil was categorized carbon content undervaried moderate in each range season, for both though cropping it was in seasons. medium Similar range to(table soil nitrogen, 1). organic carbon content varied in each season, though it was in medium range (Table 1). Table 1. Soil physico chemical properties experimental area before soybean planting. Year ph (H2O) P (mg kg 1) Total N (%) OC (%) CEC (cmol kg 1 ) K (cmol kg 1 ) Exch.Acidity (cmol kg 1 ) Texture

4 Agronomy 2017, 7, Table 1. Soil physico-chemical properties experimental area before soybean planting. Year ph (H 2 O) P (mg kg 1 ) Total N (%) OC (%) CEC (cmol kg 1 ) K (cmol kg 1 ) Exch.Acidity (cmol kg 1 ) Texture Clay Clay Cmol kg 1 = centimol per kg, Exch.Acidity = Exchangeable acidity (cmol kg 1 ) 2.2. Experimental Procedures A two-year soybean-millet rotation, which was conducted twice (i.e., same two-year rotation experiment was replicated twice over time, in in ), in same general location, in fields with a similar fertility cropping history. In cropping seasons, soybean trial consisted three factors, namely two soybean varieties (Boshe Ethio ugozilavia), three levels organic fertilizer (3, 6 9 t/ha farm yard manure (FYM)) three levels phosphorus fertilizer (8, kg P/ha) in separate plots. These factors were combined in factorial arrangements laid out in a romized completed block design (RCBD) with three replications. In addition two separate reference trials were conducted consisting : (A) a two-year soybean-millet rotation in which no fertilizer or amendment applications were applied in Year 1; (B) a two year continuous millet-millet monoculture planting, in which recommended chemical fertilizer applications (20 kg P/ha) were applied only during first year two-year planting. The Boshe variety is an early type ( days to maturity), whereas Ethio-ugozilavia is a late type ( days to maturity). The same experimental plots a Year 1 for two seasons ( ) were maintained to furr evaluate effect residual fertilizers amendments applied during Year 1 rotation on yield millet (which was second crop in rotation). Therefore, millet was planted in second year rotation, in fields that in previous year were planted with: (a) a previous soybean crop that received fertilizer or amendment applications as per treatment combinations; (b) a previous soybean crop that received no fertilizer or amendment applications; (c) a previous millet crop that had received a recommended chemical fertilizer application. An improved variety finger millet (Gute) was used as a test crop for all experimental plots. This variety has an erect growth habit matures within days. Its yield potential under research is t/h, whereas it provides t/ha under farmers management. The experimental plots for soybean trial were plowed three times at different time intervals starting from mid-may leveled manually prior to field layout. However, plots maintained for following millet planting were prepared by human labor without mixing soil each experimental plot. Decomposed air-dried FYM (20% moisture content) was applied as per treatments incorporated manually into soil, one month before soybean planting. Phosphorus fertilizer in form di-ammonium phosphate (DAP) was applied at time planting. Each experimental plot had 3.2 m 3 m gross area distance between block was 1 m, while distance between plot was 50 cm. The reference plots had also same plot sizes with main soybean-millet rotation experimental plots replicated three times. The spacing for soybean was 40 cm between rows 10 cm between plants planted on 10 June (2012) 15 June (2015). On or h, spacing for finger millet was 40 cm between rows planting was done on 15 June (2013) 10 June (2015) by drilling in manually-prepared rows, population was thinned 5 cm between plants after seedlings emerged. At time agronomic maturity, both crops were harvested from net plot areas 2.4 m 3 m by excluding border rows. The Boshe variety was first harvested at end October, while Ethio-ugozilavia was harvested after mid-november. St count at harvest was counted from net plot area, six central rows. The grain yield soybean finger millet was measured using electronic balances. Grain yield was adjusted to stard moisture contents for soybean to 10%, i.e., adjusted yield = actual yield 100-M/100-D, where M is measured moisture content. The Finger

5 Agronomy 2017, 7, millet yield was sun air dried for four days after threshing before measuring grain. Finally, yield data for both crops were subjected to analysis variance using GenStat-15 stware. Means were separated using least significant value at p < 0.05 probability level. Sigma plot Version 10 was used to sketch bar graphs. 3. Results The analysis variance revealed that seasonal variations highly affected (p < 0.001) yield performance soybean varieties in combination with integrated fertilizer application (Table 2). These significant variations were due to high rainfall variability in each season to soil fertility dynamics experimental site. Therefore, comparison treatment means was done for each cropping season individually. Even though soybean varieties were significantly different in ir yield performance, significant interactions were observed between varieties applications FYM P (Table 2). Table 2. Combined ANOVA table for yield performance soybean as affected by varieties, FYM P fertilizers application in cropping seasons at Bako, Ethiopia. Source Variation d.f. Mean Square Variance F Probability Yr (Year) 1 12,715, <0.001 SBv (Soybean varieties) 1 2,899, <0.001 Farm Yard Manure(FYM) 2 114, Phosphorus(P) 2 109, Yr * SBv 1 337, Yr * FYM 2 248, SBv * FYM 2 439, Yr * P 2 329, SBv * P 2 391, FYM * P 4 498, Yr * SBv* FYM 2 211, Yr * SBv* P 2 371, Yr * FYM * P 4 164, SBv * FYM * P 4 654, Yr * SBv * FYM * P 4 122, Blocks 2 1,991, <0.001 Residual , Total Since seasonal variations significantly affected performance crop, overall mean for each season indicated that significantly less yield was obtained in 2012 (2060 kg/ha) season as compared to 2014 (2760 kg/ha). Overall, a 33% yield reduction was observed in short rainy season. The main reason for yield reduction in 2012 was due to cessation rainfall from time pod setting to near to physiological maturity (Figure 2). Moreover, annual rainfall amount in this season was 866 mm, whereas it was 1067 mm in 2014 cropping season. Correlation between yield annual rainfall for cropping seasons also showed a strong positive correlation (R 2 = 0.96), indicating that yield could be highly affected both by amount rainfall by its distribution. This effect moisture stress at a critical stage soybean crop led to forced maturity to a significant reduction in its potential yield in accordance with or studies [22]). In same report, it was shown that a significant lack water during flowering to pod setting leads to physiological changes in plant, such as stomatal closure leaf rolling, consequently, premature fall flowers leaves pod abortion, which ultimately results in yield reductions [22].

6 Agronomy 2017, 7, Agronomy 2017, 7, Agronomy 2017, 7, Figure Figure Daily Daily rainfall rainfall (mm) (mm) versus cumulative rmaldegree degreedays days (DD) (DD) at at Bako Bako Agricultural Agricultural Research Research Center, Center, Ethiopia, Ethiopia, for for cropping seasons. seasons. Note: Note: solid solid line line indicates indicates cessation rainfall for 31 days during pod setting (2012), whereas dashed line (2014) indicates cessation Figure 2. Daily rainfall rainfall for 31 (mm) days versus during cumulative pod setting rmal (2012), degree whereas days (DD) dashed at Bako line (2014) Agricultural indicates cessation at time near physiological maturity. cessation Research atcenter, time Ethiopia, near physiological for 2012 maturity cropping seasons. Note: solid line indicates cessation rainfall for 31 days during pod setting (2012), whereas dashed line (2014) indicates Application increased rates farm yard manure considerably enhanced soybean yield in Application cessation More than time a 8% 16% increased near physiological yield rates increase farm maturity. was yard obtained manure when considerably 9 t FYM/ha were enhanced applied soybean as compared yield in with More than lower aapplication 8 16% yieldrates increase (3 t/ha was obtained 6 t/ha). when However, 9 t FYM/ha re wereno applied significant as compared yield Application increased rates farm yard manure considerably enhanced soybean yield in with differences lower observed application due to rates FYM application (3 t/ha in t/ha). The enhanced However, crop re response were to nofym significant in 2012 yield More than a 8% 16% yield increase was obtained when 9 t FYM/ha were applied as compared differences cropping observed season is attributed due to FYM to improved application soil inmoisture The holding enhanced capacity cropduring response to short FYMrainy with lower application rates (3 t/ha 6 t/ha). However, re were no significant yield 2012 season, cropping addition seasonto is attributed nutrient to supply. improved Or soil findings moisture confirm holding that high capacity manure during application short rates differences observed due to FYM application in The enhanced crop response to FYM in 2012 rainy season, significantly in addition reduced to soil nutrient water evaporation supply. Or as compared findings to confirm control that treatment high manure application increased soil cropping season is attributed to improved soil moisture holding capacity during short rainy rates significantly water storage reduced capacity soil during water evaporation period pick as compared growth on to maize control [23]. season, in addition to nutrient supply. Or findings confirm that high treatment manure application increased rates soil water storage In addition, capacity during application period organic pickmanure growth on significantly maize enhanced [23]. soybean yield as significantly reduced soil water evaporation as compared to control treatment increased soil compared In addition, to control application treatment. organic Significant manure yield significantly increases over enhanced control soybean were recorded yield as by compared 192% water storage capacity during period pick growth on maize [23]. in % in 2014 (Figure 3). Corroborating se results, or finding indicated that organic to control In addition, treatment. application Significant yield organic increases manure oversignificantly control were enhanced recorded soybean by 192% yield inas 2012 manure supplies nutrients throughout season for growth development crop, in compared 84% in 2014 to (Figure control 3). treatment. Corroborating Significant se yield results, increases or over finding control indicated were recorded that organic by 192% manure addition to improving soil moisture holding capacity, hence, increased productivity [3] supplies in 2012 nutrients 84% in throughout 2014 (Figure 3). season Corroborating for growth se results, development or finding indicated crop, that in addition organic to improving manure supplies soil moisture nutrients holding throughout capacity, season hence, for increased growth productivity development [3]. crop, in addition to improving soil moisture holding capacity, hence, increased productivity [3] Figure 3. Effect FYM application rates on yield soybean varieties in cropping seasons at Bako, Ethiopia. Figure 3. Effect FYM application rates on yield soybean varieties in cropping Figure In Effectcropping FYM application season, rates highest on yield significant soybean yield varieties was obtained 2012 from 2014 Boshe cropping variety seasons at Bako, Ethiopia. when seasons treated Bako, with Ethiopia. combined application 9 t FYM /ha 24 kg P/ha followed by treatment In 2012 cropping season, highest significant yield was obtained from Boshe variety when treated with combined application 9 t FYM /ha 24 kg P/ha followed by treatment

7 Agronomy 2017, 7, In 2012 cropping season, highest significant yield was obtained from Boshe variety Agronomy 2017, 7, when treated with combined application 9 t FYM /ha 24 kg P/ha followed by treatment combination 3 t FYM/ha 24 kg P/ha (Figure 4). Application 6 t FYM/ha with 16 kg P/ha combination 3 t FYM/ha 24 kg P/ha (Figure 4). Application 6 t FYM/ha with 16 kg P/ha also also significantly significantly increased increased grain grain yield yield as compared as compared to or to or treatment treatment means means (Figure (Figure 4). In general, 4). In general, for for Boshe Boshevariety, a a100% 200% % yield increase was wasobtained obtainedwith witha acombined application application organic organic inorganic inorganic fertilizers fertilizers when when compared to to control. Similarly, Ethio-ugozilavia Ethio ugozilavia yields were greatest with with highest highest application application rates rates FYM FYM (9 (9 t/ha) P (24 kg/ha). A linear increase yield was wasobserved when 9 9t FYM/ha t were were applied applied with with increased rates rates P in P in 2012 (Figure 4). This result in agreement with anor research finding shows shows that that yield yield could increase furr with application higher doses organic manure inorganic fertilizer since it it could enhance soil moisture holding capacity capacity in in short short rainy rainy season, season, in in addition to soil fertility improvement [24]. [24]. In Inor or studies, it it was was shown shown that that high high manure manure applications applications significantly significantly reduced reduced soil water soil water evaporation evaporation throughout throughout growing growing period period as compared as to compared controls to controls significantly significantly increased soil increased water soil storage water capacity; storage capacity; hence, it hence, was advised it was advised to apply to apply during dry or short rainy seasons [23]. during dry or short rainy seasons [23]. Figure Figure 4. Effect 4. Effect combined combined applications different rates FYM FYM phosphorus fertilizer fertilizer on on yield yield soybean soybean varieties varieties in in (left) (left) 2014 (right) cropping seasonsat at Bako, Bako, Ethiopia. Ethiopia. In In cropping season, response soybean varieties varieties to combined to combined applications applications organic inorganic fertilizerwere weredifferent differentcompared comparedto tothat that (Figure (Figure 4). 4). The The highest highest significant significant yield yield from from Boshe Boshe variety variety was was attained attained at at combined combined application application 6 t FYM/ha 6 t FYM/ha 8 kg P/ha followed by combination 3 t FYM/ha 24 kg P/ha. The combination lower rates 8 kg P/ha followed by combination 3 t FYM/ha 24 kg P/ha. The combination both fertilizer sources (3 t FYM/ha 8 kg P/ha) showed a similar effect on yield performance with lower rates both fertilizer sources (3 t FYM/ha 8 kg P/ha) showed a similar effect on yield that highest rates, but resulted in a 53% yield increase over control. Likewise, Ethiougozilavia variety showed highest yield performance when 3 t FYM/ha was applied with 16 kg performance with that highest rates, but resulted in a 53% yield increase over control. Likewise, Ethio-ugozilavia variety showed highest yield performance when 3 t FYM/ha was P/ha 8 kg P/ha, which resulted in a respective yield increase 100% 81% over control applied (Figure with 4). 16 This kgresult P/haindicate 8 kgthat P/ha, medium whichor resulted late maturing in a respective types yield soybean increase compete 100% for 81% resources over differently control (Figure due to 4). This differences result indicate length that medium ir growing or late maturing period types or growth soybean compete characteristics. for resources Ronner et differently al. [14] also due showed to that differences varietal in differences lengthin nodulation ir growing capacity, period root or growth growth characteristics. development Ronner capacity et al. [14] also nutrient showed sink that resulted varietal in different differences resource in nodulation use. The capacity, current root result growth also confirmed development that with sufficient capacity rain (2014), lower nutrient doses sink resulted organic in fertilizer different resource combined use. with The current optimum result doses also inorganic confirmedfertilizers that withsignificantly sufficient rain enhance (2014), crop lower productivity. doses organic This fertilizer might combined be due to with optimum optimum moisture doses temperature inorganic fertilizers that might significantly contribute enhance to high crop decomposition productivity. This rates might organic be due manure to optimum in moisture release temperature nutrients for that might crop. However contributeavailable to high decomposition phosphorus rates might organic not be quite manure enough for in growth release nutrients crop [25] for crop. However available phosphorus might not be quite enough for growth crop [25] Soil Fertility Status after Soybean Harvest 3.1. SoilThe Fertility result Status after analysis Soybean variance Harvest revealed that soil ph, organic carbon, total nitrogen available The result phosphorus analysis were highly variance (p < 0.01) revealed varied across that soil cropping ph, organic seasons carbon, (Table total 3). However, nitrogenno available significant phosphorus effects for were each observed highly (p parameter < 0.01) varied were recorded across cropping with respect seasons to (Table main 3). effects However, ir interaction three factors. The observed seasonal variation may be due to history soil fertility experimental sites, which were selected from different sites at Bako research

8 Agronomy 2017, 7, no significant effects for each observed parameter were recorded with respect to main effects ir interaction three factors. The observed seasonal variation may be due to history soil fertility experimental sites, which were selected from different sites at Bako research site. The result initial soil analysis also confirmed that re were considerable variations in soil chemical properties (Table 1). For instance, total nitrogen site was significantly varied found in low (2012) medium (2014) ranges. Table 3. Combined analysis variances for ph, organic carbon, total nitrogen extractable phosphorus after soybean harvest in cropping seasons at Bako, Western Ethiopia. Source Variations d.f. Probability Level (p < 0.05) ph (H 2 O) OC (%) TN (%) P (mg/kg ) Yr (Year) 1 <0.001 <0.001 <0.001 <0.001 SBv (Soybean varieties) Farm Yard Manure (FYM) P Yr * SBv Yr * FYM SBv * FYM Yr * P SBv * P FYM * P Yr x SBv * FYM Yr * SBv* P Yr * FYM * P SBv * FYM * P Yr * SBv * FYM * P Blocks Residual Total In 2012 cropping season, soil ph after soybean harvest ranged from , which was moderate to strongly acidic (Table 4). Application FYM did not significantly affect soil ph though re is a slight increase when compared to control plot. This might be due to buffering capacity organic matter by releasing some organic compounds that fix H +, AL +3 or cations [25]. Soils with a high amount organic matter due to addition organic materials have high cation exchange capacity (CEC) buffering capacities to stabilize soil ph [10]. Organic carbon nitrogen content also showed little variation due to treatment applications (Table 4), but as per classification, se values are found under moderate ranges [26] Since rainfall amount distribution over season (2012) were unexpectedly very low, decomposition rates applied organic manure soybean litter fall might be considerably affected, hence, buildup soil organic matter may have temporarily been decreased [25,27]. On or h, re were slight improvements organic carbon content due to precursor crop combined application fertilizers. For instance, early type soybean precursor with combined application 9 t FYM/ha 16 kg P/ha increased organic carbon content soil by 16% compared to result obtained before planting (Table 1). The available phosphorus was also found in low range, which could be due to lower soil organic matter status available phosphorus experimental soils, which were dominated by HPO 4 2 anion found in strongly acidic soils [10,27].

9 Agronomy 2017, 7, Table 4. Effects soybean varieties, FYM inorganic P fertilizer application on soil ph, organic carbon, total nitrogen available phosphorus after soybean harvesting in 2012 cropping season at Bako, Western Ethiopia. Fertilizer ph (H 2 O) TN (%) OC (%) P (mg/kg) FYM (t/ha) P (kg/ha) Boshe Ethio Boshe Ethio Boshe Ethio Boshe Ethio Mean LSD NS NS NS NS CV In 2014 cropping season, however, soil chemical properties experimental site after soybean harvesting were completely different as compared with 2012 due to differences in rainfall amount distribution that might have affected organic matter decomposition. Soil ph ranged from , which is strongly acidic (Table 5). Organic carbon content soil was slightly improved due to application organic manure as compared to control [27,28]. For instance, application 9 t FYM/ha with various rates phosphorus resulted in organic carbon content ranging from %, which was increased by 5 19% over control plot, respectively. Growing soybean even without fertilizer application improved organic carbon soil by 13% compared with value observed prior to planting (Tables 1 5). This improvement soil fertility might be due to a suitable soil environment, such as optimum moisture temperature, which determine rate organic manure decomposition soybean litter fall nutrient release from crop residues [29 31]. For instance, organic carbon soil after soybean harvest in 2012 was 1.63%, whereas it was 2.60% in 2014, showing a direct correlation with annual rainfall (Tables 1 5). Similarly, total nitrogen content soil varied from %, which is categorized in high range. Table 5. The effects soybean varieties, farmyard manure inorganic fertilizer application on soil ph, organic carbon, total nitrogen contents available phosphorus after soybean harvesting in 2014 at Bako, Western Ethiopia. Fertilizer ph (H 2 O) Total N (%) OC (%) P (mg/kg) FYM (t/ha) P (kg/ha) Boshe Ethio Boshe Ethio Boshe Ethio Boshe Ethio LSD NS NS NS NS CV Finger Millet Performance due to Residual Effects The yields finger millet as influenced by residual effects precursor soybean crop showed highly significant (p < 0.01) differences due to seasonal variations, FYM interactions

10 Agronomy 2017, 7, among varieties chemical fertilizer rates (Table 6). There was also a three-way interaction, though not strongly significant. Even though seasonal variations might influence yield finger millet, variations in l history experimental site (Table 1) soil fertility status after combined application fertilizers to soybean in 2012 (Table 3) 2014 (Table 4) might have contributed to significant differences in yield performance subsequent finger millet. Table 6. Analysis variance for yield performance subsequent finger millet (in cropping seasons) as influenced by residual effects soybean precursors application FYM chemical P fertilizer at Bako, Western Ethiopia. Source Variation d.f. Mean Square Variance F pr. Yr 1 4,955, <0.001 Var 1 186, FYM 2 651, <0.001 P 2 11, Yr * Var 1 184, Yr * FYM 2 505, Var * FYM 2 222, Yr * P 2 47, Var * P 2 885, <0.001 FYM * P 4 645, <0.001 Yr * Var * FYM 2 497, Yr * Var * P 2 883, <0.001 Yr * FYM * P 4 215, Var * FYM * P 4 189, Yr * Var * FYM * P 4 237, Block 2 172, Residual 70 73,614 Total 107 In 2013 cropping season, significantly higher yield finger millet was obtained when sown on a previous (2012) soybean plot that received 3 t FYM/ha as a main effect followed by 6 t FYM/ha (Figure 5). This might be due to gradual decomposition organic manure that slowly releases nutrients for subsequent crops [3,32]. However, high doses organic fertilizer application in short rainy season might take more time to be decomposed converted to soil organic matter. This could be due to limited population decomposing micro-organisms ir nutrients, particularly nitrogen, or soil environmental factors that may hamper rapid decomposition manure. However, in long run, higher doses manure may provide adequate nutrients for following crop rotation [30,33]. Interestingly, precursor soybean crop without fertilizer application significantly increased yield subsequent finger millet, which is statistically on par with yields obtained from mono-cropping practice (farmers practice with no rotation) that received recommended fertilizer applications (20 kg P/ha). This may indicate that soybean litter fall has potential to rapidly decompose increase soil organic matter, while it can also enhance availability nitrogen or nutrients [34,35]. Evidently, finger millet yield showed respective yield increments 6% 22% when planted following soybean precursor with 3 t FYM/ha 6 t FYM/ha compared with farmers practice, similar results were also reported by Hemalatha Chellamuthu [30]. In 2015 cropping season, however, yield performance finger millet was significantly higher by 20% as compared with yield obtained in 2013 (Figure 5). This might be attributed to variations in soil fertility status after soybean harvest, though rainfall amount distribution during growing two seasons were almost similar. In or words, residual effects soybean precursor (that produced higher biomass dropped as litterfall, which may enhance soil fertility) fertilizer applied in 2014 considerable enhanced yield following finger millet obtained in 2015 compared to The residual effect different rates FYM on

11 in short rainy season might take more time to be decomposed converted to soil organic matter. This could be due to limited population decomposing micro organisms ir nutrients, particularly nitrogen, or soil environmental factors that may hamper rapid decomposition manure. However, in long run, higher doses manure may provide adequate nutrients for following crop rotation [30,33]. Interestingly, precursor soybean crop Agronomy 2017, 7, without fertilizer application significantly increased yield subsequent finger millet, which is statistically on par with yields obtained from mono cropping practice (farmers practice with no rotation) that received recommended fertilizer applications (20 kg P/ha). This may indicate that following finger millet yield did not show significant difference among means, though re were soybean litter fall has potential to rapidly decompose increase soil organic matter, while it slight can yield also increases enhance when availability compared with nitrogen treatments or nutrients farmers [34,35]. practices soybean precursor receiving no Evidently, fertilizer finger (Figure millet 5). yield These showed results respective indicateyield thatincrements 100% chemical 6% 22% fertilizer when planted cost could be saved following whensoybean finger millet precursor is rotated with 3 t with FYM/ha soybean 6 precursor t FYM/ha compared crops with with farmers application practice, organic manure, similar which results is inwere agreement also reported with by a previous Hemalatha finding Chellamuthu [24]. [30] Agronomy 2017, 7, In 2015 cropping season, however, yield performance finger millet was significantly higher by 20% as compared with yield obtained in 2013 (Figure 5). This might be attributed to variations in soil fertility status after soybean harvest, though rainfall amount distribution during growing two seasons were almost similar. In or words, residual effects soybean precursor (that produced higher biomass dropped as litterfall, which may enhance soil fertility) fertilizer applied in 2014 considerable enhanced yield following finger millet Figure obtained 5. Residual in 2015 effect compared farmyard to manure The applied residual to effect precursor soybean different as rates main FYM effect on Figure 5. Residual effect farmyard manure applied to precursor soybean as main effect on following yield finger millet subsequent yield did finger not millet show at significant Bako, Western difference Ethiopia. among Mono F.M means, = farmers though practice, re were yield subsequent finger millet at Bako, Western Ethiopia. Mono F.M = farmers practice, continuous slight continuous yield increases mono cropping when compared finger millet with with recommended treatments DAP farmers fertilizer. practices soybean mono-cropping precursor receiving finger no fertilizer millet with (Figure recommended 5). These results DAP indicate fertilizer. that 100% chemical fertilizer cost could be saved when finger millet is rotated with soybean precursor crops with application The organic interaction manure, effect which is in organic agreement manure with a with previous chemical finding P[24]. fertilizer applied to soybean crop significantly The interaction affected effect organic performance manure with chemical subsequent P fertilizer finger applied millet to (Figure soybean 6). crop In 2013, significantly variable affected response performance finger millet subsequent was observed finger due millet to (Figure residual 6). In effects 2013, organic significantly variable response finger millet was observed due to residual effects organic manure combined with inorganic P fertilizer [6]. The highest finger millet yield was obtained when manure combined with inorganic P fertilizer [6]. The highest finger millet yield was obtained when planted on plot from which soybean that received 6 t FYM/ha in combination with 8 16 kg planted on plot from which soybean that received 6 t FYM/ha in combination with 8 16 kg P/ha P/ha was was harvested. harvested. In In this this case, case, yield yield increase increase over over farmers farmers practices practices was was up to up 30%. to 30%. Moreover, Moreover, effect effect soybean soybean precursor even without fertilizer use use considerably increased increased yield yield following following finger finger millet, millet, which which is is statistically on par with yield yield obtained from from farmers farmers practice. practice. In In cropping season, highest yield finger millet (2825 kg/ha) kg/ha) was was obtained obtained when when planted planted on soybean on soybean precursor plots plots that that received 3 t FYM/ha with kg kg P/ha P/ha followed followed by 9 by t FYM/ha 9 t FYM/ha with with 8 kg 8 P/ha, kg P/ha, which which are are statistically on on par (Figure 6). 6). Similar Similar to to result result 2013, 2013, yield yield finger finger millet was at statistical parity when planted following soybean precursor without fertilizer use as millet was at statistical parity when planted following soybean precursor without fertilizer use as compared with farmers practice, a similar result was also reported by Bado et al. [15]. compared with farmers practice, a similar result was also reported by Bado et al. [15]. Figure Figure 6. Residual 6. effect FYM combined with chemical P fertilizer P fertilizer applied applied to soybean to soybean precursor precursor on on yield subsequent finger milletat at Bako, Western Ethiopia. Ethiopia. Mono Mono F.M F.M = farmers = farmers practice, practice, continuous continuous mono-cropping mono cropping finger finger millet millet with recommended use use DAP DAP fertilizer. fertilizer. The interaction residual effects soybean varieties, due to nitrogen fixation crop litterfall, application FYM significantly influenced yield succeeding finger millet (Figure 7). In 2013, highest yield finger millet was obtained when planted on plot precursor Boshe variety, which received 3 t FYM/ha. This result indicates that during short rainy season, early maturing soybean type produces biomass that contributes to soil organic matter through litter fall drops (2012) hence to soil fertility improvement [12]). Moreover, this result is in line

12 Agronomy 2017, 7, The interaction residual effects soybean varieties, due to nitrogen fixation crop litterfall, application FYM significantly influenced yield succeeding finger millet (Figure 7). In 2013, highest yield finger millet was obtained when planted on plot precursor Boshe variety, which received 3 t FYM/ha. This result indicates that during short rainy season, early maturing soybean type produces biomass that contributes to soil organic matter through litter fall drops (2012) hence to soil fertility improvement [12]). Moreover, this result is in line with or research findings indicated that lower rates applied FYM also more easily decompose during Agronomy short rainy 2017, 7, seasons 42 release some nutrients for next crops as compared with 12 higher 15 doses [11]. In In 2015, however, late type precursor soybean (Ethio ugozilavia) (Ethio-ugozilavia) with with application application higher doses t FYM/ha 9 t FYM/ha resulted resulted in a significantly in a significantly increased increased yield yield subsequent subsequent crop as crop compared as compared with yield with obtained yield obtained 2013 in(figure ) with (Figure a 22% 7) with 18% a yield 22% increase, 18% respectively yield increase, respectively [36]. These results [36]. These revealed results that with revealed a good that rainy with season a good under rainy season optimum soil under conditions, optimum a late soil conditions, type soybean a late type precursor soybean crop may precursor produce crop more may biomass, produce more hence, biomass, higher litter hence, fall would higherbe litter fall dropped would be dropped decomposed decomposed in soil. in soil. Figure Residual effects precursor soybean crop appliedfym FYMon on yield yield subsequent finger millet millet crop crop at Bako, at Bako, Western Western Ethiopia. Ethiopia. Mono Mono F.M F.M = farmers = farmers practice, practice, continuous continuous mono-cropping mono finger millet finger withmillet recommended with recommended use DAP use fertilizer. DAP cropping fertilizer. Moreover, higher doses organic manure might be more easily decomposed due to Moreover, higher doses organic manure might be more easily decomposed due to adequate adequate soil moisture during good rainy seasons. Or soil environmental factors such as soil soil N:C moisture ratio might during also good contribute rainy to seasons. higher microbial Or soil populations environmental that decompose factors such as organic soil manure N:C ratio might more also rapidly contribute [1], increasing to higher nutrient microbial availability populations for thatnext decompose crop in rotation organic (Table manure 4 more rapidly Figure [1], 7). However, increasingplanting nutrient finger availability millet following for next a soybean crop inprecursor rotation crop (Table that received 4 Figure 3 7). However, t FYM/ha planting resulted in finger comparable milletyield following to those a soybean obtained precursor by following crop that farmers received practices. 3 tthus, FYM/ha resulted alternative in comparable use FYM yieldcould to those save obtained 100% by cost following chemical farmers fertilizer practices. inputs Thus, hence alternative can be use recommended FYM could especially save 100% for poor farmers cost that chemical have access fertilizer to inputs sufficient hence amounts can befym. recommended On especially or h, for poor use farmers a late that type have soybean access precursor to crop sufficient even without amounts fertilizer FYM. application On resulted or h, in use a greater a late than type 29% soybean yield increase precursor crop subsequent even without finger millet fertilizer crop application when grown resulted under moderate in a greater than soil 29% fertility yield increase adequate annual subsequent rainfall finger conditions millet (2014) cropas when compared grownto under a combined moderate short soil rainy fertility season adequate (2012) annual a low rainfall soil fertility conditions status. (2014) as compared to a combined short rainy season (2012) a low soil fertility status. 4. Conclusions 4. Conclusions Low soil fertility is one main challenges to produce surplus food for an ever increasing population, Low soil particularly fertility is one in Ethiopian main challenges context. Continuous to producemono cropping surplus food for with an ever-increasing one or two chemical fertilizer sources is one main causes gradual soil fertility depletion. However, population, particularly in Ethiopian context. Continuous mono-cropping with one or two chemical crop rotations with integrated use fertilizer sources could help to avert such problems lead fertilizer sources is one main causes gradual soil fertility depletion. However, crop rotations to soil fertility improvement. Moreover, this can increase production productivity with integrated use fertilizer sources could help to avert such problems lead to soil fertility rotationally grown crops hence address food security problem. improvement. Moreover, this can increase production productivity rotationally-grown crops The rainfall amount distribution significantly affected response soybean to fertilizers inputs. hence In address 2012, a year food with security a short problem. rainy season, re was a differential variety response to integrated fertilizer applications. Even though application 9 t FYM/ha with 24 kg P/ha to Boshe variety provided highest yield, use 3 t FYM/ha with 24 kg P/ha gave comparable yields. On or h, yield Ethio ugozilavia variety was significantly increased with application 9 t FYM/ha increased rates chemical P fertilizer rates. In 2014, a year with a long rainy season, however, lower rates both fertilizer sources (3 t FYM/ha 8 kg P/ha) showed similar yields for Boshe variety as compared with highest rates combined fertilizers applied.

13 Agronomy 2017, 7, The rainfall amount distribution significantly affected response soybean to fertilizers inputs. In 2012, a year with a short rainy season, re was a differential variety response to integrated fertilizer applications. Even though application 9 t FYM/ha with 24 kg P/ha to Boshe variety provided highest yield, use 3 t FYM/ha with 24 kg P/ha gave comparable yields. On or h, yield Ethio-ugozilavia variety was significantly increased with application 9 t FYM/ha increased rates chemical P fertilizer rates. In 2014, a year with a long rainy season, however, lower rates both fertilizer sources (3 t FYM/ha 8 kg P/ha) showed similar yields for Boshe variety as compared with highest rates combined fertilizers applied. The Ethio-ugozilavia variety showed maximum yields when 3 t FYM/ha were applied with 16 kg P/ha followed by 3 t FYM with 8 kg P/ha, resulting in significant yield increases 64% 45%, respectively. The initial soil fertility status in terms organic carbon, total nitrogen available phosphorus was considerably lower in 2012 than in 2014, but soil ph was higher in Similarly, soil fertility status after soybean harvest was lower in However, a slight improvement in organic carbon total nitrogen contents, particularly in 2014, was observed due to effect precursor crop combined use organic inorganic fertilizers. The residual effect 3 t FYM/ha resulted in a significantly higher grain yield finger millet in However, higher doses organic amendments did not significantly increase yields in same season. On or h, in 2015, residual effect FYM application resulted in a slight yield increase subsequent finger millet crop. Furrmore, a late type precursor soybean variety with an application higher doses FYM (6 9 t FYM/ha) significantly increased yield subsequent finger millet crop. Interestingly, precursor soybean without fertilizer application significantly increased yield subsequent finger millet. The results showed that yield finger millet increased by 6% 22% when planted following a soybean precursor crop with 3 t FYM/ha 6 t FYM/ha compared to farmers practice. In conclusion, use early types soybean with application lower rates organic (3 t FYM/ha) higher inorganic fertilizers (24 kg P/ha) resulted in increased yields during a short rainy season (2012) as compared to planting a late-soybean variety. Hence, we recommend this option to be used whenever a rainfall shortage is expected /or in semi-arid areas where moisture is a limiting factor. On or h, if rainfall amount distribution are optimum, as observed in 2014, a late maturing soybean variety receiving 6 t FYM/ha 8 16 P kg/ha could give significantly better yields as compared to early types. Regarding finger millet response to residual nutrient effects soybean precursor crop with a combined fertilizer application, use an early type soybean variety with 3 t FYM/ha in a short rainy season could potentially increase yields a subsequent finger millet crop. However, application higher rates organic manure (6 9 t FYM/ha) to a late type variety precursor crop in good rainy seasons could potentially enhance yield subsequent millet crop. Moreover, planting finger millet following a late type soybean precursor crop that received 3 t FYM/ha resulted in comparable yields compared to farmers practices, which could save 70 85% cost chemical fertilizer inputs. Hence, this option can be recommended for poor farmers with limited capacity to afford cost chemical fertilizers that have access to sufficient amounts organic manure. Acknowledgments: The authors greatly thank Oromia Agricultural Research Institute for financial support for execution experiment. The authors also sincerely acknowledge Bako Agricultural Research Center for technical managerial support during experimental periods. Great thanks also go to pulses oil research teams Center to Bayisa Baye who thoroughly supervised collected data regularly. Author Contributions: Abebe Zerihun conceived, designed performed experiments. Abebe Zerihun Deressa Haile analyzed data wrote paper. Conflicts Interest: The authors declare no conflict interest.

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