Soil & Tillage Research 53 (2000) 129±135

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1 Soil & Tillage Research 53 (2000) 129±135 The effects of crop rotation and fertilization on wheat productivity in the Pampean semiarid region of Argentina. 1. Soil physical and chemical properties A.M. Miglierina a,*, J.O. Iglesias a, M.R. Landriscini b, J.A. Galantini c, R.A. Rosell b a Departamento de AgronomõÂa, Universidad Nacional del Sur (UNS), 8000 BahõÂa Blanca, Argentina b Consejo Nacional de Investigaciones CientõÂ cas y TeÂcnicas (CONICET), Dpto de AgronomõÂa, UNS, 8000 BahõÂa Blanca, Argentina c ComisioÂn de Investigaciones CientõÂ cas (CIC), Dpto de AgronomõÂa, UNS, 8000 BahõÂa Blanca, Argentina Received 18 November 1997; received in revised form 4 June 1998; accepted 14 October 1999 Abstract Wheat in the semiarid region of Argentina has often been grown as a low-input crop. Rainfall scarcity and distribution are the main characteristics of this region. The knowledge of the combined effects of crop rotation and fertilization on soil physical and chemical properties are the key for a sustainable crop production. Soil properties for an Entic Haplustoll in the semiarid region of Argentina were evaluated, where different crop rotations were used for 15 years. Wheat±wheat (Triticum aestivum L.) (WW), wheat±grazing natural grasses (WG) and wheat±legume [vetch (Vicia sativa L.) plus oat (Avena sativa L.) or Triticale (Triticum aestivum L. Secale cereale L.)] (WL) rotations with and without fertilizer (64 kg N and 16 kg P ha 1 ) were studied. The annual wheat cropping system (WW) resulted in the lowest soil organic carbon (SOC) and total nitrogen (N t ) levels. Extractable phosphorus (P ext ) values were suf cient for wheat growth with all treatments and decreased with depth. Fertilizer applications signi cantly increased the proportion of large pores (>8.81 mm) in the 0±0.07 m depth of the WW and WG system plots. A decrease in the proportion of medium size pores (0.19±8.81 mm) and in the water holding capacity was observed in the WG rotation plots. The fertilized treatments resulted in the following sequence of available water: WL > WW > WG. Bulk density was similar with all treatments for each depth, except with the fertilized WG treatment that had the lowest value in the 0±0.07 m depth. These results showed the positive in uence of legume inclusion (WL) and alternate cattle grazing (WG) on SOC and N t contents. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Organic carbon; Nitrogen; Fertilization; Bulk density; ; Wheat 1. Introduction * Corresponding author. Tel.: ; fax: address: amiglier@criba.edu.ar (A.M. Miglierina). The in uence of tillage management and crop rotation on SOC and N has been investigated extensively throughout the world (Blevins and Frye, 1993). Most studies have focused on changes in concentra /00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S (99)

2 130 A.M. Miglierina et al. / Soil & Tillage Research 53 (2000) 129±135 tions (mg g 1 ) (e.g., Rasmussen and Rohde, 1988); however, fewer have examined the changes on a mass basis (kg ha 1 ) (e.g., Powlson and Jenkinson, 1981; Lamb et al., 1985; Dalal, 1989). Soil organic C and N increase as the frequency of summer fallow in the crop sequence or rotation decrease (Campbell et al., 1991a,b; Janzen, 1987; Bremner et al., 1994). This is because more crop residues are added to the soil, soil disturbance is less, and dry conditions are more frequent under continuous wheat cropping compared with wheat±fallow systems (Doran and Smith, 1987; Blevins and Frye, 1993). Whether the change in soil organic matter with time is positive or negative will depend on the initial level of the organic matter (Ismail et al., 1994). Other factors also in uence the degree of change in organic matter; it increases with fertilizer rates. In addition, crop yields and thus residue amounts are lower during droughts; therefore, soil organic matter decreases. Continuous cropping has impaired many soil physical and chemical properties in the Pampean semiarid region (Glave, 1988). Low aggregate stability, hardpan development and low SOC, N and phosphorus (P) concentrations are frequently observed in farmer's elds (Miglierina, 1991). C, N and P percentages decreased 40, 50 and 48, respectively, in an Entic Haplustoll after 80 years of cultivation (Miglierina, 1991). Losses of SOC, N, P and sulfur (S) were highest in the coarse fraction, thus showing the dynamics of this soil fraction and its important role in plant nutrient turnover and availability to growing crops (Galantini and Rosell, 1997). Structure degradation changes the pore space distribution and functionality, thus affecting soil water distribution and biological activity (Van Veen and Kuikman, 1990; Elliott and Cambardella, 1991; Hassink et al., 1993). It is essential to have a high proportion of pores with capacity to retain water available to plant roots., fertilization and residue and water management must be taken into account in order to maintain and increase sustainable land productivity in the region (Glave, 1988). The introduction of legumes in the rotation improves the organic matter and crop productivity levels (Odell et al., 1984; Johnston, 1986). Few authors have studied the combined effects of crop rotation and fertilization on the soil physical and chemical properties. For this reason the objective of this research was to evaluate the effect of 15 years of different production systems and fertilization on soil physical and chemical properties in an Entic Haplustoll of the Pampean semiarid region. 2. Materials and methods 2.1. Experimental site Field research was carried out at the INTA Agricultural Experimental Research Station, Bordenave, Province of Buenos Aires, Argentina, located in the Pampean semiarid region ( W; S). The experiment was started in 1975, and soil samples were taken in 1989, at the end of 15 years, when plots of all treatments were seeded with wheat (Triticum aestivum L.). The climate is continental, with a mean annual temperature of 158C. Mean annual precipitation is about 654 mm (1928±1992). The main soil sub-group is an Entic Haplustoll (FAO: Haplic Kastanozem), ne to medium sandy loam, having a 0±1% slope and a calcareous layer at a depth between 0.8 and 1 m from the surface (GoÂmez et al., 1981). Table 1 contains the sequence of the following three crop rotations studied: WW, continuous wheat. After harvesting the previous crop and a 4±6 month fallow (January±June) under stubble mulch for soil moisture storage and mechanical weed control, chisel ploughing to 0.20 m preceded the establishment of wheat by deep-furrow seeding, which deposits the seed 0.08±0.10 m deep. WG, wheat and cattle grazing natural grasses, alternatively 1 year each, with conventional tillage: short or without fallow; disk ploughing (0.15± 0.20 m) and harrowing; regular seeding only for wheat seeding, 0.04±0.05 m deep. WL, 2 years of mixed grazed, and 2 years of winter crops: vetch (Vicia sativa L.) plus oat (Avena sativa L.) or triticale (Triticum aestivum L. Secale cereale L.), and 2 years of wheat, and thus successively; tillage was the same as WW rotation. Imposed on the three rotation systems areas were non-fertilized (nf) and annually fertilized (f) treatment

3 A.M. Miglierina et al. / Soil & Tillage Research 53 (2000) 129± Table 1 Cropping sequence in three crop rotations studied a Year 1975 Wheat Wheat Barley clover 1976 Wheat Cattle grazing Barley clover 1977 Wheat Wheat Wheat 1978 Wheat Cattle grazing Wheat 1979 Wheat Wheat Vetch oat 1980 Wheat Cattle grazing Vetch oat 1981 Wheat Wheat Wheat 1982 Wheat Cattle grazing Wheat 1983 Wheat Wheat Vetch oat 1984 Wheat Cattle grazing Vetch triticale 1985 Wheat Wheat Wheat 1986 Wheat Cattle grazing Wheat 1987 Wheat Wheat Vetch triticale 1988 Wheat Cattle grazing Vetch triticale 1989 Wheat Wheat Wheat a WW, continuous wheat; WG, 1 year wheat±1 year grazing natural grasses; WL, 2 years wheat±2 years legume and grass mixture. plots, with 64 kg N ha 1 as urea and 16 kg P ha 1 as diammonium phosphate applied at seeding time (June) Data analysis The experiment had a randomized complete block design and a split-plot arrangement with three replications. The three crop rotations were assigned to the main plots and fertilizer applied to sub-plots. The main plots were 20 m long and 10 m wide. ANOVA was applied. The Tukey's test was used to compare the mean values taken by pairs Soil physical analysis The soil physical properties evaluated were: bulk density, with the core cylinder method (Blake and Hartge, 1986) and water capacity, by using the pressure plate (Klute, 1986) and pressure membrane apparatus (Richards, 1947). Six samples per main plot (three per sub-plot) and depth (0±0.07; 0.07±0.14, and 0.14±0.21 m) were obtained and analyzed. From the soil water characteristic curve and applying the capillary rise equation (Hassink et al., 1993) the pore size distribution was obtained. The capillary rise equation reads: d ˆ 30: h 1 ; where d (m) is the pore diameter and h the pressure head (m). The pore size distribution was obtained and classi- ed as follows: large pores (>8.81 mm), which drain gravitational water; medium pores (0.19±8.81 mm), which hold plant available water; and small pores (<0.19 mm), which hold non-available water. The total porosity was calculated as the water content in saturated soil Soil chemical analysis Six soil samples per main plot (three per sub-plot) and depth (0±0.07; 0.07±0.14, and 0.14±0.21 m) were obtained for chemical analysis. Samples were airdried, sieved (<2 mm) and analyzed for: SOC (Nelson and Sommers, 1982), N t (Bremner and Mulvaney, 1982), P ext (Bray and Kurtz, 1945), and ph (soil:water ˆ 1:2.5). 3. Results and discussion 3.1. Soil chemical properties Soil organic carbon decreased with depth in nonfertilized treatment plots of the WG and WL rotations, but not in WW rotation plots (Table 2). The shorter fallow period and alternate year tillage on WG tended to give higher SOC content than WW, but showed a layer heterogeneity due to animal compaction and inadequate moisture for optimum tillage effects. Fertilization increased the SOC content, except in WG and WL plots at 0±0.07 m. Total N levels decreased with depth in the nf treatment plots (Table 3). The WL rotation had the largest values due to legume cropping. The soil N level was greater in f than in nf treatments plots. In general, P ext values were medium in all treatments according to Olsen and Sommers (1982) and decreased with depth (Table 4). The P ext levels in the surface layer were the same order in the three crop rotations. A P ext positive response to fertilizers was observed in all rotations, except for WG at the 0± 0.07 m depth. Soil ph increased with depth with all rotations and treatments (Table 5). There were signi cant differ-

4 132 A.M. Miglierina et al. / Soil & Tillage Research 53 (2000) 129±135 Table 2 Soil organic carbon of an Entic Haplustoll under different crop rotations (data in mg ha 1 ) a 0± c 15.4b 17.0a 13.9bc 17.2a 17.9a 0.07± d 14.5c 15.8b 17.6a 15.8b 18.3a 0.14± b 13.8ab 10.5c 14.0ab 11.0c 15.1a 0± a In this and the following tables: WW, continuous wheat; WG, 1 year wheat±1 year grazing natural grasses; WL, 2 years wheat±2 years legume and grass mixture. Different letters in a row indicate signi cant differences between treatments (p < 0.05, Tukey's test). Table 3 Total soil nitrogen of an Entic Haplustoll under different crop rotations (data in kg ha 1 ) 0± c 1265b 1247b 1039d 1303b 1450a 0.07± d 1191c 1241bc 1289b 1130bc 1367a 0.14± c 1064b 859c 1151ab 1061b 1243a 0± Table 4 Soil extractable P of an Entic Haplustoll under different crop rotations (data in kg ha 1 ) 0± c 30.1a 21.4c 19.1d 21.9c 26.7b 0.07± d 26.4a 13.5e 23.6b 15.8de 20.4c 0.14± b 16.2a 5.5c 10.2b 6.8c 12.4b 0± Table 5 Soil ph of an Entic Haplustoll under different crop rotations 0± a 6.54c 6.69b 6.68b 6.56c 6.54c 0.07± a 6.64cd 6.71bc 6.73b 6.60d 6.62d 0.14± a 6.96b 7.11a 6.87cd 6.92bc 6.83d 0±

5 A.M. Miglierina et al. / Soil & Tillage Research 53 (2000) 129± Table 6 Soil pore size distribution and total porosity at each depth of an Entic Haplustoll under different crop rotations (%v/v) Size of pores (mm) 0±0.07 > c 21.5b 20.0b 32.5a 22.6b 16.1bc 8.81± a 13.2ab 17.5a 9.5b 15.1a 16.4a < a 12.6a 13.0a 10.4b 11.7ab 12.5ab Total porosity ±0.14 > bc 15.9bc 14.4c 21.0a 18.1ab 14.1c 8.81± ab 14.2ab 14.8ab 12.0b 14.3ab 16.5a < a 13.9a 14.2a 13.1a 13.3a 13.3a Total porosity ±0.21 > a 18.7a 16.1a 15.8a 18.9a 18.9a 8.81± a 14.2a 13.0a 12.8a 14.5a 14.9a < a 14.5a 10.8a 10.4a 11.9a 12.0a Total porosity ences among rotations for nf treatment plots at the 0± 0.14 m depth. Fertilizer applications generally decreased soil ph, as was indicated by Thomas et al. (1981) and Hansen and Zeljkovich (1984). Robson and Taylor (cited by White, 1990) found that ph was related to organic matter content in soils. In this study, it was found that soils with higher SOC had lower phs, especially in fertilized soils. The lowest soil ph value was found in WL plots, as was found in a previous study (Miglierina et al., 1995) Soil physical properties Fertilizer applications signi catively increased the proportion of large pores (>8.81 mm) in the 0.0± 0.07 m depth in WW and WG plots, probably due to the residue accumulation and the larger root systems with both rotations (Table 6). The short fallow period with the WG rotation contributed to the partial decomposition of crop residues. This along with the low rainfall favored the formation of larger aggregates that later allowed the genesis of large pores. On the other hand, the WL rotation resulted in large amounts of residues that decomposed almost completely due to the quality of the plant residue (high N content) and the long fallow period. The WW rotation resulted in intermediate conditions between WG and WL (long fallow and low straw N content). The medium size pores (8.81±0.19 mm) hold capillary soil water. The proportion of these pores in WGf rotation plots decreased at the 0±0.14 m depth relative to that in other rotations. This effect was attributable to the increase of the proportion of large pores. Consequently, the water holding capacity signi cantly decreased. The WG rotation resulted in a decrease in the proportion of medium pores and in the water available capacity (Table 7). No signi cant differences of the proportion of medium pores, between 13 and 17%, was observed in other treatments. The percentage of small pores varied between 10 and 14%, without any signi cant difference among treatments at the 0±0.21 m depth. Available water in the whole pro le was similar in the nf treatment plots (Table 7). For fertilized treatment plots the following sequence occurred: WL > WW > WG. This order was attributable to the responses in the soil surface layers (0±0.07 and 0.07± 0.14 m) due to the amount of initial residues and the tillage intensity effects at these depths. Bulk density was similar in all treatment plots for each depth. There was only one case (WG fertilized plot at 0±0.07 m) where the bulk density was lower due to the production of high amounts of undecomposed residues and a high proportion of large pores (Table 8). The same was reported by Campbell et al. (1996). In the 0.07±0.14 m depth, values were higher

6 134 A.M. Miglierina et al. / Soil & Tillage Research 53 (2000) 129±135 Table 7 Water available capacity of an Entic Haplustoll under different crop rotations (mm) 0± a 9.2ab 12.2a 6.7b 10.6a 11.5a 0.07± ab 9.9ab 10.4ab 8.4b 10.0ab 11.5a 0.14± a 36.9a 33.8a 33.3a 37.7a 38.7a Total 58.5ab 56.0ab 56.4ab 48.4b 58.3ab 61.7a Table 8 Soil bulk density of an Entic Haplustoll under different crop rotations (mg m 3 ) 0± a 1.18a 1.17a 0.96b 1.11ab 1.21a 0.07± a 1.23a 1.28a 1.19a 1.22a 1.28a 0.14± a 1.30a 1.21a 1.19a 1.25a 1.30a than in the 0±0.07 m depth, averaging 1.24 compared with 1.13 mg m Conclusions This experience shows the effects of 15 years of rotations with wheat although the measurements were con ned to only 1 year (1989). Little difference in the soil chemical properties was detected among crop rotations, but the OC, N t and P ext contents showed a positive response to fertilizers. In non-fertilized treatment plots, OC and N t decreased with depth and the wheat±legume rotation resulted in the largest values. Fertilized plots of the WW rotation had the highest P ext values at 0±0.21 m. The large proportion of medium pores, able to supply water to crops, was favored by the following conditions: high production of crop residues, high content of soil organic matter, long (6 months or more) fallow period and fertilization. These conclusions apply in only one particular type of rainfall season after a duration of 15 year rotations in which cumulative effects of the treatments will therefore be expected to have occurred. Acknowledgements The authors wish to thank the institutions that provided funds and personnel for this research: Consejo Nacional de Investigaciones CientõÂ cas y TeÂcnicas (CONICET); ComisioÂn de Investigaciones CientõÂ cas (CIC), La Plata; EstacioÂn Experimental Agropecuaria INTA, Bordenave. References Blake, G.R., Hartge, K.H., Bulk density. In: Klute, A. (Ed.), Methods of Soil Analysis. Part 1, Physical and Mineralogical Methods, 2nd ed., Agronomy, vol. 9. Soil Sci. Soc. Amer., Madison, WI, pp. 363±375. Blevins, R.L., Frye, W.W., Conservation tillage: An ecological approach to soil management. Adv. Agron. 51, 33±78. Bray, R.H., Kurtz, L.T., Determination of total, organic and available forms of phosphorous in soils. Soil Sci. 59, 39±45. Bremner, R.H., Mulvaney, C.S., Nitrogen-total. In: Page, A.L., Mille, R.H., Keeney, D.R. (Eds.), Methods of Soil Analysis, Part 2, 2nd ed., Agronomy, vol. 9. Soil Sci. Soc. Amer., Madison, WI, pp. 595±624. Bremner, E., Janzen, H.H., Johnston, A.M., Sensitivity of total, light fraction and mineralizable organic matter to

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