Soil Phosphorous Influence on Growth and Nutrition of Tropical Legume Cover Crops in Acidic Soil

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1 This article was downloaded by: [N. K. Fageria] On: 19 December 2013, At: 03:39 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Communications in Soil Science and Plant Analysis Publication details, including instructions for authors and subscription information: Soil Phosphorous Influence on Growth and Nutrition of Tropical Legume Cover Crops in Acidic Soil N. K. Fageria a, V. C. Baligar b, A. Moreira c & L. A. C. Moraes c a National Rice and Bean Research Center of EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria), Santo Antônio de Goiás, Goiás, Brazil b U.S. Department of Agriculture Agricultural Research Service, Beltsville Agricultural Research Center, Beltsville, Maryland, USA c National Soybean Research Center of EMBRAPA, Londrina, Brazil Accepted author version posted online: 01 Oct 2013.Published online: 02 Dec To cite this article: N. K. Fageria, V. C. Baligar, A. Moreira & L. A. C. Moraes (2013) Soil Phosphorous Influence on Growth and Nutrition of Tropical Legume Cover Crops in Acidic Soil, Communications in Soil Science and Plant Analysis, 44:22, , DOI: / To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content ) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

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3 Communications in Soil Science and Plant Analysis, 44: , 2013 Copyright Taylor & Francis Group, LLC ISSN: print / online DOI: / Soil Phosphorous Influence on Growth and Nutrition of Tropical Legume Cover Crops in Acidic Soil N. K. FAGERIA, 1 V. C. BALIGAR, 2 A. MOREIRA, 3 AND L. A. C. MORAES 3 1 National Rice and Bean Research Center of EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria), Santo Antônio de Goiás, Goiás, Brazil 2 U.S. Department of Agriculture Agricultural Research Service, Beltsville Agricultural Research Center, Beltsville, Maryland, USA 3 National Soybean Research Center of EMBRAPA, Londrina,Brazil In tropical regions, use of cover crops in crop production is an important strategy in maintaining sustainability of cropping systems. Phosphorus (P) deficiency in tropical soils is one of the most yield-limiting factors for successful production of cover crops. A greenhouse experiment was conducted to evaluate influence of P on growth and nutrient uptake in 14 tropical cover crops. The soil used in the experiment was an Oxisol, and P levels used were low (0 mg P kg 1 ), medium (100 mg P kg 1 ) and high (200 mg P kg 1 ). There was a significant influence of P and cover crop treatments on plant growth parameters. Phosphorus X cover crops interaction for shoot dry weight, root dry weight and root length was significant, indicating different responses of cover crops to variable P levels. Based on shoot dry weight efficiency index (SDEI), legume species were classified into efficient, moderately efficient or inefficient groups. Overall, white jack bean, gray mucuna bean, mucuna bean ana and black mucuna bean were most P efficient. Remaining species were inefficient in P utilization. Macro- and micronutrient concentrations (content per unit dry weight of tops) as well as uptakes (concentration x dry weight of tops) were significantly (P < 0.01) influenced by P as well as crop species treatments, except magnesium (Mg) and zinc (Zn) concentrations. The P x crop species interactions were significant for concentration and uptake of all the macro and micronutrients analyzed in the plant tissues, indicating concentrations and uptake of some nutrients increased while others decreased with increasing P levels. Hence, there was an antagonistic as well as synergetic effect of P on uptake of nutrients. However, uptake of all the macro and micronutrients increased with increasing P levels, indicating increase in dry weight of crop species with increasing P levels. Overall, nutrient concentration and uptake in the top of crop species were in the order of nitrogen (N) > potassium (K) > calcium (Ca) > Mg > sulfur (S) > P for macronutrients and iron (Fe) > manganese (Mn) > zinc (Zn) > copper (Cu) for micronutrients. Interspecific differences in shoot and root growth and nutrient uptake were observed at varying soil P levels Keywords macronutrient concentrations, micronutrient concentrations, root growth, shoot dry weight Received 22 March 2012; accepted 31 December Address correspondence to N. K. Fageria, National Rice and Bean Research Center of EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria), Caixa Postal 179, Santo Antônio de Goiás, Goiás, CEP , Brazil. nand.fageria@embrapa.br 3340

4 Soil P versus Cover Crops 3341 Introduction Cover crops are important components in crop production and maintaining sustainability of cropping systems. Cover crops improve soil fertility, control diseases, insects, soil erosion, and weeds and conserve soil moisture (Baligar and Fageria 2007). In addition, cover crops also improve or/maintain organic matter contents of the soils. Organic matter is mainly responsible for improving physical, chemical and biological properties of the soils which are responsible for improving crop yields (Fageria et al. 2005; Fageria et al. 2009). In addition, cover crops help in avoiding leaching of mobile nutrients from rhizosphere, especially nitrogen. This may help in minimizing water contamination with nitrate nitrogen and environmental pollution (Fageria 2007; Baligar and Fageria 2007). Positive effect of cover crops on subsequent annual crops is well documented (Fageria et al. 2011). Desirable attributes of a cover crop include the ability to establish rapidly under less than ideal conditions, provide sufficient dry matter and soil cover, fix atmospheric N 2, establish a deep root system to facilitate nutrient uptake from lower soil depths, produce organic matter with low residue carbon (C)/ nitrogen (N) ratios and absence of phytoxic or allelopathic effects on subsequent crops (Fageria et al. 2011). Including cover crops in the cropping systems is an important strategy to improve yields of annual and perennial crops grown in the infertile soils of the tropical region. Most of the soils in the tropical America are Oxisols and Ultisols. These soils are acidic and having low fertility. Large number of legume cover crops exist that may be tolerant to prevailing abiotic stresses such as soil acidity and low fertility (Fageria et al. 2009; 2011). Phosphorus (P) deficiency is one of the most yield limiting factors in tropical region (Fageria and Baligar 2003; Fageria and Baligar 2008). This is because soils of this region are low in natural P and having high P immobilization capacity (Fageria and Baligar 2003; Fageria and Baligar 2008). Legume cover crops that tolerate low soil P and with high P use efficiency traits have better chance of improving fertility of the infertile tropical soils. Information is limited on growth and nutrient uptake by tropical legume cover crops grown on low fertility soils of tropical region. Selection of proper cover crop with appropriate management practices it is possible to improve the persistence and productivity of cover crops. The objective of this study was to evaluate shoot and root growth and macro and micronutrients uptake differences by principal tropical legume cover crops grown under different soil P levels. Materials and Methods A green house experiment was conducted to evaluate influence of P on uptake of nutrients in 14 tropical legume cover crops. The common and scientific names of these cover crops are given in Table 1. The soil used in the experiment was an Oxisol with following chemical and physical properties before imposing acidity treatments: ph in H 2 O 5.8, calcium (Ca) 1.17 cmol c kg 1, magnesium (Mg) 0.6 cmol c kg 1, aluminum (Al) 0.1 cmol c kg 1,P 0.9 mg kg 1, potassium (K) 33 mg kg 1, copper (Cu) 1.2 mg kg 1, zinc (Zn) 1.1 mg kg 1, iron (Fe) 35 mg kg 1, manganese (Mn) 8 mg kg 1, organic matter 20 g kg 1, clay 569 g kg 1, silt 140 g kg 1, and sand 291 g kg 1. Soil analysis methodology used is described in manual of soil analysis (EMBRAPA 1997). The experiment was conducted in plastic pots with 9 kg soil in each pot. The P levels usedwere0mgkg 1 (low), 100 mg kg 1 (medium), and 200 mg kg 1 (high), applied as triple superphosphate. Each pot received 10 g dolomitic lime 4 weeks before sowing the cover crops and pots were subjected to dry and wet cycling. The liming material used

5 3342 N. K. Fageria et al. Table 1 Common and scientific names and 100-seed weight of legume cover crop species used in the experiment Common name Scientific name 100-seed weight (g) Crotalaria Crotalaria breviflora 1.70gh Sunnhemp Crotalaria juncea L. 4.91g Crotalaria Crotalaria mucronata 0.70h Crotalaria Crotalaria spectabilis Roth 1.84gh Crotalaria Crotalaria ochroleuca G. Don 0.88h Calapogonio Calapogonium mucunoides 1.51gh Pueraria Pueraria phaseoloides Roxb. 1.51gh Pigeonpea (black) Cajanus cajan L. Millspaugh 9.17f Pigeonpea (mixed color) Cajanus cajan L. Millspaugh 12.51f Lablab Dolichos lablab L e Mucuna bean ana Mucuna deeringiana (Bort) Merr d Black mucuna bean Mucuna aterrima (Piper & Tracy) Holland 73.09c Gray mucuna bean Mucuna cinereum L b White jack bean Canavalia ensiformis L. DC a Note. Means followed by the same letter in the same column are significantly not different by Tukey s test at the 5% probability level. was having 32.9% calcium oxide (CaO), 14.0% magnesium oxide (MgO) and neutralizing power of 85%. At the time of sowing basal fertilizers rates used were 200 mg N kg 1 of soil 200 mg P kg 1 of soil and 200 mg K kg 1 of soil. Nitrogen was applied as urea and K was applied as potassium chloride. After germination, four plants were maintained in each pot. Plants were harvested at an age of 35 days after sowing. Roots from each pot were removed manually and maximum root length was measured. Harvested material was washed in distilled water several times and was dried in an oven at 70oC to a constant weight. Dried plant material was grounded and analyzed for macro and micronutrients according to methodology proposed by Silva (1999). Data were analyzed by analysis of variance to evaluate treatment effects and means were compared by Turkey s test at 5% probability level. Shoot dry weight efficiency index (SDWEI) was calculated for to classification of legume species to P use efficiency by using following equation (Fageria et al. 2009): SDWEI = (Shoot dry weight at medium or high P level/average shoot dry weight of 14 species at medium or high P level) X (Shoot dry weight at low P level/average shoot dry weight of 14 species at low P level) The species having SDWEI > 1 were classified as efficient, species having SDWEI between 0.5 to 1.0 were classified as moderately efficient and species having SDWEI < 0.5 were classified as inefficient to P. These efficiency indices rating were done arbitrarily. Data were analyzed by analysis of variance to evaluate treatment effects and means were compared by Tukey`s test at 5% probability level. Regression analysis was also done wherever it was necessary. Appropriate regression model was selected on the basis of R 2.

6 Soil P versus Cover Crops 3343 Results and Discussion Seed Dry Weight One hundred seed dry weight of 14 legume cover crop species was determined at the time of sowing and there was a significant variation among crop species (Table 1). Seed dry weight varied from 0.70 g per 100 seeds produced by Croralaria mucronata to g per 100 seeds produced by Canavalia ensiformis. Seed weight was having highly significant linear positive associated with shoot dry matter production (Figure 1). Variation in shoot dry weight was 90% due to seed weight. Species like white jack bean, gray mucuna bean, black mucuna bean and mucuna bean ana were having higher seed weight (Table 1) and also having high shoot weight (Table 2). Legume seed weight is reported to be important in increasing legume yields (Fageria et al. 2009). Devine et al. (1990) reported that seed weight of soybean was positively related to yields. Shoot Growth The P X cover crops interaction for shoot dry weight was highly significant (Table 2). Hence, it can be concluded that response of cover crops to P varied with the variation in P levels and screening for P use efficiency should be done at various P levels. Shoot dry weight varied from 0.13 g plant 1 produced by Crotalaria breviflora to 5.81 g plant 1 produced by Canavalia ensiformis, with an average value of 1.31 g plant 1 at low (0 mg kg 1 ) P level. At medium P level (100 mg kg 1 ); shoot dry weight varied from 0.54 g plant 1 produced by Crotaralrai breviflora to 8.76 g plant 1 produced by Canavalia ensiformis, with an average value of 2.89 g plant 1. At higher P level (200 mg kg 1 ), the shoot dry weight varied from 0.26 to 9.28 g plant 1, with an average value of 3.50 g plant 1. Across three P levels, the shoot dry weight varied from 0.46 to 7.95 g plant 1. The white jack bean species produced highest shoot dry weight at the three P levels. Overall, the shoot dry weight was also increased (1.31 to 3.50 g plant 1 ) with increasing P level from 0 to 200 mg kg 1. The Inter species variability in shoot dry weight of tropical legume cover crops has been widely reported (Fageria et al. 2005; 2009; Baligar et al. 2006; Baligar and Fageria 2007; Fageria 2009). Inter-and intra specific variations for plant growth are known to be genetic and physiological control and are modified by plant interactions with environmental variables (Fageria 1992; Fageria 2009; Baligar et al. 2001). Figure 1. Relationship between 100-seed weight and shoot dry weight of legume cover crops. Values are averages of 14 cover crops.

7 3344 N. K. Fageria et al. Table 2 Shoot dry weight of 14 legume cover crops as influenced by P levels Shoot dry weight (g plant 1 ) Cover crop 0 mg P kg mg P kg mg P kg 1 Average Crotalaria 0.13f 0.54f 0.70fg 0.46i Sunnhemp 1.19de 3.38d 4.49d 3.02e Crotalaria 0.20f 0.77ef 0.74fg 0.57hi Crotalaria 0.31f 1.01ef 1.37efg 0.89fghi Crotalaria 0.30f 1.38ef 2.37e 1.35fg Calapogonio 0.26f 0.93ef 0.26g 0.48i Pueraria 0.17f 0.74ef 1.03efg 0.64ghi Pigeonpea (black) 0.63ef 1.90e 1.97ef 1.50f Pigeonpea (mixed color) 0.39ef 1.57ef 1.76efg 1.24fgh Lablab 0.92def 4.03cd 5.60bcd 3.51de Mucuna bean ana 2.26c 4.54bcd 5.35cd 4.05cd Black mucuna bean 1.61cd 5.71b 6.92bc 4.75c Gray mucuna bean 4.21b 5.27bc 7.14b 5.54b White jack bean 5.81a 8.76a 9.28a 7.95a Average P CV (%) Significant at the 1% probability level. Note. Means followed by the same letter in the same column are significantly not different by Tukey s test at the 5% probability level. Root Growth Root dry weight was significantly influenced by P, crop species and P X crop species interaction (Table 3). The P X C interaction significant indicates significant variation in shoot dry weight with the variation in P levels. At low P level (0 mg kg 1 ), maximum root dry weight of 0.77 g plant 1 was produced by white jack bean and minimum root dry weight of 0.01 g plant 1 was produced Crotalaria mucronata and pueraria. At medium P level (100 mg P kg 1 ), the maximum root dry weight of 1.91 g plant 1 was produced by black mucuna bean and the minimum root dry weight of 0.07 was produced by Crotalaria breviflora, with average value of 0.63 g plant 1. At greater P level (200 mg P), the maximum root dry weight of 1.42 g plant 1 was produced by gray mucuna bean and the minimum root dry weight of 0.09 g plant 1 was produced by calapogonio and pueraria, with an average value of 0.55 g plant 1. Across the three P levels, the maximum root dry weight was produced by black mucuna bean and the minimum was produced by calapogonio and pueraria. The variation in root dry weight is genetically controlled and also influenced by environmental variables, such as supply of mineral nutrition (Caradus 1990; Baligar, Fageria, and He 2001; Fageria, Baligar, and Clark 2006; Fageria and Moreira 2011). Maximum root length varied from 15.5 to 36 cm at the low P level, from 20.5 to cm at the medium P level, and from to cm at the high P level (Table 4).

8 Soil P versus Cover Crops 3345 Table 3 Root dry weight of 14 legume cover crops as influenced by P levels Root dry weight (g plant 1 ) Cover crop 0 mg P kg mg P kg mg P kg 1 Average Crotalaria 0.03de 0.07f 0.18de 0.09g Sunnhemp 0.17cd 0.83bc 0.64c 0.54d Crotalaria 0.01e 0.18ef 0.18de 0.12fg Crotalaria 0.04de 0.33ef 0.13de 0.17efg Crotalaria 0.02e 0.40ef 0.50c 0.30e Calapogonio 0.03de 0.13f 0.09e 0.08g Pueraria 0.01e 0.14f 0.09e 0.08g Pigeonpea (black) 0.16cd 0.51cde 0.13de 0.27ef Pigeonpea (mixed color) 0.08de 0.43def 0.27d 0.26ef Lablab 0.13cde 1.14b 0.96b 0.74c Mucuna bean ana 0.54b 0.79bcd c Black mucuna bean 0.26c 1.91a 1.36a 1.17a Gray mucuna bean 0.53b 0.83bc 1.42a 0.93b White jack bean 0.77a 1.12b 0.93b 0.94b Average P levels (P) CV (%) Significant at the 1% probability level. Note. Means followed by the same letter in the same column are significantly not different by Tukey s test at the 5% probability level. Across three P levels, the maximum root length of cm was produced by white jack bean and the minimum root length of cm was produced by crotalaria. Overall, root length also increased with increasing P level. The improvement in root length by improved P nutrition has been reported by Fageria (2009) and Fageria and Moreira (2011) in various crop species, including cover crops. Barber (1995), Marschner (1995), Mengel et al. (2001), and Fageria, Baligar, and Clark (2006) reported that mineral nutrition has tremendous effects on root growth, development, and function and consequently the ability of roots to absorb and translocate nutrients. These authors further reported that mineral deficiency induces considerable variations in growth and morphology of roots and such variations are strongly influenced by plant species and genotypes. Root dry weight had highly significant positive quadratic association with shoot dry weight (Y = exp. (5.5187X X 2,R 2 = ). Ninety-seven percent of variations in shoot dry weight were due to root dry weight. Similarly, root length also improved shoot dry weight in a quadratic fashion (Y = X X 2, R 2 = ). The improvement in shoot dry weight with increasing root dry weight and root length may be associated with better absorption of water and nutrients (Fageria, Baligar, and Li 2009). The variation in shoot dry weight was about 88% due to root length and 97% due to root dry weight Hence, it can be concluded that root dry weight is a better indicator in determining shoot dry weight than maximum root length.

9 3346 N. K. Fageria et al. Table 4 Maximum root length of 14 legume cover crops as influenced by P levels Maximum root lenght (cm) Cover crops 0 mg P kg mg P kg mg P kg 1 Average Crotalaria 21.0cde 20.5f 28.50c 23.33def Sunnhemp 31.5ab 24.5def 53.00ab 36.33c Crotalaria 20.0de 24.5def 22.00cd 22.17ef Crotalaria 20.0de 23.67ef 18.33d 20.67f Crotalaria 21.0cde 31.0cde 24.0cd 25.56de Calapogonio 23.5cd 30.67cde 21.00cd 25.06de Pueraria 15.5e 27.5def 23.50cd 22.17ef Pigeonpea (black) 21.33cde 30.00cde 23.00cd 24.78de Pigeonpea (mixed color) 23.0cd 26.50def 28.50c 26.00de Lablab 19.67de 32.00bcd 29.00c 26.89d Mucuna bean ana 24.33cd 47.00a 53.00ab 41.44b Black mucuna bean 27.5bc 37.50bc 60.50a 41.83b Gray mucuna bean 31.5ab 39.00b 51.00b 40.50b White jack bean 36.0a 50.33a 52.33ab 46.22a Average P CV (%) 8.31 Significant at the 1% probability level. Note. Means followed by the same letter in the same column are significantly not different by Tukey s test at the 5% probability level. Classification of Legume Species for P-Use Efficiency Shoot dry-weight efficiency index (SDWEI) was used to group cover crop species into efficient, moderately efficient, and inefficient in P-use efficiencies (Table 5). The SDWEI was used to classify crop species for P-use efficiency because it is significantly related to shoot dry weight (Figure 2). In addition, this index separates effectively efficient and inefficient crop species in P-use efficiency (Fageria 2009; Fageria, Baligar, and Li 2009). The SDWEI was significantly affected by soil P, cover crop species, and their interactions. With exception of lablab at medium soil P, the mucuna bean ana, black mucuna bean, gray mucuna bean, white jack bean, and lablab were efficient in P use. Other cover crops at medium to high soil P were classified as inefficient in P use. Cover-crop species having greater SDWEI values for P might produce greater yield when grown on soils where supply of P is limited. Interspecific variation in P and other essential nutrients uptake and utilization in various species including cover crops is well documented (Baligar, Fageria, and He 2001; Baligar et al. 2006, 2008; Fageria, Baligar, and Jones 2011). Significant differences have been reported among crop species and genotypes of the same species in absorption and utilization of nutrients including P (Clark 1990; Clark and Duncan 1991; Marschner 1995; Baligar, Fageria, and He 2001; Epstein and Bloom 2005). Variations in nutrient utilizations

10 Soil P versus Cover Crops 3347 Table 5 Shoot dry-weight efficiency index (SDWEI) of 12 legume cover crops at medium and high P levels and their classification to P-use efficiency Cover crops 100 mg P kg mg P kg 1 Average Crotalaria 0.02d (IE) 0.02d (IE) 0.02d (IE) Sunnhemp 0.18d (IE) 0.20d (IE) 0.19d (IE) Crotalaria 0.06d (IE) 0.05d (IE) 0.06d (IE) Crotalaria 0.08d (IE) 0.09d (IE) 0.09d (IE) Crotalaria 0.09d (IE) 0.13d (IE) 0.11d (IE) Calapogonio 0.04d (IE) 0.01d (IE) 0.03d (IE) Pueraria 0.13d (IE) 0.14d (IE) 0.13d (IE) Pigeonpea (black) 0.20d (IE) 0.17d (IE) 0.18d (IE) Pigeonpea (mixed color) 0.40d (IE) 0.34d (IE) 0.37d (IE) Lablab 0.99d (ME) 1.09cd (E) 1.04d (E) Mucuna bean ana 2.70c (E) 2.64c (E) 2.67c (E) Black mucuna bean 2.45c (E) 2.44c (E) 2.44c (E) Gray mucuna bean 5.86b (E) 6.55b (E) 6.21b (E) White jack bean 13.29a (E) 11.73a (E) 12.51a (E) Average P CV (%) Significant at the 1% probability level. Notes. Means followed by the same letter in the same column are significantly not different by Tukey s test at the 5% probability level. IE, inefficient; ME, moderately efficient; and E, efficient. within and between species are known to be under genetic and physiological control but are modified by plant interactions with the environmental variables (Baligar and Fageria 1997; Baligar, Fageria, and He 2001). Figure 2. Relationship between shoot dry-weight efficiency index and shoot dry weight of legume cover crops. Values are averages of 14 legume cover crops.

11 3348 N. K. Fageria et al. Macronutrient Concentrations The P crop species interaction was significant for N, P, K, Ca, and S concentrations in the plant tops (Tables 6 10), indicating that crop species accumulated nutrients differently under various P rates. In the current study, overall concentrations of N, Ca Mg, and S were in the sufficient to adequate range, whereas K concentrations were in the high range as compared to concentration ranges reported for cover crop legumes (Reuter and Robinson 1986; Jones, Wolf, and Mills 1991). Concentrations of P were at the low to deficient range with low P rate and at adequate range with medium to high P application rates. Nitrogen Concentration Nitrogen concentration varied from produced by black mucuna bean to g kg 1 produced by mucuna bean ana at 0 mg P kg 1 level, with an average value of g kg 1 (Table 6). Similarly, at 100 mg P kg 1 level, N concentration in tops of crop species varied from g kg 1 produced by gray mucuna bean to g kg 1 produced by pigeonpea (mixed color), with an average value of g kg 1. At high P level (200 mg P kg 1 ), N concentration varied from g kg 1 produced by calapogonia to g kg 1 Table 6 Nitrogen concentration (g kg 1 ) in the tops of 14 tropical cover crops under three P levels P levels (mg kg 1 ) Crotalaria 45.00ab 39.92a 36.75abc Sunnhemp 46.95ab 42.23a 37.17abc Crotalaria 54.18a 46.08a 47.77a Crotalaria 45.62ab 42.74a 39.46abc Crotalaria 45.73ab 48.48a 46.19a Calapogonio 44.78ab 41.45a 28.53c Pueraria 42.54ab 35.82a 33.89bc Pigeonpea (black) 50.12ab 47.39a 43.42ab Pigeonpea (mixed color) 42.38ab 48.52a 45.46ab Lablab 51.25ab 42.45a 38.50abc Mucuna bean ana 55.31a 41.74a 41.25ab Black mucuna bean 36.04b 34.05a 38.39abc Gray mucuna bean 42.14ab 33.50a 37.00abc White jack bean 46.17ab 37.95a 38.35abc Average P levels (P) CV (%) Significant at the 1% probability level. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test.

12 Soil P versus Cover Crops 3349 Table 7 Phosphorus concentration (g kg 1 ) in the tops of 14 tropical cover crops under three Plevels P levels (mg kg 1) Crotalaria 1.68a 2.36bc 3.00ab Sunnhemp 1.47ab 2.30bc 2.30bcd Crotalaria 1.72a 2.18bc 2.28bcd Crotalaria 1.87a 2.69bc 2.49abcd Crotalaria 1.58a 2.91abc 2.93abc Calapogonio 1.61a 2.72abc 1.47d Pueraria 1.54a 2.30bc 2.36bcd Pigeonpea (black) 1.74a 4.27a 3.63a Pigeonpea (mixed color) 1.57a 3.57ab 3.59a Lablab 0.79c 1.97c 2.38bcd Mucuna bean ana 0.88bc 2.33bc 2.60abcd Black mucuna bean 0.67c 1.53c 1.89bcd Gray mucuna bean 0.75c 1.75c 2.24bcd White jack bean 0.68c 1.63c 1.85cd Average P Levels (P) CV (%) Significant at the 1% probability level. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test. produced by Crotalaria mucronata, with an average value of g kg 1. The difference in concentration of N in the crop species tops at different P rates may be associated with different responses to applied P (Fageria 2009). The N concentration in the crops species tops decreased with increasing P rates. The decrease was 11% at medium P level and 17% at high P level compared with low P level. This type of decrease in nutrient concentration with increasing nutrient rates in growth medium is known as dilution effect in mineral nutrition of plants (Fageria et al. 2011). Phosphorus Concentration There was a significant variation among cover crop species in P concentrations (Table 7). Phosphorus concentration varied from 0.67 to 1.87 g kg 1, with an average value of 1.32 g kg 1 at low P level. At medium P level, P concentration among cover crop species varied from 1.53 to 4.27 g kg 1, with an average value of 2.46 g kg 1. At greater P rate, the P concentration varied from 1.47 to 3.63 g kg 1, with an average value of 2.50 g kg 1. Pigeonpea (black) was having maximum P concentration at medium and high P levels. Black mucuna bean was having lowest P concentration at low and medium P levels. The variation in P

13 3350 N. K. Fageria et al. Table 8 Potassium concentration (g kg 1 ) in the tops of 14 tropical cover crops under three Plevels P levels ( mg kg 1) Crotalaria 22.62abc 25.89abcd 24.47a Sunnhemp 22.45abc 23.34bcd 23.05a Crotalaria 22.12abc 32.26abc 26.43a Crotalaria 31.32a 39.32ab 29.53a Crotalaria 31.57a 40.35a 30.08a Calapogonio 26.63ab 34.70ab 23.18a Pueraria 27.23ab 37.89ab 29.82a Pigeonpea (black) 18.38bcde 33.14abc 26.19a Pigeonpea (mixed color) 20.49bcd 34.03abc 30.02a Lablab 15.20cde 29.13abcd 28.23a Mucuna bean ana 11.54de 24.94abcd 29.55a Black mucuna bean 9.77e 18.38cd 18.11a Gray mucuna bean 8.91e 10.53d 18.64a White jack bean 20.13bcd 28.97abcd 22.76a Average P levels (P) CV (%) Significant at the 1% probability level. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test. concentration of cover crop species may be due to differences in their root property such as root morphology, root diameter, and root hairs, which might have caused variation in P uptake (Hinsinger 1998; Richardson 2001; Gahoonia and Nielsen 2004). Overall, P concentration increased 86% at medium P level and 89% at high P level compared with low P level. The increase in P concentration with increasing P rate was expected due to increase in P availability to plant roots (Fageria, Baligar, and Jones 2011). Potassium Concentration Potassium concentration varied from 8.91 g kg 1 to g kg 1 at low P level, with an average value of g kg 1 (Table 8). At medium P level, K concentration varied from to g kg 1, with an average value of g kg 1. Similarly, at high P level, the K concentration among cover crop species varied from to g kg 1, with an average value of g kg 1. Overall, K concentration in cover crop species tops increased with the addition of P fertilizer in the soil. Hence, P had a synergetic effect in K uptake by cover crops. Positive interaction of K with P has been reported (Dibb and Thompson 1985; Fageria 2009). Fageria (2009) reported that the positive interaction of P with

14 Soil P versus Cover Crops 3351 Table 9 Calcium (under three P levels) and Mg concentrations (g kg 1 ) in the tops of 14 tropical cover crops under three P levels (values of Mg are across three P levels) P levels (mg kg 1) Mg Crotalaria 11.95abcd 12.95bcd 14.70ab 4.25ab Sunnhemp 11.41abcd 11.80cde 14.21ab 4.85ab Crotalaria 8.47cde 9.65de 10.26c 4.38ab Crotalaria 15.25a 17.10ab 16.16a 3.92b Crotalaria 5.60e 7.84e 9.20c 4.85ab Calapogonio 12.74abc 14.86abc 12.42bc 4.48ab Pueraria 12.37abc 12.82bcde 9.77c 5.68a Pigeonpea (black) 11.15abcd 17.73ab 14.33ab 4.47ab Pigeonpea (mixed color) 12.89abc 17.76ab 15.88ab 4.12ab Lablab 9.46bcde 15.64abc 15.70ab 4.78ab Mucuna bean ana 11.94abcd 18.82a 17.59a 5.03ab Black mucuna bean 10.31bcd 13.79abcd 14.06ab 4.10ab Gray mucuna bean 7.74de 12.74bcde 14.03ab 4.04b White jack bean 13.05ab 16.68ab 17.54a 3.63b Average P levels (P) NS NS CV (%) ,NS Significant at the 1% probability level and nonsignificant, respectively. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test. macronutrients may be associated with improvement in growth and yield of crop plants with the P fertilization. Increased growth and yield required more nutrients compared to low growth and yield. Wilkinson, Grunes, and Sumner (2000) also reported that increased growth requires more nutrients to maintain tissue composition within acceptable limits. Calcium, Magnesium, and Sulfur Concentrations Calcium concentration varied from 5.60 to g kg 1 at the low P rate, with an average value of g kg 1 (Table 9). At medium P level Ca concentration in the tops of cover crop species varied from 7.84 to g kg 1, with an average value of g kg 1.Atthe greater P rate, the Ca concentration varied from 9.20 to g kg 1, with an average value of g kg 1. Overall, Ca concentration increased with the addition of P fertilizer. Crotalaria ochroleuca had a minimum concentration of Ca at three P levels compared with other cover crop species. The Ca concentration increase was 29% at medium P level and 27% at high P level compared with the control treatment. Fageria (2009) reported positive association between P and Ca uptake in crop plants. The Mg concentration across three P levels varied from 3.63 to 5.68 g kg 1, with an average value of 4.47 g kg 1. Sulfur

15 3352 N. K. Fageria et al. Table 10 Sulfur concentration (g kg 1 ) in the tops of 14 tropical cover crops under three P levels P levels (mg kg 1) Crotalaria 2.22abcde 2.67abcd 2.93ab Sunnhemp 2.40abcd 2.32bcd 2.73abc Crotalaria 2.76ab 2.70abcd 2.70abc Crotalaria 2.92a 3.27a 3.01ab Crotalaria 2.50abc 3.15ab 3.13a Calapogonio 2.56ab 3.11ab 2.21bcd Pueraria 2.56ab 3.01abc 2.15bcd Pigeonpea (black) 2.14bcde 3.41a 2.57abcd Pigeonpea (mixed color) 2.22abcde 3.41a 2.97ab Lablab 1.78cdef 3.15ab 2.74abc Mucuna bean ana 1.61ef 2.73abcd 2.33abcd Black mucuna bean 1.28f 1.91d 1.81d Gray mucuna bean 1.11f 1.86d 2.04cd White jack bean 1.77def 2.15cd 2.33abcd Average P levels (P) CV (%) Significant at the 1% probability level. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test. concentration varied from 1.11 to 2.92 g kg 1, with an average value of 2.13 g kg 1 at low P level (Table 10). At medium P level, the S concentration varied from 1.86 to 3.41 g kg 1, with an average value of 2.77 g kg 1. At 200 mg P kg 1 level, S concentration varied from 1.81 to 3.13 g kg 1, with an average value of 2.54 g kg 1. Overall, S concentration in the tops of cover crops increased with the addition of P in the soil. Positive effect of P on S uptake is reported by Fageria (2009) in crop plants. Micronutrient Concentrations Concentration of micronutrients such as Cu, Fe, Mn, and Zn was determined in 14 cover crop species under three P levels (Tables 11 13). The P cover crops interaction for Cu, Fe, and Mn concentrations was significant, indicating different uptake of these elements by cover crops with the change of P levels. In the current study, overall concentrations of Cu were in the sufficient to adequate range and concentrations of Zn and Mn were in the low to deficient range; however, Fe concentrations were at high range as compared to concentrations reported for other cover crop legumes (Reuter and Robinson 1986; Jones, Wolf, and Mills 1991)

16 Soil P versus Cover Crops 3353 Table 11 Copper concentration (mg kg 1 ) in the tops of 14 tropical cover crops under three P levels P levels (mg kg 1) Crotalaria 13.30ab 10.34abc 11.97abcd Sunnhemp 8.28bcde 8.11c 7.36ef Crotalaria 14.51a 11.52abc 9.84abcde Crotalaria 9.72abcd 9.22bc 9.07cdef Crotalaria 9.01abcde 9.30bc 9.70bcde Calapogonio 8.83abcde 10.49abc 8.46def Pueraria 12.48abc 9.88bc 8.22def Pigeonpea (black) 14.07ab 16.32a 13.60a Pigeonpea (mixed color) 14.52a 16.26a 12.59abc Lablab 3.76e 6.32c 7.25ef Mucuna bean ana 11.12abc 14.64ab 13.48ab Black mucuna bean 4.77de 8.06c 8.84cdef Gray mucuna bean 6.82cde 10.28abc 10.85abcde White jack bean 4.36de 5.86c 5.34f Average P levels (P) NS CV (%) 17.46,NS Significant at the 1% probability level and nonsignificant, respectively. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test. Copper Concentration Copper concentration varied from 3.76 to mg kg 1, with an average value of 9.68 mg kg 1 at low P level. At the medium P level Cu concentration varied from 5.86 to mg kg 1, with an average value of mg kg 1. At the high P level, Cu concentration varied from 5.34 to mg kg 1, with an average value of 9.75 mg kg 1. Overall, Cu concentration increased with the addition of P fertilization. Fageria (2009) reported positive effect of P on Cu uptake in crop plants. Copper concentration was minimal in the cover crop tops compared to other micronutrients. Fageria (2009) reported that Cu is taken up by the plants in only very small quantities. The Cu concentration of most plants is generally between 2 to 20 mg kg 1 in the dry plant tissues (Mengel et al. 2001). Iron Concentration Iron concentration varied from to mg kg 1, with an average value of mg kg 1 at low P level. At medium P level the Fe concentration in plant tissue of cover crop species varied from to mg kg 1, with an average value of mg kg 1. At the high P level Fe concentration varied from to mg

17 3354 N. K. Fageria et al. Table 12 Iron concentration (mg kg 1 ) in the tops of 14 tropical cover crops under three P levels P levels (mg kg 1) Crotalaria a c ab Sunnhemp b c b Crotalaria b c ab Crotalaria b c ab Crotalaria b c b Calapogonio ab a a Pueraria ab ab ab Pigeonpea (black) b c b Pigeonpea (mixed color) b c ab Lablab b c ab Mucuna bean ana b bc ab Black mucuna bean b c ab Gray mucuna bean b c ab White jack bean b ab Average P levels (P) CV (%) 64.76, Significant at the 5 and 1% probability levels, respectively. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test. kg 1, with an average value of mg kg 1. The Fe concentration was greatest in the plant tissue of cover crops compared with other micronutrients. This may be related to greater Fe content in the Brazilian Oxisols. Fageria and Baligar (2005) reported that average values of Fe was 116 mg kg 1 of 200 soil samples collected from six states covering Cerrado region of Brazil with Oxisols. Overall, Fe concentration decreased with increasing P levels in the soil. The decrease was 54% at medium P level and 93% at high P level. The Fe uptake is reported to be decreased with the addition of P in the growth medium (Follett, Murphy, and Donahue 1981; Fageria 2009). The specific absorption rate of Fe decreased with increasing P supply due to physiological interaction of P and Fe (Fageria 2009). The inhibition of Fe uptake by P may be related to its competing with the roots for Fe 2+ and interfering with reduction of Fe 3+ in solution (Chaney and Coulombe 1982). Manganese and Zinc Concentrations Manganese concentration varied from to mg kg 1, with an average value of mg kg 1 at low P level. At medium P level, Mn concentration in tops of cover crop plants varied from to mg kg 1, with an average value of mg kg 1.

18 Soil P versus Cover Crops 3355 Table 13 Manganese (under three P levels) and Zn concentrations (mg kg 1 ) in the tops of 14 tropical cover crops under three P levels (values of Zn are across three P levels) P levels (mg kg 1) Zn Crotalaria 63.96abc 45.70d 54.36e 24.38defg Sunnhemp 80.95abc 87.41bcd bc 23.00efg Crotalaria a abc ab 37.80bc Crotalaria 73.38abc 84.38bcd 89.26bcde 31.95cde Crotalaria 55.02bc 67.38cd 66.73de 30.96cdef Calapogonio 52.40c 73.38cd 54.00e 28.20cdefg Pueraria ab abcd 68.71cde 33.15cd Pigeonpea (black) 86.66abc abc 98.23bcd 49.05a Pigeonpea (mixed color) 87.32abc abc 82.53cde 45.50ab Lablab 64.57abc 91.46bcd bcd 26.35defg Mucuna bean ana a a a 25.20defg Black mucuna bean 61.94abc abcd bcd 21.14fg Gray mucuna bean 72.67abc ab a 23.75defg White jack bean 29.54a 47.45d 46.58e 18.50g Average P levels (P) NS CV (%) ,,NS Significant at the 5 and 1% probability levels and nonsignificant, respectively. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test. At the greater P level, Mn concentration varied from to mg kg 1, with an average value of mg kg 1. With the increasing level of P in the growth medium improved Mn uptake by legume cover crops. Zinc concentration varied from to 49.0 mg kg 1, with an average value of mg kg 1 across three P levels. Uptake of Macronutrients Uptake (concentration dry-matter yield) of N, P, K, Ca, Mg, and S was significantly affected by P level as well as cover crop treatments (Tables 14 19). Similarly, P cover crop interactions was significant for these macronutrients, indicating variable responses of cover crops with changing P levels. Overall, uptake of N was 92% greater at the medium P level than at the low P level. Similarly, increase in N uptake at the high P level was 130% higher compared with the low P level. The uptake of P also increased with increasing P levels as expected, but there were variations among cover crop species. Similarly, overall uptake of Ca, Mg, and S was increased with increasing P levels. Fageria (2009) reported that generally P has positive significant interaction with most of the macronutrients. The positive effect of P on uptake of these macronutrients was related to increase in dry weight of cover crops

19 3356 N. K. Fageria et al. Table 14 Uptake of N (mg plant 1 ) in the tops of 14 tropical cover crops under three P levels Plevels(mgkg 1 ) Crotalaria 5.95f 21.59e 25.47ef Sunnhemp 58.18de bcd cd Crotalaria 11.11f 35.34e 36.51ef Crotalaria 13.98def 42.80e 54.27ef Crotalaria 13.89def 68.16de de Calapogonio 11.75ef 38.37e 7.32f Pueraria 7.31f 27.50e 35.63ef Pigeonpea (black) 37.90def 97.21cde 87.55def Pigeonpea (mixed color) 16.58def 76.73de 79.67def Lablab 48.32def bc bc Mucuna bean ana c b bc Black mucuna bean 57.63d b ab Gray mucuna bean b bc ab White jack bean a a a Average Plevels(P) CV (%) 24.58, Significant at the 5 and 1% probability levels, respectively. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test. Table 15 Uptake of P (mg plant 1 ) in the tops of 14 tropical cover crops under three P levels Plevels(mgkg 1 ) Crotalaria 0.22f 1.28e 2.06e Sunnhemp 1.89c 8.65abcd 11.04bcd Crotalaria 0.35ef 1.68de 1.95e Crotalaria 0.58def 2.69cde 3.45e Crotalaria 0.48ef 3.97bcde 6.93cde Calapogonio 0.43ef 2.51cde 0.38e Pueraria 0.28f 1.82de 2.44e Pigeonpea (black) 1.28cd 8.56abcde 7.32cde Pigeonpea (mixed color) 0.64def 5.91bcde 6.35de Lablab 0.84def 9.76abc 15.70ab Mucuna bean ana 1.96c 10.67ab 13.96abc Black mucuna bean 1.07de 8.79abcd 13.11abcd Gray mucuna bean 3.59b 10.09ab 19.46a White jack bean 4.37a 15.82a 19.17a Average Plevels(P) CV (%) Significant at the 1% probability level. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test.

20 Soil P versus Cover Crops 3357 Table 16 Uptake of K (mg plant 1 ) in the tops of 14 tropical cover crops under three P levels Plevels(mgkg 1 ) Crotalaria 3.04e 14.06e 17.32fg Sunnhemp 27.86bc 84.23bcde cde Crotalaria 4.49e 24.82e 20.20fg Crotalaria 9.78de 39.18cde 41.65fg Crotalaria 9.59de 54.96bcde 71.57def Calapogonio 7.27de 32.39de 5.93g Pueraria 4.77e 29.64de 31.55fg Pigeonpea (black) 12.70cde 64.63bcde 52.83efg Pigeonpea (mixed color) 8.23de 54.90bcde 50.92fg Lablab 14.23cde b b Mucuna bean ana 24.75bcd bc bc Black mucuna bean 15.88cde bcd bcd Gray mucuna bean 38.71b 60.64bcde bc White jack bean a a a Average Plevels(P) CV (%) Significant at the 1% probability level. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test. Table 17 Uptake of Ca (mg plant 1 ) in the tops of 14 tropical cover crops under three P levels Plevels(mgkg 1 ) Crotalaria 1.58g 6.99e 10.17d Sunnhemp 14.16de 40.95c 66.53c Crotalaria 1.66g 7.43de 7.93d Crotalaria 4.71fg 17.11cde 22.21d Crotalaria 1.70g 10.60de 21.77d Calapogonio 3.38fg 13.95cde 3.18d Pueraria 1.98g 9.51de 10.02d Pigeonpea (black) 7.88efg 36.25cd 28.95d Pigeonpea (mixed color) 5.12fg 28.36cde 27.93d Lablab 9.15ef 72.47b 96.70b Mucuna bean ana 26.77c 85.52b 94.13bc Black mucuna bean 16.78d 78.90b 97.37b Gray mucuna bean 36.56b 73.35b b White jack bean 79.48a a a Average Plevels(P) CV (%) Significant at the 1% probability level. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test.

21 3358 N. K. Fageria et al. Table 18 Uptake of Mg (mg plant 1 ) in the tops of 14 tropical cover crops under three P levels Plevels(mgkg 1 ) Crotalaria 0.54g 2.46d 2.86b Sunnhemp 5.70de 15.20bc 27.20a Crotalaria 0.97fg 3.04d 3.32b Crotalaria 1.20fg 3.87d 5.46b Crotalaria 1.40fg 6.48cd 12.35b Calapogonio 1.24fg 4.23d 1.09b Pueraria 1.13fg 3.91d 4.69b Pigeonpea (black) 2.78efg 11.38cd 7.88b Pigeonpea (mixed color) 1.51fg 7.42cd 6.64b Lablab 4.02def 21.60b 32.09a Mucuna bean ana 10.85c 23.17b 26.62a Black mucuna bean 7.14d 22.05b 28.25a Gray mucuna bean 17.33b 23.86b 36.11a White jack bean 21.34a 33.26a 38.51a Average a Plevels(P) CV (%) Significant at the 1% probability level. Notes. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test. Table 19 Uptake of S (mg plant 1 ) in the tops of 14 tropical cover crops under three P levels Plevels(mgkg 1 ) Crotalaria 0.30h 1.45g 2.01de Sunnhemp 3.05cd 8.90cde 13.30bc Crotalaria 0.56gh 2.08fg 2.03de Crotalaria 0.90fgh 3.27efg 4.10de Crotalaria 0.76fgh 4.26fg 7.34cd Calapogonio 0.67gh 2.90g 0.57e Pueraria 0.44h 2.29def 2.21de Pigeonpea (black) 1.62efg 7.13efg 5.31de Pigeonpea (mixed color) 0.89fgh 5.50b 5.19de Lablab 1.83ef 14.94bc 18.22ab Mucuna bean ana 3.55c 12.46bcd 12.50bc Black mucuna bean 2.06de 10.92bcd 12.56bc Gray mucuna bean 5.47b 11.53a 19.80a White jack bean 10.87a 20.25a 23.53a Average Plevels(P) CV (%) Significant at the 1% probability level. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test.

22 Soil P versus Cover Crops 3359 Figure 3. Growth of sunnhemp (Crotalaria juncea) at three P levels. Left to right 0, 100, and 200 mg Pkg 1 soil. with the addition of P. Figures 3 6 show increases in dry weight of four cover crops with increasing P levels in the soil. Uptake of macronutrients was in the order of N > K > Ca > Mg > S > P. Similar order of macronutrient uptake has been reported in many species of legume crops (Reuter and Robinson 1986; Baligar, Fageria, and He 2008). Greater uptake of N by cover crops is interesting in reduction of its loss from the soil profile as nitrate (NO 3 ), which can be used by succeeding crops. Baligar and Fageria (2007) reported that one of the important benefits of using cover crops in the cropping systems is the recycling of the nutrients, including N. Significant variability in nutrient uptake among cover crop species is associated with different growth habits and amount of dry matter accumulated in the shoot of the cover crop species (Baligar, Fageria, and He 2008). Figure 4. Growth of Mucuna aterrima (black mucuna) at three P levels. Left to right 0, 100, and 200 mg P kg 1 soil.

23 3360 N. K. Fageria et al. Figure 5. Growth of gray mucuna (Mucuna cinereum) at three P levels. Left to right 0, 100, and 200 mg P kg 1 soil. Figure 6. Growth of white jack bean (Canavalia ensiformis) at three P levels. Left to right 0, 100, and 200 mg P kg 1 soil. Uptake of Micronutrients Uptake of Cu, Fe, Mn, and Zn was significantly influenced by P level and cover-crop treatments (Tables 20 23). Similarly, P cover crops interactions were also significant for the uptake of these nutrients. Overall, uptake of Cu, Fe, Mn, and Zn increased with the increasing P levels. This was related with improvement of dry-matter yield of cover crops with the addition of P (Table 2 and Figures 3 6). The uptake of micronutrients was in the order of Fe > Mn > Zn > Cu. It was reported by Fageria (2009) that among the micronutrients, Cu uptake by annual crops is less than that of other micronutrients. The greater uptake of Fe and Mn is related to greater concentrations of these elements in the Brazilian Oxisols (Fageria and Breseghello 2004). Baligar et al. (2006) also reported greater uptake of Mn

24 Soil P versus Cover Crops 3361 Table 20 Uptake of Cu (µgplant 1 ) in the tops of 14 tropical cover crops under three P levels Plevels(mgkg 1 ) Crotalaria 1.77d 5.64f 8.33ef Sunnhemp 13.19cd 39.92bcd 40.74cd Crotalaria 2.96d 8.85ef 7.07ef Crotalaria 2.99d 9.21ef 12.42ef Crotalaria 2.73d 12.54def 23.02def Calapogonio 2.32d 9.63ef 2.17f Pueraria 2.24d 7.75f 8.50ef Pigeonpea (black) 11.64cd 38.61bcde 29.14de Pigeonpea (mixed color) 5.95d 25.79cdef 22.18def Lablab 5.16d 44.24abc 57.73bc Mucuna bean ana 25.49bc 66.88ab 72.35b Black mucuna bean 7.63d 46.41abc 61.19bc Gray mucuna bean 45.88a 73.81a a White jack bean 33.67ab 65.44ab 62.04bc Average Plevels(P) CV (%) Significant at the 1% probability level. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test. Table 21 Uptake of Fe (µg plant 1 ) in the tops of 14 tropical cover crops under three P levels Plevels(mgkg 1 ) Crotalaria b 63.63b a Sunnhemp b a a Crotalaria 27.94b 91.26b a Crotalaria 55.47b b a Crotalaria b b a Calapogonio b b 90.42a Pueraria b b a Pigeonpea (black) b ab a Pigeonpea (mixed color) 74.05b b a Lablab b a a Mucuna bean ana b b a Black mucuna bean b b a Gray mucuna bean a a a White jack bean a a a Average Plevels(P) CV (%) Significant at the 1% probability level. Note. Means followed by the same letters in the same column are not significant at the 5% probability level by Tukey s test.