Microsoft Word - 11-Agra_36936 914 Original Article Biosci. J., Uberlândia, v. 33, n. 4, p. , July/Aug. 2017 MACRONUTRIENTS RELEASE BY GREEN MANURE SPECIES GROWN IN CERRADO/PANTANAL ECOTONE LIBERAÇÃO DE MACRONUTRIENTES POR ESPÉCIES DE ADUBAÇÃO VERDE CULTIVADAS NO ECÓTONO CERRADO/PANTANAL Caio Cezar Guedes CORREA¹; Paulo Eduardo TEODORO²; Flavia Alves da SILVA¹; Larissa Pereira RIBEIRO²; Angelita dos Santos ZANUNCIO³; Gessi CECCON 4 ; Francisco Eduardo TORRES³ 1. Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ, Brasil. 2. Universidade Federal de Viçosa, Viçosa, MG, Brasil; 3. Universidade Estadual de Mato Grosso do Sul, Aquidauana, Brasil. 4. Embrapa Agropecuária Oeste, Dourados, Brasil. ABSTRACT: Assessing the nutrient release by cover crops species, especially those used in green manure, is important for planning activities aimed at the higher economic return. The use of these species in order to improve the growing conditions in the transition region between the Cerrado and Pantanal biomes, which have particular characteristics, may be a viable alternative. This study aimed to evaluate the amount of biomass produced and macronutrients released in this biomass by different green manure species grown in the Cerrado/Pantanal ecotone. The trial was carried out from April 2013 to June 2014 in the Plant Science sector at State University of Mato Grosso do Sul, Aquidauana-MS (Brazil). Experimental design was completely randomized arranged in time split plot, with four replications. First factor consisted of seven species of green manure, while the second were seven evaluation times (months). The variables evaluated were: dry mass of shoot and nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) contents as a function of time. For all variables evaluated there was significant interaction between the green manure species and the collection months. Vegetable cover showed different rates of decomposition and nutrient release. Mucuna aterrima was the species that produced higher amounts of dry mass and nutrient content. After four months of cutting the plants, green manure species do not differentiate between the amounts of released nutrients. KEYWORDS: Fabaceae. Cover crops. Nutrients. Organic matter. Mucuna aterrima. INTRODUCTION The main an most important economic activity in the Cerrado/Pantanal ecotone region is the extensive beef cattle, followed by fishing, mining, tourism and agriculture (CALHEIROS; FONSECA JUNIOR, 1996). Extensive beef cattle, whose initial reporting dates from 200 years ago, is characterized by having low performance indexes with disabilities especially in birth and weaning rates as well as poor animal and vegetable sanitary management (ÍTAVO et al., 2016). A common practice in this activity was the regular use of fire, which generated extensive degraded areas resulting in low profitability and socioeconomic return for the region, with vast territorial extensions under high degree of deterioration (CHEFER; DE SOUZA, 2016). It is necessary to encouraging conservation practices and agroecological systems in order to reverse this situation (GAMA-RODRIGUES et al., 2007). An alternative would be to accelerate the action of the biotic components in the productive environment, mainly in the soil with the use of nutrient recycling techniques. Several researches have demonstrated that the practice of cultivating green manure species as a soil cover is a method that will bring many qualitative and economic benefits to the productive environment besides ecological sustainability (DA COSTA et al., 2016; GAMA-RODRIGUES et al., 2007; PACHECO et al., 2011; TORRES et al., 2005). One of the benefits of using green manures is the nutrients release from the plant biomass. Among the nutrients, one that has received more attention due to its greater mobility in the soil lately, is the nitrogen (N), which has been one of the most limiting in the productive systems (GIACOMINI et al., 2003). The use of green manure, especially species from the Fabaceae family, it is essential because they are able to N fixation (BNF - Biological Nitrogen Fixation). This characteristic considerably increases the economic return of the main activity considerably, besides reducing the application of the conventional chemical fertilizers. Species from this botanical family also present rapid decomposition compared to other families (PERIN et al., 2003). This happens because these plants present low relation between carbon and nitrogen (C/N ratio) to (GIACOMINI et al., 2003). In this Received: 15/12/16 Accepted: 03/05/17 915 Macronutrients release... CORREA, C. C. G. et al Biosci. J., Uberlândia, v. 33, n. 4, p. 914-922, July/Aug. 2017 family there are many compounds that are easily dissolved, which increases and accelerate the decomposition and mineralization of nutrients and carbon, favoring the microorganisms present in the soil (DE SOUZA et al., 2012). Thus, undoubtedly the use of integrated techniques that seek the rational use of these species is a conservationist practice (MULVANEY et al., 2010). The use of residues on the soil surface, especially the no-tillage system is a natural reserve of nutrients, which can be released quickly or slowly according to the characteristics of the species used as cover. According to HEAL et al. (1997), the decomposition of biomass is regulated by the interaction of the soil and climatic conditions, the chemical and structural properties of the vegetation cover and the presence of the decomposing community, such as the macro and microorganisms. In general, the climate can have little influence on the variation of its properties in a wide unit of space and ends up controlling the decomposition on a regional scale. The structural and chemical characteristics of the plant tissues from each species affects the process on a local scale (BERG, 2000). Bearing this in mind, the use of green manure species together with the awareness of the factors regulating the nutrient release become of ecological and economic importance for successor crops (GAMA-RODRIGUES et al., 2007). In order to evaluate the nutrients release by several crops of green manure, some authors verified several results. In this study on Cajanus cajan (TORRES et al., 2005), the crop reached 62 kg.ha�1 of nitrogen in its dry mass at 110 days after sowing in the second harvest. This very same crop and the forage peanut (Arachis pintoi Krap. & Greg) showed the greatest macronutrients (N, P, K, Ca, Mg and S) release rates over 140 days in the study carried out by (GAMA-RODRIGUES et al., 2007). In this sense, knowing the dynamics of plant residues decomposition of several species in a certain environment such as the Cerrado/Pantanal ecotone will provide information that will support the establishment of more successful cropping systems. This study aimed to evaluate the amount of biomass produced and macronutrients released in this biomass by different green manure species grown in the Cerrado/Pantanal ecotone. MATERIAL AND METHODS The experiment was carried out between April 2013 and June 2014 in the Plant Science sector at State University of Mato Grosso do Sul (UEMS/UUA), Aquidauana-MS (Brazil), with an average altitude of 170 m. The area soil was identified by (SCHIAVO et al., 2010) as being Red Ultisol distrophic sand texture with the following chemical properties at the depth 0 - 0,20 m: pH (H2O) = 6.2; Al 3+ (cmolc dm-3) = 0.0; Ca+Mg (cmolc dm-3) = 4.31; P (mg dm-3) = 41.3; K (cmolc dm-3) = 0.2; organic matter (g dm-3) = 19.74; V (%) = 55; m (%) = 0.0; sum of bases (cmolc dm-3) = 4.51; CEC (cmolc dm-3) = 5.1. Region climate, according to Köppen’s classification, is Aw (Savanna Tropical) with hot and humid summer and cold and dry winter and the two periods well determined. Seven species of green manure were grown: Canavalia ensiformis L. DC., Mucuna aterrima Piper and Tracy (Merr.), Dolichos lablab L., Cajanus cajan L. Millsp., Crotalaria juncea L., Crotalaria ochroleuca (G. Don) and Crotalaria spectabilis (Roth). Soil preparation was carried out at the beginning of May 2013. Tillage system was adopted, with plowing and leveling. Green manure species were then seeded manually afterwards using the same spacing of 0.5 m between rows and 14 plants per meter for all species. The experimental plots had 25 m². Cultural practices consisted of manual control of weeds (weeding) whenever they reached stage 4 to 6 expanded leaves. This practice was extended until the crop caused the suppression of invasive plants. No sowing or cover fertilization was performed. On December 21, 2013, all green manures were harvested close to the soil (cutting) and the biomass left fallow for natural decomposition. In this biomass, at the cutting time, four replicates of 1 m² from each species were collected to evaluate the green mass. This amount was dried in a forced circulation air oven for 72 hours at 60°C and the dry mass was measured, which served as a proportional reference for the calculations of the later collected. In order to evaluate the nutrients release of the green manures biomass, we used the method proposed by (AITA; GIACOMINI, 2003). Evaluations were made in seven periods: time 0 (at the cutting time), time 1 (one month after cutting), time 2 (two months after cutting), and successively until time 6 (six months after cutting). For evaluating nutrient amounts, samples of 60 g from green biomass were conditioned inside decomposition bags (literbag) at the cutting time and were randomly left fallow on the soil for decomposition next to the biomass corresponding to the species. We used 28 literbags corresponding to 916 Macronutrients release... CORREA, C. C. G. et al Biosci. J., Uberlândia, v. 33, n. 4, p. 914-922, July/Aug. 2017 four replications per evaluation time for each species, that resulting in 196 literbags. Literbags have dimensions of 25 x 25 cm and 2 mm. At the collection time, literbags that were left in the experimental area were previously cleaned in running water to remove the soil particles adhered to the mesh and biomass. Subsequently, the samples were placed in paper bags and oven dried with forced air circulation at 60°C for 72 hours. After the drying period, the samples were ground in a Willey mill and sent to a specialized laboratory for the chemical analysis, where were made the determination of macronutrients contents: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) as described by (MALAVOLTA, 1997). Macronutrients content at each time in the amount of biomass was obtained by the relationship between the nutrient mass contained in a sample and the total biomass produced by species. Thus, it was possible to observe during the evaluation times the quantity accumulated of certain nutrient released. Experimental design was completely randomized arranged in time split plot, with four replications. First factor consisted of seven species of green manure: Feijão-de-porco (Canavalia ensiformis (L.) DC.), Mucuna preta (Mucuna aterrima Piper e Tracy (Merr.)), Lab-lab (Dolichos lablab L.), Feijão-Guandu (Cajanus cajan (L.) Millsp.), Crotalaria juncea (L.), Crotalaria ochroleuca (G. Don) and Crotalaria spectabilis (Roth). Second factor was composed by seven evaluation times (months): time 0 (December), time 1 (January), time 2 (February), time 3 (March), time 4 (April), time 5 (May) and time 6 (June). The following variables were evaluated: dry mass and nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) contents as a function of time. The analyzed variables were initially submitted to the Shapiro-Wilk test to verify the residue normality, Bartlett test to verify the homogeneity between the variances and Mauchly test to verify if the covariance matrix structures met the sphericity condition. After meeting the above assumptions, data were submitted to analysis of variance applying the F test. Qualitative factor (green manure species) was submitted to the comparison of means by Tukey test at 1% probability level and the quantitative to the polynomial regression analysis. For regression analysis, dispersion diagrams were initially made and from the previous analysis the models tested were linear and exponential. The best adjusted equation was chosen according to the coefficient of determination and the regression coefficients significance, tested by the t-test (P<0.001). The mean Euclidian distance was used as a measure of similarity and the Ward cluster method for the determination of species with closer characteristics. All analyzes were performed with R and SAS computational applications. The climatic conditions during the seven collections are expressed in Figure 1. Figure 1. Climatic conditions regarding the period of biomass decomposition of the green manure species grown in Cerrado-Pantanal ecotone. RESULTS AND DISCUSSION For all the variables evaluated, the analysis of variance revealed a significant effect (p>0.01) species for the factor green manure species (S), month collection (M) and their interaction (Table 1). These results are explained by the different phenologies of the species that have diverse genera 917 Macronutrients release... CORREA, C. C. G. et al Biosci. J., Uberlândia, v. 33, n. 4, p. 914-922, July/Aug. 2017 (high significance for the factor S) and the set of factors that acts during the period of the straw of these species, such as climatic conditions, action of microorganisms, C/N ratio, among others. Similar results were obtained in other studies that evaluated the nutrients release by species from the Fabaceae family over time (GAMA-RODRIGUES et al., 2007; PACHECO et al., 2011; TORRES et al., 2005). Table 1. Summary of the analysis of variance (mean squares) for the variables dry mass (DM) and nitrogen, phosphorus, potassium, calcium, magnesium and sulfur contents evaluated in seven green manure species grown in the Cerrado-Pantanal ecotone. SV DF DM N P K Ca Mg S Species (S) 6 12073255.31* 22760.35* 95.37* 2125.51* 4560.31* 94.03* 56.63* Error 1 21 95589.48 289.84 2.24 7.49 53.39 1.47 0.87 Month (M) 6 9698625.72* 29095.72* 196.79* 4292.05* 8937.32* 118.14* 76.37* S x M 36 716089.08* 2814.33* 18.13* 735.16* 764.89* 9.67* 6.13* Error 2 126 10009.05 29.39 0.70 4.07 8.78 0.17 0.17 CV 1 (%) --- 30.86 44.92 54.06 33.49 40.09 53.13 47.50 CV 2 (%) --- 9.99 14.30 30.13 24.69 16.26 17.95 20.82 *: significant at 1% probability by F test; SV: sources of variation; DF: degrees of variation; CV: coefficient of variation. M. aterrima produced greater shoot mass (4,336.59 kg ha-1) in the first month of evaluation (December) (Table 2). This position is maintained in all collection times. Results in similar magnitudes were observed by (SUZUKI; ALVES, 2006). However, these authors observed the highest dry mass production for the C. juncea species at environments with succession to soybean crops. M. aterrima, because it is a species with low growth with very vigor, extending its cycle until obtaining favorable conditions for flowering, it is more stable in producing phytomass independent of the environment (DE CAMARGO; PIZA, 2007). Table 2. Remaining dry biomass on soil for each green manure species into evaluation time (months) and nitrogen, phosphorus and potassium contents in this biomass grown in the ecotone Cerrado-Pantanal. Species December January February March April May June Equation of regression R² Dry mass (kg ha-1) C. juncea 1690.57 c 1332.55 c 1076.45 cd 820.36 c 613.84 c 415.65 cd 192.86 b -242.4x+ 1604.9 0.990 C. ochroleuca 604.09 e 539.70 e 480.27 e 420.81 d 371.83 d 260.19 de 83.31 c -79.6x + 633.2 0.942 C. spectabilis 1699.05 c 1509.17 c 1258.70 c 957.16 c 720.74 c 512.64 bc 211.09 ab -249.8x + 1730.7 0.997 C. cajan 889.14 d 619.60 d 489.46 e 359.32 d 263.27 d 182.03 e 51.89 c -129.0x + 794.9 0.963 C. ensiformis 2853.49 b 2153.51 b 1716.88 b 1280.26 b 953.01 b 673.33 b 236.71 ab -413.4x + 2649.7 0.981 D. lablab 1056.95 d 997.94 d 867.85 d 770.47 c 593.13 c 382.70 cd 114.13 c -154.7x + 1147.0 0.954 M. aterrima 4336.59 a 3489.09 a 2793.67 a 2098.25 a 1569.07 a 1112.17 a 416.75 a -633.5x + 4159.0 0.992 N (kg ha-1) C. juncea 100.77 b 56.26 c 38.43 bc 24.72 bc 16.44 bcd 10.22 ab 3.84 a -14.46x + 79.19 0.858 C. ochroleuca 28.79 e 24.52 e 18.44 de 12.90 de 9.34 cd 5.59 b 1.09 a -4.65x + 28.32 0.993 C. spectabilis 86.64 c 64.21 bc 49.02 b 34.53 b 23.01 b 13.83 ab 4.27 a -13.35x + 79.41 0.975 C. cajan 45.04 d 29.62 e 14.21 e 9.39 e 6.20 d 3.85 b 0.60 a -6.89x + 36.22 0.854 C. ensiformis 108.49 b 71.16 b 47.94 b 30.30 bc 18.48 bc 11.53 ab 4.07 a -15.50x + 91.21 0.912 D. lablab 40.03 de 34.77 e 27.47 cd 21.41 cd 14.26 bcd 8.59 b 1.99 a -6.42x + 40.47 0.999 M. aterrima 241.34 a 172.11 a 127.56 a 73.19 a 39.99 a 21.59 a 5.15 a -39.19x + 214.83 0.992 P (kg ha-1) 918 Macronutrients release... CORREA, C. C. G. et al Biosci. J., Uberlândia, v. 33, n. 4, p. 914-922, July/Aug. 2017 C. juncea 7.34 c 5.10 b 3.94 ab 2.16 abc 1.43 ab 0.75 a 0.27 a -1.16x + 6.47 0.953 C. ochroleuca 2.31 d 1.87 c 0.94 c 0.68 c 0.53 ab 0.32 a 0.07 a -0.36x + 2.05 0.907 C. spectabilis 6.63 c 5.48 b 3.26 bc 1.89 bc 1.11 ab 0.58 a 0.18 a -1.12x + 6.09 0.933 C. cajan 3.01 d 1.66 c 1.06 c 0.61 c 0.38 b 0.19 a 0.02 a -0.45x + 2.34 0.853 C. ensiformis 9.79 b 5.91 b 3.95 ab 2.47 ab 1.21 ab 0.70 a 0.20 a -1.50x + 7.95 0.889 D. lablab 4.00 d 3.28 c 2.37 c 1.91 bc 1.15 ab 0.61 a 0.09 a -0.65x + 3.87 0.993 M. aterrima 19.64 a 11.44 a 5.59 a 3.82 a 2.16 a 1.31 a 0.41 ab -2.91x + 15.05 0.992 K (kg ha-1) C. juncea 31.48 b 22.39 b 1.77 b 1.23 a 0.92 a 0.62 a 0.22 a -4.93x + 23.18 0.777 C. ochroleuca 8.03 e 3.09 d 0.72 b 0.64 a 0.52 a 0.26 a 0.08 a -1.06x + 5.09 0.632 C. spectabilis 26.13 c 14.02 c 4.99 ab 2.06 a 1.37 a 0.77 a 0.30 a -3.84x + 16.62 0.740 C. cajan 15.88 d 1.49 d 0.79 b 0.54 a 0.40 a 0.16 a 0.02 a -1.08x + 8.18 0.753 C. ensiformis 35.45 b 5.47 d 3.44 ab 2.06 a 1.43 a 1.01 a 0.21 a -4.17x + 19.50 0.789 D. lablab 12.56 d 3.13 d 1.96 b 1.54 a 1.03 a 0.53 a 0.11 a -1.55x +7.64 0.797 M. aterrima 98.09 a 74.76 a 7.40 a 4.20 a 2.80 a 1.67 a 0.63 a -26.05(0.19x) + 15.05 0.841 Means followed by lower case letters in the same column do not differ by Tukey test at 1% probability; R²: coefficient of determination. This species also has a more distributed root system over the profile (ALVARENGA et al., 1995) allowing it to explore a greater volume of soil. However, C. juncea showed to be more responsive to soils with frequent fertilization and the presence of high concentration of nitrogen fixing bacteria strains (soybean cultivation). This fact explains the intermediate performance of this species together with C. spectabilis (1690.57 and 1699.05 kg ha-1, respectively), in the collection of December. C. cajan, D. lablab and C. ochroleuca presented the lowest means of dry mass in all evaluation periods. (TORRES et al., 2008) evaluating green manure species also found low dry mass yield for these species. These authors concluded that due to low leaf area index and low C/N ratio, they produce less dry mass and decomposing at higher rates. However, these species have roots with excellent beneficial characteristics for the soil. It is possible to observe that with material at the field for longer periods, there is a uniformization trend among species in the release of N, P and K from the 6th, 5th and 3rd month, respectively. Given these results, we can infer that the use of these species for soil cover over the off-season should be carried out a few months before the crop-target be sown. This technique will benefit the subsequent crop for providing better utilization of higher contents of available nutrients and the non- fructification of the green manures will prevent them from becoming invasive plants later. High temperatures and rainfall accelerate the process of plant tissues decomposition, since these factors increase the biological activities of the soil (HEINZ et al., 2011). The conditions found in this trial (Figure 1) reinforce the rapid decrease in Ca, Mg and S contents (Table 3) in the first months (December 2013 to March 2014), and the low dry mass availability of green manures in the last collection times and, consequently, these are not different between species in these periods. In general, in relation to the secondary macronutrients, the species that provided the highest Ca content were M. aterrima (107.4 kg.ha-1) and D. lablab (95.98 kg.ha-1). The other species presented smaller results, but with differences between them. Regarding Mg, there is the same trend, with the emphasis to C. juncea and C. spectabilis. For the S, M. aterrima also was superior until the fourth month (11.17; 5.46; 5.61 and 5.36 kg ha-1). M. aterrima Immobilized twice as much (sometimes more) nutrients than the other species evaluated at all collection times. 919 Macronutrients release... CORREA, C. C. G. et al Biosci. J., Uberlândia, v. 33, n. 4, p. 914-922, July/Aug. 2017 Table 3. Unfolding the significant interaction for each green manure species into evaluation time (months) for calcium, magnesium and sulfur contents (Ca, Mg, S, respectively) evaluated in seven green manure species grown in the ecotone Cerrado-Pantanal. Species December January February March April May June Equation of regression R² Ca (kg ha-1) C. juncea 42.21 c 27.00 c 16.40 cd 12.29 b 8.56 abc 5.20 ab 1.27 a -6.22x + 34.80 0.777 C. ochroleuca 13.47 e 11.13 e 5.66 e 4.16 c 2.48 cd 1.16 ab 0.35 a -2.23x + 12.18 0.632 C. spectabilis 43.57 c 30.74 c 21.61 c 12.88 b 9.42 ab 4.26 ab 1.27 a -6.86x + 38.25 0.943 C. cajan 17.35 e 10.96 e 8.02 e 4.21 c 2.14 d 0.60 b 0.06 a -2.80x + 14.60 0.917 C. ensiformis 95.98 b 51.27 b 29.29 b 12.84 b 8.21 bcd 4.08 ab 0.81 a -21.45 (0.13x) + 80.51 0.789 D. lablab 30.43 d 21.46 d 15.15 d 10.56 b 5.65 bcd 2.47 ab 0.12 a -4.94x + 27.09 0.960 M. aterrima 107.40 a 76.87 a 53.60 a 25.01 a 14.28 a 7.96 a 1.37 a -17.69x + 93.99 0.925 Mg (kg ha-1) C. juncea 6.32 b 3.82 b 2.61 b 1.81 b 1.01 b 0.46 b 0.11 a -0.96x + 5.19 0.905 C. ochroleuca 2.04 d 1.34 c 0.98 c 0.80 cd 0.56 b 0.25 b 0.04 a -0.31x + 1.78 0.950 C. spectabilis 6.10 b 4.07 b 2.95 b 1.62 bc 1.00 b 0.50 b 0.04 a -0.97x + 5.25 0.934 C. cajan 2.58 cd 1.52 c 0.93 c 0.61 d 0.35 b 0.11 b 0.05 a -0.39x + 2.05 0.874 C. ensiformis 6.26 b 3.76 b 2.71 b 1.70 b 1.05 b 0.12 b 0.00 a -0.99x + 5.19 0.917 D. lablab 3.03 c 1.88 c 1.43 c 1.18 bcd 0.70 b 0.30 b 0.02 a -0.46x + 2.61 0.944 M. aterrima 14.65 a 10.59 a 7.91 a 5.33 a 2.97 a 1.42 a 0.24 a -2.38x + 13.28 0.968 S (kg ha-1) C. juncea 5.61 b 3.68 bc 2.69 bc 1.78 b 1.20 bc 0.77 ab 0.20 a -0.84x + 4.40 0.932 C. ochroleuca 1.92 c 1.36 d 1.05 d 0.81 cd 0.60 cd 0.35 ab 0.07 a -0.29x + 1.74 0.973 C. spectabilis 5.36 b 4.05 b 3.13 b 2.28 b 1.51 ab 0.80 ab 0.19 a -0.84x + 5.00 0.986 C. cajan 1.81 c 1.01 d 0.75 d 0.46 d 0.25 d 0.07 b 0.00 a -0.28x + 1.46 0.893 C. ensiformis 5.46 b 3.12 c 2.14 c 1.48 bc 0.78 bcd 0.34 ab 0.00 a -0.83x + 4.40 0.894 D. lablab 1.83 c 1.47 d 1.09 d 0.87 cd 0.53 cd 0.18 ab 0.00 a -0.51x + 1.78 0.993 M. aterrima 11.17 a 8.40 a 6.11 a 4.01 a 2.25 a 0.96 a 0.10 a -1.86 + 10.28 0.972 Means followed by lower case letters in the same column do not differ by Tukey test at 1% probability; R²: coefficient of determination. All species presented a linear fit in the model adjustment as a function of time for the dry mass production (Table 2). M. aterrima presented the greatest amount of masses over the months. According to the regression coefficient, the phytomass decomposition rate of this species was 633.5 g per hectare. It was the fastest rate of decomposition, and consequently, the species that releases higher nutrients contents in a smaller time unit. In contrast, C. acholeuca showed the slowest rate of biomass decomposition (79.63 grams per day) and yielded the lowest average dry mass with 604.09 kg ha-1 (Table 2). C. cajan, with rate of decomposition of 129 g per day, at the end of collection times, it presented little or no remaining material for decomposition (Table 2). With the exception of M. aterrima and C. cajan, the other species presented slow macronutrients release (decomposition of little phytomass in time unit). This fact can be explained by the high carbon/nitrogen ratio in the vegetal tissues from these species, which causes slowness of soil organisms to decompose this matter (SODRÉ FILHO et al., 2004). According to (LIMA et al., 2012), a comparison of the carbon ratio among M. aterrima (14/1) and Crotalaria spp. (30/1) it explains the faster biomass decomposition by M. aterrima. All species presented a linear adjustment in the model adjustment as a function of time for the amount of N released (Table 2). M. aterrima species had the highest amount of N released every month. According to the regression coefficient for M. aterrima, rate of release of this nutrient from the remaining phytomass was 39.19 kg ha-1 per day. The 920 Macronutrients release... CORREA, C. C. G. et al Biosci. J., Uberlândia, v. 33, n. 4, p. 914-922, July/Aug. 2017 other species ranged from 4.65 to 15.5 kg ha-1 per day (C. ochroleuca and C. ensiformis, respectively). For the amount of released P, there was a linear adjustment of the regression equation model in all species (Table 2). M. aterrima Released the highest amounts of the nutrient in the experimental period, with an average of 2.91 kg ha-1 per day. At fifth month, there were practically no remaining P content to be released. Only M. aterrima presented an exponential adjustment for the amounts of K released as a function of the months elapsed (Figure 5), being the one that released larger amounts of this nutrient. The other species presented linear adjustment and released smaller amounts of this nutrient. These results are similar to those observed by (TORRES; PEREIRA, 2008). Canavalia ensiformis presented an exponential adjustment for the amounts of Ca released (Table 2) in function of the months elapsed. This species provided the highest amount of Ca in the initial month, presenting a sudden drop in the amount of this nutrient released over the trial. The other species presented linear adjustment, where M. aterrima released the highest amounts of Ca from the second month, and on a regular way (17.69 kg ha-1). All green manure species presented linear adjustment of the regression equation for both the released of Mg and S (Table 3). Again M. aterrima stood out over the other species (which presented similar results among themselves) with larger amounts for both nutrients (2.38 and 1.86 kg ha-1, respectively). The fact that M. aterrima has released the highest amounts of nutrients in all nutrients is strictly related to the production of dry mass. M. aterrima produced more phytomass and the greater amount available for decomposition releases larger amounts of nutrientes. The product of the nutrient contents in the samples of each collection time versus the relation of the loss of mass of these samples and the total dry biomass produced by each species helps to understand the results observed in this study. It is necessary to observe some factors in order to choose a green manure species. For example, the succession of C. cajan with another summer crop in the same agricultural year is not possible due to its long cycle. However, its cultivation in fallow areas would be interesting because of its great capacity to promote physical improvements in the soil and can be used as an alternative source of animal protein supplementation (ALVARENGA et al., 1995). In addition to this, there are allelopathic effects on weeds, which also deserve attention. Several authors describe the use of green manure species for this purpose; (CAAMAL-MALDONADO et al., 2001) (SEVERINO; CHRISTOFFOLETI, 2004; ZANUNCIO et al., 2013) and (SEVERINO; CHRISTOFFOLETI, 2001) as an integrated management for controlling weeds, however, the allelopathic effect caused on the main crop also should also be observed. For example, M. aterrima, a species that best exceled in this trial due to the great amount released from all macronutrients, it exerts a strong allelopathic effect (reduction of significant yield) when grown before common bean (MENEZES et al., 2009). CONCLUSIONS Green manures showed different rates of decomposition and macronutrients release. Mucuna aterrima was the species that produced higher amounts of dry mass and nutrient content. After four months of cutting the plants, green manure species do not differentiate between the amounts of released nutrients. RESUMO: Avaliar a liberação de nutrientes por espécies de plantas de cobertura, especialmente aquelas utilizadas na adubação verde é importante para o planejamento das atividades objetivando o maior retorno econômico. O uso dessas espécies afim de se melhorar as condições de cultivo na região de transição entre os biomas do Cerrado e Pantanal que possuem características particulares, pode ser uma alternativa viável. O objetivo deste trabalho foi avaliar as taxas de liberação de macronutrientes de diferentes espécies de adubação verde cultivadas no ecótono Cerrado/Pantanal. O experimento foi realizado entre os meses de abril de 2013 a junho de 2014 no setor de Fitotecnia da Universidade Estadual de Mato Grosso do Sul, Aquidauana-MS. O delineamento experimental adotado foi o inteiramente casualizado disposto em esquema de parcelas subdivididas no tempo, com quatro repetições. O primeiro fator consistiu em sete espécies de adubação verde, enquanto o segundo em sete épocas (meses) de avaliação. As variáveis avaliadas foram: massa seca da parte aérea e quantidades de nitrogênio (N), fósforo (P), potássio (K), cálcio (Ca), magnésio (Mg) e enxofre (S) liberados em função do tempo. Para todas as variáveis avaliadas houve interação significativa entre as espécies de adubação verde vezes os meses de coleta. As coberturas vegetais apresentaram distintas taxas de decomposição e de liberação de nutrientes. 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