Marcelo Grandi Teixeira

Perennial herbaceous legumes as live soil mulches and their effects on C, N and P of the microbial biomass

The use of living mulch with legumes is increasing but the impact of this management technique on the soil microbial pool is not well known. In this work, the effect of different live mulches was evaluated in relation to the C, N and P pools of the microbial biomass, in a Typic Alfisol of Seropedica, RJ, Brazil. The field experiment was divided in two parts: the first, consisted of treatments set in a 2 x 2 x 4 factorial combination of the following factors: live mulch species (Arachis pintoi and Macroptilium atropurpureum), vegetation management after cutting (leaving residue as a mulch or residue remotion from the plots) and four soil depths. The second part had treatments set in a 4 x 2 x 2 factorial combination of the following factors: absence of live mulch, A. pintoi, Pueraria phaseoloides, and M. atropurpureum, P levels (0 and 88 kg ha-1) and vegetation management after cutting. Variation of microbial C was not observed in relation to soil depth. However, the amount of microbial P and N, water soluble C, available C, and mineralizable C decreased with soil depth. Among the tested legumes, Arachis pintoi promoted an increase of microbial C and available C content of the soil, when compared to the other legume species (Pueraria phaseoloides and Macroptilium atropurpureum). Keeping the shoot as a mulch promoted an increase on soil content of microbial C and N, total organic C and N, and organic C fractions, indicating the importance of this practice to improve soil fertility.

Decomposição e liberação de nutrientes acumulados em leguminosas herbáceas perenes consorciadas com bananeira

Evaluating the decomposition of cover crop residues added to the soil allows improving the comprehension of appropriate nutrient supply for commercial crops. This study was carried out under field conditions aiming to evaluate the decomposition and nutrient release from the shoots of perennial herbaceous legumes. The treatments were green cover crops intercropped with banana: groundnut (Arachis pintoi Krapov. & W.C. Gregory.), tropical kudzu (Pueraria phaseoloides (Roxb.) Benth.), siratro (Macroptilium atropurpureum (Sesse & Moc. ex DC.) Urb.) and spontaneous vegetation (mainly Panicum maximum Jacq.). These species were cut during the dry (April 1997) and rainy seasons (January 1998). Aboveground cover crop samples were placed in litterbags, which were distributed on the plots soil surface. Dry matter decomposition and nutrient release were monitored through collection of litterbags at 5, 10, 15, 30, 60, 90, 120 and 150 days after cutting the cover crops. Dry matter decomposition of groundnut was the fastest and the spontaneous vegetation was the slowest. The decomposition constants decreased and residue half-lives increased during the dry season. There was a faster release of N, Ca and Mg in the legumes, while spontaneous vegetation presented similar results for P. Among the chemical variables under study, the cellulose and hemicellulose contents were correlated with dry matter loss. N release was correlated with C and hemicellulose contents. Results indicate the potential of perennial herbaceous legumes for nutrient release, particularly in the case of tropical kudzu and siratro.

Bananeiras consorciadas com leguminosas herbáceas perenes utilizadas como coberturas vivas

The objective of this work was to evaluate the yield of banana plants intercropped with the perennial herbaceous legumes forage groundnut (Arachis pintoi), tropical kudzu (Pueraria phaseoloides) and siratro (Macroptilium atropurpureum). The control treatments were spontaneous vegetation (mainly Panicum maximum) and spontaneous vegetation plus nitrogen fertilizer application to banana plants. The vegetative growth of banana plants was also evaluated. Among the treatments, spontaneous vegetation and tropical kudzu promoted the highest dry matter productions; tropical kudzu had the highest amounts of accumulated and fixed N. Forage groundnut, tropical kudzu and siratro promoted the fastest vegetative growth for banana plants in this intercropped system. Tropical kudzu and siratro promoted the highest values for bunch weight and hands weight. All legume treatments result in a increase in the percentage of harvested bunches and a reduction in the harvesting time and are related to higher yields, compared to spontaneous vegetation treatment.

Nitrogen and phosphorus harvest indices of common bean cultivars: Implications for yield quantity and quality

Breeding for yield in common bean (Phaseolus vulgaris L.) should consider the efficiency of biomass and nutrient partitioning to grains. In field experiments, 9 and 18 bean cultivars were cultivated in 1998 and 1999, respectively, to identify the genotypic variability of harvest index (HI) and N and P harvest indices (NHI and PHI), and to evaluate the relationships between these indices and grain yield. Cultivars differed for grain yield, HI, NHI and PHI in both years, but these indices varied less than grain yield. Growth habit markedly influenced HI, with prostrate cultivars possessing higher HI, NHI and PHI than erect cultivars; hence selection for HI should be performed within each phenological group. Grain yield was strongly associated with grain N and P contents, and positively but weakly correlated to HI, NHI and PHI; the indices were highly correlated among themselves. Multiple-regression analysis showed that most genotypic variation of grain yield was associated with the amount of N and P accumulated by the crop at maturity, and some yield variation was associated with seed nutrient concentration, particularly P concentration, whereas NHI and PHI had a minor role. Combined analysis of both experiments showed that grain yield diminished by 57% from 1998 to 1999, whereas HI remained almost stable and NHI and PHI decreased slightly, but the significant year × cultivar interaction revealed different degrees of phenotypic plasticity of biomass partitioning among cultivars. Selection solely for increased HI would scarcely result in improved grain yield, raising concomitantly NHI and PHI and probably reducing grain P concentration.

Cobertura do solo e acumulação de nutrientes pelo amendoim forrageiro

Abstract€–€The objective of this work was to determine the rate of soil coverage, biomass yield and totalaccumulation of N, P and K in the aerial biomass of the legume Arachis pintoi Krapov. & W.C. Greg.The experimental design was a randomized block with four replicates arranged in a 2x4 factorial withtwo levels of row spacing (25 and 50€cm between rows) and four different planting densities (2, 4, 8and 16€plants/m). Complete soil coverage was achieved 224 days after planting. Planting density af-fected the rate of soil coverage and the rate of dry matter and nutrient accumulation by the shoot tissueof the legume, but these parameters were not significantly affected by row spacing. The results suggestthat the optimum planting density was 8€plants/m in rows spaced 50€cm apart.Index terms: Arachis pintoi , plant population, spacing, aerial parts, dry matter contents. (1) Aceito para publicacao em 25 de marco de 2003. (2) Universidade Federal de Vicosa, Dep. de Fitotecnia, AvenidaP.€H. Rolfs, s/n, CEP 36571-000 Vicosa, MG. E-mail:aperin@vicosa.ufv.br

Divergência genética entre cultivares locais e cultivares melhoradas de feijão

A grande variabilidade genetica presente no germoplasma de feijao (Phaseolus vulgaris L.) em uso na agricultura familiar no Brasil tem sido plenamente reconhecida. A eficiencia da conservacao e o aproveitamento desta variabilidade aumentam quando esta e devidamente caracterizada. O objetivo deste trabalho foi caracterizar a variabilidade genetica de parte do germoplasma existente em poder de produtores de feijao no Rio Grande do Sul, e de cultivares produzidas pela pesquisa, e reuni-las em grupos de similaridade genetica. Foi avaliada a divergencia genetica de 37 cultivares locais (land races) e 14 cultivares indicadas pela pesquisa no Estado, utilizando 40 descritores morfologicos; a grande maioria desses descritores sao necessarios a protecao legal. Empregou-se analise multivariada, por intermedio de componentes principais e metodo de agrupamento. O uso destas tecnicas possibilitou identificar descritores ineficientes ou redundantes no estudo da variabilidade genetica e reunir as cultivares estudadas em quatro grupos distintos de similaridade genetica. As cultivares locais revelaram variabilidade superior a encontrada nas cultivares oriundas da pesquisa, o que sugere a importância da sua inclusao em programas de melhoramento.

Ontogenetic variations on absorption and utilization of phosphorus in common bean cultivars under biological nitrogen fixation.

An experiment was conducted to evaluate the effect of plant ontogeny on traits associated with absorption and utilization of P by common bean (Phaseolus vulgaris L.) cultivars under biological N2 fixation through plant growth analysis. Eight cultivars were grown in pots at two levels of applied P (20 and 80 mg P kg−1 soil) and harvested at three growth stages (third trifoliate expanded, plentiful flowering, pod setting). The development of nodulation differed among cultivars and depended on P supply; some cultivars showed an intense decline in nodule number after flowering. There were different patterns of root growth: Some cultivars increased root area after flowering mainly by increasing root mass, whereas others by decreasing root radius. Despite the overall drift of reducing P influx into roots over time, some cultivars maintained P influx almost stable after flowering. Cultivars with greater root area had lower influx, whereas cultivars with smaller root area had higher influx, denoting a compensatory mechanism between root growth and P influx, such mechanism presenting ontogenetic variations associated to patterns of root area production. The cultivars differed in specific P utilization rate at low but not at high soil P level; hence P utilization seems an important physiological component for screening bean genotypes under limited P supply. High correlation between net assimilation rate and specific P utilization rate suggests that P utilization is strongly related to photosynthetic activity. Despite, the wide variation among cultivars on root growth, nodulation and rates of P absorption and utilization, the genotypic variability for total dry mass and P content was narrow by pod setting. Owing to growth constraints caused by a possible inefficient symbiosis, the concomitant selection of bean genotypes for tolerance to low P and high N2 fixation activity should prioritize traits related to the root system and to N2 fixation over total dry matter. The ontogenetic variations of traits associated with P absorption and utilization in common bean cultivars require evaluations at different plant growth stages.

Organic matter quality in a soil cultivated with perennial herbaceous legumes

Using herbaceous legumes in agricultural systems yields great quantities of plant residues, allowing changes in soil organic matter quality and content over the years. This study was conducted on an Ultisol, at Seropedica, RJ, Brazil, to evaluate the effects of different perennial herbaceous legumes on soil organic matter quality. A factorial scheme with three replications was used to evaluate the species: forage groundnut cv. BR-14951 (Arachis pintoi), tropical kudzu (Pueraria phaseoloides), and siratro (Macroptilium atropurpureum). After the first cut, each plot was divided into two subplots; plants were cut and left on the soil surface or cut and removed. Soil samples of a closed area covered by spontaneous vegetation (mainly C3 plants) or by Panicum maximum were also analysed. Samples were collected from two layers (0-5 and 5-10 cm), processed for the fractionation of organic matter and the evaluation of structural characteristics of humic acids (HA). Evaluated legumes did not change total organic carbon contents, but promoted HA accumulation in the superficial soil layer. Humic acids may be used as indicators of the management effects on soil organic fractions, because there was significant incorporation of carbon and nitrogen derived from the legume residues, even for the short experimentation time (28 months). Residue management did not modify quantitative aspects of the distribution of the humified organic matter, but promoted, however, a higher condensation degree of humic acids evaluated by the elementary composition, IR and fluorescence spectroscopy.

Efeito da cobertura viva com leguminosas herbáceas perenes na agregação de um argissolo

Tropical soils under continuous cultivation undergo fast degradation, leading to crop production decline, mainly due to erosion and reduction of soil organic matter levels. Soil protection with live mulching is one of the alternatives to alleviate these effects and to control soil degradation. This study was conducted to evaluate the root distribution and morphology of three perennial herbaceous leguminous species, as well as its effects on soil aggregation and organic carbon content when used as live mulching. The experiment was carried out on a Typic Haplustult soil in the experimental area of EMBRAPA Agrobiologia, Seropedica, State of Rio de Janeiro, Brazil, arranged in a completely randomized block design with three replicates. Treatments consisted of soil-covering with three herbaceous leguminous species (Arachis pintoi, Pueraria phaseoloides and Macroptilium atropurpureum) and a control treatment without live mulching, kept weed-free. Soil was sampled at depths of 0-5 and 5-10 cm for aggregate stability analysis and at depths of 0-5; 5-10; 10-20 and 20-40 cm for root distribution and morphology. A higher percentage of aggregates in the > 2.0 mm class was observed under A. pintoi and P. phaseoloides covers, 38 % above the control treatment mean. The values of mean weigth diameter aggregates of soil for leguminous treatments were also higher than in the weeded area for both depths, demonstrating the favorable effect of live mulch on soil aggregate stability. An increase in the organic soil carbon level was observed for the treatment with A. pintoi. Root morphology analysis showed that A. pintoi presented an intermediate root radius and higher root mass and area compared to other species, which may explain its positive effect on soil aggregation.

Growth and yield of common bean cultivars at two soil phosphorus levels under biological nitrogen fixation

The genotypic differences on growth and yield of common bean (Phaseolus vulgaris L.) in response to P supply were evaluated in a field experiment under biological N2 fixation. Eight cultivars were grown at two levels of applied P (12 and 50 kg ha-1 of P ¾ P1 and P2 respectively), in randomized block design in factorial arrangement. Vegetative biomass was sampled at three ontogenetic stages. The effects of genotype and phosphorus were significant for most traits, but not the genotype ´ phosphorus interaction. The cultivars presented different patterns of biomass production and nutrient accumulation, particularly on root system. At P1, P accumulation persisted after the beginning of pod filling, and P translocation from roots to shoots was lower. The nodule senescence observed after flowering might have reduced N2 fixation during pod filling. The responses of vegetative growth to the higher P supply did not reflect with the same magnitude on yield, which increased only 6% at P2; hence the harvest index was lower at P2. The cultivars with highest yields also presented lower grain P concentrations. A sub-optimal supply of N could have limited the expression of the yield potential of cultivars, reducing the genotypic variability of responses to P levels.