reSUmo decorrente dos sistemas de manejo empregados no solo, como o sistema de preparo convencional (SPC) versus o sistema de plantio direto de hortaliças (SPDH), modificações nos atributos edáficos ocorrem; por exemplo, nos índices de agregação do solo e seu teor de carbono orgânico total (COT). Objetivaram-se quantificar os teores de COT e avaliar os índices de agregação do solo e a distribuição dos agregados por classes de diâmetro sob cultivo de cebola em SPdH e SPC, comparados a uma área de mata adjacente em ituporanga, SC. os tratamentos constituíram-se da semeadura de plantas de cobertura, solteiras e consorciadas, em SPdH: vegetação espontânea (VE); 100 % aveia; 100 % centeio; 100 % nabo-forrageiro; consórcio de nabo-forrageiro (14 %) e centeio (86 %); e consórcio de nabo-forrageiro (14 %) e aveia (86 %). adicionalmente, foram avaliadas uma área de cultivo de cebola em SPC por ±37 anos e uma área de mata (floresta secundária; ±30 anos), ambas adjacentes ao experimento. Em setembro de 2013, cinco anos após a implantação dos tratamentos com plantas de cobertura, foram coletadas amostras indeformadas do solo nas camadas de 0-5, 5-10 e 10-20 cm e separados os agregados para avaliar a estabilidade via úmida. Nos agregados, foi quantificado o COT;Recebido para publicação em 7 de novembro de 2014 e aprovado em 10 de março de 2015.

ABSTRACT:Cover crops contribute to nutrient cycling and may improve soil chemical properties and, consequently, increase crop yield. The aim of this study was to evaluate cover crop residue decomposition and nutrient release, and the effects of these plants on soil chemical properties and on onion (Allium cepa L.) yield in a no-tillage system. The experiment was carried out in an Inceptisol in southern Brazil, where cover crops were sown in April 2012 and 2013. In July 2013, shoots of weeds (WD), black oats (BO), rye (RY), oilseed radish (RD), oilseed radish + black oats (RD + BO), and oilseed radish + rye (RD + RY) were cut at ground level and part of these material from each treatment was placed in litter bags. The litter bags were distributed on the soil surface and were collected at 0, 30, 45, 60, 75, and 90 days after distribution (DAD). The residues in the litter bags were dried, weighed, and ground, and then analyzed to quantify lignin, cellulose, non-structural biomass, total organic carbon (TOC), N, P, K, Ca, and Mg. In November 2012 and 2013, onion crops were harvested to quantify yield, and bulbs were classified according to diameter, and the number of rotted and flowering bulbs was determined. Soil in the 0.00-0.10 m layer was collected for chemical analysis before transplanting and after harvesting onion in December 2012 and 2013. The rye plant residues presented the highest half-life and they released less nutrients until 90 DAD. The great permanence of rye residue was considered a protection to soil surface, the opposite was observed with spontaneous vegetation. The cultivation and addition of dry residue of cover crops increased the onion yield at 2.5 Mg ha -1 .

Assis de Oliveira (1) , Jucinei José Comin (2) , Tales Tiecher (3) , Rogério Piccin (4) , Luiza Michelon Somavilla (5) , Arcângelo Loss (2) , Cledimar Rogério Lourenzi (2) , Claudinei Kürtz (5) and Gustavo Brunetto (6)*

Cover crop nitrogen (N) cycling has an important role in agricultural production and contributes to peach [Prunus persica (L.) Batsch] N nutrition. This study evaluated black oat (Avena strigosa Schreb) and ryegrass (Lolium multiflorum L.) residue decomposition dynamics, N recovery from cover crop residues, and N compartmentalization in peach tree organs. A 2-year field trial was developed with labeled (3.6-4.0 atom% 15 N excess) cover crop shoot biomass application in a 5-year-old peach orchard. The region's climate is warm temperate (Cfb), and the soil is classified as a Typic Hapludalf. Litter bags with unlabeled shoot residues were also deposited in the orchard to assess biomass, carbon (C), N, lignin, cellulose, and non-structural biomass decomposition dynamics. After 13 months, the leaves, trunk, and roots showed the greatest proportion of N derived from residues (Ndfr) (35.4, 25.1, and 22.4%, respectively) while the greatest concentrations of 15 N and Ndfr occurred in roots <2 mm (0.0376 and 0.94%, respectively). The N derived from cover crop shoots in the second production cycle was similar among tree organs. Ryegrass residues presented the highest decomposition constant (k) values for dry matter, total organic carbon (TOC), cellulose, and lignin. Hence, black oat residues presented a higher half-life (t ½ ) for dry matter, TOC, total N, cellulose, and lignin. The N derived from black oat and ryegrass residues in mature trees was expressively low (<1%) and similar between species. Within organs, the highest Ndfr occurred in peach leaves during the flowering stage, when the greatest residue decomposition rate also occurred. Soil N and plant internal N reserves are the major N sources for newly formed organs, but greater contributions to tree N nutrition may occur with long-term cover crop residue deposition and different plant species.

No abstract

O consórcio é uma alternativa considerada viável para os agricultores familiares do semiárido nordestino. Por isso, o uso dessa prática tem-se intensificado nesta região, principalmente envolvendo a cultura do algodão. Neste sentido, este trabalho teve como objetivo avaliar a influência do consórcio sobre o crescimento e a produção de dois cultivares de algodão herbáceo em consórcio. O experimento foi conduzido em condições de sequeiro, na Estação Experimental de Missão Velha-CE, no Cariri Cearense. O ensaio adotou o delineamento em blocos ao acaso (DBC), composto por quatro blocos e seis tratamentos dispostos em cultivos consorciados (T1 - algodão herbáceo BRS Aroeira + gergelim Seda; T2 - algodão herbáceo BRS 04-1515 + gergelim Seda; T3 - algodão herbáceo BRS Aroeira + amendoim BR1; T4 - algodão herbáceo BRS 04-1515 + amendoim BR1); e cultivos solteiros (T5 - Algodão herbáceo BRS Aroeira; e T6 - Algodão herbáceo BRS 04-1515). As variáveis analisadas foram: altura das plantas; diâmetro de caule; número de capulhos/planta; rendimento de algodão em rama e em fibra. Não houve diferença significativa em nenhuma das variáveis. Os consórcios algodão+amendoim e algodão+gergelim, para as condições impostas, não foram vantajosos, pois a cultura principal foi influenciada negativamente pelas intercalares, independente do cultivar de algodoeiro utilizado.