Celso Aita

Recomendação de adubação nitrogenada para o milho no RS e SC adaptada ao uso de culturas de cobertura do solo, sob sistema plantio direto

O nitrogenio, na maioria das situacoes, e o nutriente que mais influencia o rendimento do milho. O manejo da adubacao nitrogenada deve satisfazer o requerimento da cultura com o minimo de risco ambiental. Para tanto, e necessario que a recomendacao da dose de adubo nitrogenado seja a mais exata possivel. A generalizacao do uso do sistema de plantio direto e culturas de cobertura, no Sul do Brasil, criou a necessidade de ser a recomendacao da adubacao nitrogenada adaptada a este novo cenario agricola. O presente trabalho, alem de considerar o teor de MO e a expectativa do rendimento de graos de milho na recomendacao da adubacao nitrogenada conforme preconiza a CFS-RS/SC (1995), propoe a introducao de um terceiro parâmetro que e a contribuicao em N das culturas de cobertura antecedente. O efeito das culturas de cobertura foi considerado em tres situacoes: leguminosas em cultivo solteiro, gramineas em cultivo solteiro e consorciacoes. No caso de leguminosas e gramineas em cultivo solteiro, a influencia na disponibilidade de N foi considerada com base na producao de materia seca, enquanto, nas consorciacoes, a proporcao da leguminosa foi o principal fator considerado. A recomendacao de adubacao apresentada neste trabalho nao dispensa acompanhamento de campo, visando a ajustes que se fizerem necessarios, especialmente porque sistemas de producao, baseados em culturas de cobertura, dependem de processos biologicos influenciados por condicoes de clima, manejo e solo, que devem ser acompanhados localmente.

Liberação de fósforo e potássio durante a decomposição de resíduos culturais em plantio direto

The objective of this work was to evaluate the release of P and K from residues of single oat, vetch and forage radish and from mixtures of oat and vetch, under no-tillage system. The residues were placed in 0.5 mm mesh nylon bags (20x20 cm), which were placed on soil surface and taken out at 15, 29, 43, 59, 71, 82, 112 and 182 days after. At each sampling date the material was dried at 65oC and the amount of dry matter remaining and its concentration of P and potassium were determined. It was adjusted the asymptotic model ((Pr and Kr = Ae -kt + (100 - A)) to observed values for the remaining P and K (Pr and Kr) which was used to estimate the rate (k) of P and K release and the proportion of these nutrients of the labile (A) and recalcitrant (100 - A) pools of crop residues. The rate of K release was 4.5 times greater than was for phosphorus. The amount of remaining P in the initial phase of the decomposition was inversely proportional to the concentration of water soluble P in the residues. In the residues of the oat + vetch mixture the P and K release were slower than the observed for single species. These results indicate a greater potential of synchrony between commercial crops P and K demand and P and K release from residues of oat + vetch mixture as compared to single vetch.

Volatilização de amônia com aplicação de uréia na superfície do solo, no sistema plantio direto

The experiment was carried out in 2002/03, the Federal University of Santa Maria, State of Rio Grande do Sul, Brasil, in a typic Haoludal under six years of no-tillage to evaluate the effects of black oat residues left at soil surface on ammonia volatilization. The experiment was in a completely randomized design with three replications. The treatments were urea applied with and without surface residue in three times: before seeding; seeding and; topdressing. The urea was spread at a rate of 50kg ha-1 de N each time. The residues reduced the ammonia fluxes, as compared to bare soil, when under residues had higher soil moisture at urea application. On the other hand, when soil moisture for crop residue treatments were similar to bare soil the former had higher ammonia volatilization. When there was rainfall right after urea application, the treatments showed same volatilization flux. Considering the three timing of urea application for corn, the amount of volatilized ammonia was similar to conditions of with and without crop residues adding up 17 % of N-urea applied.

FITOMASSA E DECOMPOSIÇÃO DE RESÍDUOS DE PLANTAS DE COBERTURA PURAS E CONSORCIADAS

O cultivo de plantas de cobertura, no outono/inverno, na regiao do Planalto do Rio Grande Sul contribui para o sucesso do sistema plantio direto. No entanto, informacoes relativas a producao de fitomassa e decomposicao de residuos dessas especies ainda sao escassas para a regiao, sobretudo para especies consorciadas. O experimento foi conduzido em Nao-Me-Toque, RS, em um Latossolo Vermelho distrofico tipico, avaliando-se nove tratamentos, sendo quatro constituidos por plantas de cobertura em culturas puras [centeio (Secale cereale L.), aveia-preta (Avena strigosa Schreb), ervilha forrageira (Pisum sativum subesp. arvense) e nabo forrageiro (Raphanus sativus L. var. oleiferus Metzg)] e cinco por consorcios [(centeio + ervilha forrageira, centeio + nabo forrageiro, aveia + nabo forrageiro, centeio + ervilhaca (Vicia sativa L.) e aveia + ervilhaca)]. A dinâmica de decomposicao dos residuos culturais das plantas de cobertura foi avaliada em bolsas de decomposicao, as quais foram distribuidas na superficie do solo e coletadas aos sete, 14, 21, 28, 57, 117 e 164 dias. O consorcio entre leguminosas e crucifera com gramineas resultou em maior producao de fitomassa em relacao ao cultivo destas em culturas puras. O nitrogenio (N) acumulado na parte aerea dos consorcios formados por ervilha forrageira e nabo com centeio e aveia foi semelhante ao da leguminosa e da crucifera em culturas puras e superou em 220,4 % os valores de N observados para as gramineas em culturas puras. Por meio do consorcio entre as especies de cobertura foi possivel reduzir a taxa de decomposicao dos residuos culturais, em comparacao com as culturas puras da leguminosa e da crucifera.

Simulating the effects of N availability, straw particle size and location in soil on C and N mineralization

Predicting the C and N mineralization of straw added to soil is important for forecasting subsequent soil N availability during and between crop growth cycles. The decomposition module of the STICS model, parameterized under optimal conditions, was used to predict straw decomposition in sub-optimal conditions, i.e. when contact between soil and residue was poor (due to large size residues or surface placement) or when mineral N availability was restricted. The data used in the simulations were obtained from published studies of effects of residue size, location and N availability on C and N mineralization from straw under controlled laboratory conditions. We selected studies in which the dynamics of C and N mineralization were measured simultaneously. The dynamics of straw mineralization could be well predicted by the model under optimal conditions with standard parameter values as derived from measured C/N ratios of the residues, but not under sub-optimal conditions which required a new parameterization. A good fit could be obtained on these treatments by a marked reduction in the rate constants of residue and microbial biomass decomposition and a marked increase in the microbial biomass C/N ratio. Our results show the need to include in decomposition models routines for simulating effects of spatial heterogeneity of residue distribution, different particle sizes and limiting N availability.

Injection of Dicyandiamide-Treated Pig Slurry Reduced Ammonia Volatilization without Enhancing Soil Nitrous Oxide Emissions from No-Till Corn in Southern Brazil.

There is a lack of information on how placement in soil and nitrification inhibitors affects nitrous oxide (NO) and ammonia (NH) emissions from pig slurry (PS) applied under no-till (NT) conditions. Our objective was to determine the impact of injecting PS and treating it with the nitrification inhibitor dicyandiamide (DCD) on NH and NO emissions from soils under NT in subtropical southern Brazil. The emissions of these gases were compared for shallow (∼ 10 cm) injection and surface broadcasting of PS with and without DCD (8.1-10.0 kg ha; 6.5-8.4% of applied NH-N). Measurements were made at two sites during two summer growing seasons under NT corn crops. Injection reduced NH volatilization by 70% but increased NO emissions 2.4-fold (from 2628 to 6198 g NO N ha) compared with surface broadcast application. Adding DCD to PS inhibited nitrification and reduced NO emissions by an average of 28% (730 g NO-N ha) for surface broadcast and 66% (4105 g NO-N ha) for injection but did not increase NH volatilization. Consequently, NO emission factors were much higher for injection (3.6%) than for surface broadcast (1.3%) application and were reduced (0.9%) when DCD was added to injected PS. In conclusion, the injection of DCD-treated slurry is a recommendable practice for reducing NH and NO emissions when applying PS on NT corn in southern Brazil.

Nitrogen fertilizer split-application for corn in no-till succession to black oats

Na sucessao de gramineas aveia preta/milho pode haver imobilizacao do nitrogenio, especialmente no inicio do ciclo do milho, requerendo estudos de fracionamento da adubacao. Com o objetivo de avaliar formas de parcelamento da adubacao nitrogenada para o milho em sucessao a aveia preta, foram conduzidos quatro experimentos em areas de lavouras sob plantio direto nos municipios de Itaara, Santo Ângelo, Julio de Castilhos e Tupancireta no Rio Grande do Sul, durante os anos agricolas 1996/97 a 1998/99. As aplicacoes de N para o milho foram realizadas em tres epocas: a) pre-semeadura (apos o manejo da aveia preta), b) semeadura e c) cobertura. Os resultados mostraram que a aplicacao em pre-semeadura do milho de parte ou todo o nitrogenio que seria aplicado em cobertura nao conferiu produtividade de graos diferente da aplicacao na semeadura e cobertura mas a ocorrencia de precipitacoes pluviometricas acima da normal pode causar diminuicao na produtividade de graos. Por isso, a aplicacao de nitrogenio na semeadura e em cobertura no milho e preferencial.

Impact on C and N dynamics of simultaneous application of pig slurry and wheat straw, as affected by their initial locations in soil

The joint management of animal manures and plant biomass as straw on agricultural soils may be a viable option for reducing the environmental impacts associated with livestock production and recycling nutrients efficiently. To investigate this option, an incubation in controlled conditions examined how the simultaneous addition of 15N-labeled pig slurry and 13C-labeled wheat straw, either on the soil surface or incorporated into the soil, affected the mineralization of C from the organic materials and the soil N dynamics. Samples from a typic hapludalf were incubated for 95 days at 25°C with eight treatments: unamended soil (S), wheat straw left on the soil surface (Ws), wheat straw incorporated in the soil (Wi), pig slurry on the soil surface (Ps), pig slurry incorporated in the soil (Pi) and three combinations of the two amendments: Pi + Ws, Pi + Wi, and Ws + Ps. Carbon dioxide and 13CO2 emissions and soil N content were measured throughout the incubation. Pig slurry stimulated the decomposition of straw C only when wheat straw and pig slurry were left together on the soil surface. Incorporation of both wheat straw and pig slurry did not modify straw C mineralization when compared to straw incorporation alone but this promoted a higher rate of N immobilization. The results suggest that when pig slurry is used in field under no-till conditions, the best strategy to preserve environmental quality with regard to CO2 emissions would be to apply pig slurry underneath the crop residues.

Emissão de óxido nitroso com a aplicação de dejetos líquidos de suínos em solo sob plantio direto

O objetivo deste trabalho foi comparar as emissoes de oxido nitroso (N2O) para a atmosfera depois da aplicacao de dejetos liquidos de suinos, em plantio direto (PD) e preparo reduzido (PR) do solo. O delineamento experimental utilizado foi o de blocos inteiramente casualizados com cinco repeticoes. Os tratamentos consistiram na aplicacao (40 m3 ha-1), ou nao, de dejetos liquidos em PD e PR. As emissoes de N2O foram medidas in situ depois da aplicacao dos dejetos, por 28 dias. Os fluxos de N2O aumentaram com a aplicacao dos dejetos e, em apenas 20% das avaliacoes realizadas, foram superiores no PD. As emissoes de N2O relacionaram-se com o aumento do espaco poroso ocupado pela agua. Quantidades acumuladas de N na forma de N2O, emitidas em 28 dias, representaram 0,20 e 0,25% do N total aplicado com os dejetos no PD e PR, respectivamente. Os resultados demonstram que a aplicacao de dejetos liquidos de suinos em PD nao aumenta a emissao acumulada de N2O em relacao a aplicacao em PR.

Mineralização do carbono da palha de aveia e dejetos de suínos aplicados na superfície ou incorporados ao solo

The C mineralization of pig manure and cereal straw is still relatively little studied in Brazil. The aim of this work was to evaluate C mineralization of oat straw, pig slurry and pig deep-litter, applied on the surface or incorporated in a Hapludalf soil, in laboratory conditions. The experiment was a completely randomized design with four replications of the following treatments: soil; soil + incorporated straw; soil + surface straw; soil + incorporated pig deep-litter; soil + surface pig deep-litter; soil + incorporated pig slurry; soil + surface pig slurry; soil + incorporated straw + pig slurry; and soil + surface straw + pig slurry. During the 80 days of incubation, the CO2 emission was measured continuously. After this period, 59 % of pig slurry C had been mineralized and only 23 % of deep-litter C. The soil incorporation of organic materials did not result in higher C mineralization, compared with organic material on the soil surface. Ammoniacal N, applied with pig slurry did not increase C oat straw mineralization.