Clóvis Manuel Borkert

Nutrientes minerais na biomassa da parte aérea em culturas de cobertura de solo

Resumo – O objetivo deste trabalho foi estimar as quantidades de nutrientes reciclados por cinco especies vegetais utilizadas como culturas de cobertura do solo e que podem retornar ao solo pela mineralizacao da biomassa. Foram coletadas de varios experimentos amostras da materia verde de aveia-preta (Avena strigosa Schreb), mucuna-preta (Stizolobium aterrimum Piper & Tracy), guandu (Cajanus cajan (L.) Millsp), tremoco (Lupinus albus L. e L. angustifolius L.) e ervilhaca (Vicia sativa L.). Foi estimado o rendimento de materia seca e determinados os teores de N, P, K, Ca, Mg, Mn, Zn, Cu, e, a partir dessas concentracoes, foram calculadas a media observada, a media estimada e o intervalo de confianca a 95% para cada nutriente dentro de cada classe de rendimento de materia seca, em cada especie vegetal. Os dados foram tabulados dentro de intervalos de classe de rendimento de materia seca e apresentadas as quantidades estimadas de nutrientes minerais. Foram ajustadas equacoes para estimar as quantidades desses nutrientes. A aveia-preta e a ervilhaca reciclam grande quantidade de K, e a ervilhaca, a mucuna-preta, o tremoco e o guandu reciclam grande quantidade de N. Todas as especies reciclam quantidades apreciaveis de Ca, Mg e micronutrientes, porem baixas quantidades de P. A rotacao de culturas e um meio de implementar com sucesso o aumento das areas de lavoura em semeadura direta. Termos para indexacao: plantas de protecao, reciclagem de nutriente, mineralizacao, rotacao de culturas. Mineral nutrients in the shoot biomass of soil cover crops

Alterações na fertilidade do solo em sistemas de rotação de culturas em semeadura direta

The no-tillage system with grain crops occupies today 2.5 millions hectares in the state of Parana. Besides the traditional rotation system with wheat and soybean, in many areas green manure cover crops are also sown in the Winter and corn in the Summer. The objective of this study was to evaluate changes in some of the soil chemical properties after eight years under the crop rotation systems: wheat-soybean-black oat-soybean (WOS), wheat-soybean-lupine-corn-black oat-soybean (LCO), lupine-corn-wheat-soybean (LC) and compare them with the traditional system wheat-soybean (WS) grown in two Oxisols at Londrina and Campo Mourao, State of Parana, Brazil. The LC crop rotation system reduced the soil pH and the level of exchangeable calcium (Ca2+) and magnesium (Mg2+) and increased the excangeable aluminum (Al3+), the potential acidity (H + Al), and the total-N in the soil as compared to the WS system. These characteristics showed intermediate values in the other systems. There were no significant differences on soil levels of organic carbon and exchangeable-K (K+) among the crop rotation systems. The decrease on the level of Ca2+ in the LC system was larger than the amount of Ca applied as lime to the soil during the experiment. Soil acidification was related to the nitrogen fertilization of wheat and corn. The maintenance of levels of K+ and the decrease on the levels of Ca2+ and Mg2+ demonstrate that there was a change in the preference of leaching cations in the LC crop rotation system. The formation of metal-organic complexes with divalent cations was assumed to be the possible mechanism responsible for the chemical alterations in the soil.

Boron extraction and vertical mobility in Paraná State oxisol, Brazil

The deficiency or excess of micronutrients has been determined by analyses of soil and plant tissue. In Brazil, the lack of studies that would define and standardize extraction and determination methods, as well as lack of correlation and calibration studies, makes it difficult to establish limits of concentration classes for analysis interpretation and fertilizer recommendations for crops. A specific extractor for soil analysis is sometimes chosen due to the ease of use in the laboratory and not in view of its efficiency in determining a bioavailable nutrient. The objectives of this study were to: (a) evaluate B concentrations in the soil as related to the fertilizer rate, soil depth and extractor; (b) verify the nutrient movement in the soil profile; (c) evaluate efficiency of Hot Water, Mehlich-1 and Mehlich-3 as available B extractors, using sunflower as test plant. The experimental design consisted of complete randomized blocks with four replications and treatments of five B rates (0, 2, 4, 6, and 8 kg ha -1 ) applied to the soil surface and evaluated at six depths (0–0.05, 0.05–0.10, 0.10–0.15, 0.15–0.20, 0.20–0.30, and 0.30–0.40 m). Boron concentrations in the soil extracted by Hot Water, Mehlich-1 and Mehlich-3 extractors increased linearly in relation to B rates at all depths evaluated, indicating B mobility in the profile. The extractors had different B extraction capacities, but were all efficient to evaluate bioavailability of the nutrient to sunflower. Mehlich1 and Mehlich-3 can therefore be used to analyze B as well as Hot Water.