ANTECIPAÇÃO DA ADUBAÇÃO POTÁSSICA PARA O MILHO CULTIVADO EM SISTEMA AGROFLORESTAL SOB PLANTIO DIRETO

Abstract

The success of agroforestry system (AFS) is the result of appropriate combinations of crops, forage and tree component and soil fertility. Changes in the microclimate in AFS, can affect the potassium use efficiency by crops. The high absorption of potassium (K) by the plants of white oat, corn and eucalyptus make potassium fertilization an essential practice in AFS. The objectives of this study were to quantify (i) the dry matter yield (DM) and nutrient accumulation in shoots of white oat (season 2014); (ii) the DM and grain yield, and the nutritional status of maize (season 2014/15); (iii) potassium use efficiency by crops in succession (white oat - maize); and (iv) assess the main soil fertility attributes after the white oat crop (season 2014) and maize (season 2014/2015) in AFS fertilized with K. The experiment was installed in Model Farm of Agronomic Institute of Paraná (IAPAR), in the city of Ponta Grossa (PR) in an Oxisoil úmbrico. The experimental design was a randomized complete block with split plots and three replications. The plots consist of four transects - growing distances from trees (transects: 1 - 0- 4 m away; 2 - 4-8 m away; 3 - 8-12 m distance and 4 - 12-16 m away). In the subplots were studied four annual K2O levels (0, 100, 200 and 300 kg ha-1 year-1), as potassium chloride (600 g kg-1 K2O), applied to the surface, and half of each levels applied at sowing of each crop (white oat - winter and maize - summer). The DM yields and nutrients accumulation in the shoots of white oat were determined on management with herbicide. In maize, was evaluated the nutritional status and measured DM and grain yields. Also, values of pH, contents of calcium (Ca), magnesium (Mg) and K exchangeable, base saturation (V) and the percentage of K in the effective CECe were determined in the layers of 0-5, 5-10, 10-15, 15-20, 20-40 and 40-60 cm. The DM yield and the accumulation of nutrients in the shoots of white oat decreased due to the shade provided by the eucalyptus. To this culture in AFS, the levels of K2O increased the yield of DM and the accumulation of sulfur (S) in the shoot. In situation of shading of 64.5%, recycling of nutrients by white oat provided for the subsequent corn crop, better nutrition and, on average, higher DM and grain yields. In this situation, the addition of K2O (up to 230 kg ha- 1 year-1) would provide higher yield of corn grain. This decrease in K level directly implies greater potassium use efficiency, lower production cost and could make possible the cultivation of corn in AFS in the Campos Gerais region. The application of potassium fertilizer high water solubility, in the surface of the soil, reduced, in some situations, Ca and Mg content in the surface layer, it favored the mobility of K and increased its content of this nutrient throughout the soil profile and thus their participation in CECe. The tree component reduced nutrient concentrations in transecta 1 (most influential eucalyptus region), resulting in lower pH values and V in subsurface soil layers (below 20 cm deep).