FERTILIDADE DO SOLO, NUTRIÇÃO DE PLANTAS, PRODUÇÃO DE GRÃOS E RENDA ACUMULADA EM FUNÇÃO DE DOSES E PARCELAMENTOS DE GESSO AGRÍCOLA EM PLANTIO DIRETO

Abstract

Phosphogypsum (CaSO4.2H2O) has essential nutrients for plants and, after its reaction, decreases aluminum (Al³+) activity in surface and subsurface soil layers, favoring soil fertility and root growth with benefits for water and nutrient absorption and for crop yield. In this study, the alterations on soil fertility and their resulting effects on the nutrition and yield of the plants on a maize-wheat-soybean-maize succession were evaluated, as well as the accumulated yield and income as affected by phosphogypsum (PG) rates and split application to an Oxisol under no-till system (NT) in Guarapuava, Paraná State. In a long-term field experiment, treatments were arranged in a (4x3) + 1 factorial, to study four PG rates (3, 6, 9 and 12 Mg ha?¹) under three levels of splitting (P1 = non split, 100% of the rate in 2009); P2 = split in two years, 50 + 50% in 2009 and 2010; P3 = split in three years, 33 + 33 + 33% in 2009, 2010 and 2011), with an additional treatment without PG application (control). The soil was sampled in 2012 and 2013, at 6 and 18 months after the last PG application, in stratified layers up to 80 cm. Maize was sown in November, 2011, and then wheat in July, 2012, soybean in December, 2012 and maize in October, 2013, with sampling of leaves of each crop for chemical analysis. In the soil, the use of PG increased the levels of calcium (Ca²+) in all layers (2012 and 2013) and the soil pH at 20-40 (2012), 40-60 (2012 and 2013) and 60-80 cm (2012 and 2013), and reduced the levels of Al³+ in all layers and the levels of magnesium (Mg²+) up to 60 cm (2012 and 2013), without splitting effect in any of these. The Ca/Mg ratio was linearly increased by PG rates up to 80 cm in 2012 and to 60 cm in 2013, with split effect at 0-10 cm layer: P1 was overcome by P2 and P3 and these were similar to each in 2012, and P1 was overcome by P3 in 2013. The sulfur (S-SO42-) levels were linearly increased by PG rates in all layers in 2012 and 2013, and split effect occurred up to 60 cm, with higher S-SO42- for split rates. The levels of potassium (K+), phosphorus (P) and potential acidity (H + Al) were not affected by the treatments. In the leaves, the effects of PG rates were linear, increasing the levels of Ca and S and decreasing the levels of Mg in all crops, without split effect. With regard to crop yield, maize response to PG rates was quadratic in 2011/2012 and 2013/2014 crop seasons, with maximum technical efficiency (MET) at 6.38 and 6.34 Mg ha?¹ of PG, respectively, unlike wheat (2012) which responded with linear increase in a crop season under rainfall restriction, with MET at 12 Mg ha?¹ of PG. Soybean yield was not affected by PG rates, and no crop alone presented yield response to splitting. For the yield accumulated from eight grain crops since the beginning of the experiment, from 2009 until 2014, there was rate x split interaction with quadratic response to rates in all split levels, but with MET in 5.81, 7.27 and 7.96 Mg ha?¹ of PG in P1, P2 and P3, respectively. Also in this period, the financial return was better with 3 and 6 Mg ha?¹ of PG, once they gave profits in relation to control from a smaller number of crops and also on the accumulated in the period, in all split levels, but with advantage for 6 Mg ha?¹ in P1 and P2. The rate of 9 Mg ha?¹ of PG became equivalent to 3 and 6 Mg ha?¹ in terms of profit only in P3 for the last crop. With 12 Mg ha?¹, in all split levels the economic losses prevailed until the end of the period.