Dejetos de suínos: produção de culturas, efeitos na matéria orgânica e na transferência de formas de fósforo

Abstract

Swine production is an activity widely developed in southern Brazil that generates large volumes of manure, which are normally used as sources of nutrients in grain crops and pastures. However, successive applications of manure can cause changes in the concentration of nutrients in the soil, changing the dynamics in soil organic matter (SOM) and enhance the transfer of phosphorus in aquatic environments. This study aimed to evaluate the effect of successive applications of swine manure on production and nutrient accumulation in crops, changes in chemical composition and distribution of physical and chemical fractions of soil organic matter and the transfer of forms of phosphorus by runoff in subtropical soils under no-tillage. For this, three studies were undertaken: Study 1 aimed to assess how doses of manure, applied over a few years can impact grain yield, dry matter and nutrient accumulation in commercial grain crops and cover plants soil. This study consisted of an experiment conducted in Hapludalf soil with applications of doses of 0, 20, 40 and 80 m3 ha-1 of pig slurry (PS) prior to implementation of each culture of succession: black oats/millet/black beans, in 2002/2003; black oats+vetch/maize, in 2003/2004 and 2004/2005; black oat/black beans/sunn hemp, in 2005/2006; black oats/maize/black oats, in 2006/2007. For maize and black beans was evaluated grain yield and, for all crops, the production of dry matter of shoots and accumulation of N, P and K in plant tissue was determined. Study 2 aimed to evaluate the impact of successive applications of swine manure in liquid form and in the form of compost on carbon storage and chemical and structural composition of physical and chemical fractions of SOM in two subtropical environments with distinct textural characteristics. This study consisted of two experiments: the first experiment was conducted on an Hapludalf soil that received 19 applications of doses of 0, 40 and 80 m3 ha-1 PS over a period of 93 months, and the experiment 2 was conducted in one Hapludox soil that received six applications of doses of 0, 8 and 16 t ha-1 of composted wood shavings with PS, plus a treatment with mineral fertilizer, for a period of 71 months. In both experiments were performed collecting soil depths 0-4, 4-8, 8-12, 12-16 and 16-20 cm. In soil samples were quantified the total C, physical and chemical fractionation of SOM, the calculated C stocks in physical and chemical fractions of SOM and chemical composition of humic acids. Study 3 aimed to evaluate the accumulation of phosphorus (P) in the soil and transfer of P forms in surface runoff in a Hapludalf soil under no-tillage and subjected to successive applications of pig slurry. For this study the experiment 1 of Study 2 was used. Drained samples solution of this experiment samples were collected, where precipitation was sufficient to cause runoff volume, and the levels of available P, soluble P, particulate P and total P were determined. The results show that the application of manure increased grain yield and dry matter production by cultures, but for the beans, the highest yield was achieved with the lowest dose of PS, indicating that for the other doses, the amount of nutrients applied was above the demand of the crop. The highest yields of dry matter with the application of manure promoted increases in SOM levels and altered the chemical composition of humic acids, and the incorporation of compounds present in manure was the main cause of these changes. Moreover, successive applications of manure promoted increases in levels of available P in the soil, reflecting higher shipments of P forms in runoff, following this order: available P > soluble P > particulate P. Therefore, the management of waste in the soil must meet criteria that allow the fertilizer to maximize effect and minimize environmental impacts.