Forms of nitrogen and phosphorus transfer by runoff in soil under no-tillage with successive organic waste and mineral fertilizers applications

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The use of organic wastes in southern Brazil is a common practice in the farms and in many of these, the criterion for defining the doses of organic wastes is to meet the N demand by crops. This may mean the accumulation of chemical elements in the soil, especially in soils managed under no-tillage systems, and enhance the transfer of these elements by surface runoff. The aim was evaluated how successive applications of organic and mineral sources of nutrients in a long-term experiment, managed under no-tillage system in a subtropical environment, influence the transfer of quantities and forms of N and P by surface runoff. The experiment was carried out in southern Brazil, in a Typic Hapludalf soil. The treatments consisted of the application of pig slurry, pig deep litter, cattle slurry, mineral fertilizer and a control, without nutrients. The doses of organic wastes were to meet the N demand by crops. Were evaluated the surface runoff and the transfers of mineral N and forms of P (soluble, particulate, and total) from 2009 to 2013 period. The amount of solution transferred by surface runoff decreased with fertilization and present a negative relationship with the soil organic matter (SOM). The transfers of mineral N increased with the increase in the contents of SOM, but decreased with the runoff. The transfers of P forms present a great relationship with the amounts of P applied and the contents of soil P extracted by Mehlich-1, and more than 55% of total P transferred by surface runoff, in the treatments that received nutrients application, is on soluble form. In addition, the transfer of soluble, particulate and total P was lower with mineral fertilizer application, when compared with organic wastes. This suggest that the use of N demand by crops as a criterium to meet the doses of organic wastes is not adequate in subtropical environment.