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

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.

Automated summary

The use of organic wastes is common in southern Brazil, with doses often determined based on crop nitrogen demand. This practice may lead to accumulation of chemical elements in soil and increased transfer by surface runoff, especially in no-tillage systems. The study evaluated the effects of successive applications of organic and mineral nutrient sources on nitrogen and phosphorus transfer via surface runoff in a subtropical environment.