Nitrato e amônio na solução do solo em sistemas com uso de plantas de cobertura

Abstract

The introduction of cover crops in agricultural production systems has received attention due its ability to improve the multifunctionality of the soil and for many species have the capacity of biological N fixation. After the productive period the excess of N fixed or the senescence of roots and / or plants may induce an excess of nitrate in the soil, which if not used by the species in sequence can be leached and reach subsurface waters. Therefore, the objective of this study is to relate the concentrations of mineral nitrogen (nitrate and ammonium) in the soil solution with the different species of cover crops used. The study was conducted in the experimental area belonging to the Department of Soils of the Federal University of Santa Maria (UFSM) in a Typic Hapludalf (Argissolo Vermelho-Amarelo Distrófico abrúptico – braziliam soil classification). The experimental design was a randomized block design, with six treatments distributed in four blocks totaling 24 experimental units. The evaluated treatments were: 1. Bare soil (Sdes); 2. Spontaneous vegetation (Vesp); 3. Forage peanuts (Arachis pintoi) (AFor); 4. Grass pensacola (Paspalum notatum) (Gpens); 5. Oats (Avena strigosa) and turnip (Raphanus sativus) -winter- and cowpea (Vigna unguiculata) (ANFe); 6. Oats (Avena strigosa) and vetch (Vicia sativa) -winter- and cowpea (Vigna unguiculata) (AEFe). In order to collect the soil solution, suction lysimeters were installed at the depths of 0.15 m and 0.50 m. The solution was collected after rainfall events during the spring of 2018, where a suction of 50 kPa was applied to the lysimeters and the solution was collected 48 hours after suction application. Samples were analyzed using continuous flow analyzer (SKALAR). The nitrate concentration in the soil solution was higher when collected at 15 cm, than at 50 cm. Forage peanut and spontaneous vegetation had higher nitrate concentration in the soil solution at initial period of spring and Oats + Vetch + Cowpea and Oats + Turnip+ Cowpea consortia had high concentrations at the end of the spring. The detected ammonium concentrations are small and showed no statistical differences between the ground cover plant systems.