Grass-legume intercropping systems in rotation with soybean crops: C and N stocks and CO 2 and NH 3 emissions

Abstract

Understanding factors that contribute to carbon dioxide (CO2) losses and ammonia (NH3) volatilization in agricultural soils, mainly in sandy soils, is essential for determining strategies to decrease emissions of these gases and improving carbon (C) and nitrogen (N) stocks in the soil. The objective of this study was to quantify C and N inputs to the soil and CO2 and NH3 emissions in a crop-livestock integration system composed of pastures with grass-legume intercropping and N fertilizer application. The experiment was carried out in a Typic Hapludox, evaluating three consecutive soybean crops grown in rotation with the following pasture systems: mombaca grass (Panicum maximum cv. Mombaca) with N fertilizer (M + N); mombaca grass without N fertilizer (M-N); mombaca grass intercropped with the forage legume pigeon pea (Cajanus cajan) (M + G); and mombaca grass intercropped with the forage legume java (Macrotyloma axillare cv. Java) (M + J). Soil samples were collected at the beginning and end of each crop and analyzed for total C (TCS) and N (TNS) stocks. NH3 volatilization and CO2 emissions were evaluated every 15 days, with simultaneous evaluations of soil moisture and temperature. Soybean rotation with grass-legume intercropping or grass with mineral fertilizer application improved N and C inputs to the agricultural systems, although there were losses in CO2 and NH3. The M + G and M + J intercrops after soybean crops increased NH3 volatilization, whereas the use of M + N tended to decrease it. The soil moisture affected the C and N input-output balance in the production systems evaluated.