Long-term rotation effect of soybean with no-till maize on soil N availability indices and microbial activity in the Argentine Pampa

A rotation effect due to the inclusion of soybean (Glycine max L. Merr.) in the continuous, no-till maize (Zea mays L.) scheme in the Argentine Pampas region is known to exist. The magnitude and nature of the soybean contribution to N availability for the succeeding crop remains uncertain, however. This study sought to quantify the long-term (14 years) effects of the inclusion of full-season, no-till soybean in the continuous, no-till maize production scheme, on soil N availability indices and microbial activity of a silt-loam Luvic Phaeozem (Typic Argiudoll). Soil samples were collected at different stages of the maize over one growing season, and analyzed for nitrate-N, ammonium-N, protease, urease and microbial activities. Aerobic incubations were also performed to assess mineral N production. Higher nitrate-N, hydrolyzable-N, protease and microbial activities were detected in samples collected at maize flowering and harvest from the soybean-maize rotation than those from the maize monoculture. These results confirm the existence of larger labile N pools and higher capacity for N mineralization in soils under maize rotated with soybean than under maize gown in monoculture. (C) 1998 Elsevier Science B.V. All rights reserved.