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 contribu tion to N availability for the succeeding crop remains uncertain, however. This study sought to quantify the long-term (14 years) effects of the inclu sion of full-season, no-till soybean in the continuous, no-till maize produ ction scheme, on soil N availability indices and microbial activity of a si lt-loam Luvic Phaeozem (Typic Argiudoll). Soil samples were collected at di fferent stages of the maize over one growing season, and analyzed for nitra te-N, ammonium-N, protease, urease and microbial activities. Aerobic incuba tions 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 t han those from the maize monoculture. These results confirm the existence o f larger labile N pools and higher capacity for N mineralization in soils u nder maize rotated with soybean than under maize gown in monoculture. (C) 1 998 Elsevier Science B.V. All rights reserved.