Management of both crop residues and nitrogen fertilizers affects soil N reactions especially on no-till systems. The magnitude of these effects on N availability to maize was evaluated in a greenhouse study. Combinations of oat straw and urea (absence, soil incorporated or surface applied) were added to experimental units (7-dm³ per pot) of two soils, in a 3 x 3 x 2 factorial combination. Plants were sown just following treatments addition, and grown for thirty days in two soils (Typic Quartzipsammnets and Humic Hapludox) with 50 and 520g kg-1 clay and 8 and 48g kg-1 organic matter respectively. Oat straw, especially when surface applied, had a positive effect on plant growth, most likely caused by increases on soil water retention. Urea application, however, had no effect on any plant parameter on the clayey soil probably because the amount of N released from soil organic matter mineralization was greater than that immobilized during residue decomposition. On the sandy soil, however, urea was beneficial when incorporated into the soil, but was detrimental when surface applied possibly due to ammonia toxicity. Thus, soil organic matter content influences the effect of oat straw decomposition on N availability to maize.
Zea mays; N immobilization; N mineralization; soil covering
