Cumulative and Residual Effects of Swine Slurry and Mineral Nitrogen in Irrigated Maize

Swine (Sus scrofa domesticus) slurry (SS) combined with mineral N fertilizers is a common fertilization practice in irrigated monoculture maize (Zea mays L.) in northeastern Spain. This study was designed to analyze the cumulative and residual response of sprinkler-irrigated maize to SS application. A 4-yr field experiment was setup with 16 treatments combining four SS rates between 30 and 120 Mg ha(-1) and eight mineral N rates between 0 and 350 kg N ha(-1). Maximum yields (10.2-11.7 Mg ha(-1)) and also critical rate of N fertilization (0 -179 kg N ha(-1)) varied between years. Application of 30 Mg SS ha(-1) at presowing complemented with 175 kg mineral N ha(-1) at side-dressing was the sole SS treatment reaching maximum yield for all years. Significant precipitation in spring 2003 (119 mm) leached the applied N at sowing and maize responded only to the N applied at side-dressing. The 4-yr average maximum N fertilization rate that does not promote soil nitrate accumulation was established at 134 kg N ha(-1) yr(-1). Two years after the last SS application maize yield (average 5.7 Mg ha(-1)) did not differ from the control treatment (6.3 Mg ha(-1)); that is, no residual effects were detected 2 yr after SS application. The best maize N fertilization strategy was the application before sowing of a low SS rate that would cover the whole maize PK needs and initial N needs (30 Mg ha(-1) of fattening farm SS), complemented with the required amounts of mineral N at side-dressing.