Influence of time on soil response to no-till practices

The number of growing seasons required for no-till practices to improve soi l properties should be considered before changing management systems. To ev aluate this time factor, an 8-yr tillage study was conducted on a Grenada s ilt loam (fine-silty, mixed, active, thermic Glossic Fragiudalfs) using cot ton (Gossypium hirsutum L.), grain sorghum [Sorghum bicolor (L.) Moench]-co rn (Zea mays L.), and soybean [Glycine max (L.) Merr.]-wheat (Triticum aest ivum L.) as test crops. Soil samples were characterized for soil organic ma tter (SOM), pH, exchangeable Ca and Mg, extractable P, K, Pe, Mn, Cu, and Z n, aggregate stability (AS), water dispersible clay (WDC), total clay (TC), and modulus of rupture (MR) at time 0, 4, and 8 yr. Within 4 yr, net-till (NT) resulted in statistically significant (P less than or equal to 0.05) d ifferences compared to conventional tillage (CT). The surface 2.5 cm of the NT treatments had higher levels of SOM, exchangeable Ca, and extractable P , Mn, and Zn, but lower extractable K, Fe, and Cu. Tillage had no effect on exchangeable Mg and pH. No-till also resulted in higher AS, and lower MR, WDC, and TC in the top 2.5 cm, relative to CT The differences in soil prope rties between tillage treatments were essentially independent of crop. Inst ead, the results are controlled by relative amounts of SOM and clay, and th e extent to which these properties change with time. Undoubtedly, NT practi ces ran improve several fertility and erodibility-related properties of thi s soil within 4:yr, and-enhance its sustainability.