Tillage impacts on aggregate stability and crop productivity in a clay-loam soil in central Iran

To take advantage of conservation tillage systems (including direct drilling and non-inversion) in central Iran, it is important to study the effects of different cultivation practices on soil structural stability as a physical indicator. A four-year study was conducted to investigate the effects of seven tillage systems on aggregate properties of a clay-loam soil (Calcic Cambisol) with continuous wheat (Triticum aestivum L.) production. Crop productivity was also evaluated. Tillage treatments were moldboard plowing + disking (MD) as conventional tillage; chisel plowing +disking (CD); chisel plowing+rotary tilling (CR); chisel Flowing (twice)+disking (2CD); plowing with Khishchi (a regional rigid cultivator)+disking (KD) as non-inversion methods; and till-planting with cultivator combined drill (TP) and no-till (NT) as direct drilling methods. A randomized complete block design consisting of four replications was used. Samples were taken from three different soil depths. A wet sieving method was used to determine aggregate size distribution (ASD), and mean weight diameter (MWD) as indices of soil aggregate stability. Soil organic carbon was also determined. For the first three years of the experiment, ASD and MWD at 0-15 cm were similar in different tillage treatments, except for direct drilling which had a significantly higher amount of aggregate greater than 2 mm and 2-1 mm diameter compared to the conventional method. At the second and third sampling depths all treatments had similar influence on ASD and MWD. Tillage treatments showed a significant effect on ASD and MWD in the fourth year of the experiment in all three depths. Almost 70% of the aggregates in the MD system were less than 0.25 mml while only 55% of the aggregates in the direct drilling methods were less than 0.25 mm diameter. The four-year yield average for conventional and non-inversion tillage systems was 7264 and 6815 kg ha(-1), respectively. Although, direct drilling improved soil structural stability, its lower yield (5608 and 4731 kg ha(-1) for TP and NTI respectively) potential would indicate that reduced tillage systems (i.e. CD) appear to be the accepted alternative management compared to conventional practice (MD).:(C) 2000 Elsevier Science B.V. All rights reserved.