Water infiltration and clod size distribution as influenced by ploughshare type, soil water content and ploughing depth

Soil management techniques, especially tillage, have been linked to the creation of low-permeability pans that reduce soil infiltrability and increase runoff and soil erosion on agricultural soils. In Iran, the mouldboard plough is the standard tillage implement used for primary tillage and that could create a compacted plough pan, especially under wet conditions. It was hypothesised that serrations on the ploughshare would increase water infiltration into the soil. A field experiment was conducted in Isfahan (central Iran) on a silty clay loam soil (Typic Haplargids). The infiltration rate and cumulative infiltration of water into furrow bottoms after ploughing with a mouldboard plough were measured using a double-ring infiltrometer. The plough was equipped with five share types (deep-suck share (control), trapezoidal share with/without sharepoint and serrated share with/without sharepoint) and ploughing performed under two soil water contents (0.55 and 0.85 plastic limit, PL), and two ploughing depths (15 and 20 cm). The clod mean weight diameter (MWD) was determined as an index of soil pulverisation, using dry sieving. The average 90 min cumulative water infiltration for the serrated share with sharepoint was significantly greater than for the other share types due to the furrow-bottom soil cracking resulting from an increase in the thickness of cutting edge of the plough. Ploughing at 0.85 PL significantly improved cumulative water infiltration compared with ploughing at 0.55 PL. The final infiltration rate for the serrated share with/without sharepoint was statistically similar to that of deep-suck share (control). For shallow ploughing at 0.85 PL, the clod MWD for the trapezoidal share without sharepoint was significantly greater than that of the control. For the serrated share with sharepoint, the proportion of coarse clods (⩾40 mm) was significantly higher under dry condition (0.55 PL), when compared with the moist condition (0.85 PL), whereas for the rest of ploughshare types, those proportions were statistically similar. These results indicate that for improving water infiltration and still having similar soil pulverisation, the deep-suck share could be replaced by the serrated share with sharepoint in heavy soil (i.e., silty clay loam) with low water infiltration while ploughing at a moisture content of 0.85 PL.