Ground cracks from drought no substitute for subsoiling in grassland

Dry weather may have created cracks in the ground but this won’t have resolved areas of compaction in grassland, warns OPICO’s James Woolway. These need to be addressed by autumn subsoiling to restore drainage and allow air interchange in the grass root zone to benefit grass growth in the spring.

Mr Woolway explains: “Compaction prevents water from draining down into the soil. Over the winter this can result in areas of standing water in which plants will die. Also, when livestock are kept out on these fields, considerable damage from poaching can occur, further adding to the compaction problem as well as creating bare areas of ground and reducing future sward density.

“Removing this compaction before the winter months improves drainage creating drier fields and allowing an earlier turnout and/or muck spreading in the spring. Furthermore as the soil is not saturated air interchange is possible which allows oxygen into the soil and around the grass roots, improving nutrient uptake from the soil and boosting growth.

“In fact, the autumn is the best time to subsoil or sward-lift grassland, as wet weather will follow and support grass growth again. Sward-lifting is best carried out when the subsoil is dry enough to crack and fissure, but the soil at the surface has sufficient moisture to allow grass to recover from the operation. The subsoiler points should be set 50mm below the pan to ensure sufficient shatter – any deeper is just a waste of fuel. The presses which follow the subsoiler legs will then minimise damage to the sward.

“Subsoiling creates a series of vertical and angled fissures giving effective drainage and soil aeration. In contrast, drought only causes vertical fissures and these are usually in areas of the least compaction anyway.

“This autumn, the good news is that the dry ground will shatter better than wet, so the effects of subsoiling will be even greater.” 
Mr Woolway advises: “To check for compaction, simply take a spade and dig out a square clod of earth. Drop this onto the ground and vertical fissures should appear. In compacted ground, only horizontal fissures will be seen.

“Also look out for areas of rusty-coloured soil which smells of iron and sulphur. This denotes iron oxidation, where compaction has starved the soil of oxygen, another limit to grass growth.

“Where compaction is deeper than 100mm, then subsoiling is the only option improve drainage. However where only surface compaction is evident, then an aerator or slitter can be all that is is needed to break up the capping and oxygenate the sward to improve grass growth.