Key points
- Crop residues contain potentially useful, but variable amounts of plant nutrients including nitrogen, phosphorus, potassium,sulphur and magnesium.
- Choice of crop residue management is driven by many factors including establishment of the following crop, weed management, soil quality and timeliness of operations. Consideration should also be given to the value of nutrients in crop residues.
- The majority of carbon, nitrogen and sulphur in crop residues will be lost to the atmosphere when burned. Other nutrients present in the residues, such as phosphorus, potassium and magnesium will mostly be returned to the soil as ash.
- Baling and removing residues will remove the majority of nutrients present in the residue.
- The financial value of these nutrients when residues are baled and removed can be estimated using the FAR calculator found at: https://www.far.org.nz/resources/electronic_tools/economic_cost_nutrient_losses
- When incorporated, barley straw decomposes more rapidly than oat straw, which in turn decomposes more rapidly than wheat straw. The rate of decomposition of all residues depends on many factors including method of incorporation.
- Incorporation by ploughing can limit contact between the soil and result in a thick layer of residue at the bottom of the plough layer. Where residues are thoroughly mixed through the soil, e.g. with discs, greater contact between the soil and residue leads to more rapid breakdown.
- In New Zealand, contrasting residue management systems are unlikely to have major effects on soil organic matter during the arable phase of the rotation.