In this section
Reducing nitrogen losses from farms
- Measuring and modelling paddock water inputs and losses on stony soils
- Annual net inputs and losses of carbon and nitrogen for irrigated and non-irrigated lucerne
- Carbon inputs to reduce nitrogen losses
- Sward species and cattle diet effects on nitrogen losses
- Contrasting microbial activities in topsoil and subsoil
- Identifying soils with low nitrogen losses
- Mauriora Systems Framework: A guide and process for decision-making
Recommendations for farmers
From our findings, we are able to make recommendations for improved management practices that are anticipated to result in reduced carbon and nitrogen losses from farms. A strong seasonal component to these recommendations is necessary to adjust for cold temperatures and wet conditions in winter leading to low rates of plant growth and increased susceptibility for leaching, and warm and dry conditions in summer leading to increased respiration losses and limitations to plant growth.
- Minimise winter nitrogen leaching losses by maintaining winter active growth and nitrogen uptake by plants. This can be achieved by planting winter active Italian ryegrass or oats as soon as forage crops such as kale or fodder beet are grazed or harvested. Winter active plants also continue carbon inputs to soil, leading to reductions in annual soil carbon losses.
- For example, this could be achieved by grazing cattle on winter active grassland and supplement this with fodder beet transported and fed to the cattle on the same site. This would result in the fodder beet diet reducing the concentration of nitrogen in urine and reducing nitrogen losses by inhibiting nitrogen cycling while uptake of nitrogen from the urine by the pants would be increased.
- Avoid or minimise fallow periods when there are no carbon inputs to soil, leading to net soil carbon losses, and no uptake of nitrogen by plants, leading to increased leaching.
- Irrigation recommendations:
- For stony soils, avoid irrigation in excess of crop water requirements to minimise carbon and nitrogen losses, particularly in late summer and early autumn when temperatures and respiration losses are still high.
- Avoid irrigating nitrogen-fixing plants such as lucerne with effluent because the plants cannot use the additional nitrogen and it will likely increase leaching losses.
- For non-irrigated lucerne, consider grazing rather than cut and carry to retain more soil carbon from dung returns.