Report: TR 2007/42

Author: Helen Ritchie

Abstract

This study presents a review of research into options for on-farm nutrient management, identifying their relevance to the Upper Waikato and any gaps in existing information to guide policy development for this part of the region. On-farm practices were reviewed with a dual focus on their effectiveness in reducing nutrient losses from the farm system, and possible impacts (economic and practical) on the existing farm business operation. An additional focus was to identify factors that lead to differences in the range of environmental and on-farm economic impacts presented in the literature.

A review of literature and discussion with key specialists in this field has shown that:

1. A sound scientific research platform exists and principles have been identified for managing nutrient issues that can be transferred to this catchment.
2. Local climatic, soil and farm management variables will influence the magnitude of environmental gain from implementing different practices.
3. Nitrogen pathways and practices to reduce loss are well understood and there is a broad scientific consensus on their effectiveness. A possible exception is how much reduction in leaching and what pasture response will occur from using nitrification inhibitors in this area under different farm systems. There is also limited data on nitrogen losses under grazed winter crops in this region, and on the extent of land area under cropping in this catchment.
4. Phosphorus pathways are well understood, but the importance of particular sources and hotspots, and consequently the most effective ways to avoid losses, has to be assessed on a farm-by-farm basis. Excessive Olsen P levels can be identified from soil tests, and much overland runoff is observable by the farmer. Key sources can be seen by walking the farm in the rain to observe run-off or by checking for discharges to waterways following effluent irrigation.
5. The economic impacts of practices vary according to the details of each property, but a range of modelling has been done for Taupo, Toenepi, Rotorua and Hamilton farm systems that will have some relevance.
6. Beyond the scientific principles, the local issue needs to be clearly communicated. Of critical importance is assembling clear evidence showing that:
   • nutrient flows into the hydrolakes are increasing/are likely to increase further - what is happening
   • this will have a substantive effect - so what
   • land use change and intensification are linked to this effect - how this happens
   • within this, the greatest factors at play in this area/where nutrient contributions come from/relative importance of N and P losses - what influences it the most.

From this, the land use practices that have been identified through the literature can be applied to the Upper Waikato in a strategic way, focusing on what will make the most difference, where.

Applying this at a farm-scale level to some 'typical' farms of the area will help farmers to make the assessment of what will work for me.

The processes for engaging people in learning and action around these issues are reasonably well understood. However local information about different farmers' practices and how individual farm context affects farmers' choice of nutrient management practices may be a current knowledge gap.

A range of nutrient management practices are currently available. But there are only a few that are easily adopted into the farm system while having a positive impact on farm income and the environment. However, some practical options do exist within the current set of possibilities that can be promoted to farmers of the Upper Waikato catchment. The summary tables in this document outline what those practices are.

On Farm Nutrient Management Practice - Research and Applicability to Upper Waikato [PDF, 230 KB]