Development of a new in situ system to measure nitrate leaching losses from winter grazed fodder beet : A Dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agricultural Science with Honours at Lincoln University

Nitrate (NO₃⁻) leaching from agriculture has become an increasigly important issue in New Zealand. There has been an increase in NO₃⁻ leaching in recent years, with the cause of this mainly due to increases in cattle numbers and the application of N fertilisers. NO₃⁻ leaching is of importance due to its economic cost to farmers, environmental impact and potential health risk. Economic cost to the farmers occurs when leached nitrogen (N) has to be replaced with fertiliser N. There is also a major environmental concern about eutrophication. Eutrophication causes an increase in algae and aquatic life and reduces the recreational value of waterways. Winter forage grazing systems leach disproportitally high amounts of N, compared with the rest of the farming system. There are very few measurements of nitrate leaching losses from below winter grazed fodder beet (FB) in New Zealand. Measurements are needed urgently to quantify and ultimately minimise NO₃⁻ losses from these systems. The current systems of measuring NO₃⁻ leaching suffer from limitations such as being labour intensive, the inability to measure nitrate leaching under cultivation and the need to scale up results from small plots or lysimeters. The objective of this research project was to develop a new system of measuring N leaching that could accurately quantify N leaching under a winter grazed FB crop without the limitations of current systems. The suction cup and lysimeter array (SCALAR) system was developed to overcome these limitations. This was done through having a single collection/retrieval site, changing the depth of the top of the suction cup shaft to below the level of cultivation in soil, increasing the number of suction cups per unit area and having a large measurement area (0.16 ha). The SCALAR system was developed and tested in this research project. The results showed that the SCALAR system successfully overcome the limitations of previous measurement systems. The results of this study showed the total N leaching under the winter grazed FB crop was 106.9 kg N/ha. Of this, 101.5 kg N/ha was leached in the form of NO₃⁻ and 5.4 kg N/ha was leached in the form of ammonium (NH₄⁺). However, these values are likely to have been affected by the development and testing of the SCALAR system and are therefore not considered to be representative of a typical winter grazed FB crop. Future research is still needed to quantify N leaching losses under a winter grazed FB crop using the SCALAR system that has been developed in this project. The SCALAR system will potentially remain in the ground for 20-30 years, allowing it to be used in future research to quantify N leaching under a variety of farming systems