A modeling analysis of carbon and nitrogen (input, cycling and fate) in irrigated grassland in Canterbury showed reductions in soil carbon following irrigation, due to increasing nitrogen limitation. These two co-limiters of growth interact - irrigation stimulates carbon fixation and plant growth, this leads to greater nitrogen uptake by plants, which then leads to greater removal of nitrogen in products (meat, milk). So if nitrogen input is constant, over time it leads to increasing nitrogen deficiency. Our findings suggest that using irrigation during dry periods in dry regions can greatly increase plant growth, product yields and soil carbon inputs, provided nitrogen inputs are also increased. However, evidence suggests that this may not lead to increases in stabilised carbon stocks.

An excerpt from NZAGRC Highlights 2017 to be released shortly. Read more