The effect of optimum vs deficit irrigation on plant nitrogen uptake and nitrate leaching loss from soil

Abstract

Nitrate (NO₃⁻) leaching, associated with urine nitrogen (N) deposition during grazing is recognised as a significant environmental problem. In this study it was hypothesised that optimum irrigation could increase plant growth and uptake of urine-N deposited, thereby reducing NO₃⁻ leaching over winter. The objective of this research was therefore to determine the effect of optimum vs. deficit irrigation regimes on N uptake and dry matter yields from diverse and standard pasture species and their effects on annual NO₃⁻ leaching losses from soil. In this study ruminant urine was applied at two rates of N, 500 and 700 kg N ha⁻¹, to soil monolith lysimeters in late spring. Urine was labelled with ¹⁵N stable isotope at 5 atom% prior to application. Irrigation water was applied at optimum vs. deficit rates. Measurements of NO₃⁻ leaching, ¹⁵N abundance and pasture N uptake were undertaken for a 10 month period following urine application.