Can a deep-rooted spring crop recover winter-deposited urine nitrogen?

Abstract

Grazing a winter forage crop can result in a substantial increase in soil nitrogen (N) from urine deposition, with a significant proportion leached below 30 cm during winter. If a follow-on crop can be used to recover this soil N before the following drainage season, N leaching risk could be reduced. We tested if faster growing, or deeper-rooted, spring-sown crops would be more effective at recovering winter-deposited N than ryegrass based pasture. Urea-N (800 kg N/ha) was applied in June to simulate a dairy cow urine patch and was subsequently leached down the soil profile. In the spring, the plots were sown with ryegrass, chicory and clover, or barley and harvested manually. The following autumn, the amount of N in the 60-90 cm depth (70 kg N/ha) was significantly less (P<0.05) under chicory and clover than under either barley (104 kg N/ha) or ryegrass (107 kg N/ha), suggesting that chicory was able to access the deep N pool. These data, and earlier measurements, provide evidence that chicory is a viable strategy for N recovery after winter grazing. Keywords: Nitrogen, urine, forage crop, leaching, chicory