A urine patch framework to simulate nitrogen leaching on New Zealand dairy farms

• Published in: Nutrient cycling in agroecosystems 2012-04, Vol.92 (3), p.329-346
• Main Authors: Romera, Alvaro J., Levy, Gil, Beukes, Pierre C., Clark, Dave A., Glassey, Chris B.
• Format: Article
• Language: English
• Subjects: Agriculture; Ammonia; Biomedical and Life Sciences; Computer simulation; Dairy farms; Deposition; Farms; Impact analysis; Leaching; Life Sciences; Nitrogen; Original Article; Pasture; Patches (structures); Predictions; Probabilistic methods; Spatial distribution; Statistical analysis; Urination; Urine; Winter
• ISSN: 1385-1314; 1573-0867
• DOI: 10.1007/s10705-012-9493-1

On New Zealand dairy farms, it is the nitrogen excreted directly onto pasture, particularly urine, that drives nitrogen (N) leaching from the farm. A new framework (UPF: Urine Patch Framework) is presented that post-processes the results of a whole farm model and runs a mechanistic soil model to simulate the urine patches. Two alternative methods to simulate the spatial distribution of urine patches were implemented and compared ( Grid : spatially explicit, and Probabilistic : based on the probability of different temporal urination patterns). This paper describes the implementation of these two methods in connection with a Whole Farm Model; and compares the N leaching predictions with observed data. Two examples are provided, one analyzing the impact of urine patch overlap and another, the relative risk of N leaching at different times of urinary N deposition. The model showed good correlation and predictive ability between simulated annual N leaching results and observed data [R 2  = 94 %, mean relative prediction error (MRPE) = 10 % for Grid and R 2  = 72 %, MRPE = 20 % for Probabilistic ]. The two methods produced similar results across an 8-year period for monthly and annual N leaching (R 2  = 96 %, MRPE = 10 % and R 2  = 86 %, MRPE = 8 %; respectively). Only 8 % of the paddock area was covered with multiple urinations during 1 year, but as much as 39 % of the total urine volume was deposited on overlapped patches. Systematically removing all urinary N for 1 month in either May or June reduced N leaching by approximately 20 %. Avoiding urinary N deposition during autumn or early winter could be highly effective in mitigating N leached during the following winter.