Estimating Nitrate Leaching to Groundwater from Orchards: Comparing Crop Nitrogen Excess, Deep Vadose Zone Data-Driven Estimates, and HYDRUS Modeling
- S. Baram a,
- V. Couvreurd,
- T. Hartera,
- M. Readb,
- P.H. Brownc,
- M. Kandelousc,
- D.R. Smartb and
- J.W. Hopmansa
- a Dep. of Land, Air & Water Resources, Univ. of California Davis, One Shields Avenue, Davis, CA 95616
d Earth and Life Institute, Agronomy, Université Catholique de Louvain, 1348 Louvain-la-Neuve, Belgium
b Dep. of Viticulture and Enology, Univ. of California Davis, One Shields Avenue, Davis, CA 95616
c Dep. of Plant Sciences, Univ. of California Davis, One Shields Avenue, Davis, CA 95616
- Leaching below the root zone is estimated based on eight sites of intensive vadose zone monitoring.
- Across methods N losses estimated at the annual orchard scale were in the same order of magnitude.
- Simple N mass balance provided a good proxy of the orchard scale annual N accumulation in the soil
- Under current BMP N load to groundwater is likely in the range of 60 to 100 kg N ha–1.
Large spatial and temporal variability in water flow and N transport dynamics poses significant challenges to accurately estimating N losses form orchards. A 2-yr study was conducted to explore nitrate (NO3−) leaching below the root zone of an almond [Prunus dulcis (Mill.) D. A. Webb] orchard. Temporal changes in water content, pore water NO3− concentrations and soil water potential were monitored within and below the root zone to a soil depth of 3 m at eight sites, which represented spatial variations in soil profiles within an almond orchard in California. Orchard monthly average NO3− concentrations below the root zone ranged from 225 to 710 mg L−1 with mean annual concentration of 468 and 333 mg L−1 for the 2014 and 2015 growing seasons, respectively. Despite the huge variability in pore water NO3− concentration between sites, the larger spatiotemporal scale N losses estimated at the annual orchard scale from surface N mass balance, vadose zone based water and N mass balance, flow calculations, and HYDRUS modeling were all on the same order of magnitude (80–240 kg N ha−1 yr−1). All methods indicated that most of the N losses occur early in the growing season (February–May) when fertilizer is applied to wet soil profiles. Simple mass balance (i.e., N load applied minus N load removed) provided a good proxy of the annual N accumulation in the soil profile at the orchard scale. Reduction of N losses at the orchard scale would require alternative fertigation and irrigation practices to decrease the difference between the N load removed and the N load applied to orchards.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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