Assessment of orchard N losses to groundwater with a vadose zone monitoring network

S. Baram, V. Couvreur, T. Harter, M. Read, P.H. Brown, J.W. Hopmans and D.R. Smart

Agricultural Water Management, 2016, vol. 172, issue C, 83-95

Abstract: A 2-year study was conducted to explore the impact of current and alternative best management practices (BMPs) of irrigation and fertigation on nitrate (NO3−) leaching below the root zone. Using a fully randomized complete block design, three fertigation strategies were compared: current BMP with and without accounting for NO3−-N in irrigation-water, and a high frequency fertigation treatment with low-N concentration applications. 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 3m at eight sites in an almond and a pistachio orchard. NO3− concentrations below the root zone ranged from <1mgL−1 to more than 2400mgL−1 (almond), and up to 11,000 (pistachio) mgL−1, with mean concentrations of 326 and 4631mgL−1, respectively. Within the fertigation cycle, fertilizer injection at the end of an irrigation event generally resulted in lower NO3− losses below the root zone compared with fertilizer injection midway through the irrigation. Pre-bloom and post-harvest flood irrigation in the almond orchard caused deep soil wetting and flushing of NO3− below the root zone, threatening groundwater quality. Statistical analysis using principal component analysis, Chi-squared Automatic Interaction Detector and the Artificial Neural Network showed that most of the deep soil NO3− concentration variability could not be explained by irrigation duration, fertigation timing or local variations in soil physical characteristics. However, mass balance estimates for water and N indicated the annual orchard average N loss could be estimated based on eight monitoring sites in spite of the inherent spatial variations in soil properties and the spatiotemporal variations in water and NO3− applications. The study indicated that reduction of N losses at the orchard scale would require alternative fertigation and irrigation practices, including better control of fertigation amounts and irrigation duration.

Keywords: Nitrate; Best-management-practice; Leaching; Fertigation; Flooding (search for similar items in EconPapers)
Date: 2016
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Citations: View citations in EconPapers (2)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:agiwat:v:172:y:2016:i:c:p:83-95

DOI: 10.1016/j.agwat.2016.04.012

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