Irrigation water amount and salinity dictate nitrogen requirementby Peter Vaughan, John Letey

Agricultural Water Management


Water Science and Technology / Agronomy and Crop Science / Earth-Surface Processes / Soil Science


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Evagelia Stefanoudaki, Mark Williams, Kostas Chartzoulakis, John Harwood


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ARTICLE IN PRESSG ModelAGWAT-4025; No. of Pages 6

Agricultural Water Management xxx (2014) xxx–xxx

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Irrigati itro

Peter Vau a President, CM b Distinguished CA 92 a r t i c l

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N leaching

N uptake

Relative yield


Modeling d by ons a ng fro asons n (AW ; and simulations that included winter precipitation were approximately 5% greater than identical simulations without precipitation for 2 ≤ ECiw ≤ 4. Except for deficit irrigation, all AW/PET values resulted in RY equal to 100% for ECiw ≤ 2 when N was not limiting. For ECiw > 2 progressively greater AW/PET was required for full yield. For less saline waters, water stress was limiting for the AW/PET = 0.9 treatment and RY was unaffected by the N application rate. For a given N application rate, increasing water application caused decreasing RY and increasing leached N. When N applications were greater than required for maximum RY, a decrease in N application resulted in an equal decrease in leached N. When decreasing N 1. Backgro

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E-mail add 1 Deceased. http://dx.doi.o 0378-3774/© this article in press as: Vaughan, P., Letey, J., Irrigation water amount and salinity dictate nitrogen requirement. Agric. Water 2014), applications caused decreasing RY, the reduction in leached N was less than the reduction in N application.

For the very saline waters (ECiw = 4), AW/PET = 1.1 was inadequate to leach the salts and water stress was the limiting factor rather than N application. Water flow below the root zone is controlled by both water application and N deficiency which reduces plant water uptake. Regulatory attempts to restrict

N leaching to groundwater that prescribe management of N applications exclusively are likely to fail because N leaching depends on water flow as well as N application. © 2014 Published by Elsevier B.V. und a paper for the special issue of Agricultural Water Mannoring Dr. James Oster is a pleasure because he is a long lleague and friend. He made major scientific and extenutions to matters related to soil salinity and irrigation. riate that this manuscript addresses an issue that is ith Jim’s contributions. ip in obtaining funds and directing a study that comransient state models that include salinity and matric s on plant yield is one of Jim’s major contributions to the erature (Oster et al., 2012). The study included ENVIROP, HYDRUS, UNSATCHEM, and SALTMED. SALTMED ower relative yields (RY) than the other models for all ding author. Tel.: +1 5596389098. ress: (P. Vaughan). irrigation water application amounts and salinity (ECiw). For other models, RY values were similar (within about 7%) for all water application amounts when ECiw was 3 dS/m or less. The relative yield (RY) was the ratio of seasonal water uptake to potential water uptake by an unstressed crop expressed in percent (Oster et al., 2012).

Of these models, ENVIRO-GRO (E-G) is the only one that includes a nitrogen (N) module to simulate the consequence of N management variables on RY and the leaching of nitrate below the root zone. The E-G model has recently been reprogrammed by the senior author to extend the capabilities and to make it more efficient. Modifications include addition of compensation for N uptake, a two-pool model for organic matter decay, mass balance calculations, comprehensive output routines and improvements to the transport calculations for salt and nitrate. Details regarding these modifications and other information are provided in the EG user manual which is available along with the program for free at The simulated results reported here were from the updated E-G model. rg/10.1016/j.agwat.2014.10.006 2014 Published by Elsevier B.V.on water amount and salinity dictate n ghana,∗, John Leteyb,1

S Consulting, 1315 E Street, Reedley, CA 93654, United States

Professor Emeritus, Dept. of Environmental Science, University of California, Riverside, e i n f o e xxx a b s t r a c t

Crop relative yield (RY) may be reduce (N) deficiency. Elucidation of interacti program to compute RY and N leachi year simulations included growing se divided by potential evapotranspiratio (ECiw, dS/m) values of 0.5, 1, 2, 3, and 4m/locate /agwat gen requirement 521, United States matric water potential or salinity stresses but also by nitrogen mong these factors through modeling using the ENVIRO-GRO m the root zone for corn (Zea mays) was our objective. Tenand fallow periods. Simulation variables were applied water /PET) equal to 0.9, 1.1, 1.3, and 1.42; irrigation water salinity inorganic N applications ranging from 270 to 350 kg/ha. RY for

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ARTICLE IN PRESSG ModelAGWAT-4025; No. of Pages 6 2 P. Vaughan, J. Letey / Agricultural Water Management xxx (2014) xxx–xxx 2. Introduction

Although the setting for this study is the Central Valley of

California, the findings are relevant to all irrigated areas of the world. The achieving h by pumpin projects de tributed to that were f

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California g application for the pres have more t that more and there is be included application required to and maxim more N to ers have his maximum p

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That resear systems an low water t water disch ples collect into the tile ies, soil sam usually reac oped to calc water flow an estimate on fertilizer