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United States Department of Agriculture

Agricultural Research Service

Research Project: Soil and Water Conservation for Northwestern Irrigated Agriculture

Location: Northwest Irrigation and Soils Research

2013 Annual Report

1a.Objectives (from AD-416):
Objective 1. Quantify crop water productivity for irrigated crop production practices developed to reduce agriculture’s impact on water resources in arid environments in the northwestern U.S. Objective 2. Develop and validate decision tools, models and design aids to conserve soil and water resources in irrigated agriculture. Objective 3. Quantify the processes controlling sediment and nutrient losses from surface and sprinkler irrigated fields in a watershed, and contribute these data to STEWARDS.

1b.Approach (from AD-416):
The overall project goal is to reduce the environmental footprint of irrigated agriculture in an arid environment while sustaining economic return. Field research will quantify water savings and crop production impacts of rotating a non-irrigated year with irrigated crop production or implementing deficit irrigation management strategies that emphasize sugar beet production. This field research will identify alternatives to permanently reducing irrigated area in water limited situations. Model components will be developed to predict application characteristics of center pivot sprinklers, to simulate dynamic infiltration under center pivot irrigation, and estimate drift losses from center pivot sprinklers. These models will assist sprinkler selection and operation for specific field and soil conditions to reduce runoff, erosion and drift losses. Additionally, watershed monitoring will assess impacts of irrigation and management practices on the quantity and quality of water flowing from an irrigated watershed, emphasizing conversion from furrow irrigation to sprinkler irrigation.

3.Progress Report:
Objective 1. Net nitrogen mineralization was measured in sugar beet, fallow and irrigated barley plots of the irrigated/non-irrigated crop rotation study. Soil water content and infiltration were also measured to determine if prior year fallow or irrigation effected infiltration or crop water use.

The sugar beet tillage study under a linear-move irrigation system showed similar results as the first year: strip-tilled plots were wetter than conventionally tilled plots. Runoff frames installed this year showed that runoff was greater for conventional tillage. Preliminary results of this study and a prior deficit irrigation study indicate that irrigation can be reduced in August without significantly decreasing sugar beet yield.

Objective 2. A neural network model was developed to estimate furrow irrigation sediment loss using data from 747 furrows. Model input variables were furrow inflow rate, furrow length, field slope, irrigation duration, and soil texture. The model predicted sediment loss well with a model efficiency of 0.83 for the training data and 0.69 for the validation data.

Wind drift tests were conducted with a rotating plate center pivot sprinkler. Tests competed this year were limited by unfavorable wind conditions. Volume balance errors continue to range from 1 to 6% and total drift and evaporation losses were less than 10%.

A laboratory irrigation simulator was used to measure infiltration during sequential water applications to protected and unprotected silt loam soil. Surface seals developed for both surface conditions and infiltration rates decreased to less than a typical application rate under the outer spans of a center pivot irrigation system. Ponded water formed a depositional seal on the protected soil surface that reduced infiltration similar to unprotected soil. Final infiltration rate was essentially the same for each sequential irrigation when droplets impacted the bare soil, and the final infiltration rate decreased as droplet specific power increased.

Wine grape canopy temperature was monitored to investigate the effect that irrigation frequency, water deficit and number of drip irrigation emitters per vine has on canopy temperature, plant water potential, stomatal conductance and yield.

Objective 3. Weekly water samples continued to be collected for calculating sediment and nutrient budgets for the 200,000 acre Twin Falls irrigation tract. Ten drain tunnels, which contribute nitrate load to irrigation return flow, are being sampled monthly to determine water quality trends in the shallow groundwater that discharges into return flow streams. From May through September, water flow and water quality were measured at three sites in a 600 acre subwatershed. These sites isolate the contribution from sprinkler and furrow irrigated fields within the subwatershed.

Nitrate was leached from cropped and non-cropped soils that were treated with urea fertilizer or manure and incubated for more than 20 weeks. Soil nitrate was analyzed for 15N and 18O to define isotope signatures for this soil to help identify nitrate sources in drain tunnel samples.

1. New method to estimate furrow irrigation erosion. Soil erosion is often a problem with surface irrigation, which is used on 40% of the irrigated land in the US and more than 90% of the irrigated land world-wide. A neural network model was developed by ARS researchers at Kimberly, Idaho, to estimate soil loss from furrow irrigated fields using easily defined inputs. Predicted soil loss better matched measured soil loss than previous efforts with physically based models or regression models. After further refinement and validation with additional data sets, this model could be used to predict furrow irrigation erosion and the potential benefits of converting from surface to sprinkler irrigation.

2. Soil cover does not prevent surface sealing that causes runoff during center pivot irrigation. Water drops hitting the soil surface cause a seal to form that reduces infiltration, leading to runoff during irrigation. Results of an irrigation simulator study by ARS researchers at Kimberly, Idaho, found that water ponding on a soil surface, which was protected from water drop impact, reduced infiltration similar to an unprotected soil surface. Protecting of the soil surface with crop residue will not prevent soil surface seal formation when ponding occurs. Thus, center pivot sprinklers need to apply water slowly enough that water does not pond.

Last Modified: 9/2/2014
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