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An Evaluation of Soil Improvement Practices Being Used on Irrigated Soils in the Columbia Basin

An Evaluation of Soil Improvement Practices Being Used on Irrigated Soils in the Columbia Basin

Andrew McGuire, Irrigated Cropping Systems Agronomist, WSU Extension & CSANR, Moses Lake, WA, David Granatstein, Sustainable Agriculture Specialist, WSU Extension & CSANR, Wenatchee, WA, Mark Amara, Moses Lake, WA
This publication outlines the results of a 2015 study conducted on the effects of three soil improvement practices used in the Columbia Basin: organic amendments, cover crops and green manures, and high residue farming. Results indicate that these soil improvement practices can maintain or improve soils in the region.
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For a general discussion of soil quality in the Columbia Basin, see the companion publication FS252E Improving Soil Quality on Irrigated Soils in the Columbia Basin.

Abstract

Farmers in the irrigated Columbia Basin of eastern Washington are using a variety of soil improvement practices: (1) organic amendments, (2) cover crops and green manures, and (3) high residue farming. To determine the effects of these practices, we compared the soils of fields managed under these practices to adjacent fields with no soil improvement practices. The soils were evaluated through an array of measurements in 2015. Results show that these practices can maintain or improve soils in this region, though each practice differs from the others in its specific effects. A parallel study estimated the economics of soil improvement and found that the improvement practices generated positive returns on investment.

Introduction

Many farmers in the Columbia Basin of Washington are applying soil improvement practices. However, it is not clear if these practices are changing soil quality or if the practices differ in their effects on the soil. To begin to answer these questions, this study assessed impacts of soil improvement practices in the Columbia Basin.

Methodology

Focus Groups

Farmers using soil improvement practices were invited to a series of three focus group discussions in June 2014. Each discussion focused on one practice: organic amendments, cover crops and green manures, or high residue farming. Farmers received a written survey prior to the meetings to help them describe their management and identify costs and benefits. A total of nine farmers attended the meetings. Each farmer used at least one of the soil improvement practices for periods ranging from three years to over 20 years. The crops they grew included timothy or alfalfa hay, potatoes, wheat, dry edible beans, canola seed, sweet corn, field corn, peas, carrots, lettuce, onions, and radish for seed. The goal of the survey and the focus group discussions was to collect qualitative data on the costs and benefits of soil improvement practices from the participating farmers. These same farmers were asked whether

a field of theirs with the soil improvement practice might be sampled and compared with an adjacent one without the practice. Fields were identified, sampled, and analyzed, conducted as described below.

Soil Improvement Practices

As in our focus groups, for the field study we divided the soil improvement practices being used by farmers into three categories, each of which contains specific practices. The practices varied in terms of the source of added organic matter, tillage intensity, and frequency of application (Table 1).

Table 1. Differences in soil improvement practices.

Field Selection

Fields were selected where the farmers either (1) had observed changes in the soil due to their soil improvement practices, or (2) had been using the practices the longest. Once the farmers’ fields were chosen, adjacent fields (not receiving any soil improvement practices) were selected in the same soil series, based on NRCS soil survey maps. Nine pairs of fields were identified. Three pairs were fields with or without organic amendments. The organic amendments used were aged and screened compost from chicken and cow manure and waste from mint oil processing. Four pairs were fields with or

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