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Recommended Crop Species and Wheat Varieties for Acidic Soil

Recommended Crop Species and Wheat Varieties for Acidic Soil

FS169E
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Paul Froese, MS Graduate Student, WSU Department of Crop and Soil Sciences, Dr. Arron Carter, Associate Professor, WSU Department of Crop and Soil Sciences, Dr. Michael Pumphrey, Associate Professor, WSU Department of Crop and Soil Sciences
Decreasing soil pH, also called soil acidification, is a growing concern in eastern Washington and northern Idaho. Researchers and farmers have measured soil pH values below 5.0 throughout the Palouse region. Decreasing soil pH has serious implications for the cropping systems of the Palouse. This fact sheet is part of a WSU Extension series on soil acidification and discusses plant sensitivity to, and tolerance of, soil pH and acidification, as well as discussing the tolerance of specific varieties of wheat. Other fact sheets in the Soil Acidification series will cover more specific information on topics such as the influence of pH on pathogens and microbes, herbicide activity, crop nutrition, and liming.
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Introduction

As discussed in the Implications for Management – An Introduction, not all crop species—nor all varieties within species—respond the same to acidic soil (Figure 1). Of the crops commonly grown in eastern Washington and northern Idaho, legumes are the most sensitive to soil acidity, while wheat and barley are less sensitive, followed by triticale and grass hay/seed crops, which can tolerate more acidic soil (Table 1). Canola and buckwheat also fare better on acidic soils than legumes and some wheat varieties, although canola is relatively sensitive to manganese (Mn) toxicity, which can be a problem on some acidic soils.

Figure 1. Yield response of common crops to declining soil pH in the Palouse (adapted from Mahler and McDole 1987). Wheat is differentiated here by its level of genetic tolerance: “wheat-low” values indicate results for varieties with low tolerance to acidity and Al. The “wheat-high” values indicate results for varieties with higher tolerance to acidity and Al.
The response of a particular crop to acidic soil will also depend on soil characteristics other than pH, such as soil fertility, microbiology, organic matter content, concentration of available aluminum (Al), etc., so it is difficult to prescribe an absolute pH cutoff value under which a certain crop or variety will begin to lose productivity, and at what pH point yield loss will become economically prohibitive. Furthermore, productivity does not decline at the same rate for each crop, as seen when comparing alfalfa to a highly tolerant wheat variety (Figure 1), so it may be economically feasible, for example, to produce tolerant wheat at a pH farther below its critical value than alfalfa could withstand.
Table 1. Critical pH below which crop species lose significant productivity

Fine-tuned crop and variety selection decisions will therefore depend on the individual experiences of growers in their unique environments.

The following guidelines should help in the process of crop and varietal selection when farming on acidic soil, and the use of superior varieties in conjunction with other important acidity-mitigating tools in the grower’s integrated toolbox should ultimately improve farm productivity.

Relative sensitivity of common regional crops

Of the legumes (alfalfa, chickpeas, lentils, and peas), alfalfa is, in general, the most acid-sensitive, followed in order of decreasing sensitivity by lentils, peas, and chickpeas, as shown in Table 1 (Mahler and McDole 1987; Koenig et al., 2009). Legume yield on acid soil is largely impacted by the reduced ability of symbiotic rhizobia to perform in low-pH conditions. It has been observed that the rhizobial species that colonize chickpea nodules are more vigorous at low pH than those colonizing peas, lentils, and alfalfa. This explains the superior performance of chickpeas over other common legumes on acidic soil.

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