Soil water extraction and use by winter wheat cultivars under limited irrigation in a semi-arid environment
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Water supply and distribution are the main limiting factors to wheat (Triticum aestivum) yield in a semi-arid region of the U.S. southern Great Plains. To manage crop water demand, limited irrigation (also called deficit irrigation) is commonly practiced in the region. A 4-yr study was conducted to evaluate yield in winter wheat cultivars as influenced by the depth and amount of net soil water extraction (SWE) under limited irrigation. For timing the irrigation application, we considered critical growth stages (jointing, tillering, and anthesis) as well as soil water depletion at the crop root zone below 50%. Volumetric soil water content was measured in 0.2m increments to the depth of 2.4mat planting, jointing, anthesis, and physiological maturity. Since the irrigation capacity was limited, seasonal precipitation was still an important factor for determining SWE. The 2011 season was one of the historic drought seasons with only 60mm of seasonal precipitation and the net SWE in that season was limited to the upper 1.2m profile. In contrast, the 2016 season was more favorable for crop growth with 315mm of seasonal precipitation and the net SWE in that season reached to 2.0m deep. Grain yield was largely influenced by the amount of net SWE during the growing season. For the wheat with grain yield of 4807kgha, net SWE was 165mm (2016). However, wheat with grain yield of 2933kgha only extracted 70mm stored soil water (2011). The 2012 and 2017 seasons remained intermediate in terms of seasonal precipitation, SWE, and yield. Although the 2011 and 2016 seasons had similar stored soil moisture at planting, more early-season as well as total precipitation in 2016 appears to have enabled plant growth to access the deeper water. In contrast, a greater amount of stored soil water was left unused at the end of the 2011 season due to drought and poor plant growth. Hence, in addition to adding water at critical growth stages, ensuring early plant growth to promote root development for extracting soil water from the deeper profile later in the season should be a key strategy to take full advantage of limited irrigation.
