Agronomists have long been interested in how variation in soils and climate are related to crop yields. An experiment was conducted to quantify the effect of weekly plant available stored soil moisture (PASSM) during 10 weeks of the growing season on corn (Zea mays L.) yield under constant and variable climatic conditions. The objective of this study was to determine how soils, varying in the amount of water supplied to corn, affect corn yield under constant climatic conditions. Plot yields from four Illinois locations (farms) for 3 years (1969–1971) were correlated with weekly PASSM, rooting depth, and available water‐holding capacity in the rooting zone. Experimental plots had high fertility and management levels. Approximately six sites to various depths to a root‐restricting glacial till or natric horizon, giving a wide range in independent variables, were established at each location. The PASSM values were calculated from weekly gravimetric moisture samples that were adjusted for rooting depth, bulk density, and 1/3 and 15 bar water retentions. The PASSM values were summed by a method similar to Fisher's polynomial technique as previously modified. The average R2 value of quadratic regression calculated for each year location was 58%. Above average PASSM was most beneficial either during tasseling or grain‐filling stages depending on the season. Quadratic regressions for each year‐location were calculated using rooting depth and available water‐holding capacity instead of weekly PASSM as the treatment variable, with average R2 values of 73 and 71%, respectively. The effect of each centimeter of rooting depth or available water‐holding capacity, as estimated from linear regression coefficients, varied considerably with the favorableness of the season. The lower precision of the weekly PASSM models, when compared with the rooting depth and available water‐holding capacity models was due to weekly sampling variation and possibly water movement above and below the soil surface. It was concluded that with adequate fertility and a high level of management, the potential of a soil to produce corn was largely determined by the soil's capacity to store and supply water.

Agronomists have long been interested in how variation in soils and climate are related to crop yields. An experiment was conducted to quantify the effect of weekly plant available stored soil moisture (PASSM) during 10 weeks of the growing season on corn (Zea mays L.) yield under constant and variable climatic conditions. The objective of this study was to determine how much of the variation in corn yield was due to variations in soils and climate and to develop a model relating corn yield to soil, rainfall, and temperature which could be used to predict corn yields for other locations not studied. Plot yields from four Illinois locations (farms) for 3 years (1969–1971) were correlated with weekly PASSM, rooting depth, or available water holding capacity in the rooting zone and climatic data (rainfall and temperature). Experimental plots had high fertility and management. Weekly PASSM, rainfall, and temperature values were summed by a method similar to Fisher's polynomial technique as previously modified. Differences in corn yields due to soils, locations, and among years within locations are due to differences in climate (rainfall and temperature) and differences the ability of the soil to supply water. When correlated with rainfall and temperature data PASSM determined on a weekly basis was slightly less efficient (R2 = 0.80) than was rooting depth (R2 = 0.83) or amount of preseason water available in the rooting zone (R2 = 0.81) in explaining variations in corn yield. Equations fitted to the data should be useful models in predicting corn yields for other locations and soil conditions not studied. The model utilizing the amount of preseason water available in the rooting zone is particularly easy to utilize in predicting corn yield for other locations from soils and climatic data.

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