@misc{sopher_mccracken_mason_1973, title={RELATIONSHIPS BETWEEN DROUTH AND CORN YIELDS ON SELECTED SOUTH-ATLANTIC COASTAL-PLAIN SOILS}, volume={65}, ISSN={["1435-0645"]}, DOI={10.2134/agronj1973.00021962006500030003x}, abstractNote={AbstractThe objectives of this study were to determine the effects of drouth‐days by physiological growth periods on corn (Zea mays L.) grain yields and to develop a onefigure drouth index suitable for expressing these effects. A drouth‐day was defined as a 24‐hour period when potential evapotranspiration exceeds rainfall plus the effective moisture storage capacity. The physiological growth periods were: two equal‐length periods prior to tasseling; tasseling; and a maturity period. The study was conducted on two major North Carolina Soil Groups.On the better drained (Udultic) soils of the Upper and Middle Coastal Plains, drouth‐days accounted for 62.6% of the corn yield variation. The effects of drouth were detrimental in the second and fourth growth periods, and grain yields were reduced to zero after five drouth‐days during the tasseling period. For the very poorly drained (Aquultic) soils of the Tidewater Region, drouth‐days accounted for 41.2% of the yield variation. Detrimental drouth‐day effects were only present during the second and tasseling periods. The reduction of the effects of drouth‐days on these soils was attributed to moisture extration from an underlying water table.Using the derived regression coefficients for weights, the drouth‐days by physiological growth periods were weighted and summed to develop a one‐figure drouth‐index. This index may be used as a single climatic variable in regression‐correlation studies of the crop‐soil ecological system.}, number={3}, journal={AGRONOMY JOURNAL}, author={SOPHER, CD and MCCRACKEN, RJ and MASON, DD}, year={1973}, pages={351–354} }
 @article{sopher_mccracken_1973, title={RELATIONSHIPS BETWEEN SOIL PROPERTIES, MANAGEMENT PRACTICES, AND CORN YIELDS ON SOUTH-ATLANTIC COASTAL-PLAIN SOILS}, volume={65}, ISSN={["1435-0645"]}, DOI={10.2134/agronj1973.00021962006500040020x}, abstractNote={AbstractCorrelations between individual soil properties, management practices, and corn (Zea mays L.) grain yields were observed for 441 corn plots on selected North Carolina Coastal Plain soils. Correlations between different soil properties within soil horizons and correlations between the same properties in adjacent soil horizons show that many of the variables in the crop‐soil ecological system are highly intercorrelated. These intercorrelations limit the usefulness of both simple and multiple regression to characterize cause and effect relationships within the system. However, they can be useful in helping to understand the complex system and to develop soil sampling techniques for future characterizations of the system.Of the 101 independent variables (23 soil properties on each of 4 horizons plus nine management variables) included, 56 variables were significantly correlated with corn grain yields on the well‐drained (Udultic) soils Upper and Middle Coastal Plains (mainly Hapludults and Paleudults). Sixty‐one variables were significantly correlated with yields on the very poorly drained (Aquultic) soils of the Tidewater region (mainly Umbraquults and Ochraquults). The factors most affecting yields on both soil groups were soil moisture holding capacities, certain combinations of clay and sand, extractable P, percent base saturation and properties which control soil acidity, the amount of charge on the cation exchange complex, plant populations, and planting dates. Because of previous high management levels of the fields sampled, applied nutrients were deemed important but not highly limiting on the two soil groups studied.}, number={4}, journal={AGRONOMY JOURNAL}, author={SOPHER, CD and MCCRACKEN, RJ}, year={1973}, pages={595–599} }