Search

A SWAT model equipped with an alternative auto-irrigation algorithm was used to evaluate the effects of planting date on hybrid corn yield and seasonal water use in the Texas High Plains. Research field data from the USDA-ARS Conservation and Production Research Laboratory at Bushland, TX and the Texas A&M AgriLife North Plains Research Field near Etter, TX were used for model calibration. A long-term weather data set was used to simulate continuous corn using five planting dates (15-April, 1-May, 15-May, 1-June, and 15-June) for both long- and short-season corn hybrids. Results suggested that delayed planting resulted in a reduction of seasonal water use for both hybrids. Reductions in seasonal irrigation between the 15-April and 15-June were 28 % and 31 % for long- and short-season hybrids, respectively, using an application depth of 25.4 mm. Corresponding reductions in yield were considerably less at 8.9 and 8.8 % for long- and short-season hybrids. Reduced irrigation was attributed to decreased temperature stress and lower evapotranspiration of the later growing season. However, simulation of long season corn for the 15-June planting resulted in late season cold temperature stress. Further analysis of 19.1 mm and 31.8 mm irrigation depths revealed the latter resulted in an average of 4.4 and 4.7 % reductions in seasonal irrigation for long- and short-season hybrids, respectively. Results from this assessment study suggest the delayed planting of corn may result in decreased irrigation while maintaining profitable yields, potentially reducing withdrawals from the Ogallala Aquifer in the Texas High Plains region. [ABSTRACT FROM AUTHOR]

The mechanism by which chemical energy is converted into an electrochemical gradient by P-type ATPase is not completely understood. The effects of ATP analogs on the canine kidney (Na+ + K+) ATPase were compared to effects of the same analogs on the maize (Zea mays L. cv. W7551) root H+-ATPase in order to identify probes for the ATP binding site of the maize root enzyme and to determine potential similarities of ATP hydrolysis mechanisms in these two enzymes. Six compounds able to modify the ATP binding site covalently were compared. These compounds could be classed into three distinct groups based on activity. The first group had little or no effect on catalytic activity of either enzyme and included 7-chloro-4-nitrobenz-2-oxa-1,3-diazole. The second group, which included azido adenine analogs, fluorescein isothiocyanate and 5′-p-fluorosulfonylbenzoyladenine, were inhibitors of ATP hydrolysis by both enzymes. However, the sensitivity of the (Na+ + K+) ATPase to inhibition was much greater than that exhibited by the maize root enzyme. The third group, which included periodate treated nucleotide derivatives and 2′,3′-o-(4-benzoylbenzoyl)adenosine triphosphate, inhibited both enzymes similarly. This initial screening of these covalent modifiers indicated that 2′,3′-o-(4-benzoylbenzoyl)adenosine triphosphate was the optimal covalent modifier of the ATP binding site of the maize root enzyme. Certain reagents were much more effective against the (Na+ + K+) ATPase than the maize root enzyme, possibly indicating differences in the ATP binding and hydrolysis pathway for these two enzymes. Two ATP analogs that are not covalent modifiers were also tested: the trinitrophenyl derivatives of adenine nucleotides were better than 5′-adenylylimidodiphosphate for use as an ATP binding probe. [ABSTRACT FROM AUTHOR]

Corn (Zea mays L.) is a major irrigated crop grown in the Southern High Plains including the Texas Panhandle. Irrigation from the Ogallala Aquifer is required to sustain profitable corn production in the region by supplementing inadequate and erratic rainfall. Effective irrigation scheduling works to extend limited groundwater resources by avoiding water losses associated with runoff and/or percolation below the root zone. The use of crop coefficient (Kc) and reference evapotranspiration (ETo) values to estimate daily crop water use (ETc) remains an effective scheduling tool that can complement other irrigation scheduling approaches. Both Food and Agriculture Organization (FAO-56) piecewise and curvilinear Kc values for corn are found in the literature. However, advances in corn genetics have led to questions about the applicability of Kc values developed using legacy corn hybrids to irrigation of modern drought-tolerant (DT) hybrids. Lysimeter-derived Kc values for legacy corn hybrids grown in large weighing lysimeter fields at the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas, were compared with those derived from a modern DT corn hybrid recently grown in the same fields. Results indicated that although midseason daily Kc values were similar for all hybrids, average season length was ~25 days shorter for the modern DT hybrid, characterized by a shortened initial growth period followed by more rapid increase of Kc during the development period. However, plots of Kc over thermal time illustrated that the differences in season length were likely attributable to later planting dates associated with the DT corn hybrids. Average seasonal water use was 730 and 811 mm for the legacy and modern DT hybrids, respectively (three years each), with corresponding average yields of 1.2 and 1.4 kg ha-1. Results suggest that published Kc and Kcb values developed with legacy corn hybrids remain largely applicable to modern DT corn hybrids when used with accurate estimates of effective canopy-based growth stages and climate-specific Kc functions. [ABSTRACT FROM AUTHOR]