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The curve number (CN) method for estimating direct runoff from a rainfall event is commonly used in hydrologic investigations, but currently accepted CNs for no-till cropping might need revising. We derived CNs from ranked rainfall-runoff data gathered from 1972 to 2010 from a 2.7 ha, zero-order watershed (P1) near Athens, Georgia. The watershed was initially managed under conventional tillage for 2.5 years, followed by double-cropped continuous no-till rotations. During conventional tillage, on average 19% of the rainfall was partitioned into runoff (median 13%). The mean and median CN was 82 and 85, respectively. Least square fitting of CN versus rainfall produced an asymptotic CN of 81 (R² = 0.61). In contrast, the mean and median runoff during no-till was 7% and 0.6% of the rainfall, respectively. The mean CN equaled the median CN of 62. The asymptotic CN was 58 (R² = 0.78), compared with 72 from standard tables. When estimated using CN of 72, the mean runoff during no-till was 142% greater than the measured mean runoff. These results support the hypothesis that CNs for no-till cropping systems should be smaller than currently accepted values for comparable watersheds in the region. This has implications for hydrologic modeling for water quantity and quality where the use of the CN method is ubiquitous. [ABSTRACT FROM AUTHOR]

The environmental outcomes from tall fescue (Lolium arundinaceum [Schreb.] Darbysh.) pastures managed with different levels of endophyte (Neotyphodium coenophialum) infection and choices of harvest and fertilization methods are not well known. We moni-tored runoff from 14 tall fescue paddocks, 0.9 to 1.1 ha (2.2 to 2.7 ac) each, from April of 2002 to April of 2010 near Watkinsville in the Georgia Piedmont. Three grazed Jesup tall fescue-endpohyte associations (endophyte infected high alkaloid--Wild, endophyte infected low alkaloid--MaxQ, and endophyte free--Free), and two sources of fertilization (inorganic and broiler litter), were replicated twice in a randomized block design. A replicated hayed treatment was planted to Jesup MaxQ with inorganic fertilization as a grazing control. Drought reduced the maximum number of runoff events to 77. A Standardized Precipitation Index analysis showed that the degree of drought was dependent on the time scale consid-ered. The near normal period peaked at a 1-month (74%) scale and was least at a 9-month time scale (32%). Considering a 1-month time scale, there were on average 4 times as many runoff events per month during the near normal, and 16 times as many during the wet and wetter period, as those in the dry and drier period. Fertilizer and fertilizer by fescue inter-actions in grazed paddocks had significant effect on runoff, whereas main effects of fescue type and harvest methods (graze versus hay) did not. Inorganically fertilized paddocks had 30% greater runoff -than those with broiler litter fertilization. The largest runoff amount occurred with inorganic fertilizer and endophyte-free fescue, suggesting a combined impact' of reduced persistence of the endophyte-free fescue, with low organic matter input from the inorganic fertilizer. Grazing of Piedmont pastures with MaxQ-endophyte association of tall fescue, and fertilized with broiler litter, does not appear to pose additional risk for runoff, compared to tall fescue pastures under the common wild-type-endophyte association that are hayed or grazed, and fertilized inorganically or with broiler litter. These results further support a previous recommendation for increased adoption of MaxQ with broiler litter fertilization in the southeastern United States, because of excellent average daily gain by cattle and stand persistence of MaxQ. [ABSTRACT FROM AUTHOR]

Reduced tillage and surface residue increases infiltration, soil water content, and plant available water, while at the same time decreasing runoff and sedimentation. However, there is a general lack of knowledge and appreciation regarding the impact conservation tillage has on sustainable water resources. The objective of this study was to estimate water savings as a result of conservation tillage adoption in Georgia. Total acreages by crop (cotton, corn, and peanut) and tillage (conventional and conservation) were obtained via the Conservation Technology Information Center for the 2004 growing season. Rainfall simulation studies conducted over row-cropped lands in conventional and conservation tillage were obtained for soils in the Coastal Plain and Piedmont physiographies. Data were integrated within a geographical information system. In 2004, cotton, corn, and peanuts represented 85% of row crop production in Georgia, with nearly 90% of the acreage in the Coastal Plain. Conservation tillage systems are currently in place on approximately 30% of those acreages, primarily in the form of strip tillage. Results from rainfall simulation studies indicate that conservation tillage can reduce runoff and increase infiltration in these systems by 29% to 46%. Extrapolating these results to the state, conservation tillage reduced estimated statewide, irrigated water requirements from 4% to 14%. Increasing conservation tillage to 40% in intensively row-cropped counties where conservation tillage adoption rates were less than the national average (40%) increased estimated water savings by an additional 1% to 6%. [ABSTRACT FROM AUTHOR]