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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 elemental composition of soil plays an essential role in crop nutrition, but losses from croplands can negatively impact soil fertility and water quality. We compared the impact of strip tillage (ST) and conventional tillage (CT) on element concentrations and loads in surface runoff and subsurface flow from plots under rotational cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.) production with winter cover cropping. Total element concentrations (calcium [Ca], iron [Fe], potassium [K], magnesium [Mg], manganese [Mn], sodium [Na], phosphorus [P], sulfur [S], silicon [Si], and zinc [Zn]) in surface runoff and subsurface flow samples were measured using Inductively Coupled Plasma with Optical Emission Spectroscopy (ICP-OES). Element loads were estimated by multiplying the element concentrations by the surface runoff and drainage volumes. Significantly greater (p = 0.05) surface runoff loads for all elements (with the exception of K and Zn) were observed from the CT compared with the ST treatment plots only in 2006, likely due to the combined effects of hydrology and the timing of gypsum amendments that year. Surface runoff was the primary hydrologic pathway for Fe, K, Mn, P, Si, and Zn loss while subsurface flow was the primary hydrologic pathway for Ca, Mg, and S loss with both tillage treatments. Lower concentrations of Ca, Mg, Na, and S in the subsurface flow with ST compared to CT suggest that this tillage practice, in conjunction with the proper timing of fertilizer and soil amendment applications (e.g., poultry litter and gypsum) can be an effective method for reducing element losses from croplands. This finding highlights the importance of conservation practices in sustaining healthy cropland soils while reducing element losses and associated environmental impacts. [ABSTRACT FROM AUTHOR]

The Conservation Effects Assessment Project (CEAP) was established to develop a scientific understanding and methodology for estimating environmental benefits and effects of conservation practices on agricultural landscapes at watershed, regional, and national scales. CEAP's goal is to improve the effectiveness of conservation practices and programs by quantifying conservation effects and providing the science and education needed to enrich conservation planning, implementation, management decisions, and policy. Field observations and computer-based simulation of the effects of agricultural conservation are important components of CEAP. This research supports the CEAP effort by utilizing well-documented field data in conjunction with the Agricultural Policy/Environmental eXtender (APEX) model to quantify long-term conservation effects. In this study, field data collected at a research site located near Tifton, Georgia, were used to evaluate APEX and to quantify long-term benefits of implementing conservation tillage in the Atlantic Coastal Plain region of the United States. The objectives of this research were to (1) quantify differences in crop yield, hydrology, and sediment transport for conventional and conservation tillage systems in the Atlantic Coastal Plain; (2) develop a calibrated APEX simulation for these tillage systems; and (3) quantify the performance of the APEX model with respect to crop yields, hydrology, and sediment yield. Fourteen years of crop yield, surface runoff, subsurface flow, and sediment transport data were quantified comparing conventional tillage (CT) to strip tillage (ST). No treatment differences were found for either cotton (Gossypium hirsutum L.) or peanut (Arachis hypogea L.) yields. Surface runoff from the CT was found to be 1.7 times that of the ST, while subsurface flow from the ST was found to be 1.7 times that of CT. Total water loss (surface and subsurface) was nearly equivalent for the two systems: 30% of annual rainfall. Satisfactory model performance was found for APEX surface runoff simulations. Mixed results were found for model performance of crop yield while model simulations of subsurface flow and sediment yield were less than satisfactory. The APEX modeling framework provides a useful tool for assessing crop yield and hydrologic differences between tillage management systems in the Atlantic Coastal Plain. Additional refinement of modeling approaches may be necessary to adequately represent subsurface flow and sediment transport in these same systems. [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]