Runoff and persistence of selected herbicides were studied on four small Piedmont watersheds in Georgia during four growing seasons. This is part of a study designed to provide data for developing and testing mathematical models for agricultural chemical transport. Seasonal runoff losses were determined relative to watershed management, herbicide type and persistence, mode of application, and time of runoff in relation to application timing. Seasonal losses were usually < 2% of the application, unless large runoff volumes were generated shortly after application. Average storm herbicide concentrations in runoff were correlated with herbicide concentrations at the 0‐ to 1‐ cm depth increment of the watershed soils at the time of runoff. Paraquat concentrations in runoff (predominantly sediment associated) were well correlated and positive with the product of soil herbicide concentration and sediment in runoff. Equations describing soilbased herbicide transfer to runoff were power functions with exponents near unity with the form: Y = a xb. Simple relationships such as those developed in this study along with hydrology and erosion/sediment models may he useful in predicting pesticide runoff potential when assessing relative impacts of management decisions. The next step would be to describe key management practices in terms of these coefficients and exponents.
Selective management practices were used on two upland Southern Piedmont watersheds to assess their influence on overland transport of Cl, soluble‐N, and total Kjeldahl‐N (TKN). Ammonia‐N and TKN were measured in both runoff water and sediment phases and related to these transport modes. Chloride (112 kg Cl/ha) served as a tracer anion because of its inert biological activity. Optimum rates of N‐fertilizer (∼140 kg N/ha) were applied in recommended split‐applications for corn growth. Annual NH4‐N and TKN losses were 35 to 40% less when associated with terraces and double cropping of corn (Zea mays L.) and winter rye (Secale cereale L.) than from a watershed without conservation practices. This difference was related primarily to differences in sediment yield from the two watersheds. No real annual differences were detected for Cl and NO3‐N losses between watersheds. Total seasonal nutrient losses were strongly affected by the quantity of sediment transported during highly erosive periods of May, June, and July. Chloride and TKN concentrations in runoff were more constant among cropping seasons; therefore, individual storm yields were best related to runoff water volume. Nitrate‐N and NH4‐N concentrations in runoff decreased rapidly during corn canopy development causing the quantity of these N species to be best related to sediment transport. An inadequate number of runoff storms occurred during these short periods of high soil chemical concentrations, derived from Cl‐ and N‐fertilizer sources, in the surface depth (0 to 8 cm) to significantly develop a relation to runoff concentrations. Runoff water and sediment variation accounted for 82 to 93% of nutrient loss variation on the nonconservation watershed. The same variables accounted for as little as 61% of the nutrient variation on the conservation watershed. Runoff losses of plant nutrients may be reduced by shifting most of their application to periods of rapid plant canopy development and periods of less intense rainfall.
Soil profile characteristics of many soils are related to the partitioning of fertilizers for soil pool, plant uptake, overland transport, and deep seepage. Chloride and NO3‐N distribution patterns were studied on variable soil profiles of two small agricultural watersheds planted to corn (Zea mays L.). Management variables included grassed waterways, graded terraces, and winter rye (Secale cereale L.) cover crops. Landscape slope and soil characteristics of the surface and control section layers were inherent variables within and among watersheds. Average soil Cl concentrations decreased from 275 ppm to background levels (30 ppm) at the 0‐ to 8‐cm soil depth within 40 days after spring‐incorporated applications of Cl fertilizer (112 kg Cl/ha as KCl). Nitrogen fertilizers (∼140 kg N/ha per year) were applied in split applications to meet optimum corn‐growth demands. Average NO3‐N concentrations ranged from 20 to 40 ppm at the 0‐ to 8‐cm depth immediately after N‐fertilizer applications, but decreased rapidly because of biological assimilation. Nitrate‐N below 25‐cm soil depths were consistently ± 10 ppm and unrelated to watershed management or soil characteristics because of the low concentrations. Chloride distribution in soil profiles was significantly related to the depth of the B21t soil horizon below the soil surface and to surface soil texture only when the B21t horizon was uniformly located in the soil profile. Most anions available for leaching are below the B21t horizon following summer leaching, and move below the soil solum during winter leaching. A Cl balance suggests that most unaccounted for N (30 kg/ha) may be lost through winter leaching or denitrification. Recommended applications of applied N‐fertilizer for corn production provide little opportunity for overland transport and small increases in deep seepage during winter months to drainage waters. Heavy applications of Cl in April or May suggest that similar applications of commercial N‐fertilizers have little chance of overland transport because of rapid movement below the surface cm depths. The overland transport quantities may increase significantly on severely eroded Piedmont soils because of shallow B21t horizons and usually steep slopes associated with these lands.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.