An understanding of N cycling in the soil‐plant‐atmosphere components of wheat (Triticum aestivum L.) production systems is necessary to maximize yield and quality. The objectives of this study were to examine N cycling and observe the effects of N surplus and deficit on N absorption/desorption in the soil and atmosphere and to evaluate translocation within the plant. Soil, plant, and microclimate measurements were taken concurrently, and soil, plant, and atmospheric ammonia (NH3) transport determined. During the early vegetative phase, plant N concentration reached a maximum; however, during the remaining growth periods, N concentration decreased even though N uptake from the soil continued until plant maturity. More total N was translocated to grain from leaves than stems, and translocation from the leaves began earlier than that from stems. Isotope and total N studies showed that after anthesis about half of the grain N came from remobilization from leaves and stems and the other half directly from the soil. A progressively larger percentage of N came from mineralized organic matter as the season progressed. Nitrogen was lost as volatile NH3 from the plant after fertilizer application and during the senescence period. Prior to anthesis, atmospheric NH3 absorption was observed during a period when soil N was temporarily unavailable. About 21% equivalent of the applied fertilizer was lost as volatilized NH3. During the period of soil unavailability an amount equivalent to about 1% equivalent of the applied fertilizer was gained from atmospheric NH3 by plant absorption.

Little information exists on the biogeochemical effects of combining no‐tillage planting with paraplowing (to improve deep water penetration) or with secondary tillage (to control weeds). We determined surface residue and soil C and N pools (total, particulate, microbial biomass, and mineralizable) and water‐stable aggregation at depths of 0 to 25, 25 to 75, and 75 to 150 mm from a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults) in Georgia. Soil tillage treatments were a factorial arrangement of tillage type [(i) minimal disturbance with in‐row chisel at planting, (ii) no‐tillage planting with autumn paraplow, and (iii) no‐tillage planting with secondary tillage during the summer] and tillage frequency [(i) every year, (ii) every second year, and (iii) every fourth year]. No‐tillage planting without further disturbance occurred in remaining years. At a depth of 0 to 25 mm, basal soil respiration averaged 9 mg kg‐1 d‐1 with conventional tillage, 27 mg kg‐1 d‐1 with no‐tillage planting and soil disturbance every year, and 36 mg kg‐1 d‐1 with no‐tillage planting and soil disturbance every fourth year. At a depth of 0 to 150 mm, mean‐weight diameter averaged 1.03 mm with conventional tillage, 1.12 mm with paraplow, 1.17 mm with secondary tillage, and 1.23 mm with in‐row chisel. No‐tillage planting with alternative tillage types and frequencies not only improved surface soil properties compared with conventional tillage, but also improved seed cotton yield an average of 19%. Biophysical improvement of surface soil structure would presumably lead to greater water infiltration and improved water use efficiency in the long term.

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.

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In the Piedmont of the Southern Appalachian region, soil degradation is most often expressed by crop water deficit that limits crop yield in the warm season. To evaluate the nature of variability on these cropped lands, soybean [Glycine max (L.) Merr.] yield and associated soil characteristics were measured across the range of surface soil conditions in 40 farm fields. Factor analysis of the data permitted identification of variables responsible for most of the yield variability. Carbon in the surface soil was identified as the manageable soil variable that could significantly influence crop water availability and curtail soil erosion. Subsequently, selected crop cultures that supplied a range in quality and quantity of crop biomass to the soil surface were applied on three soil erosion classes for 5 yr. Large increases in rainfall infiltration and reduced soil erodibility were associated with no‐till planting of grain sorghum [Sorghum bicolor (L.) Moench] into crimson clover (Trifolium incarnatum L. ‘Tibbee’) in comparison to conventional tillage of grain sorghum and soybean. The maintenance of a decomposing mulch by crop residue additions of about 12 Mg ha−1 yr−1 generated high soil C levels in the 0‐ to 15‐mm depth and a high water stability of aggregates in the 0‐ to 80‐mm depth in comparison to incorporated crop residues. In the 6th yr, grain yield of conventionally tilled soybean was 30 to 100% greater on the previously no‐till crop culture than on the conventionally tilled. The restoration and maintenance of soil productivity commensurate with inherent site resources was associated with maintenance of a decomposing mulch on the soil surface derived from an appropriate quantity and quality of crop residue produced in situ.

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Postemergence applications or a combination of preemergence and postemergence treatments in double cropped soybeans [Glycine max (L.) Merr. ‘Ransom’] resulted in higher soybean yields than preemergence applications. Preemergence-treated plots were 98% weed free early in the growing season; however, weeds emerged later and reduced yields. Weeds had to be controlled in soybeans for 90% of the growing season to avoid yield loss. Soybean yields were higher under no-till than conventionally tilled management in two of three years and tended to be higher during the third year. Distribution and timing of rainfall were more important in determining soybean yield than the total amount received during the growing season.