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Cereal rye (Secale cereale L.) is widely grown due to its winter hardiness and adaptability to varied soil and environmental conditions. Fall and spring climate and available soil N drive biomass production. However, there is limited empirical information on the effects of these factors on cover crop performance. Farmers need early spring indicators of cereal rye performance to guide management. A 3-yr experiment was initiated to test and model the effects of climate and soil N fertility on cereal rye growth and allometric relationships in Pennsylvania, Maryland, and North Carolina under five-six fall fertilizer rates. We hypothesized that allometric relationships between early spring growth indicators can guide management decisions. Measurements included tillering, biomass, tissue N, and normalized difference vegetation index (NDVI) at Zadoks growth stages (GS) 25, 30, and 60. Nitrogen application increased biomass: maximum average biomass was 2853, 4844, and 9739 kg ha–¹, respectively, at GS25, GS30, and GS60. At GS25, biomass accounted for the greatest amount of model variation and better predicted GS60 biomass than shoot density and NDVI. Variance attributed solely to GS25 and GS30 biomass constituted 38.5 to 65.2% of total model variance. Models accurately predicted biomass and N accumulation 34 to 60% of the time. This study illustrates the difficulty in predicting late season biomass and N content based on early measurements. One extension of this research would be the development of a simple protocol to accurately sample cereal rye biomass at GS25 to estimate potential N accumulation and biomass at GS60.

Corn (Zea mays L.) producers in the southeastern United States must overcome soil and water limitations to take advantage of the expanding corn market. In this 2001 to 2005 study on a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludult) near Watkinsville, GA, we compared dry land corn biomass and yield under conventional tillage (CT) vs. no-tillage (NT) with ammonium nitrate or sulfate (based on availability) as conventional fertilizer (CF) vs. poultry litter (PL). In a randomized complete block split plot design with three replications, main plots were under tillage and subplots under fertilizer treatments. The cover crop was rye (Secale cereale L.). Over 5 yr, NT and PL increased grain yield by 11 and 18%, respectively, compared with CT and CF. Combined, NT and PL increased grain yield by 31% compared with conventionally tilled and fertilized corn. Similarly, soil water was 18% greater in NT than CT in the 0- to 10-cm depth. In 2 yr of measurements, dry matter of stalks and leaves and leaf area index under PL were an average of 39 and 22% greater, respectively, than under CF during reproduction. Values were 21 and 6% greater, respectively, under NT than CT but during tasseling. Analysis of 70 yr of daily rainfall records showed that supplemental irrigation is needed to meet optimal water requirement. Our results indicate that corn growers can use rainfall more efficiently, reduce yield losses to drought, and expect increased corn yields with a combination of no-tillage management and long-term use of poultry litter.

The tropical legume sunn hemp (Crotalaria juncea L.) could be a valuable green manure/cover crop for vegetable producers in the southeastern USA because of its rapid growth and large N 2 fixing ability. Planting and termination date effects on biomass and N accumulation are relatively unknown for the region, but would help producers manage sunn hemp between summer and winter cash crops. We determined sunn hemp biomass and N content at 30, 60, 90, and 120 days after planting (DAP) for four planting dates (mid-April to mid-July) at a Piedmont and a Coastal Plain location in Georgia. Maximum biomass at a given DAP was produced from May and June plantings in the Piedmont and from April and May plantings in the Coastal Plains. Maximum biomass and N ranged from 8.9 to 13.0 Mg ha -1 and 135 to 285 kg ha -1 , respectively. An equation for estimating sunn hemp biomass as a linear function of cumulative degree days (CDD) and cumulative solar radiation (CSR) was verified with independent data from Alabama, Florida, and Virginia. A similar equation for estimating N content as a quadratic function of CSR was not as accurate but still might be useful. Sunn hemp can fit well into short-rotation sustainable vegetable production systems in the Southeast, and these equations can be used by producers to make reliable estimates of sunn hemp biomass production.

Understanding cover crop and tillage system interactions within specific environments can help maximize productivity and economic returns of cotton (Gossypium hirsutum L.) produced on sandy coastal plain soils of the southeastern USA. A strip-plot design with three replications was used to evaluate the cover crops Austrian winter pea [Pisum sativum L. ssp. arvense (L.)], balansa clover (Trifolium michelianum Savi), crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa Roth subsp. villosa), oil seed radish (Raphanus sativus L.), black oat (Avena strigosa Schreb.), and rye (Secale cereale L.) and tillage (strip and none) influences on cotton grown on a Bonifay fine sand (loamy, siliceous, subactive, thermic Grossarenic PlinthicPaleudults)nearWaynesboro,GAfrom1999to2003.Drought influenced production 3 of 4 yr. Cover crop biomass was greatest from rye, intermediate from black oat, oilseed radish, hairy vetch, and Austrian winter pea. Hairy vetch and Austrian winter pea contained more than 80 kg N ha 21 while other cover crops averaged ,40 kg N ha 21 . Cotton yields following black oat and rye had returns above variable costs ha 21 $461 and $406, respectively. Strip-tillage increased yields by 192 kg ha 21 and annual returns by $112 ha 21 over no-tillage, most likely due to improved available water. Combining strip-tillage with black oat was the best combination for maximizing profit. Using black oat with strip-tillage could increase cotton profit by $50 to $75 ha 21 compared to systems using rye on the 1.45 million ha of cotton where conservation systems have been adopted.

Reduced tillage and residue management can have significant impacts on soil and water quality, primarily through the accumulation of soil organic C. Yet, methods of tillage and residue cover assessment are time and resource intensive, and often do not yield spatially representative results. A major goal of this study was to compare new remote sensing (RS) indices with the current line-transect approach for differentiating between conventional (CT) and conservation tillage systems. Experimental plots were located in two physiographic regions in Georgia: the Southern Piedmont and Southern Coastal Plain. Treatments consisted of no tillage (NT) or CT at the Piedmont site, and strip-tillage (ST) or CT at the Coastal Plain site. Remotely sensed data were acquired three times prior to canopy closure, using a handheld multispectral radiometer (485-1650 nm) and thermal imager (7000-14 000 nm). Soil texture and soil water content were measured to assess the impact of changes in soil background reflectance on crop residue assessments. Results showed that differences in spectral response between CT and conservation tillage systems were best observed using a normalized difference ratio of near infrared (NIR) (1650 ± 100 nm) and blue (485 ± 45 nm) spectra under dry conditions and low canopy cover (

Calibration procedures and data used to parameterize a model, including model components that may or may not have been addressed, are generally not well documented in modeling studies. A comprehensive description of the process and parameters used for calibrating the Root Zone Water Quality Model, v. 1.3.2004.213, is presented in this article. The model was calibrated to simulate tile drainage and leached nitrate under conventional tillage management practices for maize (Zea mays L.) production followed by a rye (Secale cereale L.) cover crop in Cecil soils (kaolinitic, thermic, Typic Kanhapludults), and for cotton (Gossypium hirsutum L.) development in the Georgia Piedmont. Tile drainage and nitrate leaching were simulated within 15% of the observed values in the calibrated maize scenarios with and without the soil macroporosity option. Simulated and observed tile drainage and leached nitrate were not significantly different, and the simulated values were not significantly different with and without the macroporosity option. Simulated cotton biomass and leaf area index were well correlated with observed biomass and leaf area index until the last 21 d of the reproductive stage. Simulated and observed cotton water use were different by

Tillage to disrupt root-restricting, consolidated soil zones can improve rooting capacity and crop production, but costs increase with the need for more powerful tractors. Between 1992 and 1996, agronomic and economic consequences of annual or less frequent soil disruption treatments were evaluated for cotton (Gossypium hirsutum L.) on a Typic Kanhapludult. Two soil-disruptive treatments, fall paratillage (PT) and in-row chisel (IC) at planting (spring), were compared with two shallow-tillage treatments, coulter planting plus weed control with sweeps (ST) and conventional disk tillage (DT). The IC, PT, and ST treatments were applied annually or in Years 3, 4, and 5. Lint yield with annual IC was 15 to 20% greater than with DT each year. In 1994, yields ranged from 0.53 to 0.84 Mg ha -1 with annual IC and were better than with annual ST or PT. In 1995, yields ranged from 0.92 to 1.29 Mg ha -1 , with the top yield associated with current-year IC application. In 1996, no differences in yield were observed among tillages; however, yields of two IC treatments were among the top five. For Years 3, 4, and 5, cotton yields were numerically greater with annual IC than with annual PT and ST. Yields with PT, ST, and DT were not different. Average annual net returns from annual IC were $450, $403, and $287 ha -1 greater than those with annual DT, PT, and ST, respectively. In-row chisel appears to be a more economically viable production practice for heavy Piedmont soils compared with PT, ST, and DT.

Animals influence nutrient cycling within grazed systems, and the effect may be greater with tall fescue (Festuca arundinacea Schreb.) because of endophyte-produced alkaloids that cause fescue toxicosis and alter animal behavior. Twelve grazed tall fescue pastures, established in a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludult) soil near Watkinsville, GA were used to measure fertility (134-15-56 and 336-37-139 kg N-P-K ha -1 yr -1 ) and endophyte (low, 0 to 29% and high, 65 to 94%) effects on P and K distribution. Soil samples were collected in winter 1997 at distances of 1, 10, 30, 50, and 80 m from permanently located shade and water sources at eight depth increments down to 1.5 m. Nutrient accumulation was greatest 1 m from shade and water sources where P, K, and Mg concentrations were 1.7 to 8, 2.5 to 15, and 1.1 to L5 times greater than average concentrations at the remaining distances, depending on depth and fertility level. Accumulation of P, K, and Mg in the area 10 to 80 m from shade and water was limited. When summed for the 0- to 300-mm depth and estimated on a per hectare basis, extractable P was 64% greater in high than in low endophyte-infected tall fescue pastures at 1 m from shade and water sources (703 vs. 428 kg ha -1 , LSD = 93) and averaged 252 kg ha -1 for remaining distances. Endophyte levels did not affect K distribution and only affected Mg distribution under the low-fertility treatment. Endophyte effects accrued over a long time period, which would indicate that altering grazing and pasture management (movement of animals, fertilizer and lime applications, and location of shade and water sources) to reduce these effects would be needed only occasionally to reduce potential environmental risks.

Crop residues protect soil from water and wind erosion. How long the residues remain effective depends on their decomposition rate. The crop residue decomposition submodels developed for the Revised Wind Erosion Equation (RWEQ) and Revised Universal Soil Loss Equation (RUSLE), which are used to determine the effectiveness of conservation practices, use different approaches to account for water and temperature effects on decomposition. Because of these differences, residue losses may not agree between the two models for a given location. We compared the climatic indices used in RWEQ and RUSLE to determine the similarity of results for simulated climatic scenarios, as well as for field data. Simulated climatic regimes were used to evaluate the relative responsiveness of the temperature and water functions. The two models estimated different numbers of decomposition days (DD) when water and temperature were not limiting. RUSLE usually predicted more DDs than RWEQ. Underwaterlimiting conditions, the estimation of DD was similar for the two models. In comparisons with field decomposition data, mass loss predictions by RWEQ were as good as or better than those by RUSLE for locations in Texas, Oregon, and Georgia. RUSLE overpredicted decomposition by 20 to 50% when residues were irrigated. RWEQ underpredicted decomposition by 20 to 50% in the Pacific Northwest. Interactions between the climatic indices (CF) and decomposition coefficients influenced the differences between measured and predicted values. Differences in the CF were related to the method of calculating the water coefficient (WC) and interpretation of the interaction between the temperature coefficient and WC. The models could be improved by developing water and temperature functions that give results closer to those produced with daily time-step functions.

Nitrogen availability is important for rapid establishment of small seeded legumes and is influenced by soil N status and rapid development of N 2 fixation activity. Seedlings of arrowleaf clover (Trifolium vesiculosum L. Savi) are exposed to soil temperatures (10-35°C) during the fall which can reduce seedling vigor by influencing N nutrition. Root temperature (18, 25, or 32°C) effects on N nutrition of arrowleaf clover receiving starter N was evaluated in two controlled experiments. Temperature influenced the N status of inoculated plants through an effect on N 2 fixation but not on starter N uptake []

(...) Three experiments were conducted using a growth chamber and a glasshouse to determine the influence of starter mineral N and strains of Rhizobium leguminosarum biovar trifolii on dry matter production and N 2 fixation on arrowleaf clover. In one experiment, seeds were planted in a N-deficient medium, inoculated with two strains of rhizobia and provided with five levels of mineral N. The lowest level of mineral N doubled seedling dry weights and the amount of biologically fixed N in 40-d-old seedlings. Rhizobial strain interacted with mineral N in influencing dry matter production and N 2 fixation (...)