S. B. Phillips

Defining Useful Limits for Spectral Reflectance Measures in Corn

ABSTRACT Recent work has shown that spectral measurements from a corn (Zea mays L.) canopy can be used to reliably predict differences in growth and nutrient status. Most researchers have found that the accuracy of this assessment increases as the season progresses. In contrast, real differences upon which to base management decisions need to be measured as early in the season as possible due to the time restrictions associated with fertilizer and chemical application equipment and weather. The objectives of this research were to evaluate the relationship between Normalized Difference Vegetative Index (NDVI) measurements and corn biomass and grain yield and to define upper and lower limits for effectively using NDVI measurements to make in-season management decisions in corn. Forage biomass and grain yield from eight field studies conducted in the Coastal Plain of Virginia in 2005 were compared to indirect measures of spectral reflectance and leaf area index (LAI). The NDVI was well correlated with vegetative forage biomass (R2 = 0.81) and LAI (R2 = 0.90) within the range 0.27 to 0.82. This range in NDVI values corresponds to 166 to 485 cumulative growing degree days (GDD), and a resultant developmental window of V5 to V9 when NDVI measurement are most useful and appropriate for making in-season management decisions for corn production.

Managing Nitrogen and Sulfur Fertilization for Improved Bread Wheat Quality in Humid Environments

ABSTRACT A large proportion of the wheat (Triticum aestivum L.) milled and utilized by bakeries in the eastern United States is hard red winter wheat (HRWW). Potential for producing this higher value commodity in the eastern United States is dependent on availability of adapted HRWW cultivars that are competitive with soft red winter wheat (SRWW) cultivars and implementation of management systems to enhance end-use quality. The effects of late-season nitrogen (N) (0–45 kg of N/ha) applied at two growth stages (GS 45 and 54) and sulfur (S) (0–34 kg of S/ha) applied at GS 30 on grain, flour, and milling and breadbaking quality were evaluated. Three diverse wheat cultivars (Soissons, Heyne, and Renwood 3260) were studied in two to five environments. Application of S and late-season N had little effect on grain yield. But N consistently increased grain and flour protein as well as bread loaf volume. The magnitude and significance of response to N and S varied by location and cultivar. While S alone did not ha...

CHANGES IN SNAP BEAN YIELD, NUTRIENT COMPOSITION, AND SOIL CHEMICAL CHARACTERISTICS WHEN USING BROILER LITTER AS FERTILIZER SOURCE

ABSTRACT The concern surrounding phosphorus (P)-enrichment of surface waters has lead several states to adopt P-based nutrient management planning strategies regarding land-application of broiler litter. When litter is applied on a P-basis, as much as five times more receiving cropland may be needed compared with nitrogen (N)-based applications. Additionally, many crops have N fertilizer requirements greater than what can be applied on a P-basis, resulting in additional N needing to be supplemented as a commercial source. One of the few crops that may be able to have its N requirement satisfied by a single, P-based litter application is snap bean (Phaseolus vulgaris L.). The objectives of this study were to evaluate the impact of broiler litter applications on snap bean yield and quality, pod nutrient composition, and soil chemical characteristics. A field experiment was conducted in Virginia from 1996 to 2000. Broiler litter and commercial fertilizer rates included 22, 67, and 90 kg N ha−1. Pod samples and surface soil samples were collected and analyzed following the 2000 harvest. The 67-kg N ha−1 broiler litter rate resulted in pod yields equivalent to those obtained using commercial fertilizer with no effect on pod quality or nutrient content. However, increases in Mehlich 1-extractable soil P, copper (Cu), and manganese (Mn) were observed. At the 90-kg N ha−1 litter rate, extractable soil potassium (K), calcium (Ca), and zinc (Zn) also increased, while pod yield decreased. When litter was applied at 22 kg N ha−1 (approximate rate according to a P-based nutrient management plan) no effects on soil chemical characteristics were observed, however, maximum yield was not attained.

Foliar Burn and Wheat Grain Yield Responses Following Topdress-Applied Nitrogen and Sulfur Fertilizers

Abstract The most common fertilizer sources for topdress nitrogen (N) applications to winter wheat (Triticum aestivum L.) in Virginia are a urea ammonium nitrate (UAN) solution (30-0-0) or a UAN solution with added sulfur (S) (UAN-S; 20-0-0-4). However, there are some concerns regarding leaf burning following foliar N applications, particularly at later growth stages. An experiment was conducted from 1999 through 2002 to evaluate and quantify foliar burn associated with various topdress-applied N sources, any subsequent effect on wheat grain yield, and any yield response to added S. Ammonium nitrate (AN; 34-0-0), UAN, UAN-S, and ammonium sulfate (AS; 21-0-0-24) were topdress-applied at either GS 30 or 32. Following the GS 30 and 32 foliar applications, digital images were obtained from each plot and pixel analysis was used to estimate the percentage of foliar burn. At GS 30, foliar burn increased with increasing N rate with no difference in the percentage of burn being observed between sources. At GS 32, foliar burn again increased with increasing N rate; however, UAN-S resulted in significantly greater foliar burn than UAN at both N rates. Despite the increased foliar damage that occurred when UAN-S was topdress-applied at GS 32, there was no reduction in grain yield compared with UAN or either of the soil-applied sources at either growth stage. Although there was no evidence of a grain yield response to added S in this study, many soil types common to the Coastal Plain of Virginia are likely to lack sufficient S for optimum winter wheat production.

WINTER HULLESS BARLEY RESPONSE TO NITROGEN RATE AND TIMING AND FOLIAR PHOSPHORUS

Hulless barley (Hordeum vulgare L.) is higher in energy density and protein than hulled barley but management recommendations for this new crop are lacking. Intensively managed hulled barley receives two spring nitrogen (N) applications. How this will affect winter hulless barley yield and protein is unknown. ‘Doyce’ hulless barley was planted following corn (Zea mays L.) at seven site-years in the Coastal Plain of Virginia from 2005 to 2007. Spring N was applied as urea ammonium nitrate (UAN, 30% N) in an incomplete factorial of treatments at Zadoks growth stage (GS) 25 and 30 broadcast at rates of 0, 45, 67, and 89 kg N ha−1. Six kg ha−1 of phosphorus (P) was foliar applied at GS 30 to treatments receiving 45:45 (45 kg N ha−1 at GS 25 and 45 kg N ha−1 at GS 30) and 45:67 N splits. Additionally, 34 kg N ha−1 as UAN was applied at GS 45 to treatments previously receiving either 45:45 or 45:67. Grain test weight increased with increasing N rate verifying that high spring N rates can be applied without negatively impacting grain test weight in this environment. Grain protein responded positively to increasing N rates as additional N at GS 45 increased protein by 0.7%. To maximize yields, 112 kg N ha−1 applied as 45 kg N ha−1 at GS 25 and 67 kg N ha−1 at GS 30 was necessary. Supplying the majority of spring N need at GS 30 proved important to matching barley N demand and achieving high yields.