Development of a Method for Evaluating the Yield Goal Approach

Yield goals have been used to determine N recommendations in South Dakota, North Dakota, and western Minnesota. However, some states, such as Wisconsin and Iowa have eliminated yield goals from N recommendations because of poor correlation between yield and economically optimum N rates. The objective of this study was to determine the feasibility of switching from a yield goal approach to a non-yield goal approach in South Dakota. Field experiments were conducted in Aurora, South Dakota between 2002 and 2003. Treatments were natural rainfall and natural rainfall + irrigation and four N rates (0, 60, 120, 180 kg N /ha). Plant samples were analyzed for 13C discrimination (Δ) and total N. Research results showed that; (i) adding N rates increased yield and Δ; (ii) applying supplemental irrigation increased yield and decreased Δ; (iii) yields were not influenced by an interaction between water and nitrogen; and (iv) δ15N values increased with irrigation and decreased with increasing N. These results suggest that nitrogen and water stress had independent impact on yield, and irrigation increased N mineralization. These findings partially support the hypothesis that fertilizer rates should be independent of yield goal. Research needs to be conducted to determine the long term impact of changing the recommendation approach on soil N levels

Characterization of Alachlor and Atrazine Desorption from Soils

Herbicide desorption isotherms may be affected by the amount of nondesorbable herbicide present in soil. Nondesorbable alachlor (as determined after methanol extraction) generally increased on a Waukegan silt loam (Typic Hapludolls) and a Ves clay loam (Udic Haplustolls) during five 0.01 M CaCl₂ desorptions. Atrazine was totally extracted with methanol from the Waukegan soil after one desorption using 0.01 M CaCl₂. However, after five desorptions with 0.01 M CaCl₂ an average of 5.5 and 15.5% of the total recovered atrazine from two atrazine application rates was methanol nondesorbable from the Waukegan and Ves soils, respectively. Freundlich desorption isotherms adjusted for nondesorbable herbicide accounted for as much as 71% of the difference between adsorption and desorption isotherms. Only a portion of the hysteresis observed can be attributable to nondesorbable herbicide

Role of heterogeneity in the persistence and prevalence of sin nombre virus in deer mice

Journal ArticleMany diseases persist at a relatively low prevalence, seemingly close to extinction. For a chronic disease in a homogeneous population, reducing the transmission rate by a fraction proportional to the prevalence would be sufficient to eradicate the disease. This study examines how higher prevalence of the Sin Nombre virus in male deer mice (Peromyscus maniculatus) might contribute to disease persistence

Adsorption and Desorption of Atrazine, Hydroxyatrazine, and S-Glutathione Atrazine on Two Soils

Adsorption and desorption isotherms for atrazine and two metabolites, hydroxyatrazine (HA) and S-glutathione atrazine (GSHA), were determined by batch equilibration on Plano and Waukegan silt loam soils at two soil pH levels (Plano, 6.1 and 4.5; Waukegan, 6.1 and 4.0). Freundlich adsorption isotherms were not affected by soil type except for GSHA at pH 4.0 to 4.5. When averaged over both soils, the order of adsorption at pH 6.1 was atrazine (Kf = 3.7) \u3c GSHA (Kf = 7.3) \u3c\u3c HA (Kf = 25) and at pH 4.0–4.5 was atrazine (Kf = 6.1) \u3c\u3c HA (Kf = 58) ≤ GSHA (Kf: Plano = 35; Waukegan = 78). The average slope of the adsorption isotherms (1/nads) was 0.81. The slopes of all desorption isotherms (1/ndes) were less than their respective 1/nads, indicating hysteresis. Atrazine desorbed into soil solution (1/ndes \u3e 0.0). With the exception of GSHA which desorbed from the pH 6.1 Plano silt loam (1/ndes = 0.15), desorption of HA and GSHA from other treatments was negligible (1/ndes = 0.0). Consequently, leaching of HA and GSHA in these and similar soils is not likely, due to high adsorption and low desorption

Nitrogen and Water Stress Impact on Hard Red Spring Wheat Crop Reflectance, Yield and Grain Quality

Water and nitrogen stress impact hard red spring wheat (Triticum aestivum) crop reflectance, yield and grain quality. To minimize yield losses from nitrogen (N) and water stress, it is essential to apply appropriate N in relation to water stress. The objective of this experiment was to determine the influence of N and water stress on hard red spring wheat crop reflectance, yield, and grain quality. Complete randomized block experiments were conducted in 2003, 2004 and 2004 in dryland and irrigated fields at three locations in central South Dakota. Treatments consisted of N rates and N application at different growth stages. Nitrogen fertilizer rates ranged from 0 to 200 kg ha-1. Nitrogen fertilizer application times were (1) planting; (2) planting and tillering (Feekes 2 -3) or (3) tillering (Feekes 2 -3). Reflectance data was collected using a Cropscan and a CropCircle radiometer. Reflectance data was collected at bare soil, tillering (Feekes 2-3) and flag leaf (Feekes 9-10). Carbon 13 isotopic discrimination (Ä) was used to determine yield loss to nitrogen or water stress. Reflectance data was compared to yield and Ä values or grain quality and Ä values. Correlation of crop reflectance (measured at the different growth stages and by the different radiometers) with yield loss to nitrogen or water and grain quality will be presented. Information presented will be used to make corrective nitrogen treatments and improve marketing decisions as related to grain quality

Do Synergistic Relationships between Nitrogen and Water Influence the Ability of Corn to Use Nitrogen Derived from Fertilizer and Soil?

To improve site-specific N recommendations a more complete understanding of the mechanisms responsible for synergistic relationships between N and water is needed. Th e objective of this research was to determine the influence of soil water regime on the ability of corn (Zea mays L.) to use N derived from fertilizer and soil. A randomized split-block experiment was conducted in 2002, 2003, and 2004. Soil at the site was a Brandt silty clay loam (fine-silty, mixed, superactive frigid Calcic Hapludoll). Blocks were split into moderate (natural rainfall) and high (natural + supplemental irrigation) water regimes. Nitrogen rates were 0, 56, 112, and 168 kg urea-N ha–1 that was surface applied. Water, soil N, and N fertilizer use efficiencies were determined. Plant utilization of soil N was determined by mass balance in the unfertilized control plots and by using the δ15N approach in fertilized plots. Findings showed that: (i) plants responded to N and water simultaneously; (ii) N fertilizer increased water use efficiency (170 kg vs. 223 kg grain cm–1 in 0 and 112 kg N ha–1 treatments, respectively); and (iii) water increased the ability of corn to use N derived from soil (67.7 and 61.6% efficient in high and moderate water regimes, respectively, P = 0.002) and fertilizer (48 and 44% efficient in high and moderate water regimes, respectively, P = 0.10). Higher N use efficiency in the high water regime was attributed to two interrelated factors. First, total growth and evapotranspiration (ET) were higher in the high than the moderate water regime. Second, N transport to the root increased with water transpired. For precision farming, results indicate that: (i) the amount of N fertilizer needed to produce a kg of grain is related to the yield loss due to water stress; and (ii) the rate constant used in yield goal equations can be replaced with a variable