No abstract

Though there have been numerous studies on the effect of nitrogen (N) fertilization on soybean [Glycine max (L.) Merr.], relatively few have investigated early season N application in the unique environment of the northern Great Plains. The objective of this research was to investigate the impact of starter N fertilization on soybean yield and quality in this cool environment. To achieve this objective a field experiment was established within a 2-yr corn (Zea mays L.)-soybean rotation, using a split-plot design with four replications. Whole plots were tillage [no-tillage (NT) and conventional tillage (CT)] with starter fertilizer (N source by rate) as the split plot treatments. Nitrogen was band applied at planting as either ammonium nitrate (AN) or urea (UR), at rates to supply 0, 8, 16, and 24 kg N ha 21. Yields were greater for the 2004 growing season than 2002 and 2003, possibly due to more favorable environmental conditions. In 2 of the 3 yr there was an increase in grain yield and early (V3-V4 and R1) plant biomass and plant N due to starter N. The initial increase in plant vigor resulted in a grain yield increase compared to the no N treatment. Analysis pooled over the 3 yr of the experiment showed an average yield increase of 6% for the 16 kg N ha 21 rate, compared to the no N treatment, with no difference in grain N or oil concentration. This research demonstrates that applying N as starter has the potential to increase soybean yield and early plant growth, but this may or may not translate into improved grain quality in the unique environments of the northern Great Plains.

N made available to crops that follow legumes in rotation. An estimate of soil mineralizable N is needed to determine crop While fertilization guides use total organic matter and needs for N fertilizer. The objective of this research was to estimate previous crop as indicators of N mineralization for the soil net N mineralization in soils maintained in continuous corn (Zea mays L.) (CC), corn-soybean [Glycine max (L.) Merr.] (CS), and coming season, a variety of direct and indirect lab methcorn-soybean-wheat (Triticum aestivum L.)/alfalfa (Medicago sativa ods may be used for more precise predictions (Fox and L.)-alfalfa (CSWA) rotations that have been managed since 1990 Piekielek, 1978; Hong et al., 1990). Laboratory tests with zero N (0N), low N (LN), and high N (HN) fertilization. Soil allow compositing and homogenizing soil samples to samples were taken from 0-to 20-cm depth in plots planted to corn decrease the standard deviation and required replicain 1998. In order to produce more realistic time-series data of net N tion. Aerobic incubation for 120 to 252 d is commonly mineralization, soils were incubated in filtration units in a variableused to estimate the size and decay rates of mineraliztemperature incubator (VTI) that mimicked field soil temperatures able N pools (Stanford and Smith, 1972; Cabrera and under a growing corn canopy. Rotation and N fertilization significantly Kissel, 1988). Temperature and matric potential of incuaffected net N mineralization in soil samples. Cumulative net N minerbated soils affect the rate and cumulative N mineralized. alized in a 189-d field temperature incubation averaged 133 Ϯ 6 kg ha Ϫ1 in CC, 142 Ϯ 5 kg ha Ϫ1 in CS, and 189 Ϯ 5 kg ha Ϫ1 in CSWA. Within ordinary field soil matric potentials from Ϫ1.85 Across rotations, average net N mineralized was 166 Ϯ 9 kg ha Ϫ1 in to Ϫ0.01 MPa, temperature has a greater influence on 0N plots, 147 Ϯ 10 kg ha Ϫ1 in LN plots, and 152 Ϯ 10 kg ha Ϫ1 in N mineralization than does matric potential (Zak et al., HN plots. Inclusion of a legume, particularly alfalfa, in the rotation 1999). Most N mineralization laboratory experiments increased net N mineralized. Generally, more net N was mineralized are incubated at 35ЊC, considered the ideal temperature from plots receiving no fertilizer N than from soil with a history of for maximum N mineralization. Nitrogen mineralized N fertilization. Variable-temperature incubation produced realistic in laboratory incubations at 35ЊC represents potential time-series data with low sample variability.

No abstract

No abstract

populations and reduce subsequent yield losses (Kantack et al., 1983). The efficiency of field monitoring for insect pests would be im-Crop canopy chlorosis and necrosis in small grain proved with knowledge of reflected solar radiation from crop canopies during insect outbreaks. The objectives of this greenhouse study were fields infested with greenbugs or Russian wheat aphids to characterize leaf reflectance spectra of wheat (Triticum aestivum could be used as a diagnostic tool by farmers to detect L.) damaged by Russian wheat aphids (Diuraphis noxia Mordvilko) crop damage from cereal aphid population outbreaks and greenbugs (Schizaphis graminum Rondani) and to determine (Riedell and Kieckhefer, 1995). If information on the those leaf reflectance wavelengths that were most responsive to crop exact field location of aphid outbreaks was available, stress imposed by these aphid pests. When the ligule was visible on farmers could target insecticide applications specifically second oldest leaf, wheat plants were infested with four wingless adult to those portions of the field where the insect pests were Russian wheat aphids, four wingless adult greenbugs, or left uninfested present. However, the vastness of the acreage planted (four replicate plants per treatment). Plants and aphid populations to small grains may impede the efficiency of using visual were allowed to grow under greenhouse conditions for 3 wk, after inspection to detect crop damage caused by aphid popuwhich leaf-reflected radiation (from the adaxial surface across the 350-1075 nm range), dry weight, area, and chlorophyll concentrations lation outbreaks. were measured. When compared with the control, greenbug feeding The increased sensitivity, decreased cost, and indamage caused general necrosis in oldest (first) leaves and dramaticreased availability of high resolution spectral analysis cally lowered the dry weight, leaf area, and chlorophyll concentration devices have improved the technology used for remote of the second, third, and fourth leaves. Russian wheat aphid feeding sensing (Blackmer et al., 1996). Use of remote sensing resulted in a reduction in leaf dry weight and area in the third and technology to analyze reflected solar radiation from fourth leaves, and a reduction in total chlorophyll concentration in crop canopies to search for insect outbreaks and integraall leaves. Leaf reflectance in the 625-to 635-nm and the 680-to 695-tion of these data with geographic information systems nm ranges, as well as the normalized total pigment to chlorophyll a would improve the efficiency of field monitoring for ratio index (NPCI), were significantly correlated with total chlorophyll insect pests (Everitt et al., 1994). This potential improveconcentrations in both greenbug-and Russian wheat aphid-damaged plants. Thus, both of these wavelength ranges, as well as this reflec-

Knowledge of complex relationships between soils, crops, and management practices is necessary to develop sustainable agricultural production systems. Objectives were to determine how maize (Zea mays L.) would respond to monoculture (C‐C), 2‐yr rotation (C‐S) with soybean [Glycine max (L.) Merr.], or 4‐yr rotation (C‐S‐W/A‐A) with soybean, wheat (Triticum aestivum L.), and alfalfa (Medicago sativa L.) under different N input levels. We evaluated N fertilizer input (8.5 or 5.3 Mg/ha yield goal, or no N) and crop rotation (C‐C, C‐S, or C‐S‐W/A‐A) treatment effects on soil minerals (N, P, K, S, Ca, Mg, Fe, Mn, and Zn) and their subsequent effect on shoot dry weight and mineral concentrations, grain yield, and grain composition (oil, starch, and mineral concentrations) using univariate and multivariate statistical tests. Soil under C‐S‐W/A‐A rotation had greater NO3–N and less extractable P than other rotations. Significant input × rotation interactions revealed that shoot concentrations of N, Ca, and Mg were less while P, K, and Zn were greater at no N input for the C‐C rotation compared with other N input/rotation treatments. Increased soil NO3–N, increased plant Ca concentration, and increased grain N and grain S concentrations were most important in differentiating C‐S‐W/A‐A rotation from C‐C and C‐S rotation treatments. No N input resulted in less yield and kernel N concentration within the C‐C and C‐S rotations but not C‐S‐W/A‐A. Thus, growing maize in extended rotations that include forage legumes may be a more sustainable practice than growing maize in either monoculture or 2‐yr rotation with soybean.

No abstract