Several studies have reported that corn (Zea mays L.) hybrids differ in leaf chlorophyll concentration (LCC) to the extent that Minolta SPAD 502 meter data have to be normalized (values obtained from a general field divided by those from a fully-fertilized area in the same field). However, situations exist where the normalization method can add needlessly to production expenses and even lead to nitrogen deficiencies and reduced yield. Little information was found to indicate how much potential variability exists among modern hybrids, so we evaluated 45 entries in a fully-fertilized and irrigated standard performance test over a 2-year period in northwestern Kansas to determine: (i) how much variability was present in a large sampling of commercially available, fully-fertilized corn hybrids and (ii) if results 1 Contribution No. 97-331-J, Kansas Agricultural Experiment Station. 1794 SUNDERMAN, PONTIUS, AND LAWLESS suggested alternatives to the normalization method. We used the SPAD meter to measure LCC twice during the vegetative phase and twice during the reproductive phase. Results indicated that genetic potential for maximum LCC was achieved. Quadratic regressions of LCC on days from planting yielded highly significant R 2 values of 0.88 when adjusted to common growth stages and 0.91 when data were not adjusted. A cubic model did not add significant improvements, but we prefer this model because it provided a better fit for early-season data. For quick checks, we propose that the mean values (±standard deviation) obtained at growth stages R1 (57.9±4.5) and R6 (60.0±4.6), and to a lesser degree V6 (40.0±3.2) and V10 (48.6±3.8), be used as first approximations for evaluation and refinement. As first approximations, they are subject to error and should not be used as the sole basis for deciding if or how much supplemental fertilizer nitrogen (N) needs to be applied. Although these standards are useful, their ranges were judged to be too broad for precise estimates, so we see little alternative to the normalization method.

Interest in N transformations in soils has increased greatly in recent years, particularly with increased use of urea‐containing fertilizers. However, only one procedure for determination of exchangeable ammonium, nitrate, nitrite, and urea in a single soil extract has been proposed and it requires the use of both distillation and colorimetric equipment. It would be useful to have a set of colorimetric procedures for the determination of these N forms in a single extract. Previous research indicated sodium sulfate, as an extractant, would be least likely to produce unwanted interferences in these procedures. Thus, research was initiated to determine (i) if Na2SO4, could be used as an extractant for exchangeable NH4+, NO3‐, NO2‐ and urea and (ii) necessary modifications to make desirable colorimetric procedures usable in a Na2SO4 extraction system. A procedure for the colorimetric determinations of exchangeable NH4+, urea, NO3‐, and NO2‐ in soil using a single soil extract is described. The soil sample is extracted with Na2SO4 containing phenylmercuric acetate for 30 min and then leached with four 25 ml portions of extractant and made to volume. The extract is analyzed for NH4+ by a modified Nessler reagent, urea by either diacetyl monoxime and thiosemicarbazide or p‐dimethyl aminobenzaldehyde depending on concentration, NO3‐ by chromotropic acid and NO2‐ by 4‐aminobenzenesulfonic acid and 1‐aminonaphthalene hydrochloride. The procedure gave quantitative recovery of NH4+‐N, urea‐N, NO3‐ N, and NO2‐‐N added simultaneously to five different soils.

Defining the optimum seeding rate for wheat (Triticum aestivum L.) is complex because this crop has the capacity to create and abort tillers in response to environmental conditions. Several soil physical characteristics affecting germination and emergence are altered with the change from conventional tillage (CT) to no‐till (NT), and these may influence final stand. The objective of this study was to determine whether either seed density or seeding rate influenced the performance of hard red winter wheat (HRWW) in a rainfed wheat‐fallow rotation under NT. Experiments were conducted during four growing seasons on a Keith silt loam soil (fine silty, mixed, mesic Aridic Argiustoll) in northwestern Kansas. The experimental design was a randomized complete block with four replications. Experimental variables were seed density and seeding rate in a complete factorial arrangement with four levels of seed density and three of seeding rate for a total of 12 treatments. Seed weights ranging from 27 to 35 g/1000 kernels (58–63 Ib/bu) were obtained from bin‐run, foundation‐grade, ‘Newton’ seed selectively processed in multiple runs over a gravity table. This process separates seed on the basis of seed density (mass per unit volume), which is then converted into thousand‐kernel and test weights. Hence, these units of mea‐ sure were used in this report. Seeding rates were 450 000, 600 000, and 750 000 viable seeds/acre. Seeding was done with a shop‐fabricated drill that allowed seed placement as deep as necessary to reach moisture, while maintaining a constant covering depth of 1.5 in. Heavier seed produced greater numbers of seedlings per unit area and a higher emergence percentage than light seed, but seed density had little effect on the final number of spikes per unit area, ratio of spikes per plant, or kernels per head. Increasing seeding rate resulted in more seedlings and spikes per unit area but decreasing numbers of kernels per head. Overall, responses were compensating, so that grain yield was unaffected by either seed density or seeding rate. Although test weight, protein concentration, and thousand‐kernel weight were influenced positively by seeding rate and seed quality, the responses were small and probably of little practical value. Results suggest that the HRWW plant can adapt as effectively under NT as has been reported for CT. Because future emergence conditions are unknown, large heavy seed still should be preferred over small light seed, particularly if seed costs are the same or the latter has been in storage for more than one season. Research Question Defining the optimum seeding rate for wheat is complex because this crop has the capacity to create and abort tillers in response to environmental conditions. With the current movement toward cropping systems with little or no tillage, a need exists to reexamine seed quality and seeding rate as they affect wheat production under no‐till conditions. The objective of this research was to determine whether either seed density or seeding rate influenced the prod...

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