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Incubation studies at 25°C with a Williams loam (Typic Argiboroll) illustrated that the thiosulfate ion is an inhibitor of nitrification. Inhibition of the nitrification of 10 mmol N kg−1(as ammonium sulfate) ranged from 55–80% with an addition of 1 mmol S kg−1(as sodium thiosulfate) to 82–91% with a 10 mmol S kg−1addition. Percent inhibition was greater after 28 than 14 d of incubation. Residual soil ammonium measurements confirmed the influence of thiosulfate on nitrification. A separate study illustrated that a 5% (v/v) inclusion of commercial‐grade liquid ammonium thiosulfate (ATS) to urea‐ammonium nitrate solution (UAN) inhibited nitrification by 51% in a 28 d incubation. Another experiment also illustrates that small additions of ATS to UAN dramatically reduced the rate of urea hydrolysis. Incubations were performed for 2 and 4 d at 25°C with a Williams loam and a Bearden silty clay loam (Aeric Calciaquoll). Levels of inhibition ranged from 15–35% with a 1% (v/v) addition of ATS to UAN to 40–52% with 10% (v/v) inclusion. ATS did not inhibit urea hydrolsis by purified jackbean urease. Three commercial sources of ATS were compared to reagent sodium thiosulfate, at equal rates of sulfur, and all sources inhibited soil urease similarly. Although the nitrification and urease inhibition properties of ATS are less than have been reported for some other materials, ATS deserves further laboratory and field evaluation as a possible nitrification and urease inhibitor. As commercial batches of UAN sometimes contain ATS, each lot should be tested for ATS contamination before use in research. A procedure for such a test is described.

The amount of stored soil water at seeding has long been appreciated as a critical factor in the success of annual spring wheat (Triticum aestivumL.) production in the semiarid region of the Northern Great Plains. Stored available soil water at seeding, growing season precipitation, and grain yield data from 53 spring wheat experiments in western North Dakota were analyzed by both multiple regression and an interaction chi‐square approach. Soil types were generally fine‐loamy, mixed Typic Haploborolls or Argiborolls. Regression equations explained to little of the variability of the data to be useful in drawing practical guidelines for future fallow/recrop decisions. The results suggest that stored soil moisture data are better analyzed by the interaction chi‐square test, the results of which provide easy‐to‐interpret guidelines for making future fallow/recrop decisions. For example, for a minimum acceptable recrop wheat yield of 1350 kg/ha, the following critical levels were defined: stored available soil water at seeding less than 6.4 cm, crop failure is likely and summerfallow is advised; stored available soil moisture 6.4 to 9.4 cm, approximately equal odds of crop failure or success; stored available soil moisture > 9.4 cm, crop success is likely and recropping is advised.

This study was undertaken to (i) determine the effect of nitrogen (N) fertilization on selenium (Se) content of wheat grain (‘Scout 66’) grown under the dryland fallow system of eastern Colorado and (ii) determine the relationship between grain Se and ammonium bicarbonate‐DTPA soil test levels of Se. Nitrogen fertilization did not affect grain Se where yield was increased significantly in only one out of 10 locations. The ammonium bicarbonate‐DTPA‐extractable level of soil Se was a good indicator of grain Se if 0‐ to 90‐cm soil samples were used (r2= 0.82). Surface (0 to 30 cm) soil Se levels were weakly related to Se concentration of the grain (r2= 0.13).

Malting barley (Hordeum vulgareL.) in North Dakota has a history of yield and quality responses to small additions of KCl fertilizer on soils with ample native supplies of exchangeable potassium (K). Five field experiments were established in central or western North Dakota in 1983 to determine if a chloride (Cl)‐induced repression of common root rot, incited by Cochliobulus sativus, was a possible explanation for these past responses. The soils were fine loamy Haploborolls, Argiborolls, or Haplaquolls with greater than 800 kg K ha−1exchangeable K in the plow layer. Experimental design was a factorial combination of two K rates, 23 and 94 kg K ha−1, by two K sources, KCl and K2SO4, plus a control treatment. A randomized complete block design with five or six replicates was employed. Fertilization with KCl significantly decreased root rot incidence at the boot stage at two of five sites and significantly decreased disease severity at the dough stage at three of the five sites. The high rate of KCl visually reduced the severity of spot blotch symptoms on the flag leaves at one site. Nitrate concentrations in plant foliage tended to be depressed at the highest rate of KCl. Chloride concentrations in plant foliage were dramatically increased by KCl application, although concentrations of Cl in control treatments appeared adequate enough to preclude an actual Cl nutritional deficiency. Grain yields were significantly increased by the high rate of KCl at one site. Fertilization with K2SO4significantly increased disease severity at two sites but otherwise had no effect on disease incidence, severity, or grain yield. This research substantiated that Cl‐induced disease repression may explain the history of KCl response in North Dakota, but the reason for this effect is not known.

A great majority of the dryland winter wheat (Triticum aestivumL.) producers in the west central Great Plains currently do not use soil tests to determine N fertilizer needs although most producers have grain protein data from their fields. Field experiments with N rate as the variable were conducted throughout eastern Colorado over a 4‐year period with winter wheat grown under summer fallow cropping. The objective was to determine if grain protein content could be used as a post‐harvest indicator of sufficiency of N for maximum grain yield. The soil types were of the Paleustoll, Argiustoll, Paleargid, and Haplargid great groups. The yield and protein response data from the experimental locations were analyzed by an interaction chisquare procedure. Grain protein content was found to be an effective post‐harvest indicator of N nutrition adequacy for grain production. Both a critical level and a transitional zone of grain protein content were defined using interaction chi‐square analysis. The most critical level was determined to be 11.5% protein and the transition zone between the deficient and N sufficient populations of yield observations was between 11.1 to 12.0%. The amount of yield lost to N deficiency was not related to grain protein content. Workers in other geographic areas should be able to take existing N response data and develop similar guidelines appropriate for those areas.