Establishment of adequate stands of winter wheat (Triticum aestivum L.) in northwest USA is often hampered by low soil temperature or moisture, or by deep planting to reach moisture sufficient for emergence. Because of the wide variability and interactive effects among these factors, it is often difficult to predict the rate and extent of emergence of field plantings. A model was devised to predict emergence time of ‘McCall’ and ‘Nugaines’ winter wheat as a function of soil temperature between 5 and 25 C, water potential down to —10 bars, and planting depth. Predictions were reasonably good when compared with field measurements, particularly at high water potentials and with shallow planting. In general, the emergence rate progressively decreased with lowering of water potential, lowering of temperature from 25 C, or with increase in planting depth. The lower limit or minimum water potential for emergence increased with increasing temperature. Both wheats responded similarly to temperature decreases; however, the emergence rate of each variety responded differently to change in water potential. Differences in varietal response to water potential can possibly be characterized in terms of two parameters in the function describing the water potential effect on emergence.

Synopsis Root development of winter wheat was studied in central Nebraska. Depth of soil moisture and rate of nitrogen fertilization were variables. A dense network of roots developed in soil when soil moisture tension was above 15 atmospheres. When moisture conditions were favorable, roots were observed at a depth of 13 feet. There was evidence of moisture depletion to a depth of 8 feet. Nitrogen fertilization increased root weights and moisture utilization at all moisture levels.

In classical statistics, the effect of soil trends is compensated for by replication and randomization of treatments. Two field experiments were conducted at sites with significant soil trends to evaluate the use of semivariograms for identifying spatial correlation in plot yield, and evaluate the ability of nearest‐neighbor analysis (NNA) in removing trend. The first experiment involved a P‐fertilizer trial with winter wheat (Triticum aestivum L.) on an eroded hillslope in eastern Washington. The second experiment involved a N‐ and P‐fertilizer trial with cotton (Gossypium hirsutum L.) in Dera Ismail Khan, Pakistan. One of the difficulties in using semivariograms of plot‐yield data to evaluate spatial correlation in experimental errors is that yield is affected by the presence of trends as well as by the pattern in treatment randomization and replication. To remove the influence of treatment randomization, the measured mean for each treatment was subtracted from the measured yield for that treatment in each plot. Semivariograms of these deviations in yield relative to the treatment mean showed significant structure for both experiments, indicating spatial correlation between plots resulting from soil trends. We used NNA to adjust measured plot yields for the effects of spatial correlation. Semivariograms of yield deviations after this adjustment exhibited no spatial structure, indicating removal of spatial correlation between plots. Analysis of variance (ANOVA) on measured yields before adjustment by NNA in both experiments showed nonsignificant treatment effects, while block effects were highly significant. Thus, without adjustment, the experimental results showed no response to the applied fertilizer treatments. In contrast, ANOVA on adjusted yields after NNA showed highly significant treatment effects, while block effects were nonsignificant.

Studies to increase profitability and N use efficiency in winter wheat (Triticum aestivum L.) production are needed to develop more sustainable agricultural systems in the 480‐ to 650‐mm precipitation zone of northern Idaho and eastern Washington. Field experiments were conducted on Latahco silt loam (fine‐silty, mixed, frigid Argiaquic Xeric Argialboll) soils east of Moscow, ID, during the 1982–1983, 1983–1984, 1985–1986 and 1986–1987 growing seasons. Fifteen different N placement‐source‐application timing treatments were arranged in a randomized complete block design with five replications. Fertilizer placements were (i) surface broadcast, (ii) band 50 mm below the seed, and (iii) combinations of surface broadcast and banded below the seed placements. Times of application treatments were (i) fall, (ii) spring, and (iii) various fall‐spring splits. All treatments were evaluated with two N sources: NH4NO3 (AN) and urea (U). Parameters evaluated were (i) winter wheat stand counts, (ii) early‐season plant biomass, (iii) grain yield, and (iv) apparent N use efficiency (NUE). Placement, N source and time of application had minimal impacts on winter wheat stand counts and early season biomass production. Both winter wheat grain yield and apparent NUE were greatest when N applications were split between fall and spring. Splitting time of N application resulted in apparent NUE of 58 to 61%, compared with 52 to 55% and 51 to 53% for fall only and spring only N applications, respectively. Grain yield and apparent NUE differences attributable to N source and N placement were not significant. Based on this study, ideal N management in the 480‐ to 650‐mm precipitation zone would utilize AN, U, or comparable N sources and split N applications where as little as 25% of the N is banded below the seed or surface broadcast in the fall, with the remainder applied as a spring topdress prior to Zadoks growth stage 24. This proposed management will improve both profitability and water quality by increasing both grain yield and N use efficiency when compared with systems currently employed.

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