Analysis of yield variability in winter wheat due to temporal variability, and nitrogen and phosphorus fertilization

Abstract

Field average based recommendations have been a common practice for recommending the major crop nutrients nitrogen (N) and phosphorus (P). The problem is yield will not be the same from year to year with application of the same amount of recommended rate of fertilizer. The objectives of this study were to demonstrate how recommendations generated using nutrient response experiments were dynamic; and to assess the relative contribution of temporal variability, N and P fertilizers on winter wheat grain yield and N concentration. Twelve factorial combinations of four N (0, 56, 112, and 168 kg ha 71 ) and three P (0, 14.5, and 29 kg P ha 71 ) rates were evaluated in a randomized complete block design with three replications at Perkins, Oklahoma. To address the first objective, ANOVA and orthogonal polynomial contrasts were used. To address the second objective, a ten predictor variable multiple linear regression model with two quantitative variables and their interaction (N, P and N6P) and seven-year variables was evaluated and a reduced model containing seven variables was generated. Wheat grain yield showed three distinct responses to N rates: Linear, quadratic and no response. These individual year data show that it is not always appropriate to use results of nutrient response experiments to estimate next year's N fertilizer requirement due to apparent temporal variability in the results. Wheat only responded to P during the first two years of the study. The reduced model from the regression analysis revealed that most of the variability in grain yield was accounted for by five individual indicator years and N only. High variability across years in grain yield and fertilizer (N and P) response, even between years of similar grain yield, is an indication of a given season's production dependence on factors other than N and P.

Independence of yield potential and crop nitrogen response

“…Yield potential is known to change from 1 year to the next because temporal variability, i.e. rainfall, temperature, relative humidity and so on, can vary considerably from year to year (Girma et al 2007a, b). Consequently, yield potential is specific to the season for which it is being evaluated.…”

Yield and quality of oat in response to varying rates of swine slurry

“…Because of the high cost of slurry application, especially with a tanker system, balancing environmental concerns with economic value of the slurry is challenging. Even when manure slurry is accurately applied, crops may not always respond favourably since the yield response of crops can vary among year and location (Girma et al 2007). Soil texture, chemistry and previous management history all affect crop response to slurry application.…”

Factors controlling regional grain yield in China over the last 20 years

“…Eghball and Varvel (1997) found that temporal variability was more important than management (i.e., N fertilizer and cropping sequences). Girma et al (2007) also found that temporal variability due to yield-limiting factors other than N is a major factor controlling winter wheat grain yield, followed by N fertilizer. This observation supports the current notion that "average based" N recommendation should be avoided and suggests a shift to alternate strategies for managing temporal variability.…”