Richard E. Engel

Method for Precision Nitrogen Management in Spring Wheat: I Fundamental Relationships

Wheat (Triticum aestivum L.) fields in the semi-arid Northern Great Plains are spatially variable in soil N fertility and crop productivity. Consequently, there is interest in applying variable, rather than uniform rates of fertilizer N across the landscape. Intensive soil sampling as a basis for variable-rate fertilizer management is too costly when compared to the value of wheat in this region. The objective of this research was to determine relationships between yield and protein, and protein and available N as needed to develop a cost-effective variable-rate N fertilizer strategy for spring wheat. A three-year study (1996–1998) was carried out at a site near Havre, Montana, USA (48°30′N, 109°22′W). Treatments consisted of three water regimes, four cultivars, and five fertilizer N levels per water regime in a randomized complete block design with four replicates. Scatter diagrams of relative yield vs. grain protein were consistent with earlier investigators, and indicated protein concentrations at harvest provided a method for indexing N nutrition adequacy (deficiency vs. sufficiency) in wheat. A critical protein concentration of 13.2% was defined using a graphical Cate-Nelson analysis. This value appeared to be consistent across the three water regimes and four cultivars as 159 (88%) of the 180 water×cultivar×N level episodes were in positive quadrants. No correlation could be found between relative yield and protein for episodes below the critical level (r2=0.1). Hence, grain protein concentrations could not be used to predict the magnitude of yield losses from N deficiency. Grain protein content would be useful for prescribing fertilizer recommendations where N deficiency (<13.2% protein) reduces grain yield under semi-arid conditions. Inverse slopes (dy/dx) of the protein-available N curves reveal that it takes 12–18 kg N/ha to change protein 1% (e.g., 12% vs. 13%) where wheat is under water stress during grain fill. The total N requirement could then be computed by summing the N required for raising protein and the N removed by the crop in the year when the grain was harvested.

Method for precision nitrogen management in spring wheat: II. Implementation.

By accounting for spatial variation in soil N levels, variable-rate fertilizer application may improve crop yield and quality, and N use efficiency within fields. The main purpose of this study was to demonstrate how site-specific wheat yield and protein data, and a geographic information system may be used in developing precision N-recommendations for spring wheat. The three steps in the procedure include: (1) estimate the amount of N-removed in wheat in the year in which the crop is harvested, (2) estimate the N-deficit, defined as the amount of additional N needed for raising protein concentration in a future crop to a specified target level, and (3) estimate the total N-recommendation by summing the mapped values of the N-removed and the N-deficit. A map for variable-rate application of fertilizer is derived by specifying cutoff values to divide the range in the total N-recommendation into classes representing N management zones.A field experiment was conducted within an annually cropped wheat field (101 ha) in northern Montana to determine whether the proposed method could improve grain yields and protein levels. The N-removal and N-deficit were estimated from site-specific wheat yield and protein data that were acquired during harvest of 1996. In 1997, which was a dry year, an experiment was conducted in the same field that consisted of a randomized complete block design arranged as pairs of strip plots. Variable- or uniform-rate N treatments were randomly assigned to each pair of strips. Both treatments received nearly the same amount of fertilizer, however, N in the variable treatment was varied to match patterns in grain yield and protein levels that previously existed in 1996. Yields were not significantly different between management systems, but proteins were significantly enhanced by spatially variable N application. In addition, variability in protein levels was reduced within the whole field. Field areas deficient in N fertility could be identified without having to sample for soil profile N.

Grain protein as a post-harvest index of nitrogen status for winter wheat in the northern Great Plains

The use of grain protein as a post-harvest index of N fertility status has been promoted for spring wheat (Triticum aestivium L.) through the establishment of critical levels for segregating wheat into N deficient vs. N sufficient classes. The objectives of this study were to evaluate this concept for winter wheat in the northern Great Plains; and to estimate the added N requirements necessary to achieve maximum yield when protein concentrations fall below the critical level. A field study consisting of three water regimes, four cultivars, and five fertilizer N levels was conducted near Havre, MT. A consistent relationship between relative yield and grain protein was found and a critical protein concentration of 121 mg g-1 was defined using Cate-Nelson R2 statistics. Protein concentrations below the critical level were associated with yield losses from N deficiency (79% frequency), while protein concentrations ≥ the critical level were associated with N sufficiency (93% frequency). Under conditions of mod...

On-Combine Sensing and Mapping of Wheat Protein Concentration

Site-specific measurements of grain protein concentration, in addition to grain yield, are potentially useful for assessing spatial variability in cereal crop production as needed in precision agriculture. This study investigated an on-combine spectroscopic sensor for mapping grain protein levels within farm fields. The optical, near-infrared sensor was calibrated in the laboratory to test samples of hard red spring wheat (r 2 = 0.99, SEC = 0.081%). Grain protein data for spring wheat were then acquired for a 45-acre dryland wheat field, and compared with test samples that had been manually sampled from the combine’ s exit auger. The ability of the sensor to predict protein values declined in the field (r 2 = 0.55, SEP = 0.66%). However, a map of grain protein concentration derived from on-combine sensing was highly correlated with a test map of grain protein (r = 0.93). The results are sufficiently promising to suggest that on-combine spectroscopic sensing of grain protein concentration for mapping purposes is technically feasible.

Ammonia volatilization losses were small after mowing field peas in dry conditions

Engel, R., Jones, C. and Wallander, R. 2013. Ammonia volatilization losses were small after mowing field peas in dry conditions. Can. J. Soil Sci. 93: 239-242. Ammonia losses following termination of peas (Pisum sativum L.) by mowing were measured using a micrometeorological mass-balance approach. Field trials were conducted during two seasons in a semiarid climate. Plant N in the above ground biomass was 105 and 79 kg N ha-1 in 2011 and 2012, respectively. Vertical NH3 flux estimates were nominal (0.3 to 1.7 g N ha-1 h-1) in the 2 wk following mowing. Cumulative NH3 loss represented 0.3 to 0.5% of the N in plant biomass, indicating that N fertility was not diminished by NH3 volatilization in this dry climate.