Impact of Residual Mineral N in Soil on Grain Protein Yields of Winter Wheat and Corn¹

Abstract

Fertilizer N has become a major cost input in the production of winter wheat (Triticum aestivum L.) and corn (Zea mays L.) with uncertainties remaining as to rates required for effecting optimum grain and protein yields without environmental pollution implications. For this reason investigations were conducted with the two crops to determine optimum rate of fertilizer N for grain and protein yields with varied levels of residual mineral N in the rooting profile of soil to 180 cm depth at planting. Fertilizer rates employed for wheat in 118 farmers' fields ranged from 0 to 67 kg N/ha by 22.5 kg increments broadcast in the spring and for corn in 17 farmers' fields from 0 to 225 kg/ha by 45 kg increments sidedressed at 30 to 45 cm growth stage. Residual mineral N was found to exert major influence on grain protein percentage and protein yield of both crops within nominal rates of N fertilizer application. The magnitude of residuals varies with the soil environment and amount of prior fertilizer use on the soil. The data reveal that grain yield response of wheat to applied N is unlikely when soil residual mineral N exceeds 120 kg/ha and for irrigated corn around 240 kg/ha at the yield levels of approximately 25 to 30 quintals/ha of wheat and 85 to 90 quintals of corn obtained in these experiments. Maximum protein yield for wheat required an additional 50 to 60 kg N/ha and for corn 60 kg, economics of which can be ascertained only with knowledge of the unit nutritional value of the produce in relation to the unit cost of N applied.

Nitrogen Fertilizer Sources and Application Timing Affects Wheat and Inter-Seeded Red Clover Yields on Claypan Soils

“…Wheat grain yield response to fall-applied N sources during years (2004, 2005, and 2007) with medium-to poorly-drained soils ranked PCU > AN > U + NBPT > urea ≥ UAN (Figure 2A). All N sources increased yield as N rate increased, similar to other research [15,36], but wheat yield was unlikely to increase when inorganic soil test N exceeded 120 kg N ha −1 [37]. PCU , which were below average for the region [2].…”

Factors influencing grain N concentration of hard red spring wheat in the semiarid prairie

“…Further, because more starch was being produced in the kernels than there was available N to satisfy protein synthesis, the first increments of FN resulted in a decrease in grain N concentration (dilution). As grain yield response to FN diminished at higher N rates, grain N concentration tended to increase due to the increased supply of available N. This pattern of response has been noted by some researchers in more humid climates (Olson 1984) and in growth chamber studies (Partridge and Shaykewich 1972). In these moist conditions, grain N concentration was low (< 25 g kg -1 ).…”

“…Often, the crop will have access to this N, between heading and anthesis stages, thereby increasing grain N. Olson et al (1976) hypothesized that NO 3 in the lower rooting zone may be an important contributor to grain N concentration. Unfortunately, neither our model data nor most soil testing laboratories are able to take this factor into consideration because measurements are usually made to no more than the 0.6-m depth.…”

Winter wheat roots grow twice as deep as spring wheat roots, is this important for N uptake and N leaching losses?

“…Also deeper soil measurements before sowing in studies of N recommendations in wheat often relate better to winter grain yields than shallower ones (Addiscott and Darby 1991; Bundy and Andraski 2004;Olson et al 1976). Understanding the availability of N from deep soil layers will be especially important in organic farming systems or other production systems with limited N input, as possible utilization of N from below 1 m will be more important for successful crop growth than in highly fertilized systems.…”