Nitrogen Content of Winter Wheat During Growth and Maturation¹

Abstract

Preliminary studies showed that winter wheat (Triticum aestivum L.) was losing relatively large amounts of N during the grain formation growth period. In order to further document this N loss, winter wheat plants were sampled at different times and at different locations before and after anthesis until maturity. The objective was to determine the nature and extent of dry matter and N losses that occur during the later stages of wheat development as influenced by N fertilization. While N is translocated rapidly from other plant parts to the grain after anthesis, total N losses ranged from 25 to 80 kg ha−1 in different experiments. These losses occurred during the grain filling period after anthesis. Dry matter and N losses were attributed primarily to the stems where 83 to 87% of dry matter losses occurred and 73 to 75% of the N. Dry matter and N losses from leaves and roots were relatively small. The N losses increased with increasing rates of N application. Plant N losses could account for much of the N losses found in soil N balance studies and certainly influence calculations involving fertilizer N efficiency. Grain protein could be doubled if plant N losses could be translocated instead into the grain.

Effect of nitrogen rate on plant nitrogen loss in winter wheat varieties1

“…At Stillwater, Chisholm and TAM W-101 had higher NUE, N uptake efficiency and N utilization efficiency whereas at Perkins 2180 and Longhorn had higher N use and N uptake efficiency compared to other varieties evaluated. These results agree with the work of Daigger et al (1976) and Dhugga and Waines (1989) who found differences among wheat genotypes for shoot N accumulation before and after anthesis. Differences between varieties were also found at various N rates for grain and straw yield, and straw and grain + straw N uptake and N use efficiency at Perkins (Table 7).…”

“…High N fertility levels often increase leaf area indices, but the greatest difference during maturation is the ability to maintain a larger number of green leaves late in the season as compared with low N fertility levels. Plant N losses could account for much of the N losses found in soil N balance studies and certainly influence calculations involving fertilizer N efficiency (Daigger et al, 1976). Failure to include direct plant N losses when calculating an N budget can lead to overestimation of losses from the soil by denitrification, leaching, and ammonia volatilization (Francis et al, 1993b).…”

Relationship Between Ammonium and Nitrate in Wheat Plant Tissue and Estimated Nitrogen Loss

“…Because of these conditions, wheat continued to assimilate N and redistribute it to the grain, thus limiting N loss observed by others. [6,9,16] The relationship between NO 3 ÀN content at Feekes 5 and total N at Feekes five at both locations and both years is reported in Figs. 1 and 2 F1; F2 .…”

“…When N content was lower (150 kg ha À 1 ) at anthesis, N losses were not observed. Between these N contents, N loss was highly correlated with yield, where high yields prevented N loss and low yields caused a net loss of N. Daigger et al (1976) studying N content in wheat noted that the percent N in plant tissue did not change during a 23-day period preceding maturity. He found, though, that the period between anthesis and maturity netted a total loss of 30% of the applied N, and losses of N increased with increasing N applied.…”

Responsive in-season nitrogen management for cereals

“…While it is impossible to achieve 100% efficiency for N fertilizer use in any crop production system, these numbers suggest there is significant opportunity for reducing N losses associated with current management practices. Pathways for N losses from agroecosystems include gaseous plant emissions (Daigger et al, 1976;Francis et al, 1993), soil denitrification, surface runoff, volatilization, and leaching (Raun and Johnson, 1999). With the exception of N denitrified to N 2 , these pathways lead to an increased load of biologically reactive N into external environments (Cassman et al, 2002).…”