Nitrogen fertilizer efficiency

Peng S, Cassman KG. 1998. Upper thresholds of nitrogen uptake rates and associated nitrogen fertilizer efficiencies in irrigated rice. Agronomy Journal 90 178-185. 

Table 2 Efficiency of use of nitrogen fertilizer by winter wheat, winter oilseed rape, potatoes and sugar beet.

Data of a different kind, the nitrate losses through the held drains of the Brimstone experiment,also suggest that winter oilseed rape uses nitrogen fertilizer somewhat less efficiently than does winter wheat, but this experiment did not include the other crops discussed above. 

After Flarvest. How do the memory effects shown by the other crops compare with those of winter wheat Winter wheat did not show a memory effect after one year, but oilseed rape does seem to do so. Researchers of the Agricultural Development and Advisory Service found that nitrate production by microbes in the soil after a rape crop increased with the amount of fertilizer given to the crop (R. Sylvester-Bradley, personal communication). One reason may lie in this crop s habit of shedding its leaves as harvest approaches, which means that the microbes in the soil get early access to these residues. This habit might contribute to the apparently smaller efficiency of this crop in using nitrogen fertilizer. The crop may be just as efficient as winter wheat at taking up the fertilizer but drops... 

The green chemistry principles can be precisely applied to a greener and far less harmful utilization of fertilizers. In this perspective, green chemistry procedures are involved in the synthesis of enhanced-efficiency nitrogen fertilizers, most of them being based on the use of urea, in such forms that impede too fast a degradation and elimination of nitrogen. 

A nitrification inhibitor that is fully effective would be expected to (1) increase efficiency in the use of nitrogen fertilizers, especially on coarse-textured soils where rainfall is high, or extensive irrigation is practiced (2) make more feasible the practice of fall applications of ammonia (3) make less critical the time of nitrogen fertilizer applications and the need for split applications and (4) reduce nitrogen losses that may occur via nitrite decomposition or reaction with organic matter. Whether the benefits to be expected are sufficient to more than offset the costs of the chemical, and the additional steps involved in its use, is a practical matter that must be determined by the user for his particular soil and cropping system. 

Up until 1913, the bulk of the world s artihcial nitrogenous fertilizers was made from sodium nitrate obtained from Chile. Calculations showed that this supply would soon be exhausted if demand continued to expand, and so Fritz Haber (1868-1934) attempted to make ammonia directly from nitrogen and hydrogen gases. After 8 years, Haber produced ammonia efficiently on a small scale. Collaboration with the brilliant chemical engineer Carl Bosch (1874—1940) enabled the production to be scaled up, and ammonia was first manufactured on a large scale in 1913. The world s production of ammonia now exceeds 100 million tonnes. About 80% of all ammonia produced is used to make fertilizers with another 5% being used to make nylon, and a further 5% used to make explosives. 

Multiple application of nitrogen fertilizers to obtain more efficient use of nitrogen fertilizer. 

Ironically, within the EEC, efforts are now being made to reduce food production, something which one hopes is just a quirk of the current economic and political situation, and one way to do this would be simply to limit the amount of nitrogenous fertilizer which can be applied. A more constructive long-term approach would be to modify fertilizer application (both in its method and its form) so that nitrogen uptake would be more efficient and the runoff of surplus nitrate consequently diminished. Work of this kind is proceeding in several research establishments. 

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