Submitted to: Soil and Water Conservation Society
Publication Type: Book / Chapter
Publication Acceptance Date: 7/1/2008
Publication Date: 2/10/2010
Citation: Herrera, J., Delgado, J.A. 2010. Integrated nitrogen management. Soil and Water Conservation Society. p. 94-127. In Delgado, J.A. and R.F. Follett (eds). Advances in Nitrogen Management for Water Quality. SWCS, Ankeny, IA.
Interpretive Summary: The physiological process of linking the supply of N (N fertilization) with the demand of N that will ultimately determine the extent of the previous effects is N uptake. The form of N (NO3 and NH4) absorbed has a significant effect on the physiological mechanisms of uptake, transport, assimilation, and storage of N and, in some crops, on the functioning and architecture of the crop. In addition, certain forms of N can increase or prevent certain pathways for N loss. NO3-N is the form of N most susceptible to losses from the rooting zone. Guaranteeing a mixed N supply can minimize N losses and increase crop productivity. A mixed N supply can be achieved to a certain extent by deciding the N source and the method of application. Although there are a high number of options for N mineral fertilizers, the sources that are currently used are very few and are mainly influenced by cost of production, storage, and application. Therefore, the efficiency of the application at the farm level is usually last in the list of priorities that influences the selection of a certain product. Slow N release fertilizers offer a good option for increasing N use efficiency, but the current costs of these materials prohibits their use on most farms growing row crops. Both N source and the growth stage of the crop determine the methods that are suitable for applying N. Although, these two factors restrict the scope of methods to use in the application of N, there are still a good number of options that orientate the kind of transformations at which the N source will be exposed. The great success associated to Rhizobium inoculation in leguminous crops has interested researchers in the use of other microorganisms in crop production. Although the use of other inoculums is lower than Rhizobium, significant progress has been made to try to integrate the management of microorganisms, such as Azospirillum, Micorrhiza, and others, into the agronomical management of fields. Finally, the need to account for numerous variables of very different natures and to consider effects at different scales (e.g. at the farm for environmental efficiency and at the regional level for global food security) makes developments in information technology promising tools to orientate and guide N management research and decisions.
Technical Abstract: N fertilization is necessary to support desired production levels on most farms in the world. The achievement of minimum production levels associated with N fertilization is necessary to guarantee global food production. In addition, the efficient use of N is a fundamental agronomic goal to maximize yield potential, while minimizing negative effects of N on the environment. However, the most efficient use of N fertilizers (as other resources) occurs while yield increases linearly as a function of applied N fertilizer. It thus seems impossible to maximize total production and efficiency because there is a fundamental trade-off between them. This introduces an important dilemma in the discussion of the future needs of global food production: whether it is more environmentally sustainable to attempt to maximize resource use efficiency or total production. An argument for the former is that losses and damage to the global environment are likely to be lower, however conversely more land area has to be used to meet the demand for food, since production would be below its potential maximum level (de Wit, 1992; Zoebl, 1996). Improved crop productivity from N fertilization can result from increases in yield and/or improvements in quality factors. However, the complexity associated to the cycle of N in the environment and the uptake and use of N by the crop makes N fertilizer management complex and uncertain. Almost every agronomic practice has an effect on N nutrition. Therefore, any N management strategy should consider agronomical goals and integration into the whole field management.