Agroecosystems, Nitrogen-use Efficiency, and Nitrogen Management

Abstract

INTRODUCTIONThe focus of this paper is on nitrogen-use efficiency (NUE) in cereal production systems because maize (Zea mays L.), rice (Oryza sativa L.), and wheat (Triticum aestivum L.) provide more than 60% of human dietary calories either as cereals for direct human consumption or embodied in livestock products produced from animals fed with feed grains and their by-products (http:/apps.fao.org/, agricultural production). It is likely that these same cereal crops will continue to account for the bulk of the future human food supply because they produce greater yields of human-edible food, are easily grown, stored, and transported, and require less fuel and labor for processing and cooking than other food crops. Our analysis will examine the NUE of these primary cereals in the world's major cropping systems, which also account for the majority of global N fertilizer use. We define the NUE of a cropping system as the proportion of all N inputs that are removed in harvested crop biomass, contained in recycled crop residues, and incorporated into soil organic matter and inorganic N pools. Nitrogen not recovered in these N sinks is lost from the cropping system and thus contributes to the reactive N (Nr) (1) load that cascades through environments external to the agroecosystem.Our evaluation will focus on NUE in on-farm settings because estimates of NUE from experimental plots do not accurately represent the efficiencies achieved in farmers' fields. This lack of agreement results from differences in the scale of farming operations and differences in N-management practices-some of which are only feasible in small research plots. The effect of scale not only influences N fertilizer application, but all other management operations such as tillage, seeding, weed and pest management, irrigation, and harvest, which also affect efficiency. As a result, N-fertilizer efficiency in well-managed research experiments is generally greater than the efficiency of the same practices applied by farmers in production fields. For example, the average N-fertilizer uptake efficiency (defined as the percent-

Responsive in-season nitrogen management for cereals

“…Preliminary research results indicate our proposed strategies hold promise for improving NUE over current approaches. Since corn and wheat provide a significant portion of human dietary calories (Cassman et al, 2002) and they account for a majority of global fertilizer N use, we conclude that adoption of our proposed strategies should lead to improved fertilizer NUE, reduced fertilizer costs, and diminished environmental impacts (Raun and Johnson, 1999).…”

“…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). In the U.S. for example, the amount of biologically reactive N delivered from the land to coastal waters has increased noticeably over the past century (Turner and Rabalais, 1991), and has been proposed as a primary causal factor in oxygen depletion of coastal waters (Rabalais, 2002).…”

“…Additionally, we highlight problems associated with these strategies, and how computer and electronic technologies can be employed to address these problems. The consequence of current N management strategies is low N fertilizer use efficiency (NUE), leading to economic losses and environmental contamination (Raun and Johnson, 1999;Cassman et al, 2002;Fageria and Baligar, 2005). In this paper, NUE is defined as the percent of applied fertilizer N recovered in the aboveground crop biomass during the growing season.…”

Nutrients in the nexus

“…The N cascade can be mitigated by increasing the nutrient use efficiency (NUE) of crops and livestock production (Cassman et al 2002) and by modifying dietary choices, which in turn, alter the N demand due to food production (Smil 2002). The following sections address how these losses to the environment can be mitigated by improving agronomic efficiency and human dietary choices.…”

Extended statistical entropy analysis for the evaluation of nitrogen budgets in Austria

“…The worldwide NUE for cereal production has been estimated at approximately 33 % (Raun and Johnson 1999). The global NUE of industrialized countries has been increasing steadily, from 48 % in 1970 and 49 % in 1995 to its current value of 60 %, and it is expected to reach 62 % in 2030 with the potential for further improvement (Bouwman et al 2005;Cassmann et al 2002;Liu et al 2010). Despite their usefulness in facilitating the more efficient use of N and, therefore, in reducing the effect of N on the environment, neither the N surplus nor the NUE can quantify the dispersal of various N compounds resulting from agricultural activities.…”