Agriculture Reference
In-Depth Information
In the twenty-first century, improving nutrient use efficiency in crop plants will be an impor-
tant topic compared to the twentieth century, mainly due to limited land and water resources
available for crop production, a higher cost of inorganic fertilizer inputs, declining trends in
crop yields globally, and increasing environmental concerns. Furthermore, at least 60% of the
world's arable lands have mineral deficiencies or elemental toxicity problems, and on such soils,
fertilizers and lime amendments are essential to achieving improved crop yields. Fertilizer inputs
are increasing the cost of production of farmers, and there is a major concern for environmental
pollution due to excess fertilizer inputs. Higher demands for food and fiber by increasing world
populations further enhance the importance of nutrient-efficient cultivars that are also higher
producers. Nutrient-efficient plants are defined as those plants which produce higher yields per
unit of nutrient, applied or absorbed, than other plants (standards) under similar agroecological
conditions (Fageria et al., 2008).
During the last four decades, much research has been conducted to identify and/or breed nutrient-
efficient plant species or genotypes/cultivars within species and to further understand the mecha-
nisms of nutrient efficiency in crop plants. However, success in releasing nutrient-efficient cultivars
has been limited. The main reasons for limited success are that the genetics of plant responses to
nutrients and plant interactions with environmental variables are not well understood. Complexity
of genes involved in nutrient use efficiency for macro- and micronutrients and limited collaborative
efforts between breeders, soil scientists, physiologists, and agronomists to evaluate nutrient effi-
ciency issues on a holistic basis have hampered progress in this area. Hence, during the twenty-first
century, agricultural scientists have tremendous challenges, as well as opportunities, to develop
nutrient-efficient crop plants and to develop best management practices that increase the plant effi-
ciency for utilization of applied fertilizers (Fageria et al., 2008).
During the twentieth century, breeding for nutritional traits has been proposed as a strategy to
improve the efficiency of fertilizer use or to obtain higher yields in low-input agricultural systems.
This strategy should continue to receive top priority during the twenty-first century for developing
nutrient-efficient crop genotypes, since an efficient use of N in plant production is an essential goal
in crop management. This chapter overviews the importance of nutrient-efficient plants in increas-
ing crop yields in modern agriculture. Further, the objective of this chapter is to discuss the latest
available information on NUE in crop plants. This information may be helpful in improving NUE
in crop plants and will produce significant economic and environmental benefits for worldwide
agriculture (Fageria, 2009, 2013, 2014).
5.2 DEFINITIONS OF NUTRIENT-EFFICIENT PLANTS AND NITROGEN
USE EFFICIENCY
Before discussing in detail the NUE in crop plants, it is important to discuss or define nutrient
use efficiency and nutrient-efficient plants and finally discuss NUE. There are several definitions
of nutrient use efficiency as well as nutrient-efficient plants. Large variations in defining nutrient-
efficient plants and methods used in calculating nutrient use efficiency make it difficult to compare
results of different studies (Fageria et al., 2008). The effort to measure yield response to an applied
nutrient is further confounded by other factors, such as variable soil fertility levels, climatic condi-
tions, crop rotations, and changes in production practices that affect nutrient use efficiency (Stewart
et al., 2005). Shaviv and Mikkelsen (1993), Munoz et al. (2005), and Sato et al. (2012) also reported
that the efficiency of fertilizers applied to crops varied due to diversity in production systems, crop
type, growing season, fertilizer placement, irrigation, soil type, weather conditions, and chemical
transformations of nutrients in the soil.
Since N is one of the most expensive nutrients to supply, one of the objectives of crop improve-
ment programs is to measure and maximize NUE (Good et al., 2004; Castellanos et al., 2010).
While the literature contains several definitions and methods for evaluating this index, it is essen-
tially the ratio between crop output and nutrient inputs. In simple terms, efficiency is the ratio of
