Nitrogen, sustainable agriculture and food security. A review

Abstract

-The impact of modern agriculture on natural resources has become a major global concern. Population growth and expanding demand for agricultural products constantly increase the pressure on land and water resources. A major point of concern for many intensively managed agricultural systems with high external inputs is the low resource-use efficiency, especially for nitrogen. A high input combined with a low efficiency ultimately results in environmental problems such as soil degradation, eutrophication, pollution of groundwater, and emission of ammonia and greenhouse gases. Evidently, there is a need for a transition of current agricultural systems into highly resource-use efficient systems that are profitable, but at the same time ecologically safe and socially acceptable. Here, opportunities to improve nitrogenuse efficiency in cropping and farming systems are analyzed and discussed. In the past and present, increased productivity of the major plant production systems has been derived from genetic improvement, and from greater use of external inputs such as energy, fertilizers, pesticides and irrigation water. Aiming at improving resource-use efficiencies, in high-input systems the focus should be on more yield with less fertilizer N. In low-input systems additional use of N fertilizer may be required to increase yield level and yield stability. Developing production systems that meet the goals of sustainable agriculture requires research on different scales, from single crops to diverse cropping and farming systems. It is concluded that N supply should match N demand in time and space, not only for single crops but for a crop rotation as an integrated system, in order to achieve a higher agronomic N-use efficiency. A combination of quantitative systems research, development of best practices and legislation will be needed to develop more environmentally-friendly agricultural systems. The growing complexity of managing N in sustainable agricultural systems calls for problem-oriented, interdisciplinary research. productivity / nitrogen-use efficiency / cropping systems / biodiversity / land use / environment

Long-term experiments for sustainable nutrient management in China. A review

“…to maintain crop yield and soil fertility needs to be emphasized, legumes should be integrated into the cropping systems as much as possible, new sensing technologies should be developed and used to estimate nutrient content better and supply of different organic fertilizers, diagnose crop nutrient status and determine crop nutrient demand during the growing season, and chemical fertilizers should be applied as supplements only when and where nutrients from other resources are not enough to meet crop requirements. Such precision nutrient management systems should not only match field-to-field and year-to-year variability in nutrient supply and crop demand for single crops, but for crop rotations as integrated systems as well (Spiertz, 2010), leading to more balanced nutrient management, less reliance on chemical fertilizers, and improved nutrient-use efficiencies as well as higher crop yield. Such complicated technologies need to be simplified to be farmer-friendly and suitable for smallscale farming.…”

Winter and growing season nitrogen mineralization from fall-applied composted or stockpiled solid dairy manure

“…Manure's agronomic N use efficiency (NUE), defined as the harvested mass of an agronomic crop per unit mass of manure N applied (Wen et al 2003), can be optimized by synchronizing N mineralization with plant N uptake Crothers 1980, 1993;Appel 1994;Schoenau and Davis 2006;Spiertz 2010). For example, incorporating organic sources in late fall, at lower soil temperatures, rather than in early fall at higher temperatures, slows or delays (1) N mineralization (van Es et al 2006), (2) nitrification (Brown 1988), or both.…”

“…An improved understanding of the competing processes of N mineralization and N immobilization, along with their temporal dynamics, may improve our ability to manage N cycling, increase NUE by minimizing N losses whatever the form, and increase the sustainability of agricultural systems that utilize typically applied organic N sources (Cabrera et al 2005;Spiertz 2010). The objective of our 2-year field study was to improve our understanding of N availability from organic sources by monitoring N mineralization with time from fall-applied dairy manure, either composted or stockpiled.…”

The Influence of Bahiagrass, Tillage, and cover crops on Organic Vegetable Production and Soil Quality in the Southern Coastal Plain

“…Conservation management, which includes using cover crops and conservation tillage, improves soil quality. Cover crops add organic matter into the soil (Powlson et al, 1987;Sanchez et al, 2001), improve soil aggregate stability (Tisdall & Oades, 1982;Peregrina et al, 2010), reduce soil erosion (Langdale et al, 1991;Spiertz, 2009) and weed pressure (Zotarelli et al, 2009), and potentially increase available soil N to subsequent crops (Ladd et al, 1981;Sanchez et al, 2001). …”