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Fluid Journal : Fluid Journal 1996-1998
Dr. Raun Lohry FFFFFine-tuning N F ine-tuning N F ine-tuning N F ine-tuning N F ine-tuning N For The Environment or The Environment or The Environment or The Environment or The Environment Understanding the nature ofN and howit can be managed are essential to making fertility practices environmentally friendly. Winter 1996 Summary: Technological advances in the last fifty years such as genetic improvements, increased fertilizer use, expanded irrigation and im- proved management have raised average corn yield from 30 to over 135 bu/A. One mighty propellant of such proliferation has been nitrogen (N) fertilizer. However, while increas- ing N fertilizer use has improved plant performance, it has also raised environmental concerns. Attempts to define systems requiring lower N and pesticide inputs, often called "sus- tainable," nearly always increase time and management as substitutes. Discussion of such systems is shrouded by vague terms and less rigorous factual or scientific docu- mentation. Truly sustainable systems should be 1) resource conserving, 2) environmentally compatible, 3) socially supportable, and 4) commer- cially competitive. The goal of sustainability is, in its final form, to manage inputs such that farm productivity is optimized and environ- mental stresses are minimized. The quest for higher farm productivity demands that the producer and fertilizer dealer be more knowledgeable and implement scientifically proven tech- niques that will increase farm profit while being environmentally friendly. The discussion that follows will explore nitrogen management and define techniques to manage nitrogen effec- tively to minimize environmental impact. Before we get into nuts and bolts of how to better manage N, a quick refresher on its nature and sources is in order. Nitrogen cycle Nitrogen is required by plants in large The Nitrogen Cycle Atmospheric Nitrogen Ammonium Fertilizer Conversion Legume Conversion Atmospheric Conversion Denitrification Nitrate Protein Plant Absorption Plant & Animal Wastes Urea Urea + NBPT Average yield - bu/A N Rate 92 lbs/A 166 lbs/A 150 145 140 135 130 125 120 Figure 2. Average effect of NBPT on corn yields in 78 trials performed by university scientists. quantities and, when water is not limiting, can be the most common limiting factor in crop production. One handful of soil that supports vegetable and field crops contains more living creatures than all the people whoever walked the earth. These subterranean citizens of the soil make up the biologi- cal factory that relentlessly manufac- tures different forms of N. Without them, the soil would be lifeless, yet they can make N unavailable to crops, causing economic and environmental losses. Plants obtain N from residual N in the soil and from applied sources such as fertilizer. All nitrogen moves through various phases as it is used by plants and soil organisms. This dynamic process of N movement through various pools is known as the nitrogen cycle (Figure l). Nitrogen cycling models depict plants removing inorganic N from soil N pools and returning energy and nutrient-rich residues. The concept of N cycling is important in plant nutrition because: 1) N from organic residues is a substantial portion of plant N uptake, and 2) it helps to explain where applied N goes. Al- though nitrogen in residues and other organic forms is the largest fraction of Figure 1. Nitrogen Cycle
Fluid Journal 1993-1995
Fluid Journal 1999-2001