A farmer tested the soil in a field and found that there was a high nitrate salt concentration. The farmer then grew a crop in this field. After the crop was removed, the soil was tested again.
The nitrate salt concentration had decreased.
(a) Suggest reasons why the nitrate salt concentration had decreased
(b) Some species of plant grow well in soil that is always low in nitrate salt. Explain how
they can obtain a source of nitrogen compounds.
Answers
Answer:
Nitrogen is ubiquitous in the environment. It is one of the most important plant nutrients and forms some of the most mobile compounds in the soil-crop system. Nitrogen is continually cycled among plants, soil organisms, soil organic matter, water, and the atmosphere (Figure 6-1). Nitrogen enters the soil from many different sources and leaves the root zone of the soil in many different ways. This flux of nitrogen into, out of, and within the soil takes place through complex biochemical transformations.
The mounting concerns related to agriculture's role in nitrogen delivery into the environment are reflected in several detailed reviews (Follett and Schimel, 1989; Follet et al., 1991; Hallberg, 1987, 1989b; Keeney, 1986a,b; Power and Schepers, 1989). A brief review of the nitrogen cycle and nitrogen budget or mass balance considerations is necessary to understand the options for management improvements in farming systems to mitigate the environmental impacts of nitrogen.
THE NITROGEN CYCLE
The nitrogen cycle is critical to crop growth. The balance between inputs and outputs and the various transformations in the nitrogen cycle determine how much nitrogen is available for plant growth and how much may be lost to the atmosphere, surface water, or groundwater.
Nitrogen is an important component of soil organic matter, which is made up of decaying plant and animal tissue and the complex organic