Crop rotation originated in the 16th century and grew in popularity in the 18th century.1 George Washington Carver contributed to crop rotation greatly.2 Crop rotation is still used today.
The increase of the use of nitrogen in the past 5 decades has led to an increase of nitrogen in the soil profile of a few agricultural fields.3 The influence of agricultural practices on water quality has led to studies to develop the best management practices to optimize the use of fertilizer nitrogen and reduced nitrogen loss to the surface and groundwater.4 Crop rotation can play a major role in minimizing the potential risk of nitrate leaching to the surface and groundwater by enhancing soil nitrogen availability.
Crop rotation is planting different crops sequentially on the same plot of land to improve the soil, optimize nutrients in the soil, and get rid of pest and weed pressure. For example, say a farmer has planted a field of corn. When the corn harvest is done, he might plant beans, since corn consumes a lot of nitrogen, and beans return nitrogen to the soil. A simple rotation might involve two or three crops, and complex rotations might incorporate a dozen or more.5 Bone meal and blood meal are really great, natural ways to add a nitrogen and phosphorus source to your planting soil.6
One great crop to plant for nitrogen contributions are legumes. Legumes, like alfalfa or green beans, could be planted in a certain rotation. They are widely used in crop rotations because they are an excellent source of nitrogen for the soil. Many factors go into planting this crop like species, soil, crop, climate, length of time growing the crop, and management of the crop.7 These factors affect how much nitrogen is added to the farming system. The amount of nitrogen added to a crop by different types of legumes can range from 50 to 200 lbs. per acre.8
Another good crop to plant is animal manure. Grass-eating animals tend to produce waste that is very high in nitrogen. The manure has to be composted fully and done well because in some cases it can harm the crop rather than benefit it.9
There are several benefits to using crop rotation. This includes improved nutrient cycling, soil tilth, and soil physical properties; and enhanced weed control.10 It may also influence the rate of nitrogen mineralization or the conversion of organic nitrogen to mineral nitrogen by modifying soil moisture, soil temperature, pH, plant residue, and tillage practices.11 The rate of this nutrient release is affected by the availability of carbon sources (energy for the soil microbes), soil temperature, soil moisture, tillage, types and numbers of soil organisms, and quality of the soil organic matter.12
Nitrogen is the seventh element on the periodic table, the molecule that makes up almost eighty percent of the air we breathe, but the essential question is, how does it get into our soil? As stated earlier, Legumes are a great way to introduce a natural source of nitrogen into the soil, but how exactly? It is through Rhizobium bacteria. These bacteria live off of nodules in the roots of the plants, and form a symbiotic relationship with their host, siphoning plant sugars and converting nitrogen into something that can be used by the plant.13 Not all plants are like this, as some cannot create their own nitrogen like Legumes, but instead have to take it directly from the soil. Legume cover crops, also known as green manure can introduce a plethora of nitrogen into the soil, to assist other plants. Practices like planting alfalfa, red clover, or hairy vetch predating the planting season can help provide an adequate amount of Nitrogen into the soil.14
Some of the fantastic organic nitrogen sources that farmers use to benefit plant growth include composted grass clippings, used or fresh coffee grounds, manure, and human urine. Each different example contains over a 3% nitrogen concentration. Sources like manure can contain 4% to 9% nitrogen and are a common and reliable source.15 Another common source of nitrogen comes from bone meal, which can be easily acquired at garden stores in bulk.16 Plants need hydration to survive, so using leaves for mulch could help with water retention in plants and maintaining the plant's temperature by keeping them cool.17Nitrogen is found in many places and is so beneficial, so it is great to experiment with many types of fertilizers.
Certain plants create their own source of nitrogen, legumes for example. If these plants are colonized by a certain strain of Rhizobium bacteria, this bacteria creates nodules on the roots. The bacteria use the plant's sugars as an energy source, and turn un-usable nitrogen into usable nitrogen for the plants. Other plants that create their own source of nitrogen through this process are grass crops like corn and wheat, and non-leguminous crops like sunflowers, potatoes, and cotton.18