A fertile soil for crop production should contain the 14 essential mineral elements for normal growth and reproduction. Each of these nutrients has a function in plants and is required in varying amounts in plant tissue. Macronutrients (nitrogen, phosphorus, potassium, calcium, magnesium and sulfur) are required in the largest amounts. Micronutrients (iron, copper, manganese, zinc, boron, molybdenum, chlorine and nickel) are required in relatively smaller amounts in plants. Other mineral elements that are beneficial to some plants but are not considered essential include sodium, cobalt, vanadium, selenium, aluminum and silicon. To determine whether fertilizer is need on your field, send a representative soil sample from the field to an accredited laboratory for nutrient analysis.
Macronutrients (N,P,K). Nitrogen (N) is required in the largest amounts of all nutrients in plants. Nitrogen is necessary for the production of enzymes, proteins, and nucleic acids. Plants with nitrogen deficiency are often light green or yellow in color. Corn leaves sometimes have a yellow strip down the midrib of the leaves.The price of N fertilizer is impacted by energy costs because natural gas is used in the manufacturing of nitrogen fertilizer. For farmers, managing N is tricky because it can be lost or made unavailable to plants by leaching, denitrification, volatilization, and immobilization. Obtaining ammonium nitrate which is not subject to volatilization has become more difficult to obtain because of terrorism bomb concerns. We found that urea can be broadcast on cotton when it is incorporated or a chemical mixed with it to reduce volatilization (Urea volatilization). Over 30 N response curves have been created from field tests in the Mid-South with cotton, corn, rice, and sorghum. To determine what the most profitable N rate with current crop and nitrogen prices with this database click on NITROMAX. In cotton, a study is being conducted to test three light sensors (CropScan, CropCircle, and GreenSeeker) for determining optimum sidedress N rates. Results in 2006 showed that the N deficiency was to early to detect at first square, but mid-square through first bloom results looked promising. ( On-the-go cotton N ). For rice, new methods were recently developed using digital photography and visual measurment for predicting response to midseason N ( Rice midseason N ). IThe effect of plant population and planter skips on N response in grain sorghum was also studied at the Delta Center (Grain sorghum N). Results indicated that in uniform grain sorghum stands, N at 100 to 150 lb/acre produced the highest grain yield under both high and low plant density conditions. In non-uniform stands with frequent 6- to 9-ft skips, sorghum had significantly reduced grain yield when compared to a uniform stand or 3-ft skips. These results do not support reduced N rates in either uniform or uneven grain sorghum stands with less than optimal plant densities.
Potassium (K) is used in plants to regulate plant/water/mineral relationships. One of the key functions of K is the opening and closing of stomates (pores) on the underside of leaves. This effects how much water loss for evaporative cooling occurs and how CO2 gas goes into the leaves for photosynthesis. Potassium is the only nutrient that is not a part of the structure of plant tissues. Plant leaves with potassium deficiency often have yellow or white areas between the veins. Other symptoms are yellow or bronzing of the edges of the leaves. At the Delta Center Dr. Bobby Phipps completed a study comparing soil and foliar K fertilizer on cotton. Generally, we are finding that foliar K can be applied as a rescue application for insufficient soil potassium but preplant K fertilizer is the most effective remedy for low K (Foliar K soybean). A study at the Missouri Rice Research Farm in a field with low soil K showed that applying potash at mideseason increased yields ( MU rice K research ) . Also a fast diagnostic method for detecting low K in rice plants was developed using a Cardy K meter and rice stem sap (Rice stem sap K) .
Phosphorus (P) is sometimes called the energy nutrient. It is required for plants to convert sunlight into sugars. Although the parent material of most soils in the Delta was high in P, continued cropping without adding P to offset crop removal can cause deficiency. Although less P is required in plants than N or K, P moves more slowly in the soil to plant roots. For this reason, phosphorus is often a major part of starter fertlizers (ex. 11-37-0 fertilizer). Phosphorus deficient plants are often have purple colored leaves and stunted growth. Of the three macronutrients, P is the most sensitive to soil acidity. In low pH soil fertilizer P because unavailable in insoluble compounds with aluminum. To avoid wasting money, correct low pH problems with lime before applying phosphate fertilizer. A three year study funded by Cotton Incorporated evaluated MU cotton soil test Precommendations. In most fields, the current P recommendations were satisfactory (MU cotton soil recs). However in fields that are recently land levels, deep cut areas often need inorganic P fertilizer or chicken manure, which contains high amount of P, to help return the soil to optimum soil productivity- (Land leveling and chicken manure).
