MU stacked logo Crop Production University of Missouri and CAFNR Delta Research Center Division of Plant Sciences


Plant Nutrients

cotton plant row

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.

nutrient availablity
Relative availability of nutrients to
plant roots is affected by pH level of
the soil. Low pH values are acid and
high pH values (above 7) are alkaline.

Primary and secondary macronutrients are often limiting factors for crop production in Missouri depending on soil conditions and prior management. Most soils in Missouri have sufficient amounts of micronutrients to supply plant needs for crop production, but individual crop species may have special micronutrient requirements, and soil properties may vary. Factors such as soil pH and moisture can affect the solubility of nutrients or interfere with the ability of plant roots to absorb nutrients. Deficiencies of micronutrients occur most often in soils with high pH (with the exception of molybdenum). Phosphorus availability is reduced by soil acidity and alkalinity. Low soil pH increases the availability of aluminum and manganese, which can result in toxic levels of these elements. Lime is often applied to neutralize acidity in soils. Click to see our webpage devoted to lime issues. READ ABOUT LIME.


Plant nutrient disorders can produce unique color patterns on crop leaves. These symptoms are useful in identifying the cause of the problem. This IMP extension booklet contains color photos taken of field crops in the Delta Region with nutrient deficiencies. ORDER HARDCOPY or DOWNLOAD PDF

audio Reducing losses from broadcast urea
(click arrow for audio)
dry soil
wet soil
N losses favored
by wet soil, warm
and wind.

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). The 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.

Soybean plant
with potassium

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).

corn plant
Corn plants with

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).

Soybean leaves
on the left were
deficient in
manganese. Mn
deficiency is rare
in most parts of
Missouri but occurs
often on a small
group of sandy
soils near Benton,

Micronutrients Crop deficiencies of micronutrients are less common in the Delta region than N, P, and K. Sulfur Crop response to sulfur has become more frequent since coal burning power facilities started using low S coal to reduce emissions and meet EPA standards. The incidence of S deficiency is greatest on sandy soils with low organic matter content. Plants that are deficient in S are usually light green or yellow in color with similar symptoms as N deficiency. The ratio of N:S in leaf tissue is often a good indicator of plant S deficiency. A cotton field test at Clarkton, Missouri is evaluating ammonium sulfate, epsom salt, gypsum, and elemental sulfur to correct low S (Cotton sulfur fertilization). Boron Tank mixing soluble boron with pesticides and plant growth regulators for cotton has been a common practice in the Delta for many years. Recent field research in Southeast Missouri showed that rice yields were greatest when soil B levels were 0.25 to 0.35 ppm by the hot water extraction method. In 2000, rice receiving soil-applied B produced significantly greater yields than rice with foliar-applied B and rice with no B applied. In 1999 and 2001, there was no significant difference between yields obtained with foliar or soil B applications. (Rice boron).

esser probe
Esser soil
sample probe

Soil sampling. Field experiments were conducted to compare the time required to collect samples for soil testing using four types of soil robes. Soil sampling time on sandy loam and clay soils was reduced significantly with a cone probe compared with the straight tube and foot-pedal probes. Composite samples were collected from a 20-acre field with clay soil in 22 minutes with a cone probe compared to 38 minutes with straight tube and foot-pedal probes. The cone design saves time by reducing probe clogging and allowing 8 to 10 cores to be collected before emptying soil from the probe. READ MORE

cardy k meter
Cardy K Meter

Stem sap K. A rice experiment was conducted at the Delta Center to determine the accuracy of a fast tissue testing method using a Horiba Cardy K+ meter. Rice was field-grown in three soil potassium regimes. At three early reproductive growth stages (R0, R1, and R2), stem samples from the basal six inches of rice plants were collected and analyzed for K content. Basal stem samples were tested with extracted sap analyzed by a Cardy K+ meter and digested stem tissue analyzed with an Atomic Absorption Flame Spectrophotometer (AAS). Regression correlations between basal stem sap K and total K ranged from r2 = 0.57 to 0.89 for the three growth stages. Both methods of measuring lower stem K content at the R1 growth stage were equivalent in their ability to predict grain yield response to potassium fertilization. READ MORE

pH meter
pH meter

Soil test pH kits. Hand-held portable pH meters can be used by farmers and crop managers to quickly determine whether soil acidity or alkalinity is a probable cause of poor crop health. Hand-held pH meters and pH color indicator kits were found to provide reliable in-field soil pH measurements. Personnel using a pH color kit were able to distinguished between soils with and without lime. However, interpolating between whole pH values with the color kit was difficult. A soil probe that was inserted into moist soil in plots provided poor response to soil pH and is not suitable for diagnosis of soil pH problems. READ MORE

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