Role of Manganese in Cotton Production

Manganese deficiencies appear when soil conditions combine to create shortages. With increasing soil pH, insoluble Mn oxides are formed, limiting plant supplies. pH readings higher than 6.0 cause supply problems on sandy soils, while on heavier textured soils, the critical soil pH level is higher. Over-liming and the occurrence of very loose, highly aerated soils commonly render manganese unavailable. Under cold, wet, soil conditions, manganese becomes unavailable. Equally in dry, hot conditions when there is inadequate moisture for uptake, manganese supply is limited.

High levels of soluble Mn occur in acid (<pH 5) or waterlogged soils and this can lead to toxicity problems. Toxicity symptoms in cotton cause leaves to appear crinkled and cupped with stunted growth. This may be confused with thrips injury and needs to be confirmed with soil and tissue tests. Liming to raise the pH above 5.8 may help relieve toxic effects.

Manganese deficiency commonly occurs in some coastal plain soils and soils with high pH. Cotton growers with soil pH above 6.3 are encouraged to tissue test to avoid deficiencies. If detected, it can be corrected with foliar Mn applications.

Manganese and other nutrients

Oversupply of other cations (K, Ca,) can limit Mn uptake. For this reason it is quite common for manganese and zinc deficiencies to occur at the same time. In addition there is often antagonism between iron and manganese uptake. High levels of iron can induce a manganese deficiency and vice versa.

Application

Manganese availability decreases with increasing pH. Therefore Mn levels should be monitored according to soil tests and field pH before making an application decision. Note from the graph on the right, that if soil pH determines appropriate level of soil test Mn. If above acceptable level, or even slightly below, it is recommended that the crop should be monitored using tissue testing between first square and first bloom and foliar Mn can be applied if a deficiency is confirmed. Multiple foliar applications of Mn are recommended because there is only limited movement of Mn from the old to new leaves. Small amounts of Mn can also be added to starter fertilizer applications or as an impregnation component. 

Applying Mn above 5lb/A in a single application is not economical. Build soil Mn slowly and monitor the cotton crop through tissue testing and correct any deficiencies with foliar Mn.

Relationship between pH and manganese availability

(Maintain soil test manganese levels above the line to help avoid Mn deficiency)