ISSUE 8   July 2, 2009

PLANT ANALYSIS INTERPRETATION

Plant analysis or tissue testing is one way to determine whether a poorer growing area of a field is caused by nutrient problems. When the analysis is completed, interpretation of the results is important. It is most helpful to have analysis from a poor area and a good area. If values of all nutrients are similar, the cause of the problem is likely not nutritional. The values returned and the critical levels they are compared with a good interpretive tools for N, P, K, S, Cl for all crops. Values for Zn are valid for our four sensitive crops- corn, dry beans (not soybean), potato and flax. The rest of the micronutrient values are questionable. It is common to find nearly all micronutrient values near, below or slightly above the critical level, so to interpret the findings is nearly impossible. The exception to this is Fe, which is usually found to be very high since soil contains a great quantity of Fe and the sample leaves may not have been washed. Washing can lower K levels, so if Fe is suspected and the leaves are washed, the K values are not valid.

Copper has only been found to be helpful on low organic matter sands for small grains, and even then the frequency of deficiency is very low. On responsive sites, foliar sprays have not helped to alleviate a deficiency. Manganese (Mn) has not been found in the state outside of occasional greenhouse studies. Foliar treatment for Mn is generally about 2 lb/a Mn as manganese sulfate dissolved in water and has been found helpful in Mn deficiency-prone areas of northern IN, MI and ON, Canada. If you suspect a micronutrient deficiency, treat a very small area, wait a couple days and see if there is a noticeable difference in growth. Donít treat the whole field because you wonít know if the treatment was helpful or not.

 

LOSS OF N IN-SEASON

Heavy rains have been a part of living in the paradise of the Great Plains for a long time. Recent storms that dumped up to 8 inches of rain in the northeast and southeast part of the state inundated fields for up to two days. Rains above 2 inches can leach the rooting zone in sandy soils. Rains in the east, especially the Valley area that saturate a field of heavy clay soils for several days can result in nearly complete loss of N through denitrification. In sandy soils, if prospects for decent crop yields are present and the crop is not too far along, some supplemental N and perhaps S fertilization would be wise. Row crop sidedressing is a good plan in sands. Use of liquid products permits mixing of different fertilizers and avoiding broadcast application which can seriously injure the plants. In heavy soils, liquids may be the only choice since soil drying may be slow and deep placement of ammonia may not be practical. After heavy rains, anticipate loss and prepare to supplement N where needed. Sulfur loss is usually not experienced in heavy soils. Fortunately, the cost of N fertilizer is greatly reduced compared with last year.

 

SULFUR REMEDIATION OF CORN

I have had a flurry of calls lately now that corn is tall enough to evaluate and they all point towards S deficiency in coarser textured soils. This is not unexpected given the nature of the soils and the wetness of the fall/winter/spring preceding seeding. There are several options that might be considered.

Gypsum at about 50 lb/a or ammonium sulfate granules at 25 lb/a over the canopy. The gypsum is not as soluble as ammonium sulfate, but it is relatively low in salt and I have not seen it burn tissue at all in my experiences with it applied post. Ammonium sulfate might burn tissue due to salt/ammonia, although it is on the University of Georgia website as an option.

This would be applied by air or ground as a granular application.

A more preferred application would be dribbling, as previously described for N, ammonium thiosulfate at about a 3 gallon/a rate between the rows. DO NOT BROADCAST ammmonium thiosulfate! Ammonium thiosulfate is sometimes applied broadcast to canola to rescue a S deficiency, but canola has a very thick waxy cuticle, while corn has no protection. One way to help avoid any semblance of a broadcast application even in wind is to have the spray orifice near the boom, and drag a stiff hose from the drop tube. If any disruption of the spray occurs, it will be near the base of the plants.

Rainfall will be needed to achieve best efficacy of the application.

Dave Franzen
NDSU Extension Soil Specialist
701-231-8884
david.franzen@ndsu.edu


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