Northeast - 5/1/08

Why don’t soybeans react to fertilizers?

They do; just not as dramatically as other crops. One reason is that soybeans often follow corn, and corn leaves a lot of K behind in the stover. It’s one of the first nutrients released as the stover decomposes. A lot of other problems in soybeans are related to K levels. Aphids congregate wherever plants are most K-deficient. In general, K helps the plant do the best it can to resist pests and diseases, including cyst nematodes and rust.

-- Dr. Tom Bruulsema, IPNI

Tips for more effective fertilization. This series examines a few tips for making the most of your fertilizer dollar.

Keep soil pH in line – soils that are too acid reduce the effectiveness of many nutrients.

-- Dr. Scott Murrell, IPNI

Sulfur Fertilization Rates are Difficult to Predict Because of In-Field Variability

Of the four major soil nutrients applied as fertilizers, (i.e. N, P, K, and S) S availability is one nutrient that is more difficult to assess due to large spatial variability within a field. Nitrogen, P, and K soil test results are more reliable to use when deciding on how much fertilizer to add. Because of this, many growers will base their S fertilization rate on which crop is grown rather than the soil test level of S. High S using crops such as canola and alfalfa receive higher rates of S fertilizer (e.g. 20 lb S/A) compared to lower S using crops such as wheat or barley (e.g. 5 to 10 lb S/A).

-- Dr. Tom Jensen, IPNI

K in cotton production

Potassium is an extremely important nutrient in cotton production. Bolls are major sinks for K. Thus, the need for K increases dramatically during early boll set. About 70% of uptake occurs after first bloom, and uptake peaks at about 3 to 4 lb K2O/A/day. Potassium deficiency may be expressed as a full season deficiency, or it may not appear until late season during the period of greatest demand. When a heavy boll load is set, the demand for K may exceed the ability of the soil and leaves to supply it, resulting in a late season deficiency. Mid-season foliar K fertilization can be effective in correcting late season deficiencies.

-- Dr. Mike Stewart, IPNI

Zinc is one of the most commonly deficient micronutrients for plants. Deficiency symptoms vary among crops, but are most commonly manifested as interveinal chlorosis of the younger leaves. Zinc fertilizers are commonly added to soil to correct deficiencies, but foliar sprays can also be effective in eliminating problems associated with low zinc.

-- Dr. Rob Mikkelsen, IPNI

Bermudagrass Fertility – N

The goal in bermudagrass production is to produce a quality feed source high in protein and total digestible nutrients and good N management can help. A ton of bermudagrass forage will take up approximately 45 lb N. So, a 7-ton yield in the southeast will require about 300 lb N/A. Nitrogen should be split-applied for best results. Typical recommendations suggest applying 60 to 100 lb N/A when the grass begins to green up, then an additional 60 to 100 lb following each hay cutting. For pasture, apply 60 to 100 lb N/A in the spring, then an additional 40 to 60 lb after each graze-down.

-- Dr. Steve Phillips , IPNI