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Reduce fertilizer rates and maintain yields

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Column by David Harrison

By David Harrison

The prices of fertilizers have increased at an astounding rate the last two years. With the decrease in commodity prices, fertilizer costs now may be the dominant factor in determining a profit. Efficient and wise use of fertilizers and the nutrients in the soil become important in determining your profit.

Let’s consider some points you should consider to make the fertilizer purchased and the nutrients in the soil most profitable. Soil testing is probably the most important step. If there was ever a year to use the reserves of Phosphorus (P) and Potassium (K) in the soil – this is it. To do this, a good soil test should be taken.

Make sure a large number of samples are taken from each field.  Do not sample a field or area of a field larger than 20 acres, especially if the different areas in the field vary a lot in yield or have been managed differently in the past (crops, manures). Consider using grid sampling if you are unfamiliar with the field’s past history. If you are mainly no-till, use a 4-inch deep soil sample.

Next, use the fertility in your soil. If you soil test P is 45 lbs/acre or greater and soil test K is 250 lb/ac greater, no additional fertilizer is required for that crop that year. You already have enough in the soil to take care of it. Why add fertilizer just to increase your expense?

If the soil test P is between 30 and 45 or the soil test K is between 200 and 250, use only a maintenance amount of P and K fertilizers. That is sufficient for maximum yields.

If you are in the low range for P and K (below 30 and 200), add the UK recommended rate of fertilizer or use row fertilizer to reduce the amount needed. This way, the fertilizer can be banded beside the row and improve the efficiency of use. Fertilizer rates can be reduced by one third to one half off that recommended for broadcast treatments.

Maintain a proper pH. The best pH for most crops is between 6.2 and 7.0. When in this range, fertilizers are used more efficiently. Phosphorus can be as much as 20-25 percent more available in this pH range as opposed to a pH in the 5 range.

Manures are an excellent source of fertilizers and are usually much cheaper than purchased commercial fertilizers. Good distribution and nutrient testing of manures are the keys to their use as fertilizers. They will usually build P levels and maintain K levels when used. The nitrogen (N) availability is somewhat unpredictable but good estimates can be made for the conditions under which the manure was used.

Potassium (K) fertilizer timing is important on crops when the vegetation is the harvested crop such as silage, hay or straw. The plant will take up more K than is needed for production if it is available for uptake. This is called luxury consumption. If vegetation is going to be removed, then K fertilizer should be applied before each crop. For example, if wheat straw is to be harvested, then K fertilizer should be applied before wheat and again before double crop soybeans. If growing alfalfa, K should be applied after the first harvest and again after the third harvest.

Nitrogen rates for grain cannot be changed with the present economics. However, sidedressing some of the N on poorly or somewhat poorly drained soils will improve nitrogen efficiency and rates can be reduced by 35 pounds per acre from preplant recommendations.