With most plant nutrients, it is always better avoiding deficiencies rather than remedying. This is because some yield losses may have already occurred by the time symptoms show up. Certain nutrients such as manganese can be an exception. Building up available manganese in the soil is difficult. Therefore if a manganese deficiency occurs in a field one year, it will likely reoccur each year, especially when responsive crops such as soybeans are grown. To avoid deficiencies, supplemental manganese may have to be provided each year.
Local farmers have to manage nutrients within the framework of economic, environmental and social constraints in Michigan. Profitability and environmental stewardship will require applying the right amount and conserving it, without losing most of it to the environment. Updated nutrient recommendations for Michigan are found in the MSU Extension Bulletin E2904 ‘Nutrient Recommendations for Field Crops in Michigan’.
Some options available for farmers to proactively avoid nutrient deficiencies include the following practices:
- Conduct routine soil tests to determine nutrient requirements of crops based on representative soil sampling and realistic yield goals. Refer to the soil sampling tips in Figure 1 to ensure that a representative sample is taken. Realistic yield goal should be the average yield of 4-5 preceding normal years, discarding any abnormally high or low yielding intervening years.
Even if soil-testing results are not available, farmers should have a good understanding of nutrient removal rates of different crops so that at least this amount is replenished every year in the form of fertilizer. Overall, corn removes more phosphorus (P) and less potassium (K) than soybeans.
A 150 bu/A corn crop removes 56 lbs/A P2O5 and 41 lbs/A K20, while a 40 bu/A soybean crop removes 32 lbs/A P2O5 and 56 lbs/A K20. The P and K fertilizer can be applied every year or every two years. If it is done every two years, then a combined two-year corn and soybean removal rate of 88 lbs/A P2O5 and 97 lb/A K20 should be applied. Advanced soil sampling schemes such as grid sampling are more effective in preventing nutrient deficiencies.
- The P and K content of manure applications should be taken into consideration along with soil tests to determine if and when more synthetic fertilizer nutrients are required. On average 80 percent of the P and 100 percent of K in the manure will be available in the first year of application. A lab analysis of the manure will provide the proper nutrient content and credits.
- Michigan soil test data show that nearly 65 percent of Michigan farm fields contain adequate P levels. However, only 20 to 25 percent of fields contain adequate K levels. Therefore, K fertilizer may provide a higher return to investment compared to P fertilizer.
- The soil test should indicate if lime is needed to rectify soil pH. Correct soil pH (6.5-6.8) is critical for nutrient availability in the soil (Figure 2). Long-term experiments in Michigan have revealed that lime (when applied according to a soil test recommendation) will improve crop yield and generate a good return for investment.
- Implement the “Four Rights” (4R) nutrient stewardship concept namely the right source, right rate, right time and right placement as a guide to fertilizer practices on the farm. When the 4R’s are integrated with the site-specific factors of crop, weather, soil, labor and logistics, farmers will be able to achieve the desired economic, social and environmental outcomes from fertilizer practices, sought by all stakeholders in the food system.
- The right timing and right placement are critical for nitrogen and phosphorus management because of their potential losses to the environment. Split application of nitrogen and the use of nitrification inhibitors are vital to avoid nitrogen deficiencies during the growing season. Phosphorus is generally immobile in the soil.
Therefore applying phosphorus as a starter fertilizer band to the side and below the seed is the most efficient placement method to avoid phosphorus deficiencies. Likewise fall potassium fertilizer applications on sandy soils with low organic matter are discouraged because of potential leaching losses.
- Be aware of the common macro and micronutrient deficiency symptoms. The most mobile nutrients within the plants are nitrogen, phosphorus, potassium, and magnesium. Because of their rapid translocation to new tissues, their deficiency symptoms appear first in older leaves and then spread throughout the plant.
The relatively immobile nutrients are manganese, sulfur, copper, iron, zinc, calcium, boron and molybdenum. Their deficiency symptoms first appear in new growth as they do not readily translocate within the plant. Macro nutrients are needed in large qualities so they are best applied to the soil. Micronutrients are needed in small qualities and they can be both soil and foliar applied.
- Plant tissue analysis is generally not practiced as diagnostic tests because of the short turnover time. Tissue testing is, however, the most widely used for nutrient recommendations on perennial crops such as established orchards.
There are some exceptions such as sulfur where soil testing is least reliable. In this instance a tissue test is the recommended practice. However with the advent of rapid tissue analysis techniques and modern instrumentation it may become more feasible in field crops in the future.
Nutrient sufficiency ranges have been established for most field crop species. Typically the nutrient ranges are established for a specific plant tissue at a specific growth stage (See MSU Extension Bulletin E486 Secondary and Micronutrients for Vegetable and Field Crops). Other diagnostic tests such as chlorophyll meters and end of season corn stalk tests are available as tools to avoid nitrogen deficiencies on corn.