As this is being written, weather forecasts are calling for a wintry mess including ice. Here’s hoping everyone is safe and sound with electricity. This promises to be a challenging year for crop and livestock producers with commodity prices. The next few weeks will focus on several items that can improve efficiencies by minimizing costs and optimizing output. The term “optimizing” output is used because maximizing production seldom results in maximizing profits per acre. Today’s topic concerns the value of soil testing for pH and nutrients.
Fertilizer costs make up a major portion of input costs, especially for grass crops such as corn, wheat, and grain sorghum. Soil pH plays an important role in many aspects of crop production. While soil testing has become much more common over the last two decades, there are still producers who seldom if ever soil test, some who occasionally soil test, and some who regularly test but ignore certain tests. So what are we discussing with soil testing?
With precision farming technologies, grid sampling, associating a group of samples with specific locations to develop maps of nutrient variation are possible. Depending on the extent of field variation, they may be of value. A producer won’t know till they test. It is possible to decrease fertilizer use and variably apply nutrients to optimize yields. As a side note, with technology such as Green Seeker, nitrogen application rates may be determined on the go and variably applied without a soil test. The other option is bulk sampling where a group of samples is collected across a field. This may be adequate if the field is fairly uniform and is better than nothing. And if a producer has completed a recent sampling, it may not be necessary to sample for many nutrients and pH every year depending on the results and the keeping of adequate yield records to determine nutrient uptake.
What testing is most beneficial? If you farm in higher pH soils you can ignore this but if you farm many of the soils in the southern part of the area, especially sandier soils, pH is critical to gauge soil acidity. Low pH soils can result in significant yield loss for a number of reasons, including:
• Legumes like soybean and alfalfa won’t nodulate and be nitrogen deficient.
• Many herbicides are rendered ineffective at lower pH resulting in decreased weed control.
• Nutrient availability is affected at pH extremes which can result in decreased yield, plant susceptibility to diseases and stress, and in certain instances toxic level of nutrients and other compounds.
• Acid soils lose their ability to hold onto cations such as potassium, zinc, iron, calcium and magnesium which makes fertilizing more difficult.
• Low pH also favors plant diseases directly and indirectly. And it changes the overall soil biological part of the ecosystem which can have negative effects on plant growth.
• Certain crops root systems are extremely sensitive to aluminum which can be present at low pH and significantly damage root systems.
• Low pH can be corrected with lime which while not cheap pays for itself. And for the beneficial effects of liming to occur, you need as much time as possible between lime application and planting, preferably nine to twelve months.
Next week the benefits of nutrient testing.