Soil fertility summary emphasizes need for soil testing
The MU Soil Test has been flooded with soil samples from early March. Spring is the time when normally the labs receives heavy loads of soil samples for testing. Even though fall sampling is ideal for farmers as it gives the starting point to plan for next year’s nutrient management plan, we have many who wait until spring to test their soils. The 2013 growing season was dominated by anomalous weather conditions for much of the spring and summer, and made it another challenging year for Missouri farmers. The cool, wet weather during April delayed spring tillage and planting opportunities across the state resulting in pushing behind the harvest dates. The severe winter weather conditions during the winter made it difficult to sample the fields until early March.
click image to zoom The soil fertility summary provides a valuable index of the soil fertility status of Missouri farmland and identifies broad soil fertility trends in the state. The trends in soil fertility status summary in the state for 2013 emphasizes the importance of soil testing (Fig.1 and Table 1). Out of the total of 17373 field crops samples tested by the MU soil testing labs in the state during 2013, about 26% tested very low to low in soil pHs (less than 5.3) indicating lime should be applied for economically viable crop production. Another 37% of the samples received tested medium in soil pHs (5.4 to 6.0) is likely to need lime to avoid profit loss. For example the desired soil pHs range for alfalfa and row crops is between 6.1- 6.5. The lower soil pHs will hinder alfalfa establishment and nodulation. The statewide trend in soil P indicated 42% of the samples tested low to very low, and P fertilizer is essential to avoid profit loss by crops. Another 24% of the P tests were medium (23 to 45 lbs of P/ac) indicating P fertilizer is required for economic crop production. The desired soil P levels for row crops, small grains, and alfalfa are 45 lbs/ac and for forages are 40 lbs/ac. The majority of soils (39%) in the state tested medium in soil K (111to 220 lbs/ac) and 16% tested low to very low (less than 110 lbs/ac) and indicating K fertilizer will be required to avoid profit loss by crops. Fertilizer response to high and very high P and K testing soils are unlikely. However, may need maintenance requirements at the high levels depending on the soil test K levels. In Missouri the soil organic matter (OM) tests are used to estimate N availability in soil. The N credit from soil OM varies depending on soil texture. A general rule of thumb is every 1% of soil OM in the soil will release about 20 lbs of N/ac for crop. Majority of the soils tested (47%) had medium levels of soil OM (2 to 2.9%). (Table 1).
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