Project Details - Full Facts for Selected Year
Information and Results
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Kansas is a naturally phosphorus (P) deficient region. The soils of Kansas contain significant quantities of P, but it is generally present in relatively unavailable or slowly available forms. In the 50 years after original settlement, P availability decreased and crop yields gradually declined. Early work linked this trend in reduced yield to a decline in soil organic matter and nitrogen (N) availability. The key role of P mineralized from soil organic was yet to be realized. Workers in Iowa later showed that up to 50% of the P utilized by crops from soils came from mineralization of soil organic matter (OM). Thus as soil OM declined, the release of both N and P through mineralization would decrease.
The traditional soil test based fertilizer recommendations used in Kansas for the past 75 years have focused on economical crop response to P with little concern over impact of the recommendations on soil test (ST) levels. As a result, P applications are generally lower than crop removal at most ST levels, and ST levels equilibrate at levels below those considered adequate to meet the nutrient needs of most crops. The most recent surveys of ST labs working in Kansas show that over half the soils tested in 2010 had P ST levels below the currently used critical level of 20 ppm ST P, and crops would be expected to respond to direct applications of P (IPNI, 2010). Discussions with many Kansas soybean growers over the past five years have indicated that many growers believe soybeans will not respond to direct applications of P, especially starter fertilizer, and fertilizer is applied with the intent of supplying the nutrients needed for the corn or wheat grown in rotation with soybeans. The soybeans in the rotation are normally not fertilized directly, but are expected to benefit from an increase in soil fertility, which may or may not occur. Especially when application rates on one crop, are substantially below removal from two.
Recent work in Kansas would suggest that these general beliefs are not correct, and failure to fertilize soybeans directly at low soil test levels is likely resulting in lower yields for many farmers. An on-going study initiated in 2006 and conducted at three locations in Kansas has addressed this issue of direct vs. residual response of soybeans. At the NC KS Experiment Field near Scandia, under supplemental irrigation, high yielding soybeans grown at low ST P levels, have consistently responded to an annual application of P, in addition to rotational applications applied to corn the previous year. A similar experiment conducted at the ECK Experiment Field near Ottawa though, has shown very different results. At much lower yield levels, but similar soil test levels, no response to the additional P applied to beans has been seen. This suggests that responses are likely to be more soil and region specific than previously believed.
1. Quantify the response of soybeans and common crops grown in rotation with soybeans to phosphorus at varying soil test levels in Kansas. This process is commonly referred to as soil test correlation and calibration, and defines the soil test level above which no economic response to fertilizer would be expected, and the rate of fertilizer needed to optimize yield at soil test levels below the critical level.
2. Determine at what soil test levels soybeans respond to direct fertilization as opposed to residual fertility or multi-year/ rotational fertilization.
3. Determine if the use of starter fertilizer, particularly surface band applied starter fertilizer, will enhance soybean yield when used alone or in combination with broadcast applications of phosphorus fertilizer.
4. Examine the potential for response of Kansas soybeans to Sulfur, Zinc, Manganese, Iron and Boron and the effectiveness of soil tests at predicting potential response.
Progress of Work
Broadcasting P on soil with 0-6in. Mehlich-3 soil test level has increased yields. Band applying 20lb/a P did not increase yield over broadcast alone however. More sites may have responded to applied P in 2012 if water was not limiting. Applications of S, Fe, Mn, Zn, and B did not increase yield in these experiments.
Final Project Results
Benefit to Soybean Farmers