Soil Fertility--The Solution is in the Plant and Soil
Two items came to my attention this week. They both reinforce the importance of the soil as a reservoir for nutrients that are needed for high soybean yields.
The first item is an article entitled “Research lacking to back claims for foliar-applied fertilizers” that appeared in the June 22, 2016 issue of Delta Farm Press. The title of the article summarizes its content, but a few of the more pertinent points are presented here.
● Producers who are considering the application of foliar-applied fertilizers should ask 1) what is the frequency of crop response; and 2) what is the expected average yield increase, and will this increase pay for the applied product? The answers to these questions should be based on valid, verifiable research.
● Recommendations to producers for foliar application of nutrients are usually based on tissue analysis. The tissue values that are used to define nutrient sufficiency or deficiency 1) are not always based on research; 2) there is inadequate published information that defines the relationship between crop yield increase and the tissue values for many nutrients; 3) there is inadequate information to define the exact nutrient concentration that is needed to verify a yield response to foliar feeding; 4) many of the cited critical nutrient concentrations are specific to a particular plant part and growth stage; and 5) there is not usually a single tissue nutrient concentration that can be used to define nutrient sufficiency or deficiency for the duration of the growing season.
● Oftentimes, the amounts of nutrients supplied by foliar-applied products are too small and may be applied too late to benefit crop performance.
● Micronutrient deficiencies are rarely observed, and there is limited research that verifies that significant yield benefits will be obtained from their application.
● Although foliar fertilizer application may be touted as having a low cost, this cost can become significant across applications and result in decreased net returns if an assumed yield increase is not achieved.
● University research has not found products that will out-perform the proven management practice of a sound soil fertility program.
The authors conclude that mid-to late-season foliar application of fertilizer nutrients to crops is likely not justified.
The second item is a thesis by Justin McCoy entitled “Soybean yield and biomass response to supplemental nitrogen fertilization” that presents the findings from research conducted under the direction of Dr. Bobby Golden at the MSU-DREC. The work that culminated in this thesis was supported by the MSPB as Project No. 57-2015. The major findings from this research appear below and in the Final Report.
● Even though soybean yield was significantly increased by adding N to both low- and high-CEC soils in this study, the increases were small (4.3-8.6 % and 3.7-5.9 bu/acre) and likely were not economical. These small yield increases were the result of more seeds per plant where N was added.
● Addition of N to soil in greenhouse studies had no positive effect on root growth parameters.
● Addition of N to soil in greenhouse studies resulted in large and significant reductions in number of nodules present on soybean roots.
Information in these cited items, as well as results from a veritable plethora of previous research and demonstrations (N fertility summary here) and the findings summarized in a previous blog on this website lead to this conclusion: There is neither a substitute nor replacement for a sound program of soil sampling and testing, followed by the consistent replacement of nutrients that are removed from the soil by a crop.
Click here for articles that provide detailed information about soil sampling and soil fertility subjects.
Composed by Larry G. Heatherly, July 2016, larryheatherly@bellsouth.net