Home Discussion Forum Nutrient Management Nitrogen and organic matter

This topic contains 4 replies, has 3 voices, and was last updated by Profile photo of Fabian Fernandez Fabian Fernandez 2 years, 1 month ago.

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  • #889
    Profile photo of Fabian Fernandez
    Fabian Fernandez
    Participant

    How important is soil organic matter to supply nitrogen to the crop?

  • #907
    Profile photo of Jerome Lensing
    Jerome Lensing
    Participant

    The link below provides an excellent summary of the value of OM.
    http://agwaterexchange.com/2017/03/08/value-soil-organic-matter/

    The mineralization of the soils organic matter is very weather dependent. Various states have incorporated OM values in the N suggestions. With MRTN method that Minnesota utilizes for N suggestions, the equation provides a range of suggested rates. In fields that have higher OM levels, one may consider the lower suggest N rate vs. field with lower OM levels, consider the higher suggested N rate. Fields that you have yield history from yield monitor data, evaluate how various OM levels maybe influencing corn yields if a flat rate of nitrogen has been applied across the fields. When soil sampling dividing a field into zones by soil type, OM, etc. may allow for improved N suggestion.

  • #910
    Profile photo of Fabian Fernandez
    Fabian Fernandez
    Participant

    We are looking at mineralization potential (under ideal conditions in the lab) of soils across Minnesota and also quantifying mineralization under field conditions. In general there tends to be a good relationship between mineralization potential and the amount of organic matter: greater organic matter=greater mineralization. However, in the field the relationship is not as clear because as Jerome mentioned, wheater (and other conditions) impact the amount of mineralization one can expect. In general corn after corn fields have less net positive mineralization than corn after soybean fields. In general averaged across many soils, locations and years I have seen that in Minnesota one can expect about 130 lb N/ac from mineralization and produce about 115 bushels of corn/ac  from the mineralized N. Of course there is a large spread in mineralization; in some sites I have seen around 50 lb of N/ac and in others the soil supplied all the crop needed.

  • #942
    Profile photo of Todd Prill
    Todd Prill
    Participant

    Are fields with a soil organic matter levels over 3% or have a majority of nitrogen supplied from organic sources (rotated legumes or manure) the most likely candidates to not see a yield response of more than 50 lb of N/ac?

  • #943
    Profile photo of Fabian Fernandez
    Fabian Fernandez
    Participant

    Todd, in general the answer to your question is yes. The more soil organic matter or supply from organic sources you have the less nitrogen fertilizer is needed for the crop. That is the reason why, for example when using the N rate calculator (http://cnrc.agron.iastate.edu/), corn-corn needs more N than corn after soybean. For Minnesota that comes to about 40 lb N/ac. If you are planting corn after a good established alfalfa stand the amount of N needed for corn the first year can be as low as no N. The reason I say at the beginning “in general” is because in natural systems the “norm” does not mean “always”  as there are many variables in addition to mineralization that can impact nitrogen availability and the response of the crop.

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