Forms of Nitrogen in the soil
Nitrogen (N) availability is the main determinant for plant development worldwide. This nutrient is supplied either by fertilization or by the mineralization of organic matter. The presence of N in the soils is usually reported as total N, which includes inorganic N (nitrate and ammonium) and organic N. Inorganic nitrogen is directly available for plant uptake, but organic N first needs to be mineralized by soil microbes and transformed into inorganic N. Although in many agricultural practices it is common to measure inorganic N, the concentrations of inorganic N can change within a day as a result of microbial activity in organic matter, increasing or decreasing its concentration, which generally makes it difficult to measure this parameter accurately. Total N can provide an insight into the soil quality status and is ideally combined with additional soil indicators to estimate plant-available N more accurately. For this reason, AgroCares released expanding its services a new parameter: Potential Mineralizable Nitrogen (PMN).
Potential Mineralizable Nitrogen
PMN estimates the potential of soils to supply N available for crops via mineralization during the growing season. PMN is determined by three factors that are included in the simulation models: weather, soil texture and organic matter. PMN is highly dependent on the weather (soil moisture and temperature variations), so its value can be constantly recalculated based on the weather forecast. Soil texture is key as clay particles protect organic matter from mineralization, which affects the capacity of the soils to release plant-available N. Lastly, organic matter quality determines how much N is eventually released for plant uptake.
This new indicator PMN provides a more accurate description of the actual N that the soil microorganisms will naturally supply. In this way, based on the PMN value, decisions can be made regarding the application of organic fertilizers to increase microbial biomass and organic N in addition to regular N-fertilization. For instance, if your PMN is low, that means that the soil will not be able to supply enough N for good crop development. Thus, applications of fertilizers will be crucial to obtain adequate yields. If PMN is high, then the soil can naturally supply N to the crops, thus fertilization will only be necessary to replenish what the crop takes up. Additionally, if PMN is low, management practices can be targeted to enhance it for the next seasons. For that, the use of manure or leaving the crop residues on the field is recommended, as well as conservative management practices that favour the build-up of soil organic matter and PMN (e.g. reduced tillage and cover crops). Overall, this enables better and informed decision making for farmers to manage their N fertilization more efficiently and sustainably.