Simulation of nitrogen behaviour in soils

The problem: In the majority of soils most of the nitrogen is in organic compounds and only a small percentage is present in inorganic compounds. Depending on the type of decomposition process of the organic matter, organic nitrogen is mineralized into ammonia or inorganic nitrogen is immobilized by transforming it into organic nitrogen. The inorganic soil nitrogen is mainly present in the form of nitrate and ammonia. Ammonia may be transformed to nitrate by nitrification while nitrate may be transformed to volatile nitrogen compounds. All these processes are carried out by soil micro-organisms and consequently are influenced by temperature, moisture, pH and aeration of the soil. Since both the turnover rate between the organic, ammonium, nitrate and elementary form of nitrogen is very high and the influence of external factors like temperature and precipitation considerable, it is hardly possible to estimate the inorganic nitrogen available for plants during a growth season, on the basis of chemical and physical experiments at one certain moment. An alternative approach of attaining a reliable estimate would be to use the information available in literature about the separate microbial processes. Then the problem is to integrate the knowledge about the separate processes into a larger model where all the involved processes are acting simultaneously. A unique opportunity to solve this problem is provided by the modem digital computer simulation techniques. The ‘Continuous System Modeling Program’ (CSMP/ 360), developed for the IBM 360 series of machines, has proved t be very suitable to simulate biological processes. Information about CSMP is given in the ‘User’s manual of the system / 360 Continuous System Modeling Program’...