MIMYCS.Moisture, a process-based model of moisture content in developing maize kernels

Maize grain moisture content during maturation and post-maturity dry-down are very important factors influencing harvest and post-harvest management, and the technological and safety of maize grain: it influences the harvest timing and the consequent drying process and drying costs, the feeding activity of some maize borers, and the development of toxigenic fungi. Thus, an improved understanding of the process of moisture loss during maize grain development would allow: i) to assess risk regarding weather factors that may impede harvest timing, ii) to evaluate the costs associated with an increased need for mechanical drying, iii) a better understanding of maize development during the field phase and the relationships with insect pests and diseases development. Development of maize in the field can be partitioned into three phases: i) lag phase, ii) grain filling and maturation drying, iii) and post-maturity dry-down. The lag phase is characterized by a rapid increase in moisture content. During the grain filling and maturation drying phase moisture content decreases almost linearly until the reaching of physiological maturity. During post-maturity dry-down, moisture content decrease primarily due to water loss from the kernel. Starting from the available knowledge about maize seeds development and maturation, a simulation model was developed to simulate moisture content of maize grain during maturation and in field post-maturity dry down. The model was developed according to the information found in literature: in fact it is known that while during the second phase of development moisture decrease is due to a displacement of water based on an exchange between dry matter and water through the pedicel, after physiological maturity pedicel tissues cease to function and dry-down occurs primarily by evaporative loss from the kernel itself, mainly under the influence of temperature and relative humidity. Thus, the model was developed as composed by two main components: i) a component simulating moisture content during grain filling, and ii) a component simulating moisture content during post-maturity dry-down. The first phase was simulated as an exponential decay process in which moisture content decreases proportionally to its value and depends on the duration of the maturation process. The second phase was simulated following information coming from the industrial drying of maize grain where the process of grain drying has been studied in conditions of constant temperature and relative humidity: during the drying period, the moisture removal rate is inversely proportional to the moisture to be removed, which is given by the difference between actual moisture content and equilibrium moisture content (tendency of a stored product toward a water content value that is controlled by the ambient environment). Parameters required by the model are: i) duration of lag phase, ii) degree-days to flowering and iii) to physiological maturity, iv) moisture at physiological maturity. Inputs required are air temperature and relative humidity. The models were implemented in a software component (MIMYCS.Maize) composed of discrete model units. This is one of the models of the framework MIMYCS (Maize Infection and MYcotoxin contamination Simulator – FP7 Marie Curie Project) being developed at the European Commission JRC for the simulation of mycotoxin contamination in grain maize. The component based software implementation of MIMYCS models can be easily re-used in any framework based on the Microsoft .NET platform, and it was used in the BioMA platform of the European Commission. The model was tested using data of maize grain moisture during maturation (Figure 1) and post maturity dry-down (figure 2) from literature and field surveys.Results showed that the model was accurate in the explored conditions, reproducing correctly the loss of moisture during maturation and dry-down.

JRC.H.4 - Monitoring Agricultural Resources