Modelling the effect of weather on moisture fluctuations in maize stalk residues, an important inoculum source for plant diseases

Maize residues on the soil surface are a major inoculum source of several fungal pathogens of maize. Because the moisture content of crop residues can greatly affect fungal survival and inoculum production, we studied the effects of rainfall and relative humidity (RH) on the moisture content in maize stalk residues on bare soil and on soil under a wheat crop at the heading stage (i.e., when the canopy provides the maximum soil cover). The moisture content of residues that were initially saturated and that were then placed on soil outdoors declined to a minimum value after approximately 32 h. On each of the following days and in the absence of rain, the moisture content showed a diurnal pattern with decreasing values between 08.00 and 18.00 h and increasing values between 18.00 and 08.00 h. The pattern was the opposite for vapor pressure deficit. A simple model was developed to predict the wetting-drying dynamics of maize stalk residues based on environmental conditions. The model has three compartments: (i) wetting of maize stalk residues during rain; (ii) drying after rain; and (iii) diurnal fluctuations in the absence of rain. The model was calibrated and then validated against independent data collected in Italy and France. Comparison of observed vs. predicted data showed no systematic deviations of model predictions from real observations, with R2 = 0.84 and standard error of estimates = 8.7%. The correlation concordance coefficient (=0.89) and model efficiency (=0.75) showed a satisfactory goodness-of-fit to the real data, with a slight overestimation (coefficient of residual mass = 0.11). The model should be a useful component of models for those plant pathogens, including Aspergillus flavus, Fusarium verticillioides and Gibberella zeae, that produce inoculum in maize residues.