Quantification of dynamics of soil-borne pathogens and their consequences for yield in crop rotations

In The Netherlands crop rotation experiments were performed that required a continuation over many years so that long term effects of treatments and rotations may build up. Usually, analysis of variance is performed on within year data or on data from the final years when treatment/rotation effects are maximal. In this thesis the scope is on rotation experiments in the presence of soil-borne pathogens. Instead of estimating the mean densities of these pathogens and the mean yields of the crops over the whole duration of the experiment, dynamics of the pathogens and yield were registered yearly. Two types of dynamical models were applied. In the first model the dependence of the final  (end of the season) pathogen density upon the initial density was represented by a monotonically rising function. The model was applied to an experiment on the dynamics of Pratylenchus penetrans in vegetable crops. In the second model with a Ricker type of functional relation between initial and final pathogen densities, the dynamics of Globodera pallida on 6 cultivars of potato was studied. In both models the pathogen density tended to a stable steady state in the long term. For this steady state an economic evaluation of crop rotations was made. In a third study potato tuber yield was predicted taking into account the presence of three nematode species and the fungus V. dahliae. Also the effect of abiotic factors such as pH and the P content of the soil were taken in consideration. Based on information theory the results of a large class of feasible models was combined by using a suitable method of averaging values of parameters of the different models. Moreover, this method also ranks the predictors with respect to their predictive power. In a fourth study, optimum designs of experiments on pathogen dynamics and yield loss were derived for one of the cultivars already tested in the second study. Furthermore, a measure for the efficiency of a design was introduced so that designs can be compared.