Simulation of the effect of pruning and topping on cotton growth using COTTON2K model

COTTON2K, like most other cotton production models, does not always adequately represent local growth conditions owing to the fact that it fails to take into account some indigenous cultivation practices. For instance, pruning and topping, a common practice for cotton cultivation in China is not included in the model simulation of COTTON2K. The objective of this research therefore was to: (1) modify COTTON2K source code and slot pruning and topping simulation switch on to the model, and (2) calibrate and validate the modified COTTON2K model with field data from pruning and topping cultivation practice. First, field collected data in 2003 and 2004 were compared between the treatments, with and without pruning and topping, and the COTTON2K source code updated with the ‘pruning and topping’ switch. This was followed by the calibration and validation of the updated model with field data and simulation of the effect of pruning and topping on cotton performance. It was noted from field observations that pruning and topping reduced total fruit sites, but at the same time, increased retained boll number, possibly due to significant reductions in abscised fruit sites. Though total dry matter production dropped, more dry matter allocation to reproductive organs, however, enhanced higher cotton lint yield in the pruning and topping treatment. Results of the modified model simulation showed that growth in the number of main-stem node ceased after topping. Furthermore, there was more biomass allocation to reproductive organs, such as green and open bolls under pruning and topping. Coefficient of determination above 0.8 for most of the growth factors was obtained in the calibration and validation processes under pruning and topping, a strong indication of the level of success of the model modification.