Submitted to: Transactions of the ASABE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/27/2009
Publication Date: 1/14/2010
Citation: Ortiz, B.V., Hoogenboom, G., Vellidis, G., Boote, K., Davis, R.F., Perry, C. 2009. Adapting the CROPGRO cotton model to simulate cotton biomass and yield under southern root-knot nematode parasitism. Transactions of the ASABE. 52:2129-2140. Interpretive Summary: The southern root-knot nematode (RKN) is the most significant pathogen of cotton in the USA. The extent of yield losses are usually not known until after harvest, but the potential yield reduction can be estimated before planting by using crop simulation models. The main goal of this study was to adapt the Cropping System Model (CSM)-CROPGRO-Cotton for simulating growth and yield of cotton plants infected with RKN. Two possible ways that damage could be caused by nematodes were modeled: (i) nematodes causing plants to direct nutrients to feeding the nematodes rather than producing cotton fiber, and (ii) nematodes causing a reduction of root length and root density. The model was calibrated using data collected in 2007 from a long-term study which had plots with three levels of drought stress and high or low nematode levels (created by having fumigated and non-fumigated plots in each drought level). Our simulations indicated that the amount of leaf area, total plant biomass, boll weight, and seed cotton weight (weight of cotton lint plus seeds) decreased with greater nematode population levels, and the combination of high nematode population levels and severe drought stress was the most harmful. The model predicted biomass 6% to 18.4% above the actual biomass and seed cotton weight within a range of -11.2% below actual to 2.7% above actual weights. Seed cotton weight losses associated with RKN infection increased with the level drought stress (9%, 20% and 18% for the low, medium and severe drought stress). The results showed the potential for using the CSM-CROPGRO-Cotton model to account for root-knot nematode damage and simulate the resulting yield reduction. However, further model evaluation might be needed to adapt the model for use in different environmental conditions and management practices.
Technical Abstract: Cotton (Gossypium hirsutum L.) yield losses by southern root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] (RKN) are usually estimated after significant damage has been caused. However, estimation of potential yield reduction before planting is possible by using crop simulation models. The main goal of this study was to adapt the Cropping System Model (CSM)-CROPGRO-Cotton for simulating growth and yield of cotton plants infected with RKN. Two hypotheses were evaluated to simulate RKN damage: (i) RKN acting as a sink of soluble assimilate, and (ii) RKN inducing a reduction of root length per root mass and root density. The model was calibrated and adapted using data collected in 2007 from a long-term study having split plot design, replicated six times, with drought stress levels assigned to the main plots and fumigation levels assigned to the subplots. The fumigation treatments were used to create various levels of RKN population densities. The model was adapted by coupling the RKN population to the removal of daily assimilates and decreasing root length per unit mass. The assimilate consumption rate was obtained after minimizing the error between simulated and observed biomass and yield components for the limited drought stress-non-fumigated (1-) treatment. Different values of root length per unit root weight (RFAC1) were used to account for early symptoms RKN damage on LAI and vegetative biomass under the non-fumigated-drought stress conditions. After model adaptation, the simulations indicated that LAI, total biomass, boll weight and seed cotton decreased with elevated RKN population. However, the combination of high RKN population-severe drought stress was the most harmful. The lowest RMSE of LAI simulations occurred for the non-fumigated treatments under medium and severe drought stress, 0.71 and 0.65 m2 m-2 respectively. Biomass was simulated with a prediction error within a range of 6% to 18.4% and seed cotton within a range of -11.2% to 2.7%. Seed cotton weight losses associated with RKN infection increased with the level drought stress (9%, 20% and 18% for the low, medium and severe drought stress). The results showed the potential for using the CSM-CROPGRO-Cotton model to account for RKN damage as well as simulate yield reduction. However, further model evaluation might be needed to evaluate the values of assimilate consumption and root length per unit weight for different environmental conditions and management practices.