Comparison of developing WOFOST to model growth between typical fruit (chili pepper) and leafy (Chinese cabbage) vegetables

Most existed crop modelling studies are mainly cereal crops. Vegetables, the most economical and nutrient-dense crops, recieves insufficient attention, particularly on nutrient-uptake predictions. In open-field vegetable systems with shallower roots, shorter lifespan, and higher nutrient requirements, it is even more challenge to minize water pollution from fertilizers. To ensure both food and environment security, there is an urgent need of precise vegetable models to optimize productivity against fertilizer usage.

We adapted the WOrld FOod STudies (WOFOST) crop growth simulation model for chili pepper (Capsicum annuum L.)  and Chinese cabbage (Brassica rapa L.) to support better fertilizer management under various climate and soil conditions. We conducted field experiments with six various fertilizer strategies (etc., mixed synthetic and organic fertilizers, denitrification products, and slow-control-release fertilizers) in southwestern China from 2019 to 2021. In total about 20 parameters relevant to physiological development, dry matter accumulation, photosynthesis, and nutrient uptake were measured and used in model adaptation.

Our study shows that it is possible to model chili pepper’s growth without changing much from the WOFOST-generic model structure. We provide solutions by adapting user-defined developmental stages to mimic the growth from transplanting to fruiting and subsequently ripeness. As for WOFOST-Chinese cabbage, we further modify the phenological module to mimic the special vernalization habits of Chinese cabbage. Additionally, we design a new data re-analyzation method for accurate biomass partitioning predictions. Overall, both WOFOST-Chili and WOFOST-Chinese cabbage models show good model performance on biomass assimilation (rRMSE = 0.23/0.17 for chili/cabbage leaf dry weight; rRMSE = 0.06/0.17 for chili/cabbage storage organ dry weight) and nutrient uptake (rRMSE = 0.46/0.29 for chili/cabbage leaf N amount; rRMSE = 0.12/0.41 for chili/cabbage storage organ N amount). Besides, an improved leaf area index (LAI) simulation is found in WOFOST-Chinese cabbage (rRMSE = 0.11) than WOFOST-Chili (rRMSE = 0.76).

These findings improve our understanding of yield-nutrient interactions within crop models, provide insights on expanding application of original-designed-for-field crop models to different vegetable versions, also call for a refined dynamic nutrient simulation flow within soil module to evaluate mitigation effect of expanded fertilizer strategies under climate change.