Understanding Functional Relationships Affecting Growth and Quality of Field Grown Leaf Lettuce in the Greenbelt of Buenos Aires, Argentina

Earlier studies in the horticultural production area around Buenos Aires (Argentina) indicated that field grown leaf lettuce fertilised with 150 kg N ha-1 accumulated NO3-N in the leaves up to concentrations well above the reference limits adopted by European countries. Previous studies also showed that the planning of sowing dates and a sound management may help overcome nutritional quality problems, reduce risks of environmental pollution and increase the efficiency of the system. As an aid to crop planning, a management decision-tool is being developed following a modelling approach to predict growth and quality (i.e. NO3 content) of field-grown lettuce in the area. The model was conceptually based on that of Seginer et al. (1997) for greenhouse lettuce, in which a negative correlation between C assimilates and NO3 concentrations in vacuole is used. The first step in the development of the model was to asses the simplest (and satisfactorily accurate) approach to model growth of a leaf lettuce crop under field conditions relying on few, easily available parameters, and then to identify source-limited conditions along the year. The model was calibrated with data from several experiments in the area. The model predicted crop (R2 = 0.97) and plant (R2 = 0.98) growth quite accurately when compared with independent data. A first analysis revealed that since leaf lettuce does not need to form a ¿head¿ to be commercially mature, growth can be fairly described by a simple exponential model. NO3 contents varied widely (from 990 to 7590 ppm) under different growing conditions, suggesting that there is room to model the interaction of factors creating source-limited conditions that eventually lead to NO3 accumulation in leaves.