Substrate formulation to improve vegetable seedling quality and environmental sustainability

The aim of this study was the development of growing media that could contribute to improve the environmental sustainability of vegetable nursery production. The reduction of chemical inputs needed by the growers was addressed by supplying a complete substrate, containing all nutritional elements for growing high quality seedlings. Three main factors were investigated: substrate pH close to planting soil values, fertilization (nitrate-ammonium ratio and phosphorus content) and biostimulant addition. Firstly, different pH were studied mainly for their effect on seedling quality and recovery time after transplanting. Secondly, the nutrient composition was considered for the potential influence on root development and plant firmness. Lastly, the seaweed biostimulant impact on nutrient absorption and chlorophyll content was exploited in order to support the plant to cope with reduced fertilizer availability. The trials were performed on a processing tomato variety in both nursery and open field stages. In the nursery phase, the measurements were taken twice in order to assess the effects of different growing media formulation on seedlings ready to transplant and on aged plants. Trial results of the first year were promising, showing a significant impact on the seedling quality in both ages, especially with respect to pH values, nitrate-ammonium ratio and biostimulant addition. In particular, the latter made possible a reduction of fertilizer amounts by 50% with no detrimental effects to the plant's quality. Finally, the pH effect was visible in the first 15 days after planting; pH substrate values had an effect on the dry matter accumulation in the field trial, showing that substrate pH values close to soil pH could improve the recovery speed after transplanting.