Agronomic Effects of Different Rock Powder Rates Associated with Irrigation Water Depths: Potential for Lettuce ( Lactuca sativa L.) Production

Lettuce is among the 10 most valued vegetables for fresh consumption in Brazil. The use of rock powder in lettuce crops for soil acidity correction or fertilization is an option for reducing production costs. In this context, the objective of this study was to evaluate the effects of rock powder rates mica schist and irrigation water depths on the development and production characteristics of lettuce crops. The study was conducted in the experimental area of the State University of Goiás, using pelletized seeds of the lettuce cultivar Crespa Vanda. A randomized block experimental design with four replications was used, in a 4 × 4 factorial arrangement composed of four irrigation water depths: 50%, 75%, 100%, 125% of crop evapotranspiration (ETc), and four rock powder rates: 6, 8, 10, and 12 tons per hectare (t ha −1 ), associated with mineral soil fertilizer application, totaling 16 treatments and 64 experimental plots. The variables evaluated were plant height, stem diameter, number of leaves, head diameter, total fresh weight, commercial fresh weight, leaf area index, useful leaf area, estimated yield, chlorophyll a, chlorophyll b, and water use efficiency. The data were subjected to regression analysis and principal component analysis. The variables studied exhibited predominantly low to medium coefficients of variation in all treatments, confirming the homogeneous conditions and precision of the study. The treatment with the highest rock powder rate (12 t ha −1 ) provided the best results regarding agronomic effects for all lettuce crop variables evaluated. This rate provided better plant growth and development, resulting in improved response for production variables that are agronomically and economically relevant. The highest water use efficiency was found for the water depth of 50% ETc; however, the best lettuce production results were found for the irrigation water depth of 100% ETc. This water depth highlighted the strong correlation of commercial and total fresh weights with commercial and total production, as they are production components of the crop.