Development of an expolinear growth model for pak-choi using the radiation integral and planting density

Abstract

The objectives of this study were to develop a growth model of pak-choi using an expolinear function and to estimate the effect of the radiation integral and planting density on the crop growth rate. The growth and yield of hydroponically grown pak-choi (Brassica campestris ssp. chinensis) were investigated at four different planting densities (27, 33, 44, and 67 plants/m2). The shoot dry and fresh weights per m2 increased with increasing planting density and could be expressed as expolinear functions based on the daily photosynthetically active radiation (PAR). A linear relationship was observed between the shoot dry weight and fresh weight, regardless of the planting density. The maximum crop growth rate and light use efficiency (LUE) increased with increasing planting density, but the lost daily PAR integral decreased. The maximum relative growth rate was not significantly different among the planting densities. Using the relative growth rate per the daily PAR integral and LUE, an expolinear growth model of pak-choi was developed. The measured and estimated shoot dry weights exhibited strong agreement with Y = 1.010·X (R2 = 0.982***) using the PAR and leaf area index as inputs. The expolinear growth model was determined to be useful for quantifying the growth and yield of pak-choi in controlled environments.