TOMATO PLANT GROWTH DURING ESTABLISHMENT AS AFFECTED BY ROOT ZONE TEMPERATURE UNDER COLORED MULCHES

Abstract

Soil warming is one of the benefits associated with the use of plastic film mulches. However, under high temperature and intense solar radiation, further warming of the soil may negatively affect plant growth during establishment. Greenhouse-grown tomato seedlings were transplanted to the field and exposed to a range of root-zone temperatures (RZTs), resulting from growing the plants in different seasons and by utilizing colored mulches that differed in their soil-warming ability. The objective was to determine the relationship of RZT to plant growth during the first 28 days after transplanting (DAT). Experiments were carried out in Fall 1999, Spring 2000, and Fall 2000. Black (n = 2), gray, red, silver (n = 3), and white (n = 2) mulches, and unmulched soil were used. RZT under mulch was measured with copper-constantan thermocouples placed 10 cm below the soil surface. Irrespective of the season, the highest mean RZT (from planting to 28 DAT) occurred under black mulch, and the lowest under white mulch. The mean RZT under black mulch was 4°C greater than under white mulch. In the spring season, vegetative top dry weight (DW) at 28 DAT was higher with increasing mean RZTs. In the fall seasons, vegetative top DW at 28 DAT decreased with increasing mean RZTs. Pooling data from fall and spring seasons, vegetative top DW at 28 DAT was found to fit a quadratic relationship with RZT. From this relationship, optimal RZT for vegetative top growth was calculated to be 25°C. Vegetative top growth during the first 28 DAT was correlated with subsequent vegetative top growth and fruit yield. In conclusion, RZT under colored mulches significantly affected tomato plant growth during the establishment period. INTRODUCTION In the United States, commercially produced fresh market tomato (Lycopersicon esculentum Mill.) are commonly grown on plastic film mulch (Lamont, 1993). The benefits associated with use of plastic mulches include higher yields, earlier harvests, improved weed control, and increased efficiency in the use of water and fertilizers. Increased plant growth, yield and earliness have been attributed to the soil-warming effect of mulches at northern latitudes (Lamont, 1993; Wien and Minotti, 1987). Colored plastic film mulches influence plant growth and yield through modification of the light environment around the plant. Red mulches reflect far red light, resulting in a modified red:far red ratio in plants (Decoteau et al., 1988; Kasperbauer, 1992). Thus, in addition to the light effects of mulches, possibly colored mulches modify RZT in ways that may influence plant growth during the establishment period. Colored mulches have also been shown to affect plant growth and yield by modifying insect behaviour (Schalk and Robbins, 1987; Csizinszky et al., 1995). Under conditions of high ambient temperature and high solar radiation, plants often grow poorly and produce low yields because mulches warm the soil to temperatures that may be deleterious to plant growth (Miller, 1986; Tindall et al., 1991; Diaz-Perez et al., 2002). Root-zone temperature is important in plant growth and development because it affects physiological processes in roots such as uptake of water and nutrients (Cooper, Proc. XXVI IHC – Transplant Production and Stand Establishment Eds. C.S. Vavrina et al. Acta Hort. 631, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA) 12