Effects of Calcium and Magnesium on Plant Growth, Biomass Partitioning, and Fruit Yield of Winter Greenhouse Tomato

Tomato (Lycopersicon esculentum Mill) ‘Trust’ was grown on rockwool with nutrient solutions containing two levels of calcium (150 and 300 mg·L–1) in factorial combination with three levels of magnesium (20, 50, and 80 mg·L–1) in Winters 1997 and 1998, to investigate the effects of calcium and magnesium on growth, biomass partitioning, and fruit production. Plants grown at 20 mg·L–1 Mg started to show Mg deficiency symptoms (leaf chlorosis) at 8 weeks after planting. The chlorophyll content of middle and bottom leaves increased with increasing Mg concentration in the nutrient solution. At 300 mg·L–1 Ca, total fruit yield and fruit dry matter increased linearly with increasing Mg concentration; marketable fruit yield and total plant biomass showed similar response but to a lower degree. At 150 mg·L–1 Ca, total plant biomass, fruit dry matter and yield peaked at 50 mg·L–1 Mg. The biomass allocation to fruit increased while allocation to leaves decreased with increasing Mg concentration. The Mg effects on total and marketable fruit yield were mainly due to its influence on fruit yield in the late growth stage. Incidence of blossom-end rot (BER) at 150 mg·L–1 Ca increased linearly with increasing Mg concentration while it was not affected by Mg concentration at 300 mg·L–1 Ca. For a winter greenhouse tomato crop, the appropriate Ca and Mg concentrations for tomato production appear to be at 300 and 80 mg·L–1, respectively. Greenhouse tomato production and consumption in North America has increased substantially in the last few years. The share of greenhouse tomato in the fresh tomato market has increased from 1% in 1990 to 16% today (DeGiglio, 2003). In North America, almost all the greenhouse tomatoes are produced with a soilless culture system, mostly on rockwool. Rockwool releases little or no mineral nutrients and has a very low buffering capacity. Precise management of plant nutrition has a much larger influence on greenhouse tomato production in rockwool than on soil-based tomato production systems. Effects of calcium (Ca) nutrition on growth, fruit yield and quality of greenhouse tomato have been investigated extensively in northern Europe (Ho et al., 1999). Leaf Ca deficiency in tomato reduces leaf size, and causes necrosis of young leaves and yield loss in extreme cases (Adams and Gizaway, 1988; Adams and Holder, 1992; Holder and Cockshull, 1990). Low supply of calcium to tomato fruit leads to more fruit with blossom-end rot (BER) (Ho et al., 1999; Saure, 2001). Excessive supply of calcium to fruit causes goldspeck/goldspot, cells containing a granular mass of tiny calcium oxalate crystals (De Kreij et al., 1992; Den Outer and van Veenendaal, 1988; Ho et humidity and temperature. Leamington (41 °N, continental climatic type) in Ontario, Canada, where one-third of North America greenhouse tomatoes are grown, has quite different climatic conditions from northern Europe (close to 50 °N, maritime climatic type). Therefore, there is a need to conduct experiments in this area for optimizing Ca and Mg nutrition. Furthermore, in a previous study designed to develop closed cultivation systems in Ontario, it appeared that high levels of Ca and Mg caused by accumulation in closed hydroponic systems may had been beneficial to tomato growth (Hao and Papadopoulos, 2002). This suggested that the standard recommendations for the Ca and Mg nutrition of greenhouse tomatoes in Ontario (Papadopoulos, 1991) might need adjustment. This study was undertaken to investigate the effects of Ca and Mg, and their interactions, on plant growth, biomass partitioning, and fruit yield for optimizing the mineral nutrition of greenhouse tomato grown in winter. Materials and Methods Two winter experiments were conducted at the Greenhouse and Processing Crops Research Centre, (GPCRC), Agriculture and Agri-Food Canada, Harrow (41 °N), Ontario, Canada. The experiments were conducted in two double-inflated polyethylene greenhouses (45 m each) from September 1997 to January 1998, and from September 1998 to January 1999, respectively. ‘Trust’ tomato seeds were sown in small rockwool cubes (3.8 × 3.6 × 4.0 cm, Pargro Inc., Orillia, Ont., Canada) in seedling packs. After cotyledons became fully unfolded, the seedlings were transplanted into large rockwool blocks (7.5 × 7.5 × 7.5 cm; Pargro Inc., Orillia, Ont., Canada). The transplants were raised on benches and flood irrigated using a Harrow Fertigation Manager (Climate Control Systems Inc., Leamington, Ontario, Canada) according to standard nutrient recommendations (Papadopoulos, 1991; Papadopoulos and Liburdi, 1989). On 11 Sept. 1997 and 18 Sept. 1998, at the fourto five-leaf stage, transplants were transferred onto sleeved rockwool slabs (90 × 15 × 7.5 cm, Pargro Inc., Orillia, Ont., Canada) in the greenhouses, at a 3 plants m plant population. Day/night heating temperature was set at 19/18 °C while ventilation temperature was set at 23 °C. Day/night relative humidity was set at 70%/65%. Plants were trained to a single stem according to commercial practices. An electrical vibrator was used to assist flower pollination daily. The plants were drip-irrigated with appropriate nutrient solutions. To avoid nutrient buildups in the rockwool, 20% to 30% extra nutrient solution was applied (Papadopoulos, 1991). The plants were topped on 1 Dec. 1997, and 3 Dec. 3 1998, respectively. Nutrient treatments. In both experiments, six nutrient treatments were applied as a factorial combination of two Ca concentrations (150 and 300 mg·L) and three Mg concentrations (20, 50, and 80 mg·L). In each polyethylene greenhouse, 8 rows of plants were grown. Two side rows were used as guard rows while the al., 1999), which not only affects the appearance of the fruit, but also reduces its shelf life (Janse, 1988). Magnesium (Mg) deficiency occurs regularly in greenhouse tomatoes (Ontario Ministry of Agriculture and Food, 2001). Because the deficiency symptoms, usually in the main spring crop, occur on the oldest (bottom) less productive leaves, this has not been seen as a major problem. However, in fall or winter tomato crops, the deficiency may occur in the middle leaves, which could have significant influence on plant productivity (Sonneveld and Voogt, 1991). This reduction in plant productivity could be due to reduced biomass production (from low leaf photosynthesis) alone, or due to both a reduced overall biomass production and a lower biomass allocation to fruit. Information on the effects of mineral nutrients on biomass partitioning is useful for clarifying the mechanisms of their influence on fruit yield and is valuable for developing tomato growth models (Marcelis et al., 1998). There has been limited or no information available on the effects of Ca and Mg concentrations in the nutrient solution on biomass partitioning in greenhouse tomatoes. Most of the information on Ca and Mg nutrition of greenhouse tomatoes is derived from research conducted in northern Europe; little such research has been done in North America. Past research (Adams, 1994; Ho et al., 1999; Papadopoulos and Hao, 2002; Sonneveld, 1987; Sonneveld and Voogt, 1991) has shown that the optimum levels of Ca and Mg for greenhouse tomatoes are strongly affected by climatic conditions such as solar irradiance, HORTSCIENCE 39(3):512–515. 2004. Received for publication3 Sept. 2002. Accepted for publication 29 Sept. 2003. Use of trade names in this publication does not imply endorsement of products by Agriculture and Agri-Food Canada nor criticism of similar ones not mentioned. This research was funded, in part, by the Ontario Greenhouse Vegetable Growers. We thank A. Mosca and J. Blackburn for invaluable technical support.