Effects of γ-poly glutamic acid on substrate mineral nutrient supply and growth of tomato plug seedlings

【Objectives】 The objective is to evaluate effects of -poly-glutamic acid(-PGA)on tomato plug seedling production. 【Methods】 Tomato seedlings were grown in the 50 cell-plug trays, with substratescontaining peat moss, vermiculite and perlite(3 ∶1 ∶1,v/v)as the growth medium. -PGA was applied in the substrates by mixing with substrate before the sowing. Changes in physical, chemical and biological properties of the substrates and growth parameters of tomato plug seedlings caused by -PGA addition were measured. -PGA was applied by overhead irrigation 16 days after the sowing. The growth parameters of tomato plug seedlings were measured. 【Results】 In the beginning of the treatment, -PGA improves the water filled porosity, water holding capacity, EC value, and the contents of NH＋4-N, NO－3-N, Olsen-P, readily available K, exchangeable Mg in the substrates, and reduces the pH values. At the seedling growth stage, -PGA increases the available N, P, K and Mg contents in the substrate, and especially improves the activities of phosphatase and catalase at the later growth stage. For the tomato seedlings, the chlorophyll contents are increased with the increasing of -PGA. The highest root activity is obtained in the treatment of 3 kg/m3 -PGA. -PGA mainly improves the shoot growth but restrains the root growth applied by either mixing with the substrates before the sowing or watering with -PGA solution. -PGA shows a delayed effect on the growth of tomato seedlings, and the effect is much better for the later-stage seedlings than early-stage seedlings. 【Conclusions】 -PGA application can enhance the water and fertilizer retention capacity of substrates, and therefore improve the growth of tomato seedlings.