Fertigation of Field Vegetable Crops

A research field experiment with tomato was conducted in 2017 at Gornaya Polyana Research Farm, Volgograd State Agrarian University, Volgograd. The light Chestnut soil (Haplic Kastanozem Chromic) had a clay texture, low salinity, low organic matter (OM) content (1.8%), alkaline pH (7.9), and very high concentrations of available phosphorus (P) and potassium (K) extracted with ammonium carbonate solution (49 ppm P₂O₅ and 521 ppm K₂O) in the 0 to 20 cm soil layer. Calcium was a predominant exchangeable cation in the soil. The initial soil sampling was done before tomato transplanting, after a complex nitrogen (N), P, and K fertilizer application in the spring that consisted of 21 kg/ha of each N, P₂O₅ and K₂O. The following fertigation treatments were applied to tomato (20 kg N/ha х 6 fertigation events = 120 kg N/ha): 1) Ammonium nitrate (AN) (Grower Practice); 2) AN + Foliar fertilizers; 3) Calcium nitrate; 4) Calcium nitrate + foliar fertilizers; 5) Calcium nitrate (#1 through 4 fertigation events) and Calcium Nitrate + Potassium Chloride (KCl) (5 and 6 fertigations); 6) Calcium nitrate (#1 through 4 fertigations) and Calcium Nitrate + Potassium Chloride (5 and 6 fertigations) + foliar fertilizers.

From tomato flowering to fruit set, treatments 5 and 6 received 12.7 kg chloride (Cl)/ha and 16.9 kg К₂О/ha during both fifth and sixth fertigations. Foliar fertilizers were sprayed as 0.6% solution at 300 l/ha including the following two products: 1) Folicare 18-18-18 at intensive vegetative growth; 2) Folicare 10-5-40 at flowering to fruit set.

Fertigation with AN, calcium nitrate, and calcium nitrate + potassium chloride (Treatments 1, 3, and 5) gave the following marketable yields of tomato: 61, 64, and 79 t/ha, respectively. The spraying of foliar fertilizers increased the marketable yield of fruits by only 1% when AN or calcium nitrate were used for fertigation. Foliar fertilization, however, resulted in a 15% yield increase when a combination of calcium nitrate and KCl were used for fertigation. The maximum yield of 91 t/ha was thus obtained in the sixth treatment. Both of the increases in fruit number per plant and fruit weight contributed to such a considerable yield improvement. This also represents a much better water use efficiency by tomato plants. The highest content of total soluble solids in tomato fruits was also obtained in treatment 6. Fruits harvested from this treatment, moreover, had a longer shelf life.