Fertigation of Field Vegetable Crops

An on-farm experiment with field tomato was conducted in 2016 at Gornaya Polyana Research Farm, Volgograd State Agrarian University, Volgograd. The light chestnut soil (Kastanozem) had a heavy texture, low salinity, low organic matter (OM) content (1.82%), slightly alkaline pH (7.40) and very high levels of available phosphorus (P) and potassium (K) extracted with ammonium carbonate solution (70 ppm P₂O₅ and 644 ppm K₂O) in the 0 to 20 cm soil layer. Calcium was a predominant exchangeable cation in this soil. The initial soil sampling was done before tomato transplanting (i.e., after a complex NPK fertilizer application in spring that gave a 32 kg/ha of each N, P₂O₅, and K₂O.

The following fertigation treatments (20 kg N/ha in six fertigation events = 120 kg N/ha) with and without foliar fertilizer were applied to tomato in these N sources: 1) ammonium nitrate (typical farmer practice); 2) ammonium nitrate + foliar fertilizers; 3) calcium nitrate; 4) calcium nitrate + foliar fertilizers; 5) calcium nitrate (1 to 4 fertigations) and calcium nitrate + ammonium chloride (5 to 6 fertigations); 6) calcium nitrate (1 to 4 fertigations) and calcium nitrate + ammonium chloride (5 to 6 fertigations) + foliar fertilizers. Since tomato flowering – fruit set in treatments 5 and 6, ¾ of N was sourced from calcium nitrate and ¼ from ammonium chloride (5 to 6 fertigations). Foliar fertilizers were sprayed as 0.3% solution at 300 l/ha including the following two products (N-P₂O₅-K₂O): 1) 20-20-20 + microelements (B, Cu, Fe, Mn, Mo, Zn) at intensive vegetative growth; and 2) 12-6-36 + Mg + S + microelements (B, Cu, Fe, Mn, Mo, Zn) at flowering-fruit set.

Fertigation with ammonium nitrate, calcium nitrate and calcium nitrate + ammonium chloride (Treatments 1, 3, and 5) gave the following marketable yield of tomato: 53, 59 and 62 t/ha, respectively. Foliar fertilizer use increased marketable yield of fruits by 12 to 29%. Fertigation with calcium nitrate + ammonium chloride with foliar fertilizer use in Treatment 6 resulted in the highest marketable yield of tomato of 79 t/ha. Both increase in fruit number and fruit weight contributed to such a considerable yield improvement. This also means better water use efficiency by tomato plants. The highest content of the total soluble solids in fruits was also obtained in Treatment 6. Fruits harvested from this treatment, moreover, had a longer shelf life following harvest.