The impact of starter fertilizer to flue-cured tobacco growth
An increasing number of flue-cured tobacco farmers are including water soluble fertilizer products in transplant water applications. The goal of these starter fertilizer programs is to supply a small quantity of phosphorus, which may stimulate early-season plant vigor particularly in cold, damp soil conditions.
Commonly, some of these fertilizer products have not been evaluated by independent researchers and their impact is sometimes questionable across a wide range of growing conditions. Our objective was to evaluate a small number of commercially available transplant water fertilizer products (Ultrasol 9-45-15, 11-37-0 ammonium polyphosphate, 6-20-0 Black Label Zinc, 6-24-6 Advance RTU, and 8-31-4 Exceed), each providing 5.6 (1×) and 11.2 kg P2O5 ha-1 (2×), in order to quantify their impact on vegetative growth up to six weeks after transplanting. Two non-treated controls were included for comparison, transplant water only and no transplant water. Data are reported from two locations in 2021. In the first data analysis (Fertilizer Product × Application Rate), Ultrasol treatments were more vigorous than all other products and had a higher shoot dry mass at two and four weeks after transplanting. The 1× application rate was also superior to the 2× rate, regardless of fertilizer product, thus indicating that excessive starter fertilizer may be more harmful due to soluble salts injury. Treatment differences were not observed by week six, which suggests that plant recovery from minor injuries is possible. In the second data analysis (Fertilizer Product × water only × no water), those treatments absent of fertilizer or with 1× rates (Ultrasol and Black Label Zinc) had the highest vigor ratings two weeks after transplanting. The Ultrasol 2× treatment produced a similar response. All other treatment combinations resulted in visual vigor ratings that were poorer than the non-treated controls, again, indicating that soluble salts were inhibiting seedling recovery after transplanting. These observations were not documented at four and six weeks after transplanting. Our results suggest that the inclusion of transplant water fertilizer solutions is no more beneficial than water alone – particularly in transplanting seasons characterized by dry soil and air conditions, such as were experienced in 2021.