Assessing the tolerance and response of pulse crops to seed-row placed fertilizer blends and composite products containing nitrogen, phosphorus and sulfur

Legumes can obtain a significant portion of their nitrogen (N) requirements from atmospheric N2 through the symbiotic relationship with Rhizobia spp of bacteria, termed biological nitrogen fixation (BNF). The development of actively fixing nodules on the roots typically takes one to two weeks. Onset of BNF may be further extended by stress conditions such as low temperature, moisture, and root disease, and coupled with low available N levels in the soil, could negatively affect growth and development of pulse crops grown on prairie soils. Therefore, low rates of starter N supplied as mineral fertilizer in the seed-row along with phosphorus (P) and sulfur (S) may increase early growth and N, P, S nutrition. However, too much fertilizer in close proximity to seed can damage the seedling through osmotic effect and ammonia toxicity. But, there is limited information on safe starter rates of fertilizer blends and combination products containing N, P and S for pulse crops in prairie soils. Therefore, a controlled environment study and a field experiment was conducted to evaluate emergence, yield and N, P, S uptake responses to starter fertilizer blends applied at 0, 10, 20 and 30 kg N ha-1 in the seed-row under a common 15% seed bed utilization configuration. Six different pulse crops: soybean, pea, faba bean, black bean, lentil and chickpea were evaluated on a N and P deficient loamy textured Brown Chernozem soil from southern Saskatchewan. The general sensitivity (injury potential) for starter N, P, S fertilizer products and blends placed in the seed-row was lentil > pea > chickpea > soybean > black bean > faba bean. Lentil, pea and chickpea could generally only tolerate the 10 kg N ha-1 rates while soybean and black bean could tolerate 10 – 20 kg N ha-1. Faba bean emergence appeared relatively unaffected by all three rates of N (10, 20 and 30 kg N ha-1), and showed least sensitivity to seed row placed fertilizer. In terms of 30 day biomass response, soybean and black bean were most responsive to fertilization, and pea, faba bean, lentil and chickpea early biomass production and nutrient uptake showed no benefit going above the 10 kg N ha-1 rate. Soybean and lentil were evaluated under field conditions in 2018 at the location near Central Butte, Saskatchewan where the soil was taken for the controlled environment studies in a seed-row placed urea-MAP blend (28-26-0). Confirming the controlled environment work, a rate of 10 kg N and P2O5 ha-1 appeared to be the rate that did not significantly reduce emergence, stand count or biological nitrogen fixation, and was sufficient to maximize yield, N and P uptake for both soybean and lentil under field conditions. Rates higher than 10 kg N ha-1 in the seed-row as starter 28-26-0 blend reduced emergence and decreased the proportion of N derived from biological nitrogen fixation