Nutrients Requirements of Field Crops
Dr. Tarlok Singh Sahota CCA
Even if we seed crops at the optimum times and use the best varieties for the area, maximum economic yields can’t be obtained without adequate nutrient supply and management. Mineral nutrients are normally listed in the order of N, P, K, S…; however, I would recommend writing it in the order of S, N, P, K, … because without meeting S requirements of crops proper response to N and other nutrients can not be obtained.
Canola is one of the crops that requires ample supply of N and S. LUARS has been recommending 36 kg S (through 150 kg ammonium sulphate/ha that also supplies ~30 kg N/ha) and 180 kg N/ha to canola. Deducting 30 kg N/ha from ammonium sulphate, two third of (the remaining) N should come from urea (100 kg N/ha) and one third from ESN (50 kg N/ha). However, we have recorded response to N in canola at rates higher than 180 kg N/ha (240 or 270 kg N/ha) in the past. For example, last year maximum canola yield was obtained with seeding on May 12 and application of 270 kg N/ha (through ammonium sulphate, urea and ESN). For canola seeded on May 19, 180 kg N/ha was enough. Canola growers may try rates higher than 180 kg N/ha for earliest seeded canola in small acreage (20-30 acres) and if it works better, they can adopt this practice.
Corn too requires N application at high rates (150-200 kg N/ha). Ammonium sulphate @ 100 kg/ha should be applied to corn to supply 24 kg S/ha that would also supply ~20 kg N/ha. Rest of the N should come from urea and ESN in 2:1 ratio on N basis. By this application, corn canopy will retain its green colour from bottom to top till harvesting.
N supply to spring cereals could come from 50 kg ammonium sulphate/ha (= ~10 kg N/ha and 12 kg S/ha), 50 kg N/ha from urea and 20 kg N/ha from ESN. For winter cereals, apart from 50 kg ammonium sulphate/ha, 70 kg N/ha should be supplied through urea and 40 kg N/ha by ESN.
Soybean could get 100 kg ammonium sulphate/ha to supply 24 kg S/ha (and ~30 kg N/ha). In addition, urea @ 15 kg N/ha should be applied to soybean to meet its N requirements (45 kg N/ha).
For grasses, 140 kg N/ha is optimum; ~20 kg N/ha should come from 100 kg ammonium sulphate/ha to supply 24 kg S/ha, 80 kg N/ha from urea and 40 kg N/ha from ESN.
Alfalfa should get 150 kg ammonium sulphate to supply 36 kg S/ha (and ~30 kg N/ha). In addition, urea @ 15 kg N/ha should be applied to alfalfa to meet its N requirements (45 kg N/ha).
P and K to all crops should be applied on soil test basis. Minimum of 20 ppm P and 120 ppm K is required in the soils. If these nutrients in soils are a bit higher than the minimum requirements, some P and K (@ 20 kg P2O5 and 20 kg K2O/ha) should be applied to all crops to maintain soil status of these nutrients. In case these nutrients are very high or are in excess in the soil, then their application could be omitted. Farmers may try banding of P at seeding (up to 20-26 kg P2O5/ha) for its easy availability to field crops.
Micronutrients too should be applied based on the soil test. Often zinc application to corn and boron application to alfalfa and canola would be required. Please don’t hesitate to contact me (at tssahota@lakeheadu.ca), if need be.
This project is funded under the Sustainable Canadian Agricultural Partnership, a federal-provincial-territorial-initiative.
