Adequate soil fertility promotes efficient soil moisture use. The gain in efficiency is due primarily to fertilizer, since similar amounts of water were used in both cases. The moisture supply throughout the growing season must be reasonable to get yield responses from added fertility. Yield increases will be above average in good moisture years and below average in dry years. Under irrigation, rainfall does not limit crop production.
Irrigated canola depends more on soil fertility for increased yields than on any other factor.
Research studies on irrigated canola with high rates of nitrogen fertilizers broadcast and incorporated on stubble have shown yields were nearly doubled at Vauxhall, Alberta, while at Outlook, Saskatchewan yields increased nearly four-fold over dryland. Added nitrogen on dryland in these trials was not economical. Without adequate moisture, crop responses to added fertilizer will be limited. Yields were reduced by a similar amount for either a nitrogen deficiency or a lack of water. A strong interaction occurs between nitrogen and water.