Wayne Smith is an internationally recognized agronomist. His work is sometimes controversial in agronomy circles.
Farmers across the globe share the same conviction when asked to finger the main culprit limiting their yields, but an Australian agronomist says they are wrong.
“Water isn’t your problem,” Wayne Smith told producers attending an Edmonton agronomy conference earlier this year.
“It’s nutrients …. If your crop is deficient in even a single nutrient, you have lost 20 percent of your yield.”
Cereal yields on the Canadian Prairies averaged 25 bushels per acre from 1955 to 1980. Between 1980 and 2005, yields were closer to 45 bu.
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“It didn’t rain any less then. Yes, better genetics and conservation tillage tools became available, but farmers in the 1960s gave the same answers you give me now when asked why you don’t yield more: ‘lack of water,’ ” he said.
“If I was God and I gave every farmer in Alberta an ideal amount of rainfall and (spring) soil moisture, they wouldn’t all have wheat crops with the same yields. It would vary from 25 to 120 bu. (per acre) and almost no one would reach their potential.”
Smith said cereal producers can expect to grow 70 bu. per acre with 150 millimetres of growing season rainfall.
“And you’d all have a ‘yeah but’ excuse as to why you didn’t have a better crop,” he said. “Those ‘yeah buts’ cost a lot money.”
Smith said his observations are based on research that established potential crop yields for cereals 25 years ago and on his global agronomy experience since then.
Many factors undermine those yields in the real world, he added, even where ideal moisture is available. Disease, insects, seeding timing, pesticide applications and nutrition all reduce a crop’s potential. Smith is convinced nutrition management is the greatest threat to crop yields.
He said recognizing problems and treating them quickly prevents pests and less-than-ideal moisture from hampering crop production.
“I met with a client in Kenya,” Smith said.
“His land is located at high altitude, near the equator where it never freezes. Every night temps fall to about 5 C and it never goes over 25 degrees during the day. He gets 50 inches (1,200 mm) of rain every year and has never had less than eight inches (200 mm of moisture) in the top foot of soil.”
His problem? Lack of moisture.
“If it doesn’t rain for three weeks, his crop starts dying and his yields were stuck at 50 (bu. per acre).”
Smith said a big mistake made by farmers is not listening to what their crops are telling them.
“They speak to you in colour and you need to listen with your eyes. When you learn to hear what they are saying, you have to act.”
Agronomy generally recognizes nutrient deficiencies with a single set of colour clues for each deficiency. However, fields tend to have multiple issues happening at the same time, including drought, heat and water stress and pest pressures.
On the Prairies, that means a six week period from the time plants establish their roots to when they begin to fail. Farmers have that much time to determine what they need to do to increase yields based on a nutrient intervention.
“Over time, farmers become used to seeing dead leaf tips or lost plants. This is seen as normal. Plants do not see this as normal. The plants are speaking to you,” Smith said. “Normal for the plant is green from the tip of the leaf to the start of the root. Anything else is costing you money.”
The rules according to Smith
- Check the roots. They should be long, white and fibrous with many root hairs at the end of new roots. Root disease should be ruled out before looking any further into nutrient deficiency.
- To measure overall nutrient deficiency, turn off the phosphorus for 100 metres once in every field. Without the phosphorus, the crop will show off all its other problems. If the plants without phosphorus are half the height or smaller than the plants with phosphorus, then phosphorus is still in short supply.
- If the plants without phosphorus are only slightly smaller than the ones with phosphorus, then the phosphorus levels are close to ideal and other nutrients are in short supply.
- If there is no difference, cutting back on phosphorus next season won’t hurt the crop and will save money on inputs.
- There are few nutrient problems if only one colour of crop is found in a strip. Two colours, such as the base colour and yellow, means there is one nutrient shortage. Two colour differences means two nutrient shortages. Three differences mean three shortages, et cetera.
- Yellow at the top, green at the bottom and leaves pointing up indicate a sulfur deficiency.
- If the middle of the leaves are dying and they are folding, it’s a zinc shortage.
- If the newest leaves are dead and twisting at the ends, it’s a copper issue. Copper dies from the top down.
- Not every plant will show symptoms and the soil will be inconsistent. All soil has good and bad spots.
- Don’t rely on soil tests to tell you what a plant needs. They are only good for approximate planning. Look at plants to discover what nutrients they are getting.
- Move to wide row spacings, up to 36 inches.
- Herbicides with chemical names ending in fop and dims create copper deficiencies; sulfentrazone creates other shortages. Producers should be prepared to apply foliar treatments to adjust for this if damage from herbicides occurs.
- Place 10 to 25 percent of a crop’s required trace elements such as zinc, copper, sulfur and molybdenum with the seed to prevent problems. Use foliar applications in-crop to correct for shortages.
