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Pea Problem Rooted In Solonetzic Soil

When the opportunity to purchase a new parcel of land presented itself last year, Dan happily expanded his farm. He carefully planned the introduction of peas to a new 350-acre field. He was more than curious about how his first crop on the new field would yield. Dan’s curiosity quickly changed to concern after he noticed some of the plants in the middle of the field stopped flowering and appeared stunted in growth.

It was the first week of July when Dan called me to come out and have a look at the oval-shaped area of damaged plants developing in his field. “A section of my field is ripening before the rest of it. It doesn’t make sense,” he said.

Dan, who farms 7,500 acres of wheat, lentils, peas and canola near Herbert, Sask., told me the rest of the field looked completely normal. He thought perhaps herbicide carryover was to blame.

When I examined the field, I noted about 50 out of 350 acres, located in the middle of the field, appeared to be affected. The plants were stunted in growth with poor root and nodule development when compared with the surrounding plants. The damaged plants seemed to be ripening, while the rest were still flowering. The healthy-looking plants were developing normally when compared with his other fields.

We contacted the previous owner to determine what chemicals had been applied to the field over the past few years. We learned that no residual herbicides had been used, thus carryover was not causing the damage to Dan’s plants. Herbicide drift was also not the issue because there were no patterns in the field often associated with cases of drift. Pests were also ruled out as the cause of the damage because we found no evidence of pea leaf weevils, aphids, wireworms or cutworms.

Environmental conditions were wet that spring, but the field was well drained and there was no standing water. Besides the rain, the weather conditions had been average with no frost, hail or wind.

Next we sent samples of the soil profile from a zero-to six-inch and six-to 12-inch depth from the affected and non-affected areas of the field for analysis. Dan was completely surprised by the results of the soil test. The soil from the affected area contained very high levels of sodium compared with the rest of the field. The high sodium level must be responsible for the poor root and nodule development. “But what’s causing the high sodium level?” he asked me.

“The area in the middle of your field has solonetzic soil,” I said. “Never heard of it,” said Dan.

I explained solonetzic soils are almost exclusively found in Western Canada, and have a sodium-rich hardpan layer found about five to 30 centimetres below the soil surface. The hardpan restricts root and water penetration of the subsoil. Solonetzic soils are formed from materials naturally high in sodium salts, or from those enriched with sodium salts from the capillary movement of groundwater. As in Dan’s case, a field of perfectly normal soil can contain patches of solonetzic soil. “Unfortunately,” I told him, “Crops planted on solonetzic soils often produce lower yields.”

But there are a number of ways to improve the productivity of solonetzic soils. Deep ploughing or subsoiling (ripping) have increased production on solonetzic soils, but these methods are costly and not suitable for all circumstances. Gypsum (calcium sulphate), or another calcium source, can also be added to the soil to help improve the soil structure, but again, it is costly, and as with deep ploughing or ripping, may not be the most effective solution in areas with drier climates.

Due to the small size of the area of solonetzic soil in Dan’s field (50 acres), the cost that would be incurred, as well as the importance of conserving soil moisture, I recommended against deep ploughing, ripping or the application of gypsum in this case. Instead, I recommended no-till to improve soil quality and function, as well as increase organic matter levels.

No-till helps reduce compaction and conserve moisture. It is also important to maintain trash levels with no-till. Going forward, we will use a well-balanced fertility program based on the capabilities of Dan’s land. The yield potential of this field may always be limited compared with Dan’s other fields.

That year the area planted with peas on solonetzic soil yielded about 21 bushels per acre compared with 34 bu./ac. for the rest of the field — a 30 per cent reduction. No-till and the new fertility program may increase the yield on the solonetzic soil in the future.

CoreyPriceisacropinputmanagerat RichardsonPioneerLtd.inHerbert,Sask.

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