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Potash – the building block of plant health

Feed the crop to reduce root rots and lodging.

November 12, 2007  By Cliff Metcalfe

12aCrop producers often concentrate on providing adequate levels of nitrogen when fertilizing corn and cereals. We rely on residual phosphorus and potassium left over from last year's crop to feed our current season's soybean crop, especially when producing soybeans using no-till techniques.

We provide soil sampling services on behalf of our clientele on a three year 'monitoring' basis. The soil test results clearly indicate a very noticeable decline in available soil potassium levels. The quantity and severity of visual potassium deficiency symptoms that are seen during crop monitoring trips and field visits, especially later in season, are rapidly increasing, particularly on sandy loam and loam type soils.

Potassium is taken up in relatively large quantities by locally grown crops. Soybeans, for example, will remove at least 2.6lb of potassium per bushel of soybean harvested. Many agronomists believe the 'true' removal of potassium by soybeans is almost double this level. Corn silage production has increased rather dramatically within the past three to four years. A good deal of potassium is removed from the soil, with the harvesting of whole plant silage, as most of the potassium is stored in the leaves and stalk of the plant. A decent crop of corn silage will remove well in excess of 150lb of potassium from the soil.


There was a time when almost every farmer in eastern Ontario had a relatively significant quantity of livestock present on the farmstead, as a portion of the overall 'mixed' farming operation. Many of the cattle are gone, and so is the valuable source of soluble potassium which was once 'recycled' onto the adjacent fields in the form of manure. Thus there was a reduction of the overall supply of this nutrient to the soil nutrient 'bank'.

The advent of no-till technology has presented its challenges with regards to the proper application and placement of both phosphorus and potassium. Few farmers have no-till equipment with the capability of placing these nutrients close to the root zone of the plant to allow for efficient uptake by the crop root. Many producers rely on residual nutrient application, or 'scavenger' type crop feeding. They will over-fertilize the previous season's corn crop to feed the current season's soybean crop. This technique works relatively well on clay loam type soils which have the natural ability to retain potassium supply from one season to another. I have found that results of this type of fertilization practice are very inconsistent on sand to sandy loam soils in eastern Ontario. The soils do not appear to have the ability to retain the residual potassium at levels required to sustain a high yield environment.

12bWe are consistently experiencing problems with increased levels of stalk rot in corn, elevated levels of root and stalk diseases on soybeans and dry beans and increased lodging problems on cereal type crops on the coarse textured soils within our region.

We are encouraging growers to focus on placement of phosphorus and potassium as close as practical, without creating root injury potential, to the root zone of crops of high nutrient utilization. 'Feed the crop, not the soil' is an apt description of this method of crop nutrition.

Eastern Crop Doctor's primary focus is in providing agronomic crop production programs and soil testing services to its client base. A secondary function of the company involves the operation of a 50 acre plot location just west of Winchester, Ontario. The plot site has been in continuous operation for 15 years. We work with 22 to 23 crop input supply businesses on an annual basis conducting trials relevant to seed and pesticide screening trials, foliar fertilizer trials and seed treatment trials, with an ever-increasing focus on fertility trials, on both conventional and no-till crop production techniques.

The fertility trials are conducted utilizing replicated treatments, with a focus on efficiency of nutrient placement. The results of our fertility trials, relevant to corn production, and fertilizer (P and K) placement are very consistent on a year-to-year basis. Side-banding of potassium on one replicated no-till corn trial conducted during the 2004 season did show very good response, with respect to yield and reduction in lodging (stalk rot). This plot was conducted using Syngenta Seeds' NK2555Bt. Soil test values are medium for both phosphorus (12ppm) and potassium (108ppm). Soil pH levels are 7.4. All treatments received 77 units of P205. All treatments received 131lb/ac actual nitrogen (impregnated with Agrotain nitrogen stabilizer).

Certified crop advisers across Ontario assist growers with crop management decisions. Since 1996 individuals from most growing regions in Ontario have entered this intensive program. They maintain their designation with continuing education credits by attending courses and workshops. Look for the CCA emblem!

*Cliff Metcalfe is a Certified Crop Adviser with Eastern Crop Doctor, based at Winchester, Ontario.


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