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Potash matters—Wars of the Titans!

Potassium, along with nitrogen and phosphorus, constitutes the three most essential nutrients for crops. For alfalfa, a predominant legume forage crop for the dairy industry, sufficient potassium in the cell plasm means smooth and effective sugar transportation to all parts of the plant during the harsh winter. Potassium is supplied through potash, its fertilizer form. The origin comes from the burning residue of plant tissue or ash. Though fertilizer prices are generally influenced by energy prices, and the latter has dropped sharply since the outbreak of financial crisis worldwide, the current crude oil price has steadied at about $60 per barrel. This trend of the potash price hike seems irreversible. Within a couple of years, one ton of potash has risen from around $300 to a current price of $900! Without doing careful price forecasting and farm financial management, dairy farmers may face a dire scenario.

My internship research project this summer is to evaluate the current three widely used potassium management recommendation systems and compare their relative effectiveness; generating a feasible solution for alfalfa growers.

The three approaches currently used are:

1) Soil test

Take several soil samples cores from the field of interest and submit them to the soil nutrient laboratory (Cornell Nutrient Analysis Laboratory, or CNAL) for chemical analysis. The result tells how much potassium, expressed in concentration, like parts per million (ppm) or pounds per acre.

2) Potassium saturation (K%)

This also requires doing the same soil chemical analysis, but the focus is on the K’s relative level, in other words, K’s amount versus the summation of potassium, calcium, and magnesium—other major soil cations.

3) Crop removal

This soil test is free! You do not have to do any soil test to calculate your potash needs. Based on the previous harvest, let’s say 5 tons/acre, use the general rule of thumb of one ton of alfalfa can absorb 0.2 ton of potassium. Then you know you need to put 1 ton of K to replenish the loss, right?

Those three approaches all have very long history and are deeply entrenched in our recommendation systems. Cornell has been long dedicated to the first method, generating the Cornell Recommendation every year, which is distributed to farmers for free. This soil test and field trial proves that soil tests work well. The second method, proposed by a group of prominent soil scientists in the 1940s, says that an ideal soil, should have x% of Ca, y% of Mg and z% of K, and of course, xyz may vary a little bit based on years of modifications. The last one, intuitively the most practical one, is believed to be the most useful tool.

Different soil labs and soil consulting businesses may choose different approaches, which makes the whole system pretty chaotic. Basically, if you want to raise your soil’s K% to 5%, as recommended by some consulting firms, the cost will be astronomical (most of the fields here our area is around 2%)! Is it worth it? Maybe, but you also risk ending up with no extra benefit in yield after applying those expensive fertilizers. What about crop removal? Soil will supply some K, but water will carry some away, so you never know. I do hope that we can have some answers by the end of this summer.

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