Liebig’s “Law of the Minimum” principle was developed in the 19th century by German agricultural scientist Justus von Liebig; the thesis is that if one essential plant nutrient is deficient, plant health and growth will be poor, even if all other nutrients are present and abundant.
In other words, growth is controlled not by the total nutrients available, but by the scarcest. Liebig used a wooden barrel to explain his law: The capacity of the barrel is limited by the shortest stave.
Liebig’s Law applies particularly to nutrient management in cotton, and a simple example is this: You can use 200 pounds of nitrogen per acre, if you choose, but if your soils are deficient in phosphorus or potash, or even essential micronutrients, your cotton crop cannot reach its full potential.
“Rule number one is to always make a fertilizer decision based on a soil test for phosphorus and potash,” says Dr. Larry Oldham, Extension soil specialist at Mississippi State University.
But soil sampling across the Cotton Belt is sort of like flossing. You want to do it. You mean to do it. And probably you tell your dentist you do it. But do you?
Soils constantly undergo physiological changes. Plant uptake, leaching, volatility and erosion can all remove nutrients from the soil. That’s why soil testing is so valuable. Measuring available nutrients in the soil serves as the best guide to profitable use of fertilizers.
With fertilizer prices being what they are, it’s also essential that you put out exactly what you need, when you need it. “Make sure equipment is in good shape and calibrated,” continues Oldham. “You want to be sure you are putting out what you think you are putting out. Put it where it is supposed to go and when it is supposed to be there.”
And face reality: “Be realistic,” he says. “Know what your production potential is, considering the soil type and irrigation.”
Oldham says much higher fertilizer prices also make it essential that growers establish and cultivate relationships with fertilizer retailers. “The increases in prices are not just happening at the retail level – it’s happening all up and down the supply chain,” he says.
“A company has to make a healthy investment to buy a barge load of fertilizer. Sellers have to make sure they have the fertilizer marketed properly,” he continues. “They can’t have their capital tied up in fertilizer sitting in a warehouse. Growers need to understand that a dealer has to look at his business, too.”
Oldham writes in his “Nutrient and Soil Management” newsletter that fertilizer price volatility didn’t just happen over night. Factors he pointed to were:
- Disruptions in manufacturing and shipping caused by Hurricanes Katrina and Rita in 2005.
- Higher energy prices.
- Depressed global grain stocks have increased grain prices around the world, which has increased demand for crop nutrients.
- The declining value of the American dollar. Imports cost more.
- Transportation costs have increased all along the supply chain.
- Economic conditions in Brazil, India and China have increased the demand for meat protein, which increases fertilizer-based crop production to produce meat.
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Average Farmer Prices for DAP
Average Farmer Prices for Potash
Decrease in Buying Power
Average Farmer Prices