I have heard farmers say that so and so depleted the soil of its nutrients...
I have heard farmers say that so and so depleted the soil of its nutrients and when they started farming the field it took them several years to get the soil built back up. I thought applying fertilizer is an annual event, done every year, and only what is needed for that year was applied which should be about the same each year for about the same result—holding all other variables the same. What do you say?
Erie County Ohio
Thank you for the question and it is a good one. When you say field, I not sure if you are referring to a hay field or a row crop field. Regardless, plants need and will use nutrients from the soil. If nutrients are not replenished or reapplied to these fields, either through fertilizers or organic material, then overtime the soil can become nutrient deficient. The best way to know if farmer "so and so" depleted the soil's nutrients is to take a soil test. Soil testing is the first step (and one of the most important) in a good nutrient management program. Fertilizer is typically added every year to replace or buildup the soil's nutrient levels, especially phosphorus and potassium. But the question is how much fertilizer do you add every year? The answer is soil testing. If you add fertilizer without testing then you are simply guessing. Our motto is: "Don't guess, Test!" A good quality soil test will tell you exactly what the soil's phosphorus, potassium, calcium, and magnesium levels are as well as another very important factor directly related to nutrient availability within the soil - pH. The soil's pH level is very important. If the soil's pH levels are really low or high, the nutrients in the soil get bound to the soil particles and are not available for plant root uptake. This is one reason I always say correct pH, then add fertilizer. It is a good practice to add lime (adjusting pH) in the fall and by spring the acidity in the soil will be lower (pH = 6.5 is ideal) and ready for fertilizer.
In summary, you should always test your soil so you know exactly what your nutrient levels are and how much fertilizer and lime you need to apply to the fields. Without a soil test, you are simply guessing and making assumptions. Who knows, maybe you have been applying too much fertilizer and the soil test will recommend a lower rate which in turn will save you money. And if you are saving money, your profits will increase. That's the main purpose for putting effort into farming is to make money, right?
Thank you very much for your wonderful answer. I greatly appreciate your time and effort. I’d like to follow up with another question. Let’s say a good quality soil test was done on a row crop field, and the soil was found to be nutrient deficient in phosphorus, potassium, calcium, and magnesium levels. How many years will it take to “build the soil back up,” and what, generally speaking in theory will the lime, fertilizers and yield curves look like; for example if it takes 100 units of lime, fertilizers in year one will it take 50 units lime, 70 units of fertilizers in year two? If the yield in year one 100 units, would the yield be somewhere around 200 units in year two or three?
Your last question has too many "ifs" and "what-ifs" to give you an exact answer. If your soil was deficit in nutrients, it should only take one year to build to nutrient back up. Then again, how deficit is the soil? If the ppm (part per million) or lbs/ac is extremely deficit then it can take multiple years. If it is slightly deficient, it should only take around 1 year. Of course you have to consider how much nutrients the crop will remove per acre and adjust accordingly.
As for the yield and it's related inputs (lime fertilizer), again that can depend on how deficit. Typically lime is added to the soil in fall and by the time spring rolls around, the pH should be adjusted (the lime has time to react with the soil acidity throughout the winter). Liming should solve your Mg and Ca problems for the next season (then again - it depends on how deficit the soil is). The fertilizer you put down at planting (spring) should be available throughout the growing season(of course some N should be side dressed during the growing season to improve N use efficiency). Saying that, if you meet your lime recommendation in the fall and your fertilizer recommendation for N, P, and K, your yields should be about the same for year 1, year 2, year 3, etc..