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Phosphorus: A Limited Resource

Soil is a living, breathing ecosystem. Just as you and I breathe, soil too re­spires, and we measure that respiration rate as an indicator of microbial activity in soil. While there are large, non-mi­croscopic organisms living in soil such as worms, insects and small mammals, none of them exist by the billions in just a handful of soil except the microbes.

Nitrogen can play a close second in the nutrient race, but in most soils phosphorus is the most limiting nutrient.

There are many scientific classifica­tions for microbes in soil, but from the farmer’s perspective only two catego­ries are relevant. Good microbes (major­ity) and bad microbes (small minority). Good microbes enhance plant growth, and bad microbes cause disease in plants. Of course, things are never quite so clear-cut in nature. Some things can be good under some circumstances and bad under other circumstances. So keep in mind this is a simplification of what are, in reality, very complex interactions.

Our management practices should be refined to support the good (most of the time) microbes and suppress the ones known to cause diseases in crop plants. Diseases are not always caused directly by organisms. Sometimes the balance of the system gets thrown off and something ordinarily not a prob­lem finds a new niche and can become problematic.

Weak plants may also be susceptible to organisms in the envi­ronment that normally would not have much impact on them. For instance, a nutrient deficiency might weaken a plant and lead to susceptibility. The good news is, of the thousands of microorganisms identified in soil thus far, only a handful of those really fall into the bad category. The good far outweigh the bad, and with a little thoughtful management, you can keep it that way.

In the case of good microbes, we can take this a step further and narrow our focus to the most crucial organisms within this group, which are those that provide the macro and micronutrients plants require for growth. The most limiting of these nutrients is typically phosphorus.

Nitrogen can play a close second in the nutrient race, but in most soils phosphorus is the most limiting nutrient, often occurring in quantities a thousand times lower than other miner­als. One of the reasons for this is the high reactivity of phosphorus. It tends to bind to soil particles and complex with metals in the soil. This makes it unavailable to plants even if it is present in the soil.

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Soil Organic Matter: Tips for Responsible Nitrogen Management

For soil organic matter to work the way it should, it depends on a careful balance of nutrients and minerals, including one of

Healthy, homegrown carrots in rich soil.

the most important elements — nitrogen. One of the great paradoxes of farming is that lack of nitrogen is regarded as one of the great limitations on plant growth, and yet plants are bathed in it because the atmosphere is 78 percent nitrogen.

Most plants cannot use nitrogen in this form (N2) as it is regarded as inert. It has to be converted into other forms — nitrate, ammonia, ammonium and amino acids for plants to utilize it.

In conventional agriculture most of these plant-available forms of nitrogen are obtained through synthetic nitrogen fertilizers that have been produced by the Haber-Bosch process.

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Healthy Soil, Defined

What is healthy soil? Most farmers strive for a healthy, fer­tile soil that has good tilth. But do these terms — soil health, soil fertility and good tilth — all mean the same thing to all of us? I bet you have an image in your mind of what the soil and the crop grow­ing in it should look like. But in today’s

A worm comes up from the earth.

world, with all the available technology, plant protective fungicides, insecticides, etc. along with plenty of soluble nutri­ents, looking at a “good” crop can be deceiving. It may in fact be wearing a lot of ‘make-up,’ covering up its true state of health. In recent years, the USDA Natural Resources Conservation Service (NRCS) has started to focus more on soil health and what constitutes a “healthy” soil.

If we define soil health using the NRCS’ definition, it is “the capacity to function.” I thought about this definition for quite some time and decided I need­ed to add to it, clarifying the thought as “the capacity to function without inter­vention.” I define intervention as plant alterations, fungicides, insecticides, etc. Healthy soil should produce healthy crops without intervention.

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Dairy Farming: The Framework of Biological and Sustainable Practices

Biological dairy farming is a dynamic system of farming that works with natural principles. Its purpose is to make a profit by growing healthy, mineralized foods that are nutrient-rich and of maximum quality for people. In order for this to occur, all stages of production — including soil, forage, crop, animal, business, and lifestyle management — must be healthy and interdependent.

Dairy cattle graze freely on healthy forage options.

The biological cycle begins in the soil and is based on a healthy population of balanced microbiology (bacteria, fungi, protozoa, earthworms, etc.), which require soils with an adequate supply of properly balanced nutrients including, but not limited to, nitrogen, potassium, phosphorus, calcium, magnesium, sulfur, zinc, manganese, iron, boron and additional microelements.

The biological farming approach we use at Otter Creek Organic Farms aims to improve and balance soil fertility and forage/crop mineral levels by using a balanced fertilizer program, growing green manure crops, practicing proper tillage, employing tight crop rotations, utilizing a wide diversity of plant species, and measuring and monitoring all of these aspects. Mineralized soil produces high-quality forages, which yield healthy, productive livestock; cows that have minimal or no health complications, breed back easily, and efficiently produce ample, high-quality milk with potentially fewer dollars invested in fertilizers, off-farm feed and supplements, and vet bills. Biological farms often have decreased cost of operation. When using a biological system, the production of organic milk becomes a viable and profitable endeavor.

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Boosting Corn Yields

corn.tifEnsuring that corn absorbs the right balance of nitrogen, phosphorus and potassium is crucial to increasing global yields, a Purdue and Kansas State University study finds.

A review of data from more than 150 studies from the United States and other regions showed that high yields were linked to production systems in which corn plants took up key nutrients at specific ratios — nitrogen and phosphorus at a ratio of 5-to-1 and nitrogen and potassium at a ratio of 1-to-1. These nutrient uptake ratios were associated with high yields regardless of the region where the corn was grown.

“The agricultural community has put a lot of emphasis on nitrogen as a means of increasing yields, but this study highlights the greater importance of nutrient balance,” said Tony Vyn, Purdue professor of agronomy. “We will not be able to continually boost global corn yields and achieve food security without providing adequate and balanced nutrients.” The paper was published online in the Agronomy Journal.

While U.S. corn producers have long relied on nitrogen fertilizers to improve yields, they should not overlook other nutrients such as potassium and phosphorus, Vyn said.

“Growers need to be as concerned about the amount of potassium available to their plants as they are about nitrogen,” he said. “Corn’s demand for nitrogen and potassium is similar. We need to focus on the nitrogen-potassium balance because that’s where we have the greatest deficiency in terms of application, especially in the eastern Corn Belt.”

This report appears in the November 2014 issue of Acres U.S.A.