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Root System Architecture & Nitrogen Management

Researchers questioned whether current improved rice varieties are suitable for organic agriculture. Through an experiment focused on nitrogen use efficiency (organic and inorganic sources) and root system architecture, they concluded that varieties bred for high-nitrogen inputs may not be suitable for organic agriculture — reinforcing the need for varieties to be bred specifically for organic agricultural systems. Here the researchers present their work:

The production and extensive application of N fertilizer to crops worldwide has contributed to major environmental problems due to soil leaching and greenhouse gas emissions that play a large role in ozone depletion. Sustainable agriculture aims to conserve natural resources with the mitigation of climate change, and there is increasing interest to move toward organic agriculture. An important issue regarding the acceptance of organic agriculture is the question of productivity. In addition to readily available ammonium and nitrate ions, the soil of organic agriculture can contain a wide range of organic nitrogen compounds such as peptides, proteins, free amino acids, amino sugars and nitrogen heterocyclic compounds. Continue Reading →

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 Testing: The Need for Total Testing

What many farmers probably don’t know about soil testing is that most soil tests only tell us what is soluble in the soil. They do not tell us what is actually there in the soil, no matter what fertilizer salesmen might like to imply. To find out what is actually there requires a total acid digest similar to what is used for plant tissue analysis. Mining labs run these total acid di­gests on ore samples which are crushed, ground and extracted with concentrated nitric and hydrochloric acid solutions, but a mining assay does not determine total carbon, nitrogen and sulfur as a plant tissue analysis would. These ele­ments need a separate procedure essen­tial for evaluating soil humic reserves.

Total soil testing is key to understanding your soils’ needs.

Most soil tests measure total carbon, which then is multiplied by 1.72 to calcu­late soil organic matter. This assumes that most of the carbon in the soil is humus of one form or another. While this may or may not be true, determining the car­bon to nitrogen, nitrogen to sulfur, and nitrogen to phosphorus ratios is a good guide for evaluating organic matter, and this requires testing total nitrogen, sulfur and phosphorus as well as carbon.

While carbon in almost any form is a benefit to the soil, it helps enormously if it is accompanied by the right ratios of ni­trogen, sulfur and phosphorus. Though these ratios are not set in stone, a target for carbon to nitrogen is 10:1, for nitro­gen to sulfur is 5.5:1 and for nitrogen to phosphorus is 4:1. This works out to an ideal carbon to sulfur ratio of 55:1, and a carbon to phosphorus ratio of 40:1. Because soil biology is very adjustable these targets are not exact, but achieving them in soil total tests is a good indica­tion of humus reserves that will supply the required amounts of amino acids, sulfates and phosphates whenever the soil food web draws on them. Continue Reading →

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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Composting Tips and Strategies for Balanced Compost

Composting tips are common to find, but information to build a composting program is really what most people are seeking.

A wheelbarrow full of compost that is ready to apply.

Charles Walters, as quoted in Secrets of the Soil, by Peter Tompkins and Christopher Bird, says of microbial life: “There are more kinds and numbers of minute livestock hidden in the shallows and depths of an acre of soil than ever walk the surface of that field.”

As much as a cattle rancher’s livelihood depends on healthy livestock, he and his cattle’s very lives depend on armies of beneficial microbes for survival. Microbes are the foundation for all life on earth; without them the earth would be nothing more than a barren rock. There would be no fertile soils, no plants, no trees, no insects, no animals and no humans.

Soil bacteria secrete acids that break down rocks, and enzymes that break down dead plant and animal matter into rich, life-giving soil, while transforming minerals into forms that are usable to plants. Microbes help prevent soil erosion, combat disease organisms that attack plants, animals and humans, and are an important link our food chain.

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Organic Nitrogen: When are Nitrogen Units Not Nitrogen Units?

Organic nitrogen and inorganic nitrogen: what’s the difference?

A farmer gives a plant organic humus fertilizer to plant.

Organic growers frequently attempt to quantify the amount of organic nitrogen they add to their soil ecosystems in the same manner that conventional growers use inorganic nitrogen units to calculate their nitrogen requirements. Logically, they reason that a ton of organic material with 4 percent nitrogen content as verified by a laboratory test will provide 80 pounds, or units by some determinations, of nitrogen.

The truth is that organic nitrogen sources vary in their efficiency of transformation into soil components over a much broader range of response than do inorganic synthetics, which offer precision measurement and a repeatable predictability of release. Use of inorganic nitrogen units to determine nitrogen needs for organic growers is therefore problematic. A popularly available and reliable conversion algorithm between tested inorganic nitrogen and untested organic nitrogen in organic soils does not exist, however. Without such an algorithm there can be no scientific basis of comparison. Continue Reading →