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Archive | Soils

Carbon Cycling, Carbon Building

In this article I hope to provide some ideas concerning carbon cycling and how to effectively build soil carbonic organic matter. There seem to be three primary means by which we can increase a soil’s carbon content: carbon imports, carbon generation and carbon induction. Each of these possible methods can also offer other strengths to a soil-building program, compost can provide a biological inoculum, humates can provide a biological stimulant.

Adequate levels of functional organic matter and a robust soil digestive system are sorely lacking in most all agricultural soils. This lack of humic substances and biology significantly reduces a soil’s water-holding capacity and the ability to release nutrients, all of which leads to large losses in crop quality and yield.

Meanwhile, increasingly higher levels of atmospheric carbon or CO2 are being produced by the burning of fossil fuels and land desertification. Carbon sequestration — the term has been thrown around like a rubber ball. What does it really mean for agriculture? How can carbon be stabilized in soils most effectively?

Importing Carbon

There are three primary carbon imports: Humates or leonardite, and their derivatives such as fulvic and humic acids. The humic substances present in these materials generally provide very good nutrient exchange. Biochar is also a stable carbon import but not as active as leonardite seems to be. Compost can also be a viable carbon import with the added benefit of a strong biological component. Compost, however, tends to have a lower level of stable humic substances when compared with other materials. A fair proportion of compost can degrade over a period of a few years. Continue Reading →

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.

Continue Reading →

Biochar: Prepping it for Soil

Biochar can benefit your soil, but only if properly prepared prior to application. In November 2007, scientists at the USDA National Laboratory for Agricul­ture and the environment (NLAE) in Ames, Iowa, began multi-year field trials to assess the effects of biochar on crop productivity and soil quality. Scientists amended almost 8 acres with biochar made from hardwood. Twelve plots re­ceived 4 tons per acre; 12 were treated with 8 tons per acre.

Author David Yarrow helps install a biochar test plot at Subterra in Kansas.

They found no significant difference in the three-year average grain yield from either treatment. Other USDA field and laboratory studies in Idaho, Kentucky, Minnesota, South Carolina and Texas showed hardwood biochar can improve soil structure and increase sandy soils’ ability to retain water. But soil fertility response was more variable.

USDA scientists violated four key principles for biochar use: 1) bulk char, in one large load 2) raw, uncharged char 3) sterile, uninoculated char, with only a tad of microbial life 4) synthetic salt fertilizer, tillage and other antibiotic practices.

After all, soil may get 25 or more inches of rain a year, but not all at once in a single event. Biochar, like water, is best added in a series of small doses so soil has adequate time to distribute and digest it. We already know from research in the Amazon that dumping five, 10, even 20 tons of raw char all at once into poor soil retards plant growth for one year and maybe two. But after that, plants erupt in impressive, vigorous growth.

But a dip in yield isn’t acceptable for production agriculture. Farmers can’t wait a year or two to harvest a profit­able crop. Professional growers need fast response and strong stimulus to growth. Economics and handling logistics require convenience and low cost, with vigorous growth from minimal applied material.

Fortunately, we are learning how to prepare char for optimum results in soil and on crops. Biochar research in America is hardly 10 years old, but solid research shows that properly prepared, intelligently applied biochar has dramatic effects on soil structure and plant growth at as little as 500 pounds per acre.

To prepare biochar for optimum effec­tive use in soil, there are four fundamen­tal steps: moisten, mineralize, micronize and microbial inoculation. Continue Reading →

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 →

Cover Crops on the Farm

Cover crops are increasingly being used by farmers across the country to suppress weeds, conserve soil, protect water quality and control pests and diseases.

A mix of rye, clover and vetch.

The fourth annual SARE/CTIC Cover Crop Survey, collected data from more than 2,000 growers from 48 states and the District of Columbia and provides insight into cover crop usage and benefits as well as farmer motivation for including cover crops as components in their farm management and soil health plans.

Responders reported a steady increase in the number of acres they have planted to cover crops over the past five years. They said the most important benefits of cover crops include: improved soil health, reduced erosion and compaction and increased soil organic matter. Other key benefits of using cover crops include: weed and insect control, provides a nitrogen source, attracts pollinators and provides deep taproots.

In the 2015-2016 survey, SARE and CTIC sought data on how farmers manage their fertilizer inputs as a result of their cover crop practices. Cover crop users were asked to indicate their level of agreement with a series of fertilizer-related statements, using a scale ranging from 1 (strongly agree) to 5 (strongly disagree). The statement that got the highest level of agreement was, “Using cover crops has enabled me to reduce application of nitrogen on my cash crop,” with 134 of 1,012 respondents strongly agreeing and 244 checking “agree.” The statement that had the highest level of disagreement was “Using cover crops has required me to use additional crop fertility inputs over time to meet the needs of my cash crop.” Continue Reading →