Organic matter helps soil retain more moisture

Contribution of organic matter to soil and plant health was detailed during the annual Sustainable/Organic Production seminar in Tulare by Tim Stemwedel, founder of California Organic Fertilizers.

One of the most valuable contributions of organic matter—especially in drought years—is the increased waterholding capacity of the soil. A 1 percent increase in organic matter in the soil equals 0.5 acre-inch of available soil water, or 13,000 more gallons, said Stemwedel.

Organic matter in the soil is defined as anything that was alive at one time. The decomposition of organic matter is the first step in the nutrient cycle and involves many types of microorganisms. Their concentration and diversity determine the speed and extent of nutrient cycling in the soil.

Stemwedel said a biologically active soil stimulates the active nitrogen and carbon cycles—releasing nutrients. Lack of biology will inhibit the release or mineralization of organic matter and reduce nutrient availability.

In agricultural systems, crop residues make up a majority of the material that will cycle into soil nutrients. Ten pounds of crop residue will eventually break down into about a pound of organic matter. It adds free nitrogen and helps reduce erosion. Organic matter also fosters a wealth of soil organisms including bacteria, earthworms, algae and fungi. One teaspoon of soil, Stemwedel noted, can contain about 1 billion bacteria.

"Those are the decomposers; they do it all," Stemwedel said.

Bacteria in the soil are nitrogen fixers, suppress soil disease and convert sulfur into sulfate. Algae are also a nitrogen fixer and a nutrient source for fungi and bacteria. Soil microorganisms also produce antibiotics to control soil pathogens.

Healthy soil, Stemwedel said, is composed of solids, air and water. Biological properties are the living organisms, physical properties are the types of soil and chemical properties are the nutrients in the soil. Organic fertilizer, he added, impacts all properties.

The total economic benefits of biodiversity with special attention to the services that soil organisms provide worldwide are estimated to be more than $1 billion annually, he said.

Adding compost—a form of organic matter—said Aaron Rumble from crop amendment company Recology, has become a water-saving tactic for some growers. Besides increasing a soil's water-holding capacity, it also replaces soil carbon.

A lot of soil carbon was lost in the 1960s and 1970s, Rumble said, when fertilizers were applied without previous soil testing. Soil sampling can answer a lot of questions about soil health, he added. Soil amendments can be added to improve health, but Rumble said to ask questions of the supplier—such as the source of the compost and compatibility with food safety regulations.

Compost production has changed in the past 20 years, with more temperature monitoring and the addition of water and more frequent turning.

Blending compost with other soil amendments, including gypsum and limestone, is done frequently, Rumble said, with 80 percent of their loads delivered containing blends of different materials. Compost is no longer just being broadcast over the ground, Rumble noted. Applicators can tailor placement depending on the grower's need. With drip irrigation, compost can be applied at any time.

He advised growers not to wait until "something is broken" in their soil to ask for help. Avoiding compaction, soil sampling and making sure nutrient levels are correct will help build healthy soils.

Dennis Chessman, with the U.S. Department of Agriculture Natural Resources Conservation Service, emphasized soil health and the role of crop consultants in sustainable production. His agency is moving forward with an emphasis on soil health rather than erosion as in years past, he said. With soil models provided by University of California conservation-tillage specialist Jeff Mitchell, Chessman looked at soil structure. Soil with little organic matter does not have micro-aggregates to hold it together and is more likely to crust over after irrigation or rain, Chessman noted.

Healthy soils can absorb water and resist compaction, Chessman said. NRCS and Mitchell have been promoting conservation tillage—leaving crop residues and minimizing soil disturbance. Soil carbon is released with tillage and that impacts function of the biological system, he added.

Natural systems and cropping systems have significant differences. Natural systems harvest the most sunlight, leak very few nutrients—including carbon dioxide—and have diversity. They also make maximum use of applied water and nutrients. Chessman said intensive crop production affects soils by disturbance, loss of diversity, less cover of living and dead plants, and no continual root presence.

Those differences impact how water is cycled through soils, nutrient cycling, soil temperatures and carbon sequestration. Natural systems have more resistance to disease and resilience. Conservation tillage, which more closely resembles a natural system, has developed into a technically viable and economic alternative to current crop production practices, said Mitchell.

Conservation tillage is the integration of ecological management with modern, scientific agricultural production. The practice is gaining acceptance worldwide, Mitchell noted, and is considered an alternative to both conventional agriculture and organic agriculture.

"It's not easy but it is important," Mitchell said. "People are working on it and believe progress is possible."

(Cecilia Parsons is a reporter in Ducor. She may be contacted at ceciliaparsons8@gmail.com.)