Friday, December 30, 2011
Of all the components of soil, organic matter is probably the most important and most misunderstood. Organic matter serves as a reservoir of nutrients and water in the soil, aids in reducing compaction and surface crusting, and increases water infiltration into the soil. Yet it's often ignored and neglected. Let's examine the contributions of soil organic matter and talk about how to maintain or increase it.
What is Organic Matter?
Many times we think of organic matter as the plant and animal residues we incorporate into the soil. We see a pile of leaves, manure, or plant parts and think, "Wow! I'm adding a lot of organic matter to the soil." This stuff is actually organic material, not organic matter.
What's the difference between organic material and organic matter? Organic material is anything that was alive and is now in or on the soil. For it to become organic matter, it must be decomposed into humus. Humus is organic material that has been converted by microorganisms to a resistant state of decomposition. Organic material is unstable in the soil, changing form and mass readily as it decomposes. As much as 90 percent of it disappears quickly because of decomposition.
Organic matter is stable in the soil. It has been decomposed until it is resistant to further decomposition. Usually, only about 5 percent of it mineralizes yearly. That rate increases if temperature, oxygen, and moisture conditions become favorable for decomposition, which often occurs with excessive tillage. It is the stable organic matter that is analyzed in the soil test.
How Much Organic Matter Is in the Soil?
An acre of soil measured to a depth of 6 inches weighs approximately 2,000,000 pounds, which means that 1 percent organic matter in the soil would weigh about 20,000 pounds per acre. Remember that it takes at least 10 pounds of organic material to decompose to 1 pound of organic matter, so it takes at least 200,000 pounds (100 tons) of organic material applied or returned to the soil to add 1 percent stable organic matter under favorable conditions.
In soils that formed under prairie vegetation, organic-matter levels are generally comparatively high because organic material was supplied from both the top growth and the roots. We don't usually think of roots as supplying organic material, but a study in the Upper Great Plains showed that a mixed prairie had an above-ground (shoot) yield of 1.4 tons of organic material per acre, while the root yield was about 4 tons per acre. The plants were producing roots that were more than twice the weight of the shoots.
Soils that have developed under forest vegetation usually have comparably low organic-matter levels. There are at least two reasons for these levels: (1) trees produce a much smaller root mass per acre than grass plants, and (2) trees do not die back and decompose every year. Instead, much of the organic material in a forest is tied up in the tree instead of being returned to the soil.
Soils that formed under prairie vegetation usually have native organic matter levels at least twice as high as those formed under forest vegetation.
What Are the Benefits of Organic Matter?
Organic matter is a reservoir of nutrients that can be released to the soil. Each percent of organic matter in the soil releases 20 to 30 pounds of nitrogen, 4.5 to 6.6 pounds of P2O5, and 2 to 3 pounds of sulfur per year. The nutrient release occurs predominantly in the spring and summer, so summer crops benefit more from organic-matter mineralization than winter crops.
Organic matter behaves somewhat like a sponge, with the ability to absorb and hold up to 90 percent of its weight in water. A great advantage of the water-holding capacity of organic matter is that the matter will release most of the water that it absorbs to plants. In contrast, clay holds great quantities of water, but much of it is unavailable to plants.
Soil Structure Aggregation
Organic matter causes soil to clump and form soil aggregates, which improves soil structure. With better soil structure, permeability (infiltration of water through the soil) improves, in turn improving the soil's ability to take up and hold water.
This property of organic matter is not widely known. Data used in the universal soil loss equation indicate that increasing soil organic matter from 1 to 3 percent can reduce erosion 20 to 33 percent because of increased water infiltration and stable soil aggregate formation caused by organic matter.
How Can I Maintain or Improve Soil Organic Matter Levels?
Building soil organic matter is a long-term process but can be beneficial. Here are a few ways to do it.
Reduce or Eliminate Tillage
Tillage improves the aeration of the soil and causes a flush of microbial action that speeds up the decomposition of organic matter. Tillage also often increases erosion. No-till practices can help build organic matter.
Most soil organic matter is in the topsoil. When soil erodes, organic matter goes with it. Saving soil and soil organic matter go hand in hand.
Soil-Test and Fertilize Properly
You may not have considered this one. Proper fertilization encourages growth of plants, which increases root growth. Increased root growth can help build or maintain soil organic matter, even if you are removing much of the top growth.
Growing cover crops can help build or maintain soil organic matter. However, best results are achieved if growing cover crops is combined with tillage reduction and erosion control measures.
A good supply of soil organic matter is beneficial in crop or forage production. Consider the benefits of this valuable resource and how you can manage your operation to build, or at least maintain, the organic matter in your soil.
- Barber, S. A. Soil Nutrient Bioavailability: A Mechanistic Approach. New York: Wiley, 1984.
- Brady, N. C. The Nature and Properties of Soils. New York: Macmillan Publishing Co., 1974.
- Plaster, E. J. Soil Science and Management. 3rd ed. Albany: Delmar Publishers, 1996.
- Tisdale, S. L. and W. L. Nelson. Soil Fertility and Fertilizers. 3rd ed. New York: Macmillan, 1975.
Thursday, December 29, 2011
(Fit Sugar) Deciding whether to buy organic or conventional bananas is a toughie. Organic ones are more expensive (usually at least 30 cents more per pound), and I've noticed that they seem to bruise more easily – anyone else notice that, too? The major difference between the two are that conventional bananas are grown with synthetic fertilizers, insecticides, and herbicides to protect the crops from mold, bugs, and disease. On the other side, organic farmers use natural fertilizers such as manure and seaweed, insect predators and barriers to prevent pests, and they weed by hand or mulch in order to prevent weeds.
You may be thinking that all those chemicals used to grow conventional bananas are no big deal because you peel the fruit. But the chemicals are not just on the outside of the banana — they leach into the soil that is used to grow the produce. So even if you peel your banana, it doesn't prevent you from ingesting small amounts of those chemicals. Although you may feel better knowing most experts agree that the amount you ingest poses little threat to your health. If you're concerned about the nutritional value of your food, there are ongoing studies exploring the connection between pesticides and nutrients in foods; so far it looks like organic is healthier. Organic produce is also better for the planet since chemical pesticides make their way into the soil and run off into water sources.
With the sky-rocketing prices of food, buying organic may not be feasible all the time. Bananas, along with avocados, mangos, papayas, and pineapples have been found to have the lowest pesticide residue. However, apples, cherries, grapes, nectarines, peaches, pears, raspberries, strawberries have very high pesticide residues so you might want to splurge on organic.
Tuesday, December 20, 2011
(Napa County Master Gardeners) Over the past few months, Napa County Master Gardeners have been conducting a field trial of two types of shelling beans. We wanted to find out which of the two would perform better in our county’s varied microclimates. The plants needed to mature before the rains arrived so that we could harvest the dry beans. Well, we almost made it.
Napa County has four main climate zones, as defined by Sunset’s Western Garden Book. Carneros and American Canyon fall in Zone 17, where marine effects make for cool summer temperatures in the 60- 75 degree Fahrenheit range. In this zone, the growing season lasts from May to early December.
Zone 15 includes the area around Mt. Veeder, Spring Mountain and Howell Mountain. This zone is described as “cool coastal,” with frequent afternoon summer wind and a growing season from May to November.
The valley floor is considered Zone 14, or coastal warm, with some marine air moderating the heat. The growing season can begin early, in mid-March, and last until mid-November.
Finally, the foothills of Pope Valley and Lake Berryessa belong to Zone 7, characterized by hot summers and a growing season from May to mid-October. Cool fall temperatures arrive early in Zone 7.
Our field testers began the project with heirloom bean seeds from Rancho Gordo, the Napa store. We selected two varieties: ‘Tepary’ and ‘Christmas Lima.’ Tepary is a small golden bean, about the size of a lentil. Christmas limas are large, kidney-shaped beans with a colorful cream and burgundy skin. We selected these two types because they vary in the number of days from transplanting to harvest, although they require the same growing conditions.
Beans are a warm-season crop. They need a soil temperature of at least 65 degrees to sprout, and they grow best when temperatures are in the seventies and eighties. Our 25 team members reside in all four climate zones. They planted their seeds between June 15 and June 30.
Some gardeners sowed their seeds directly in the ground, bypassing the transplanting process. In most gardens, the seeds sprouted readily in five to eight days and grew steadily after that. Those who started seeds in containers transplanted the seedlings when they had their first true leaves. A few gardeners had poor germination and replanted near the end of June.
If you want to plant shelling beans next summer, here are a few pointers:
Avoid planting beans in beds where you grew beans or peas the previous year. Bacteria that inhibit growth can accumulate in the bed.
Beans grow best in full sun and prefer fertile, well-drained soil. Plant them one inch deep, two to six inches apart, and in rows 12 to 14 inches apart. For large beans, allow more space between them. Plants need to be far enough apart to allow for air circulation to prevent disease. This is particularly important for dried beans since they stay on the vine a long time.
Provide one inch of water every seven to ten days. Regular watering is critical during flowering and pod growth. Beans do not typically need much fertilizer.
Christmas limas are pole beans. Stake them when they start to vine. They can reach seven to eight feet in height, depending on their support. In contrast, Tepary beans are bush types that do not require staking for good production, although they don’t object to it.
Pods form about two weeks after flowering. When blooming ends, stop watering. This alerts the pods that it is time to begin drying out.
Potential bean pests include birds, cutworms, beetles, aphids, spider mites and whiteflies. In our Napa Valley trial gardens, aphids were a recurrent problem that most gardeners controlled with a vigorous water spray, although the spray did disturb some blossoms and pods. Insecticidal soap is an alternative; be sure to spray the underside of the leaves as well as the top. For more pest management information, visit the Master Gardeners during office hours (see below) and inquire about University of California publications on integrated pest management.
When green beans appear, pick them frequently to ensure continued production. For dried beans, leave the pods on the plant until they begin to dry out. When the pods are at least half yellow, it’s time to harvest them. Both types of shelling beans need to dry completely before shelling.
Uproot bush beans and place them, dirt and all, on an old sheet. Put them where they will have good air circulation and low humidity. When they are completely dry, put the pods in an old pillowcase and bang them around to loosen the beans from the pods.
Our trial team is harvesting Christmas limas now. Some gardeners simply cut the plant at ground level, leaving the vine to dry. Then they harvested the individual brown pods and spread them out to dry thoroughly. These shrunken pods may not look like they have viable beans inside but they do. When they have dried sufficiently, the beans can be easily removed from the pod by hand.
The Master Gardeners participating in the bean trials harvested just under a pound of dried Tepary beans for each 20 plants. Initial data for the Christmas limas suggest about a pound per 10 plants. This is a satisfactory yield, and we are pleased with our trial.
We concluded that both the Tepary bean and the Christmas lima can thrive in Napa County, with only moderate attention and care. Whether planted in Calistoga, Carneros, East Napa or on the valley floor, these two varieties performed well.
Unlike fresh beans, the dried beans store well. When you have eaten or processed all the tomatoes, zucchini, cucumbers and figs you can manage, try Rancho Gordo’s recipe for Tepary Bean Dip. People tell me it rocks.
Napa County Master Gardeners (http://cenapa.ucdavis.edu) answer gardening questions Monday, Wednesday and Friday, 9 a.m. to noon, at the UC Cooperative Extension office, 1710 Soscol Ave., Suite 4, Napa, 253-4221, or 877 279-3065.
Copyright 2011 Napa Valley Register.
Saturday, December 10, 2011
(The Nation) Organic agriculture is considered to be a holistic food production system that sustains the health of soils, ecosystems and people. This system is a set of natural ecological processes, biodiversity and cycles adapted to local conditions, which discourages the use of inputs that adversely affect the environment. Further, this method avoids the use of hybrid seeds, synthetic pesticides, fertilisers and genetically modified organism to influence the growth of crops. The main objective of organic farming is to protect the earth’s resources and produce safe, healthy food with almost zero residual impact on the soil and environment.
The main source of organic matter is top and roots of the plants, especially Jantar, Barseem and Guvara (leguminous crops), while animal and poultry wastes are deemed to be a second source. Its (organic matter) chemical composition shows that it consists of carbon, hydrogen, oxygen and content of water. The microorganisms present in the soil decompose the matter that not only increase the water, but also the air and water flow rates through fine textured present in sandy soils. The organic matter also act as a mulch thus reducing erosion, shades of the soil and keep it cool in summer and warm in winter.
The other way is conventional farming system characterised by mechanisation, monocultures and the use of synthetic inputs, such as hybrid seeds, fertilisers and pesticides, with an emphasis on maximising productivity and profitability. Scientists believe that It degrades the soil structure, texture and topography. Therefore, besides maintaining the soil quality, the organic system sustains biodiversity.
According to the International Federation of Organic Agriculture Movement (IFOAM), organic cultivation is developing rapidly. The statistical data obtained from 141 countries indicate that the share of organically operated agricultural land continues to grow in many countries. Reportedly, “32.2 million hectares of agricultural land are managed organically by more than 1.2 million producers, including smallholders. In addition to the agricultural land, there are 0.4 million hectares of certified organic aquaculture.” The regions with the largest areas of organically managed agricultural land are Oceania, Europe, and Latin America.
Pakistan is quite different as the farming community here is mainly concerned with productivity, instead of quality which usually motivates the producers to adopt farming methods that help to boost their production/profits. The Green Revolution in Pakistan during the 1960s brought substantial changes in the farming system. But with the passage of time, it proved ineffective and deteriorated the soil fertility due to the excessive use of chemical fertilisers. Its impacts on human and animal health were also disastrous. The improper use of pesticides started to pollute land, air and underground water resources, while pests gradually develop resistance to chemical pesticides.
Agriculturists and researchers believe that organic farming has long lasting and positive effects not only on soil texture, but also on human and animal health. Various studies conducted by agricultural economists to compare organic and conventional farming in Pakistan reveal that initially the yield obtained through organic method is less than conventional method. But over the passage of time it will either become equal or surpass the quantity obtained through conventional method. The organic products would also fetch higher prices than the conventionally produced products, if they would reach in specialised organic markets. Although the supply of animal/poultry manure in Pakistan is very low as compared to the demand. However, proper management of the farming system can overcome the shortage specifically by growing leguminous crops.
Regrettably, in Pakistan no specialised organic market exists where organic products can be sold at reasonable prices. That is why local organic produce cannot be sold at better prices. It is high time that the government, in collaboration with local NGOs, make an effort to promote organic agriculture to save the environment. More so, there is need to develop markets for local organic products in the cities to encourage cultivators by selling their produce at higher rates, besides motivating consumers to purchase residual free fruit and vegetables at cheap rates.
Yasir Mehmood, Muhammad Bahzad Anjum and Mukhtar Ahmad
The writers are freelance columnists.