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Fluid Journal : Fluid Journal 1996-1998
Winter 1997 Anutrient analysis of each soil in Figure 1 shows a similar NPK-S- Zn plus micronutrient content in each. Yet there is considerable difference in productivity. Why? Though each soil is chemically about equal, there is a large difference in organic matter content. The soil on the right (lifeless, high in clay, compacts easily) is low in organic matter. The soil on the left, which is high in organic matter, has extremely high microbiological activity. The grower's challenge is to develop the skills required to convert poor soil into productive high-yielding soil through good residue management, smart cropping practices, and proper fertilization. It is not a short- term program but a long-term commitment. This discussion will center on the specifics that must be learned in meeting that challenge. Organic matter a key Even though organic matter represents only two to four percent of the soil, its presence significantly improves root environment and soil productivity. The time and expense involved in converting residue into organic matter are well worth the effort because organic matter: • makes heavy soils friable, easier to work • promotes a crumbly soil structure • promotes greater water-holding capacity • improves water infiltration rate • increases aeration, which is important for phosphorus availability, nitrification of nitrogen, and microbial activity • supplies nitrogen and other nutrients in summer months when crops need them most. Organic matter contains tremendous amounts of nutrients as a reserve in the soil. That is why black soil is worth $2,000/A and lighter soil is worth only $500/A. Soil containing 5 percent organic matter contains 100,000 lbs/A of organic matter in the top six inches. Tied up in that organic matter is 5,000 lbs of nitrogen that can be broken down to feed crops in the summer. Residue cycle Understanding the residue cycle (Figure 2) is important in learning how organic matter can improve soil productivity. Nitrogen is the star player in the residue cycle. From the beginning of time, plants have grown, died, and decayed. The decaying process leaves the black residue we call organic matter. Billions upon billions of bacteria go to work, feeding on residue, digesting it, leaving behind the organic matter. But the process doesn't end there. Mineralization. Other families of bacteria decompose organic matter further into available ammonium nitrogen, phosphorus, and sulfur. Agronomists call this process "mineralization." The mineralization process can provide tremendous reserves of nitrogen, phosphorus, sulfur, and other nutrients to feed crops in July and August when demand is heaviest. Immobilization. Nitrogen and other nutrients that are released into the soil solution are absorbed by plant roots. Bacteria that digest residue require large amounts of nutrients that are taken from the soil solution and fertilizer. When nitrogen is removed from the soil by residue-digesting bacteria, the process is called immobilization because the nitrogen is taken away from the plant roots and is tied up in the residue. This is the residue cycle. Warmth, moisture best The process of decaying residue into organic matter requires nitrogen, phosphorus and sulfur, which are taken from the soil. Bacteria literally rob plants of nutrients during certain times of a growing season. The residue-decaying process works best in the top four or five inches of soil where aeration is better, and when the soil is warm, moist, and has a neutral pH. The process does not take place when the soil is cold, compacted, too wet or too dry, or too acid or too alkaline. Management critical Residue should be considered an asset, not a problem. Managing residue properly is the key to soil productivity and high yields. In every acre of land as many as 10 billion microorganisms live, work, and die. These tiny organisms make up the "microscopic society" beneath the soil. They devour and digest plant residue. They need warmth, moisture, and oxygen from the air. They release tremendous quantities of carbon dioxide. Without these bacteria and fungi, the best ground would become useless. We can help these organisms convert residue to organic matter by using proper tillage, and by providing enough food. Bacteria require a diet that consists of nitrogen, phosphorus, and sulfur to balance content of nutrients in the residue. Organic matter produced by these microscopic workers adds tilth and productivity to the grower's soil. Carbon/nitrogen ratio. Likening it to what happens to ruminants in the field will help us understand what happens FFF Review Good Residue Management Improves Soil Productivity Helps produce a more favorable high-yield environment for the conversion of residue into organic matter.
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