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Fluid Journal : Fluid Journal 1993-1995
2 Fluid Journal Spring 1993 temperatures, residue tie-up and denitri- fication loss. In other words, broadcast- ing fertilizer on residue, where levels of fertility are already high, can be a wast- ed effort. In addition, surface residue can immobilize tremendous quantities of nitrogen, phosphorus and sulfur. The result is poor fertilizer response. Liquids the answer Now that we're familiar with some of the problems, let's investigate how liq- uid starter can help solve them. Weed pressure. Placing liquid starter about 2 inches below and 2 inches to the side of the seed is ideal for young corn plants and below germinating weed seed's roots. "Starter will get plants up faster so they will form a canopy sooner to shade out weeds," says Dr. Allen Bandel, Extension Soils Specialist at the University of Maryland. Stratification. When starter fertilizer is used in a conservation tillage system, it is placed deep enough in deficient soil to optimize uptake. Lack of tillage has a tremendous effect on the distribution of nutrients in the soil. The data in Table l show stratification from five years of minimum tillage. Because of the lack of mixing of non-mobile nutrients, phos- phorus accumulated in the upper 3 inch- es of soil. The sub-surface from 3 to 24 inches was deficient. Table 1. Phosphorus stratification after 5 years minimum tillage. Depth Phosphorus (in) (ppm) 0-3 84 3-12 10 12-24 8 A deep root system plays a critical role in raising high yields at a low cost per bushel. The root system is a dynam- ic, vital system that expands, lives and dies-day after day. In a single plant, 14,000 new roots can emerge each day, replacing old roots no longer alive. Some roots may live about three to five days, turn brown and die. Measurements on a single rye plant have averaged a total root growth of three miles per day. A healthy corn crop, therefore, needs a large functioning root system to col- lect moisture and nutrients to feed each plant. Higher yields require higher pop- ulations and higher populations require a large volume of moisture and nutrient- rich soil for the more extensive root mass to exploit. The more extensive root mass requires deep fertility with high nutrient concentrations. If one studies high yields (over 200 bushels), the common thread is deep fertility with high soil test levels of the major nutrients deep in the soil profile. Again, liquid starter, together with root zone banding, preplant or sidedress, is the key program for producing high yields under conservation tillage. Nutrient tie-up. Placing liquid fertiliz- er under residue can reduce nutrient im- mobilization loss. Starter fertilizer ap- plied at planting time on conservation tillage will feed the crops and "cheat" the microorganisms by placing nutrients out of reach. "Residue tie-up" or "immobilization" results from the high biological activity in the surface soil in conservation till- age. Conditions are close to ideal for residue digestion. The necessary ingre- dients (warmth, moisture, pH and aera- tion) tend to promote a highly reactive biological environment or the decompo- sition of residue. The amount of nutri- ents absorbed in this process is different for different types of residue. For corn, decomposition absorbs roughly 20 pounds of nitrogen, 8 pounds of phos- phate (P2O5) and 3 pounds of sulfur (S) per ton of corn residue! Wheat residue may absorb up to 30 pounds of nitrogen per ton of residue. Any fertilizer applied on the residue will be swallowed by hungry organisms. It's only temporary, but it can cut yields by reducing nutri- ents available to the crop at a time when they are needed. Certainly, an argument can be made that immobilization loss "is not all that bad" because these nutrients can be re- leased to feed the crop at a later date. Meanwhile, the organic matter produced by immobilization can be used to im- prove soil structure. The benefits of or- ganic matter are well-known: it reduces compaction, which increases aeration and increases water-holding capacity. Organic matter also increases the capac- ity to retain exchangeable nutrients (es- pecially ammonium, potassium, calcium and magnesium). Table 2 gives the approximate amounts of nutrients that can be tied up by residue. Several conditions---includ- ing residue amount, tillage practice, temperature, and moisture --- control nutrient immobilization. From Table 2 one can see that significant amounts of nitrogen, phosphorus and sulfur are tem- porarily immobilized into the organic fraction. Research in Kentucky has shown a 34-bushel per acre increase from 80 pounds of nitrogen applied sub-surface at planting time, compared to broadcasting (Table 3). Positionally unavailable K. Potas- sium in the starter can give excellent response (Table 4). In this Wisconsin test, starter proved to be the big equal- izer. That is, yields from conservation Table 2. Approximate amount of nutrients tied up during residue decomposition per ton of residue or by a 125 bu/A corn crop (3 tons residue). per ton per 125 bu crop Nutrient (lbs) Nitrogen (N) 20 60 Phosphorus (P2O5) 8 24 Sulfur (S) 3 9
Fluid Journal 1996-1998