Robert E. Leiby and David L. Dunbar Lehigh County Cooperative Extension Office Crop rotation is a practice that has been used for centuries in grain production around the world. In the northeast United States, crop rotations are used extensively. Generally, we know that better crop yields are achieved when we rotate, even in the absence of serious weed, insect, disease or fertility prob lems. Even so, the effects of crop rotation are still not completely understood. Greg Roth, Penn State agronomist, relays recent research from the University of Minnesota which sheds some new lighten the effects of crop rotations and how they might be exploited even more. In this series of studies, several corn and soybean rotation schemes were compared to conti nuous com, continuous soybeans, and continuous com and soybeans with alternating varieties each year. The objective of these exper iments was to compare yield levels among the various cropping sequences. The researchers found no advantage to alternating crop var ieties each year under continuous com or soybeans. With continu ous cropping, second year com and soybean yields were lower than first year com and soybean yields. The pattern of yield decline after the first year differed, though, between the two crops. For com, yields declined from 172 bushels per acre to 145 bushels per acre in the second year. Yields then increased slightly the follow- Lime application during the winter allows the limestone time to react and Hi-Calcium Martin LIMESTONE Crop Rotations ing year to 151 bushels per acre and remained essentially the same in subsequent years. Soybean yields declined from 48 bushels per acre to 45 bushels per acre in the second year, and dropped again to 43 bushels per acre in the third year. Bean yields in subse quent years then remained at this level. Consequently, it appears that com yields drop sharply at first in a continuous system and then recover somewhat, while soybean yields decline slowly, reach a bottom, and then stay there. It appears that soybeans would follow themselves better than com in a rotation. Yields of alternated com and soybeans averaged 164 to 44 bushels per acre and were not as high as first year corn (172 bushels per acre) or soybeans (48 bushels per acre). Compared to monoculture, alternating crops improved yields by 10 percent for com and 8 percent for soybeans. First year yields compared to monoculture were 15 percent higher for com and 17 percent higher for soybeans. This indi cates that both crops respond near ly the same to rotation and that the full rotation effect is not achieved with alternating crops. These results suggest that a three crop rotation might yield more than the two-crop corn-soybean rotation, commonly used in many areas today. Researchers have documented similar crop rotation responses for corn in Pennsylvania. These responses may be even greater where specific pest problems associated with continuous com are prevalent. In Pennsylvania, It's the right time to apply lime Hi-Magaesium Boost Corn, * some of the most serious of these pests include com rootworms, perennial weeds, shattercane and gray leaf spot. Where these pests are a problem, rotation should help to maintain or increase yields while reducing pest control and fertilizer expenses. The Secondary Nutrients While calcium, magnesium and sulphur are called secondary nutri ents, they are essential for the growth and good health of all plants and animals. Calcium (3.2 percent) is the fifth most abundant element in the earth’s crust, while magnesium (2.5 percent) and sulphur (0.1 per cent) are ranked eighth and thir teenth, respectively. These plant nutrients occur naturally in soils, but are usually present in mineral or organic forms unavailable to plants. The growth of food and fiber crops is frequently limited by availability of these nutrients. The soil must be fertilized to provide amounts adequate for optimum plant nutrition. Many factors can affect the availability of calcium, magne sium and sulphur to plants. The best estimates of availability of these nutrients can be determined by soil analysis or a combination of soil and plant analyses. Howev er, field observations and defi ciency symptoms are also impor tant diagnostic tools. Soil texture indicates the rela tive amounts of sand, silt, and clay present. Sandy soils are most often deficient in die secondary nutri ents. Higher amounts of clay and organic matter enable soil to retain these nutrients against weathering For prompt delivery contact your local Martin Limestone dealer or call Blue Ball, Pa. (800) 233-0205 (717) 354-4125 Soybean Yields (leaching) and to provide more nutrients as soil minerals decom pose and organic matter is miner alized by soil microbes. Organic matter is particularly important as a source of sulphur for plants. Low soil temperatures tend to limit the ability of plants to take up the secondary nutrients. Release of sulphur from organic matter is slowed by low tempera ture. This is one reason why sup plemental sulphur may be benefi cial to crops planted in cold, wet conditions. Highly weathered, acid soils usually contain relatively low amounts of available calcium and magnesium because they have been leached. Soil acidity affects the availability of many nutrients. Uptake of the secondary nutri ents can be affected by the pre sence of large amounts of other nutrients in the soil. Magnesium absorption is particularly depress ed by the presence of large amounts of available potassium. Uptake of calcium can also inter fere with magnesium utilization. When magnesium uptake is depressed in grasses, cattle graz ing that forage may suffer from “grass tetany,” caused by low levels of blood serum magnesium. Recent data indicate high availa bility of phosphorus can boost magnesium uptake. Sulphur uptake can be depressed by the presence of large amounts of available nitrogen. Crop plants get their require ments for calcium, magnesium and sulphur from one or more sources, including: soil clay, soil organic matter, soil minerals, commercial fertilizers, agricultur al limestone, irrigation water, rainfall and snow, and kiln dust. Sulphur in soils is present in a number of organic and inorganic forms. Soil bacteria and fungi play an important role in making sul phur available to plants. Energy For Farming The USDA’s Economic Research Service offers the fol lowing observations and predic- tions about agricultural energy /’'iLENWOOD ■ FORMING 809 Glonwood Drive Ephrata, PA 17522 717-733-9590 Roofing And Siding 29 Gauge Gahani/.e 29 Gauge Painted 26 Gauge Galvalunic 26 Gauge Painted All Panels Cut To Length - Coverage 36” Width We Also Stock The Following Items: • Pre-Hung Doors • Ridge Vents • Agri Build Windows • Ridgolators • Roll Door Track • Trolleys and Hardware \ new Product In Our Line . STANDING SEAM ROOFING \l.mul.u.uirett it the mb mu NOW YOU CAN CALL US TOLL-FREE AT 1-800-582-9956 Lancaster Farming, Saturday, April 6,1991-C3 consumption: If the world price of crude oil averages $3O per barrel this year, farm energy expenses for diesel fuel, gasoline, liquified natural gas, and electricity will probably rise 10-15 percent from 1990. An average price of $4O per barrel would raise farm energy expenses around one-fourth. In addition, the increase in the motor fuels tax will increase farm energy expenditures 1.5 percent. With only a modest change in planted acreage forecast for 1991, energy use likely will remain about even with last year. Although rapid petroleum price increases tend to encourage ener gy conservation in the long run, short-run adjustments in energy consumption are often difficult to make because farmers tend to change their holdings of equip ment slowly. Fanners’ consumption of per troleum products has been steadily declining since 1982, regardless of planted acreage. While acres planted influence energy use, other factors are more important. The switch from gasoline to diesel engines, reduced tillage opera tions, larger multi-function machines, and innovations in crop drying and irrigation have contri buted to the decline in fuel consumption. While no-till fanning has not been widely adopted, reduced til lage systems are now as prevalent as conventional tillage systems in many parts of the country. It is clear that crude oil prices dictate the price fanners pay for diesel fuel. As of November, the U.S. Department of Energy fore cast that crude oil and diesel fuel prices would increase 30-40 per cent in 1991, but unpredictable geopolitical forces will shape the final 1991 petroleum price structure. Since agriculture directly con sumes only 3-4 percent of all ener gy used in the U.S., changes in the farm sector’s use will have little impact on petroleum prices.
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