III. SOILS, AGRICULTURE, AND ENVIRONMENT
Crop Nutrient and Pest Management Next Section>>
Most farmers in Indiana use chemical soil amendments, such as fertilizers and pesticides. If they are used properly, they promote productivity and do little harm to the environment. In fact, high-technology agriculture might enhance the environment, because if cropland is more productive, less of it is needed to produce the food we require. The lower land requirement leaves more land for natural areas. For soil evaluation, we consider herbicides and the major plant nutrients, nitrogen, phosphorus, and potassium. As for many other practices, the rules apply mostly to cropland.\
Subsections:Crop Nutrient Management | Major crop nutrients | Pest management | Soil evaluation rules - Crop nutrients and pest management
Crop nutrient management is the practice of applying the proper amount of plant nutrients at the right time and right place to accomplish production goals while protecting the environment. The first step is to get a good soil test and to continue testing every three years. Then, when planning how much fertilizer to apply, all sources of plant nutrients must be considered, including animal manure, crop residue, contributions from previous crops (e.g., N from soybeans or alfalfa), and chemical fertilizer.
In most cases the farmer’s concern is to add enough fertilizer for optimum crop yield. In some cases, however, fertility levels of soils are excessively high, usually because of over-application of manure from confined livestock operations. Sometimes too much manure has been applied to fields near the feeding operation just to get rid of it and to avoid having to transport it long distances. Occasionally chemical fertilizer is applied to fields already fertilized adequately or excessively by manure. The main problem of excess nutrients is that they can leach through the soil and get into ground water supplies or erode with the soil and get into surface water bodies that are used for drinking water. In water, the nutrients can have direct or indirect effects. Excess nitrate nitrogen in water can cause illness in adults and death of babies. Too much phosphorus results in excessive algae growth in surface waters. The algae can kill fish because it covers the water surface and prevents light from reaching the plants growing on the bottom of the lake. These plants die, and as organisms decompose them, they use up all the oxygen in the water. Some algae may give off toxins that kill fish directly. If fertility levels are too high, they can be decreased by taking grain, hay, or other plant material off the field. Forage crops such as alfalfa remove large amounts of P and K.
back to topMajor Crop Nutrients
The nutrients needed in largest quantity by Indiana crops are nitrogen, phosphorus, and potassium. These nutrient elements are the main ones in chemical fertilizer and are also abundant in livestock manure, most of which is applied to fields. Excess soil acidity is controlled by adding lime, which also adds the plant nutrient calcium and often magnesium.
Nitrogen
Nitrogen (N) is a major plant nutrient and is the first nutrient listed on the fertilizer label. It exists in soils in three main forms—organic-N, ammonia-N, and nitrate-N. There is not a fully reliable soil test for N, so N recommendations are based on expected yield levels.
The N recommendations considered for soil evaluation apply mainly to corn and wheat crops. Sometimes N is used on hay or pasture to maximize production. Soybeans and other legumes, such as alfalfa and clover, fix N from the air to supply their own needs. On fields that regularly receive farm manure or where legumes are grown in rotation with row crops, fertilizer N recommendations will be lower than on fields depending entirely on mineral fertilizers. Usually N is not added to trees except when they are used for some special purposes such as biomass production.
Nitrogen levels cannot be built up permanently by fertilizing land, since excess quantities are lost by leaching, denitrification, or other means. Leaching of nitrogen into the groundwater or into streams is a serious form of water pollution that can occur when soil is over-fertilized. It is not only a waste of money but also harms the environment. Thus, it is important not to supply more N to the soil than is needed by the crop.
Fertilizer N is recommended according to the potential of soils to produce crops, especially corn and wheat (Table 6). Crop yield potential depends on water-holding capacity, plant rooting ability, and other important soil properties. For soil evaluation, soils with the highest yield potential have a “high” recommended N rate. Those in the “medium” group have a somewhat lower expected yields and a somewhat lower N requirement. Many of these soils are still very productive.
One of three nitrogen application rates (Low, Medium, or High) should be checked for soil evaluation according to soil properties, regardless of the tillage-cropping practice checked. Keep in mind, however, that in practice, the rule applies mainly to corn and wheat.
Table 6. Nitrogen fertilizer recommendations for corn and wheat.
Phosphorus
Phosphorus (P) is a very important element for plant growth. It can be referred to as “the key of life” because of its role in many critical life processes such as cell division and forming genetic material of the cell nucleus. Most soils in Indiana contain abundant amounts of phosphorus, but it is not available to plants. When crops are removed from a field, P goes with them, so the available P content of soils is gradually reduced. To offset those losses, P fertilizer is added. Chemical soil tests determine the available P levels of soils, and farmers add P according to recommendations based on these tests. Recommendations usually include phosphorus application at seeding. On pastures, P is usually applied at the time of renovation. Over the years, many farmers have added more P than the minimum required, so available P in the soil has been built up.
On some farms, P levels have been built up to very high levels. Previously, soil P had been considered to be immobile in soils—that is, it did not leach or move through the profile. We know now that if P levels become high enough, soluble P can leach into drain tile lines, and from there get into streams and lakes. Most P remains in surface horizons, however. If these soils are eroded, P accompanies the sediment into streams and lakes. Once in the water, the P attached to soil particles dissolves and adds more soluble P to the water. This P promotes algae growth, which can cause fish to die. On farms with high levels of available P in soils, special precautions should be taken to prevent soil erosion, and soil P levels in the soil should be reduced. This is done by growing crops that take up a lot of P and removing the crop from the field. Alfalfa contains much P, so taking an alfalfa crop off the field, in hay or silage, for example, will gradually reduce the available P level in the soil.
For soil evaluation, levels of P in the soil are given on the site card in units of pounds per acre. Some soil testing laboratories report P levels in parts per million (ppm). Ppm values are half of the pounds per acre values, i.e., 15 ppm = 30 lb./acre. If the level of available P is low, fertilizer P should be added. If the level is moderate, normal farm operations should continue but with no P application. If P levels are high, special consideration should be given to lowering P levels. The value of 200 lb. P per acre for excessive P is arbitrary. Research is underway to determine the level at which P becomes too high.
Potassium
Potassium (K) is also very important as a plant nutrient. It controls stomate opening and closing which influences transpiration of water from the plant leaves. It tends to improve stalk strength and reduce lodging that can be caused by heavy nitrogen fertilization. It can delay early ripening that can be caused by phosphorus. Application of potassium according to soil test results can increase both yield and quality of crops produced.
Unusually high available K soil tests are rare in Indiana, but provision is made in soil evaluation for very high levels.
Lime
Liming is the application of material that will reduce the acidity (raise the pH) of the soil and supply it with calcium (Ca). Lime is any material which is added to the soil to correct an acid condition. Usually ground limestone is used.
Soil acidity is measured on the pH scale; pH 7.0 is neutral, higher pH values are alkaline, and lower pH values are acid. For most agricultural crops, the soil should have a pH of 6.5 to 6.8. For corn and soybean rotations, soil pH values in the range of 6.0 to 6.5 are adequate.
back to topPest Management
Pest management is a comprehensive approach to controlling weeds, insects, and diseases. It includes scouting fields, using crop rotations, planting resistant crops, encouraging beneficial insects, and appropriately applying crop protection products. Crop scouts examine a field to determine the nature of damage (whether it is due to disease, insects, soil compaction, or other causes), the extent of the damage, and what parts of the field are damaged. With this information, the farmer can provide the correct action at the proper time to only the part of the field affected. Without scouting, the farmer might apply too much chemical to the entire field just to “make sure” the problem is addressed. This wastes money and resources and could result in contamination of the environment.
Some insects and disease organisms can survive only on one kind of crop. If that crop is grown every year, such as continuous corn, the population of the pest can build to very high levels. If, however, other crops are grown in alternate years, the pest might not be able to survive, or it may become less of a problem. In soil evaluation, the rule to apply chemicals appropriately is illustrated with herbicides.
Some soil-applied pesticides (herbicides, insecticides, fungicides, etc.) react with organic matter in soils, thus, application rates may need to increase as organic matter content increases. Usually within any soil texture class, a darker soil has more organic matter than a lighter colored one. However, a certain amount of organic matter darkens a sandy soil more than it does a clayey soil. This is recognized in the pesticide rule below.
It is very important to read the labels on all pesticide containers before using the chemicals. Some herbicides have two or three recommended application rates, depending on the organic matter content of the soil. This is because some of these chemicals are partially inactivated (made less effective as weed killers) by soil organic matter. There is also danger of crop damage from applying too much of some herbicides on sandy soils that have a low organic matter content.
back to topSoil Evaluation Rules—Crop Nutrient and Pest Management
Mark Nitrogen Application Rate: High for soils with all these properties: 1. more than 40 inches to any limiting layer, Medium for other soils with all these
properties: Low (or no nitrogen) for all other soils. |
Mark Phosphorus: Apply if available P is <30 pounds per acre. Do not apply if available P is 30 to 200 pounds per acre. Deplete excess if available P is >200 pounds per acre. |
Mark Potassium: Apply if available K is <210 pounds per acre. Do not apply if available K is 210 to 500 pounds per acre. Deplete excess if available K is >500 pounds per acre. |
| Mark Lime Apply for soils that have a pH 6.4 or lower as noted on the site card. |
Mark High herbicide rate YES for soils with either of these combinations of properties: 1. poorly or somewhat poorly drained, any surface texture, and
dark surface color; or |
