Aug 24, 2010

Lime can improve your bottom line

By Darryl Warncke, Michigan State University

Lime is an investment that will need to be made in most fields sooner or later. Farmers are continually looking for that miracle material that will improve growth, quality and yield of crops. That miracle material may eventually come along, but until that happens, good soil management is the answer for good crop production.

Good soil management starts with collecting soil samples and having them tested. Soil pH is probably the most important number on a soil test report because it influences the availability of all nutrients, the activity of soil macro and microorganisms, the severity of soil-borne disease organisms and the efficacy of herbicides. A nutrient management program in terms of nitrogen, phosphorus, potassium and the micronutrients can be top notch, but without having the soil pH in the correct range, crop growth and production will be poor.

During each growing season, I receive calls regarding poor plant growth in certain areas of vegetable and crop fields. Is the problem disease, nematodes or soil acidity? In most situations upon checking the soil pH in the poor and good areas, the cause of the problem is clear: acid soil conditions. In nearly every case, a soil test revealed very acid soil conditions.

Depending on the field, the soil pH in the poor areas ranged from 5.3 to 4.6. Most vegetable, fruit and field crops grow best when the pH of mineral soils is between 6.2 and 6.8. Depending on the severity of the soil acidity, the aboveground plant growth may appear slightly stunted to very spindly. As the soil pH decreases, especially below 5.5, availability of calcium and magnesium decreases and availability of aluminum, iron and manganese increases.

Initially, plants growing under these quite acid conditions may grow OK, but with time the plants gradually accumulate toxic amounts of aluminum that cause gradual browning and death of the roots. This generally occurs in mineral soils when the pH is near or below 5.0.

In muck soils, most crops will grow well down to a soil pH of 5.2 or 5.3, since these soils contain only small amounts of aluminum. When the pH does drop below 5.0, plants begin to accumulate toxic amounts of manganese that cause the browning and eventual death of the roots. If farmers or consultants observe poor crop growth in small areas, look at the roots. Browning roots may be an indicator of acid soil conditions. Small acid soil areas in a field are an indicator that the whole field needs lime. When lime is needed, as indicated by a soil test, lime can be the “wonder” material farmers are looking for. Application of lime when needed will provide an excellent return on your investment.

How do soils become acidic?

Over time, soils become acidic due to: 1) leaching of calcium and magnesium, 2) application of nitrogen fertilizers, 3) removal of calcium and magnesium in harvest portions of a crop, 3) decomposition of plant residues and soil organic matter and 4) acidic rain. Therefore, it is important to monitor the soil pH over time by sampling at least every two years when growing vegetable crops. Farmers need to recognize that the soil pH is not uniform within a field. Due to glaciation in the past, soils in Michigan are quite variable, even when they appear uniform. Grid soil sampling studies done a number of years ago in numerous fields across Michigan showed soil pH to commonly vary by 1.0 pH unit (e.g. 5.5 to 6.5), and in some fields by as much as 2.0 pH units. Hence, it is good to not have one soil sample represent too large an area. For vegetable crops, I suggest one sample for 10 acres or less. Soil sampling is an averaging process. The pH value on a soil test report is an average of all the soil cores taken, and the pH throughout the field will vary around that value. For example, if the soil test is 5.9 for the field average, the pH may vary from 5.4 to 6.4. This is why acid spots show up in fields even though the soil test may show the field soil pH is reasonably OK.

Over the years, soil test summaries have shown around 20 percent of farm fields need at least 2 tons of lime per acre. This past year, the Michigan State University soil test summary showed 25 percent of farm fields had an average soil pH below 6.0, with 8.8 percent having a soil pH below 5.5. Yield and quality are definitely being lost on those fields with a soil pH below 5.5. The lime recommendation for soils with a pH below 6.0 will be at least 2 tons per acre.

Sandy soils tend to become acidic more rapidly than clayey soils due to more rapid leaching out of calcium and magnesium. The table shows that the sandy soils are more likely to need lime than loam or clayey soils. For the loamy sand soils, nearly 15 percent are in serious need of lime (pH is less than 5.5). Since most vegetable crops are being grown on sandy soils, it is very important for vegetable farmers to regularly monitor the soil pH in their fields.

Some fields are becoming acidic due to lime not being applied when needed. Part of this may be due the increasing acreage of land being rented. Farmers tend to be hesitant about applying lime to land that they may or may not have for crop production the next year. Farmers need to recognize the benefit they can receive in crop production during the application year and landowners need to recognize that lime maintains the quality of their land. When lime is needed on rented land, farmers need to seek a multiple-year lease to guarantee the return on their investment or ask the landowner to share the cost of the lime, prorated over a four-year period.

Return on investment

Lime not only neutralizes soil acidity, it also is a valuable source of calcium and magnesium, which are essential for producing good-quality vegetables. Calcitic limes primarily provide calcium, and dolomitic limes provide both calcium and magnesium. Agricultural lime contains a range of particle sizes. The small particles react quickly in the soil to neutralize acid conditions. The larger particles react slowly to continue neutralization of soil acidity and maintain the soil pH in a favorable range over a number of years, usually three to five.

When lime is needed, it is suggested to apply it six months prior to planting the next crop. This allows time for the lime to react and raise the soil pH to a more favorable level. Fall application after crops are harvested allows for this to occur. However, if soils are sampled in the spring and a need for lime is determined, application and incorporation prior to planting will still provide good benefit. When lime is needed, the most important thing to do is get the lime applied.

At $22 to $25 per ton, lime may initially seem like quite a large investment. But when one considers that yield is being lost under acid conditions, the investment may not be that great. Lime will provide benefit for many years. Push the pencil. How much increase in crop yield will be needed to cover the cost of 2 or 3 tons of lime (about $55 to $78, including a spreading fee)?

Depending on the crop, increasing the soil pH from 5.5 to above 6.0 may increase crop production by 25 percent or more. Therefore, chances are pretty good that investment in needed lime will pay for itself with improved crop quality and yields in one or two years. Over a four-year period, lime will definitely put more money in your pocket.

Investment in lime will need to be made at some point in time. It is better to make that investment before the soil becomes too acidic and starts costing crop yield.

Periodically applying 2 tons of lime per acre, as indicated by a soil test, stabilizes the soil pH and crop production and is easier on the budget. In addition to neutralization of soil acidity and improved crop productivity, other benefits from applying lime include: 1) increased supply of calcium and magnesium, 2) improved microbial activity, 3) improved soil structure and quality and 4) improved efficacy of herbicides.

Bottom line: When lime is needed, get it applied. It will put more money in your pocket.