Soil sampling practices should reflect the tillage system which will be used on former CRP acres.
Returning Conservation Reserve Program land to crop and forage production will require soil sampling and pre-planning several months in advance of establishing a crop. To reduce risks of production problems related to soil fertility, soil samples should be taken four to six months ahead of crop establishment. This provides time for thoughtful decision-making and for ordering needed inputs. A large portion of land enrolled in CRP was not highly productive for various reasons, which adds to the necessity for soil testing to determine nutrient needs.
Soil sample test results obtained prior to placing land in CRP can be used in making fertilizer recommendations. But current test information will provide a better picture of current soil fertility conditions.
Soil sampling practices should reflect the tillage system which will be used on former CRP acres. If deep tillage such as plowing or chiseling is planned, samples for P, K, and lime should be taken from a standard 0-8 inch depth. However, if no-till or very shallow mulch tillage is planned, two samples are needed-0-8 inch deep for P and K and 0-4 for lime.
Plant residue on soil surface and the roots below the surface will contain some nitrogen. But availability of this nitrogen for use by crops will vary with the rate at which it decomposes. Not all of this nitrogen will be available in the first year of cropping.
In areas of grass sod, a 40-pound per acre nitrogen credit should be taken into consideration when selecting a nitrogen rate for corn.
If no-till corn is to be grown, some nitrogen will be needed early in the growing season, supplied as a pre-plant application or as starter fertilizer. Conventional tillage systems probably will not need starter nitrogen unless planted early in cool, wet soils
Broadcast applications of nitrogen in no-till corn will result in reduced nitrogen-use efficiency and be susceptible to volatilization and immobilization losses.
Regardless of the form of nitrogen fertilizer, placing it below plant residue reduces the potential for nitrogen losses. Urea or solutions containing urea are very susceptible to volatilization when surface applied in no-till systems.
Phosphorus and potassium soil test levels may have changed very little during the fallow CRP years, although some nutrient cycling may have occurred, bringing nutrients up from deeper in the soil profile.
Some sites may have received manure applications. This will have resulted in soil test level changes. Consider current soil test levels and develop an application plan if necessary.
Pay particular attention where perennial crops will be established and schedule fertilizer applications prior to any tillage. Utilize manure if available as a nutrient source. On soils with deficient levels of phosphorus or potassium, consider a starter fertilizer placed in a 2 x 2 band.
If soil pH is below recommended levels, a lime application should be scheduled. In cropping systems utilizing tillage, plan to apply lime if needed prior to tillage.
In no-till systems, lime will only react with the top four-to-five inches of soil. Standard lime recommendations normally are made assuming an eight-inch reaction zone and should be cut in half for no-till. Do not apply more than two tons per acre per year in no-till systems. Higher rates of lime on the surface can raise the pH higher than desired and may result in undesirable interactions with some herbicides.
It will be difficult to determine if sufficient rhizobia are present for adequate legume nodulation. To insure proper nodulation by soybeans or other legumes use inoculant for that crop. Those crops may have not been present over the last 10 to 11 years to permit desirable microbes to maintain adequate populations required for crop production.
Costs associated with this practice will be minimal and risks of reduced crop yields due to the problem can be eliminated. Rescue treatments are difficult to apply and have minimal effects in relation to the cost.
AY-281 Soil Sampling for P, K, and Lime
AY-256 Managing Nitrogen Fertilizers for Maximum Efficiency in Reduced Tillage Systems
Source: Stephen E. Hawkins 494-8367, David B. Mengel 494-4801
Rev 1/96
Cooperative Extension work in Agriculture and Home Economics. state of Indiana, Purdue University, and U.S. Department of Agriculture cooperating: H. A. Wadsworth, Director. West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30,1914. Purdue University Cooperative Extension Service is an equal opportunity/equal access institution.