Soil Sampling for Fertilizer and Lime Recommendations

Why soil sampling and testing? Soil sampling and testing is an investment which leads to profitable use of lime and fertilizers. A nutrient management program starts with a representative composite soil sample and continues with the lab analysis, interpretation of the results and ends with an appropriate recommendation. Evaluation of changes in soil pH and available nutrient levels over time requires collection of soil samples.

Soil Sampling Goals: 1.To collect a soil sample that is representative of a field or portion of a field 2.To obtain info. about a field and use that info. to make management decisions Nutrient management Herbicides Crops Others

3 Basic Approaches Random Grid Management Zones

Before Soil sampling… Get the knowledge (County Soil Survey Report) about the differences in soil characteristics within the fields and these differences include: - Productivity - Field topography - Texture - Drainage - Color of topsoil - Past management

Continue… A composite sample: consists of a number of sub- samples thoroughly mixed. If the sampling area and past management features are reasonably uniform, each composite sample in a random system can represent 10 or 15 acres. Grid sampling will represent considerably less area. Management Zone sampling will generally represent larger areas. However, most likely these soil features are quite variable within a single field. Thus, areas with reasonably uniform soil characteristics (management zones) should be identified before sampling.

Sampling a Field 1.Random Sample should represent no more than a 20 cores composited to produce one sample Collected in a zig-zag pattern across the field Advantage Relatively inexpensive Disadvantage Get an average not a measure of variability

Sampling a Field 1.Random

Sampling a Field 2.Grid Field is divided into equal areas Generally 300’ x 300’ (2 a) 10 cores (min.) composited within each grid cell in a 10” radius around a georeferenced point Advantage Provides a good assessment of variability Disadvantage Expensive

Intensive soil sampling Variable rate technology (VRT) allows different amounts of fertilizers to be applied across the field on the basis of available nutrient levels. Intensive soil sampling is required to produce a nutrient map with various levels. Grid sampling is the main approach. From the economics standpoint, grid size 300 * 300 feet is enough, but for some research purposes, a finer grid size is desirable. A continuous nutrient level map can be developed based on intensive grid sampling.

A grid sampling and nutrient map of P

Sampling a Field 2.Grid

Sampling a Field 3.Management Zone Divides field into areas that are similar for a defining characteristic Utilization of a dense data set (next slide) to define mgt zone boundaries 20 cores composited to produce 1 sample/zone Collected in a zig-zag pattern across the zone Zone borders & sampling points can be georeferenced Advantage/Disadvantage Provides an assessment of variability better than random, not as good as grid Cost Effective

Precision Ag technologies for defining boundaries of soil sampling mgt zones Grid sampling results Soil conductivity Aerial imagery Soil pH Near-infrared Yield maps Slope

Determine the uniform soil areas Consult your County Soil Survey Report to determine the soil types.

Soil Maps

ElevationSlopeEc

Soil conductivity (Veris & Em38) On-the-go pH On-the-go NIR

Average standardized yield Variability in yield

Some other factors… Management history -Cropping rotation -manure spreading -Limestone application and stockpiling. Unusual spots should be avoided or sampled separately when needed - Atypical or exhibits plant growth problems -Trees in the fields Field edges

Soil sampling equipment Soil sampling probe/screw augers/shovel Plastic pail Clean containers for samples: sample boxes or paper bags

A sketch map indicating each soil unit/management zone to be sampled will be helpful. Here are some examples:

Sample collection Once the sampling area has been defined, a composite sample may be made from each unit. - Use a zig-zag sampling pattern Each sample should consist of vertical cores or slices of soil approximately inch thick. Keep the core/slice depth consistent. Especially for reduced-tillage and no-till systems because of nutrient stratification. Subsoil Samples can provide additional information on lime or fertilizer recommendation,when - Coarse textured soils with finer textured zone in the subsoil - The soil is organic

Timing of sampling and testing Soil pH and extractable nutrient levels do vary some with the time of the year. Therefore, it is best to take samples at the same time of the year to track changes in nutrient status. Do not wait when additional soil sampling is needed, for example when crop management systems are changed. Early soil test results may allow a timely development of a fertility management plan. For example, liming should be done 6 month before planting to let the lime fully incorporate into the soil.

Frequency of sampling In most cases, it is adequate to sample and test the soil once every 3 years. Some soils (e.g. sandy soil) with low (<6 me/100g) cation exchange capacities (CECs) may need more frequent sampling. Intensive cropping systems undergoing large fertilizer input and possible high crop removal. Annual soil sampling and testing is suggested (e.g. vegetable crops grown on sandy soils). In large farm operations, the fertility program based on entire farm sampling at one time may not be practical, although good practice, sampling and testing 1/3 of the acreage each year is an alternative.

Soil sampling summary Develop a map of uniform areas within the field. Make use of soil survey maps, topography and management history. Designate the sampling areas of economic importance. For each composite sample, collect 20 cores to the appropriate depth using a zigzag pattern. Thoroughly mix the soil cores in a plastic bucket. Partially dry very wet samples before mixing. Fill a soil sample bag or box with the composite sample. Fill out the information form with all the pertinent cropping management information. Send the composite soil sample and information sheet to a reliable soil testing lab for analysis.