By Todd Whitney
Fall is a popular time to collect soil samples from pasture and hay fields for nutrient testing. Time invested in soil sampling generally provides a good return on investment versus soil lab testing costs. Samples should be randomly gathered before the ground freezes with 1 composite sample per 15 probe samples (mixed in a plastic bucket) and used for the actual lab testing sample. Ideally, each sampling probe location should be Geo Tagged using a cell phone or other alternative marking methods. Consistency in sampling depths and using the same locations for repeat sampling years with increase comparison accuracy.
For extremely dry or lightly frozen soils, auger probes usually work better than standard cheaper straight cylinder probes. If lots of samples are needed, consider using a hydraulic soil sampling probe with a pickup mount or 4-wheeler to increase consistent 8 inches depth sampling.
For cropping or hay acres, each annual sample might represent 2 acres on a grid or 40+ acres in a field. Conversely, pastures are only core samples once every 3-4 years with two composite samples per rotational pasture. The key is knowing where soil types change and then gather representative samples from the different zones. For example, lower elevation hay meadows nutrient levels are likely higher than side slopes or plateaus. So, splitting pastures into testing zones may be useful and reduce overall fertilizer costs.
Whether you take samples in the fall or spring, be consistent and account for winter mineralization. Warmer average winter temperatures may result in more soil microbes mineralization and thus more nutrients available for spring root update. So, it may pay dividends to recheck soil nutrient levels in the spring and compared to fall tested levels.
In Nebraska, well nodulated, established alfalfa fields usually fix their own nitrogen needs from the air or soil, so the main alfalfa fertility focuses are usually pH, phosphorus and potassium. Sulfur content levels may also be analyzed with sandy, low organic matter soils.
For native grass hay and pastures, soil water content is the most limiting factor rather than fertility. Livestock producers may still benefit from pH, phosphorus, potassium and sulfur fertility testing especially for differing pastures and soil texture zones comparison. Again, it is recommended to soil test pasture every 3-4 years and at establishment.
More information regarding pasture and hay fields soil sampling is available at: https://cropwatch.unl.edu or https://beef.unl.edu