As soils dry producers can gear up for next year's growing season by soil sampling now to determine the status of soil nutrients in fields and pastures. A year with above normal rainfall followed by excellent crop yields produced conditions that have allowed many of our soil nutrients to become depleted. Moreover, fertilizer prices have started to rise again—all the more reason to soil test now to determine which soil nutrients will need to be added for the coming crop season.
How often should I spend the time and money to soil sample? How many samples should I collect in a field? How is the profit from soil testing affected by crop and fertilizer prices?
These are all questions you might ask regarding soil testing your fields. Many farmers agree that soil testing provides important information for fertilizer decisions; however, it is likely that most farmers do not use soil testing on a routine basis. Research has shown that soil testing, especially for nitrogen, is likely to be most profitable in especially dry or wet years and in years when fertilizer prices are unusually high.
Due to the cost of fertilizer materials, annual soil testing has become the standard recommendation to ensure that application rates are correct. In addition, since nitrogen is subject to leaching and volatilization, annual soil testing is essential to predict residual soil levels and to determine proper supplemental fertilizer rates.
The objective in soil sampling is to obtain a composite that represents the entire area to be fertilized or limed. A composite sample is comprised of 12 to 15 cores or slices of soil (approximately 1 inch wide by 6 inches deep) collected from the sampling area and thoroughly mixed. A sampling area can be any field or pasture or portion thereof that is relatively uniform in soil type and cropping history. Typically, the sampling area for a composite sample should not be greater than 40 acres.
Typically, soil samples are collected to a depth of 6 inches, measured from the soil surface after non-decomposed plant materials are pushed aside. Deviations from the traditional 6-inch sampling depth may be required if fertilizer has been placed deeper in the soil by tillage or banding.
Moreover, in recent work in Nueces County, deep soil sampling found a significant amount of plant nutrients stored in the soil profile down to 24 inches. In fact, in two separate studies this past year in grain sorghum crops soil samples collected to 24 inches contained 117 and 159 pounds per acre of plant available nitrogen prior to fertilizer application. Research plots at these sites fertilized at traditional rates produced the same yields as those that were not fertilized, because residual, stored nutrients were sufficient to meet plant needs. This makes a strong case for soil testing and for sampling at depths greater than 6 inches.
The Coastal Bend Soil Testing Campaign, coordinated by local offices of the Texas AgriLife Extension Service, for farms in Aransas, Bee, Jim Wells, Kleberg/Kennedy, Live Oak, Refugio, Nueces, and San Patricio Counties is underway now through November 30, 2010. Soil samples may be turned in at your local County Extension Office for analysis at up to a 33 percent reduced testing fee.
Soil tests will be run by the Texas A&M University Soil Testing Laboratory for a reduced fee of $6 per sample for the Routine Analysis and $10 for Routine /Micronutrient Analysis during this campaign. This special soil testing campaign is for row crop farmers and ranchers with improved pastures. Soil sample bags and test information sheets may be obtained in the County Extension Office. For more information call the Nueces County Extension Office at 361-767-5223.