From Senior Lab Agronomist Fred Vocasek:
“Servi-Tech Laboratories has changed the method they use to measure soil organic matter on routine soil tests. Soil organic matter is composed of about 60 percent carbon. Soil testing for organic matter now involves heating a soil sample to ‘burn off’ the carbon-containing materials and leave behind the mineral components (like clay or sand). The resulting weight loss is attributed to organic matter. The challenge for the laboratories is to streamline the organic matter procedure to be able to test hundreds of samples per day.
“The traditional method (called ‘modified Walkley-Black’) uses concentrated sulfuric acid and a potassium dichromate solution to ‘oxidize’ the organic matter. The sulfuric acid generates the heat required for the chemical reaction to occur. The potassium dichromate solution actually changes color during the reaction with the soil organic matter. Laboratory instruments can measure this color change and relate this back to an organic matter value.
“The modified Walkley-Black process generates two hazardous wastes – sulfuric acid and chromium. These must be stored in approved containers, transported and treated by a federally-licensed firm, then buried about 500 feet below-ground in an federally-licensed disposal facility. Under federal law, Servi-Tech will be responsible for these wastes forever, even though they are in the custody of someone else, and located in another state.
“The ‘new’ method (called ‘loss-on-ignition’ or ‘LOI’) uses a high-temperature forced-air oven to provide the heat and air necessary to ‘burn off’ the organic materials. The sample is weighed before and after this ‘ignition’ or ‘ashing’ step and the weight difference is used to estimate the organic matter content.
“The automated weighing instrument is actually a custom-built piece of equipment currently in use all three of the Servi-Tech Laboratories. Its robot-like movements carry little ceramic crucibles (containing the soil) to one of five computer-controlled balances on the instrument. The five balances operate simultaneously. Hence five samples are weighed at once to 0.001 g. By recording a ‘before’ and ‘after’ weight for each sample, we can use this weight loss to estimate soil organic matter.
“The Servi-Tech Laboratories staff has studied the LOI method for several years before making the switch. Dropping the Walkley-Black method frees the company from future environmental liability. Many other soil testing laboratories have been using the LOI method for determining organic matter for several years, so the numbers are common throughout agriculture.
“Our own research and research by many others have found slight differences between the two methods. A difference of 0.1 percent to 0.2 percent OM is not uncommon. There are a few soils showing differences of around 0.5 percent. Temperature control and timing are critical for the LOI method. We know there are certain soils that may be affected differently by these factors and may exhibit a “greater than normal” difference between the two methods, but at this time we cannot predict exactly which ones might be affected. We are continuing to evaluate, refine, and update this method to deliver the most accurate organic matter values we can, while maintaining the turn-around time necessary to help you make sound agronomic decisions.”
HASTINGS, Neb. — An increase in grid sampling and a post-harvest race against the weather has farmers in Nebraska eagerly awaiting their soil tests and analyzing the results.
Servi-Tech’s Hastings Laboratory is in the midst of soil season and has tested more than 50,000 samples since October.
An ideal time for farmers to get their soil tested is right after harvest and before the ground freezes, said Orvin Bontrager, Servi-Tech’s director of education, who works out of Aurora, Neb.
Without testing the soil to see what nutrients are needed, a farmer is less likely to produce a sustainable crop for the next growing season.
Another reason for the increase of samples, Bontrager said, is because after harvest the ground is dry and vehicles can easily be driven across fields to get samples.
Farmers are wanting more of their fields to be grid sampled, a process that produces significantly more samples per field. In precision agriculture, grid sampling is used to look at variability in soil fertility in a given field, so growers can better manage the fertilizers they apply to their fields.
During the busy season of soil sampling, the Hastings lab can test 1,300 to 1,500 samples per day, said Nancy Jenny, lab manager. As many as 6,000 samples are stacked in the hallway waiting to be tested.
“We’re running as hard and fast as we can,” Jenny said.
The soil is tested for nitrogen, phosphorus, organic matter, pH level, zinc, sulfur and other micronutrients.
Farmers should get their soil tested for these nutrients just as a person adding oil to a vehicle should check the dipstick first.
The goal, Bontrager said, is to meet the needs of the crop to give it the most economic yield from the fertilizer that is used.
“If we don’t test the soil, we’re just guessing what nutrients it needs,” Bontrager said. “And that’s not what we want to do.”
When the lab is not busy, samples can be processed and results can be sent to the customer the next day. During the busy season, Jenny said it can take up to six days to return results to customers.
Servi-Tech was organized in 1975 by three farmer-owned cooperatives to provide technical service for agricultural producers in southwest Kansas. Today, Servi-Tech provides consulting to approximately 2,000 farmers across five states and over 1 million acres.
By Orvin Bontrager
Planting turnips or other cool season cover crops is gaining in popularity in Nebraska, especially on seed corn production fields. Usually the seed at 2-5 pounds per acre is broadcast behind the machines that are chopping out or removing the male inbred. This allows the plants to become established while the field is still being watered. Taller and denser foliage corn inbreds have enough shading that the young turnip plants will grow very little, if at all, until the corn is harvested.
As the crop is removed the cover crop grows rapidly from more light exposure and removing the residual nitrogen in the soil. This fall the very dry conditions have limited the growth to some degree.
Cattle have been placed in most of the fields to graze the tops and even the turnip root that is largely exposed above the soil surface. Below is a field that has been heavily grazed and shows the top feeding on some of the roots.
The down side of the turnips are some cattle may be negatively effected by eating the tops, until they get used to eating the plants. The large roots can cause some choking and even death if not monitored very closely.
The turnips this fall have dried out the soil significantly because of lack of rain. Winter and spring moisture will need to refill the top 2-3 feet of soil or the 2012 summer crop will start off short of moisture.