Historical aerial land photos can save money on lime use

Careful soil sampling can save money when applying lime, according to Harlan Palm, MU agronomy specialist. As an example Palm describes his work with farmers Tom and John Becker near Laddonia who wanted to bring rented cropland up to date in fertility, especially for lime. Normally many farmers apply two to three tons per acre. Palm helped the Beckers take extensive soil samples on 147 acres of rented land near Farber. At the customary rate two or three tons per acre would be applied. Two tons per acre on a 147 acre field would require a total of 294 tons and at three tons per acre an application of 441 tons would be needed. However, following the variable rate application due to careful soil sampling the Beckers applied only 95 tons for a savings of $2,000 to $3,000 on the 147 acres.

When applying lime, producers can save money by first taking a history lesson on land use, said a University of Missouri agronomy specialist.

"Farmers should go to their Farm Service Agency office and request aerial photographs of how the land was managed back as early as the 1940s to find causes for field variability," said Harlan Palm.

Information about prior land use helps in taking soil samples to determine proper rate of lime applications, he said.

Many farmers today are farming land that they did not grow up on. They may not know where things were on the land such as buildings, disturbances where a pond was dug out and filled in, or where fence rows were cleared.

"These areas are atypical from the rest of the field and their pH levels should be sampled separately," Palm said.

He studied historical aerial photos showing a 147- acre farm near Farber in Audrain County from 1939 to 1995. Photos indicated locations of buildings, farm yard, and two ponds prior to 1995.

The current renters consolidated smaller fields, typically 40 acres, into larger fields for greater efficiency and use of larger equipment. The impact on the soil of these disturbed areas is real whether it is soil pH or nutrients, he said.

Palm took soil samples on a varying grid density based on a 1962 photo. Fields uniformly farmed for 75 years were sampled every 2.5 acres. Around pond areas sampling was done at one sample per acre. Where buildings once stood, samples were taken in a denser 0.5 per acre grid.

"You would expect spatial variability where the farm yard and buildings once stood," Palm said.

Soil pH indicated on a prescription map showed great variability. About 40% of the land needed no additional lime at all. A trucker, equipped with a GPS guidance system, used the map to apply various rates of lime.

At their normal fixed rate of two to three tons per acre they would have applied 294 to 441 tons on the 147 acres. Because of grid soil sampling and variable rate application they needed only five tons for a field savings of $2,000 to $3,000.

Some areas needed five tons per acre where pH was low," Palm said, while other areas needed no lime.

"The premise of precision agriculture is recognizing variability within a field and the causes of variability. Soil pH is one of the principle factors that can vary across a field.

Even if all other inputs are at an ideal level , if the soil pH is not adjusted properly there will be variability in crop production, Palm said.