Brush up on soil knowledge

Gloria Hafemeister

Juneau — Every year farmers, prepare the soil, plant seeds, add fertilizer, manage weeds, hope for rain and anticipate a good harvest.

With margins getting tighter, however, farmers who are serious about making a living at it know they must learn as much as possible about soil health, keeping soil in place and putting fertilizer on at the exact right amount and at the right time.

During the last month, University of Wisconsin soil and crop specialists have been touring the state, providing the latest research updates to guide farmers and their consultants as they prepare for next year’s growing season.

The last of the series of meetings was held in Juneau on Friday Dec. 9, with about 50 farmers and crop consultants in attendance.

One of the topics of discussion was the use of cover crops as a means of holding and growing nutrients and building the life in soil. Cover crops also provide a protective blanket over winter so that the bare soil is not exposed to wind and water erosion.

These two soil samples are the same soil type. The one on the left is after 11 years of continuous no-till farming, and the one on the right is conventional tillage.

Frost seeding

One specific topic covered by Matt Ruark, associate professor UW-Madison, was frost seeding red clover. Ruark shared results of tests at Arlington on red clover and Sheboygan County research on berseem and crimson clover.

“The magnitude of nitrogen credits from clover varies from year to year," Ruark said. "There are many trade-offs, and you will need to consider your crop rotation system and what you are trying to accomplish.”

He said red clover as a cover crop is an excellent way of providing nitrogen for the next crop, and it also captures growing degree day accumulation.

The nitrogen credit to corn is frequently cited as the major economic benefit of the practice, Ruark said; however, there is growing evidence that properly managed cover crops can cause a yield increase in the following crop.

In the Arlington study, the red clover was killed off in the fall. The Sheboygan study of crimson and berseen clovers did not terminate the crop.

In the Sheboygan study, the berseem clover was taller and the crimson clover was patchy, shorter and denser, but both provided good nitrogen credits.

As a rule of thumb, Ruark said, each 6 inches of growth will provide 40 pounds of nitrogen.

Timing and application

Carrie Laboski, soil fertility and nutrient management specialist with UW-Madison, reported findings of several studies related to timing and application of nutrients.

“Weather makes a difference in how plants use nitrogen," Laboski said.

Soil type and the amount of moisture going into the growing season also make a difference.

She provided preliminary conclusions of studies on nitrogen application timing at Lancaster and Marshfield research stations.

Timing is not the biggest issue in yield results, Laboski said. Other factors include the amount of carbon in the soil, drainage and cumulative precipitation prior to planting.

She concluded her presentation by mentioning some of the frequently asked questions she gets about soil fertility.

The No. 1 question she gets is “Why are my soil tests fluctuating so much?”

Laboski pointed to several factors, including sampling depth, sampling location and sampling time.

"Results on soil tests taken right after harvest will be different than if you wait a month because of the decomposition of the trash," she said. "The amount of rainfall, will also influence results.”

Lab differences can be a factor, but not as likely, she said. Weather and soil pH at sampling time will also influence soil test results.

Laboski suggested taking a longer view of what is happening in the fields and looking at trends.

A second question she frequently gets is “Why are there some dead spots in my field?”

She suggested looking at several factors, beginning with a soil sample.  Tissue samples of nearby plants or checking for things like nematodes may also be helpful.

Often, it is problems with the pH of the soil, Laboski said. If pH is the problem, she suggested looking at the various nutrient levels, including calcium, magnesium and manganese.  When lime is called for, consider what type of lime is being applied. If a lime is high in magnesium and soil tests show magnesium levels are okay, it may be appropriate to apply a different type of lime that is lower in magnesium.

A final question referred to concern about a field of corn that looked pale and unhealthy.

Laboski pointed out that when fields are fertilized with manure, cool weather makes it take a little longer for the plants to reap the benefits of the nutrients supplied by the manure. As the temperatures go up, plants take up the nutrients, and the plants catch up later in the season.

Regarding taking tissue samples of plants to determine the problem with a particular field, she said timing of the sampling is important. If sampling is done too late, the test results will not be accurate; and once results are received and corrections are made, it is too late to make an improvement in the condition of the plants.

Wet harvest

Regarding this year’s wet harvest conditions, Francisco Arriaga, Extension soil specialist, offered advice to producers.

“Reducing axle loads and maintaining low equipment tire pressure will help,” he said.  “Managing the equipment traffic pattern can also help contain and reduce soil damage.

“Don’t assume subsoiling is needed. First, use a penetrometer to measure the extent of the compaction. In some cases, surface tillage may be needed just to address any ruts that may have been made in the field.”

Finally, he suggested cover crops might be helpful for preventing problems with wet soil at the time of harvest because of their ability to loosen the soil.