Continuing Study Relating Potassium Uptake to Manure and Tillage

Final Report for FNC94-060

Project Type: Farmer/Rancher
Funds awarded in 1994: $2,500.00
Projected End Date: 12/31/1995
Matching Non-Federal Funds: $25,500.00
Region: North Central
State: Iowa
Project Coordinator:
Richard Thompson
Practical Farmers of Iowa
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Project Information


The 300 acre Thompson farm is a diversified grain and livestock farm. Corn, oats and hay are fed to the hogs and beef cattle. The fertility needs for the farm are primarily met by the manure from the 75 cow-calf operation, 80 sow farrow to finish operation and the bio-solids from a city of 12,000 people. All of these materials are stored in a sealed concrete bunker that was built in 1986. Since 1984 all the row-crop acres (150) are in randomized-replicated test plots. The Thompson farm was involved in the early development of the following concepts: 1) Farmer managed research design. 2) Ridge-tillage without herbicides. 3) Two row cover crops on ridges for weed control. 4) Swine management systems without antibiotics in the feed or water. 5) Deep row planter starter fertilization for ridge-tillage. 6) Manure/sludge storage and applications. 7) Three crop narrow ridge-till strips. 8) Rotation of tillage, reintroduction of the moldboard plow into a reduced tillage program. 9) Practical application of tillage in the dark. 10) Farmer and wife as dual presenters for off-farm presentations.

The Thompson farm has been practicing sustainable agriculture since 1968. This farm is well known through presentations and field days given to 30,600 people since 1986. Visitors from forty-two different foreign nations have toured the farm. Each year a research report is sent to all Land Grant University libraries in the United States, farmers, researchers, state and federal personnel and environmental groups around the world. Approximately 1000 copies of the 1995 report are being printed. All attendees at the annual field day, all other scheduled farm tours and off-farm programs receive the report.

The project goal is to answer the following questions.
1) Will plowing under manure/bio-solids in the fall following the hay crop solve the potassium uptake problem?
2) How much manure can be applied and plowed under following hay?
3) At what place in the row crop rotation should manure be applied in the spring ahead of planting?

Description of Trials:
Question! How effective is spring manure application just prior to corn planting? Treatments were randomized and replicated eight times. Treatment #1 – fall manure application on the ridges and not covered. Treatment #2 – spring manure applied just prior to corn planting and covered with the planter. Treatment #3 – no manure. Treatment #4 – planter row fertilizer. Treatment #5 – fall manure plus planter row fertilizer. Treatment #6 – spring manure plus planter row fertilizer. Answer! 1994 field #2 results in Figure 7.

[Editor’s note: Some figures and graphs could not be posted online. If you would like to see these, please email us at or call us at 800-529-1342. Thanks]

Question! Do we need additional potassium when plowing under hay and manure? Randomized and replicated 4 times. Treatment #1 – broadcast potassium. Treatment #2 – no potassium. Answer! 1994 field #5 results in Figure 9.

Question! Do we need planter row fertilizers for corn following the fall manure plow down? Randomized and replicated 6 times. Treatment #1 – 20+14+27 (PRF) 2 inches below the seed. Treatment #2 – No PRF. Answer! 1993 field #4 CD results in Figure 1.

Question! Do we need planter row fertilizer (PRF) for corn following soybean ridges and spring applied manure? Randomized and replicated 6 times. Treatment #1 – No PRF. Treatment #2 – 20+14+27. Treatment #3 – 26+17+34. Treatment #4 – 34+23+46. All starter placed two inches below the seed with the planter. Answer! 1993 field #1 N results in Figure 5. Field #1 had rye growing on the ridges in the spring of 1993, this was the year of the flood and very cool summer weather. The results of 1995 are different and show no yield advantage for (PRF) planter row fertilizer (Figure 10). 1995 was a hot, muggy summer and field #4CD was fall manured/moldboard plowed in 1992.

The same variety of corn will be used for all experiments so that comparisons can be made about different treatment effects following fall manure/plow down and spring manure over the top of ridges.

Question! Should we spring apply manure and/or use planer row fertilizer for soybean production when following the fall manure/plow down after hay? Answer is NO. The data is shown in Figure 11.

History of Manuring and Fertility Management:
Before 1983, all of the cattle and hog manure were composted in an effort to reduce weed populations, a common problem on farms using manure as a fertility source. Although composting was effective in killing weed seed, it was time consuming. Furthermore, nitrogen leaching became a problem if composting was not completed on schedule due to unfavorable weather. Potassium leaching from the pile was also a problem when using wet materials, despite proper handling.

Corn and soybeans yields increased 25 to 30 bushel per acre when manure was properly composted and incorporated, in comparison to fall-spread raw manure. The question was whether the yield increase as a result of composting, or whether yield was suppressed by improperly handled raw manure.

After much trial and error, composting was abandoned as ridge-till weed management without herbicides developed. Nevertheless, it was necessary to find a way to handle stockpiled manure to decrease nutrient leaching. Municipal bio-solids was added as an additional nutrient source in 1984

In 1986, a large concrete holding tank, or bunker, was built to store manure and sludge prior to spreading. The bunker helps reduce nutrient losses by retaining all the liquids. Both leaf and soil samples now test higher for nitrogen and potassium.

All manure/bio-solids were spring applied and covered with the planter from 1987 through 1992. the corn crop in the dry May and June of 1992 showed potassium deficiencies even though the field had spring manure applied that contained 100 pounds K20 in 90,91 and 92. The manure was spread over ridges and covered by the planter action and later cultivated twice. The corn roots in this experiment did not find the fertility.

Starting the fall of 1992, the hay and pasture fields had manure applied in September and October and plowed under. The reasons for fall application were several, the bunker was full and spreading all the manure in the spring was a tremendous work load. The reasons for plowing were to save the nitrogen, move the phosphorus and potassium lower in the soil profile, and eliminate the odor. The 1993 corn was planted on the flat surface of these fields with the Buffalo planter, the split depth bands were lowered as far as possible and the residue guards raised to a horizontal position. The new practice of split depth bands gives much better flotation of the row units on the soft tilled soil. The Buffalo ridge-till planter does an excellent job of planting on soft tilled fields, so there is no reason to have another kind of planter to plant flat tilled fields. The sweep is left on the planter to level the soil and remove weeds.

1993 Results:
Fall manure/plowed fields grew faster than spring applied manure ridged field. A liquid starter (20+14+27) placed two inches below the corn seed did not increase yields in the fall manure/plow plots in field #4 CD (figure 1). 1993 was a very wet year.

Tests are in place during 1994 to determine if additional purchased potassium should be applied ahead of the plowing operation. The plowing will occur only once during the five and six year rotations. Research done by Gyles Randall at Minnesota shows that plowing moves the stationary nutrients, like phosphorus and potassium lower, in the soil profile.

In 1993 corn yields in the two fields that were fall manured and plowed were considerably higher than the field where manure was spring applied over ridges and then tide-till planted (Figure 2). Is the yield increase due to the timing of manure application or manure placement? The 1994 experiments (Figure 7) tested the practices of fall and spring manuring broadcast over ridges versus no manure for control. These corn yields and management returns will be compared to the fall applied manure and plowed under system Figure 10.

The 1993 management return was about $150.00 more for the fall applied manure that was plowed under compared to the spring applied manure spread over the top of soybean ridges (Figure 3). The spring applied manure needed planter row fertilizer and side-dress nitrogen while the fall applied system did not respond to either application of purchased fertilizer.

All manure was spring applied to the corn following hay in the years 1988 through 1992. Figure 4 shows corn yields following hay were less than corn following soybeans during these years. In 1993, when the manure was fall applied and plowed under, the corn following hay was 31 bushels per acre more than the corn following soybeans. We will be able to follow the fall/plow vs. spring/planter manure applications for several years regarding the corn yields and management returns.

There was a significant 18 bushel corn yield increase per acre with planter row fertilizer added to the spring applied manure ridge system (Figure 5). The fertilizer was placed two inches below the seed with the new Buffalo liquid fertilizer runner. This test along with many other tell the same story of nutrient tie-up with fall rye cover crop and spring applied manure n the ridge-till system. Applying all the rye residue and livestock manure on the soil surface at corn planting time is overloading the soil system with carbon. The micro organisms take nitrogen from the soil to balance all the carbon and the small corn plant is nitrogen deficient. Also, 1993 was the flood year with cool temperatures.

Three different plows were used during the fall of 1993 to turn under manure and hay stubble. The three plows used were: a two-way swing plow, a roll over two-way plow, and a standard one-way plow. None of the plows did an acceptable job of turning over the sod and turning under the manure. All plows set the soil up on-edge, leaving manure exposed and bunches of orchard grass on top to regrow and leaving weed seeds near the surface to grow next year. The two-way swing plow pulled very hard. It was difficult to maintain a uniform plow depth because it did not have a trailing wheel. The roll over two-way plow does not have enough clearance for residue. The standard one-way plow set the soil up on-edge on the field is uneven with black and dead furrows. Both of the two-way plows were returned and the moldboards have been changed on the one-way plow to turn the soil over completely. Moldboard extension have also been added to completely cover manure, grass and weed seeds. Twenty pounds of grain rye is dribbled through old herbicide boxes placed on the plow. The rye is covered by the plow leveling bar.

Figure 6 tells many stories about diversity of crops, tillage, and fertilization. The crop rotation is what my father used during his farming career. A rotation of tillage practices is used for several reasons. The plow is used to cover manure and destroy the sod crop and move the potassium and phosphorous lower in the soil profile. Ridge tillage is used during the row crop part of the rotation to reduce erosion, lessen weed pressure, and reduce fuel and labor costs. The chisel plow, with 16 inch sweeps, is used in the spring ahead of oat planting if Canada thistle is a problem. Manure is applied in the fall prior to spring corn planting. Soybeans do not care if manure is applied in the spring. If needed, purchased planter fertilizer will be applied for the corn following soybeans. Ground cover is 100% for the two years during the oats and hay part of the rotation. Ground cover during the three years of row crops is as follows. Rye broadcast as hay and manure is fall plowed, two rye drilled on ridges after corn harvest and oats broadcast with hi-boy over soybeans at leaf yellow.

1994 Results
The six fertility treatments in field #2 produced yields ranging form 165.9 to 173.8 bushels per acre. The manure treatments were placed on top of ridges and covered with the Buffalo ridge planter. The individual treatment yields are shown in figure 7. The additional yield of certain treatments did not pay the increased cost. The 1994 weather provided excellent growing conditions with good release of nutrients to the corn plants.

The addition of 0+0+120 per acre did not increase corn yields in field #5 (figure 9). This fertilizer was applied during the previous years hay crop.

Corn ear leaf samples were taken from all fields in 1994. Samples from the fall plowed field met the desired potassium levels. This is the first time since we started testing in 1987 that the test results were above the 1.75% potassium critical level. The fall manure/plow average level was 1.90% and the spring manure/planter was 1.54% (figure 8).

The National Soil Tilth Lab took soil samples form field #3 in 1994 before moldboard plowing. This field had not been plowed for 26 years. They sampled in two inch increments and the results are shown in Figure 8a. They will sample this field in the same manner for the next five years.

The potassium and phosphorus levels were stratified. The top two inches were significantly higher than the deeper soil levels. Probing the top six inches in one soil sample does not tell the whole fertility story, the average of the six inch soil sample may seem adequate but most of the potassium could be in the top dry two inches of soil.

1995 Results:
The corn yield was 179 bushels per acre following fall manure/moldboard plow while the spring manure/ridge till was 160 bushels. The additions of planter row fertilizer to the spring manure/ridge till corn did not raise the yield enough to pay for the fertilizer (figure 10).

The addition of spring manure or planter row fertilizer for soybeans production during 1994 and 1995 did not increase the yield, therefore these two treatments lost money (Figure 11). These two fields have followed the fall manure/moldboard plow in 1992 and 1993.

The potassium uptake problem has been solved on the Thompson farm y using the fall manure/moldboard plow practice following hay. The fields where the cows are intensively grazed for three or four years are just moldboard plowed without additional fertilizer and then planted to corn. The increased corn yields, higher ear leaf potassium and accelerated growth of corn, leaves no doubt that this practice should be continued. The rates of 4 and 8 dry tons have been used for both the fall and spring manure applications. The decision on manure rates has not been determined at this time.

Tests show that there is no need for purchased fertilizers in corn production with the above fall manure/moldboard plow practice every five years (Figure 10).

We need to spread manure both fall and spring to spread out the work load. Figure 11 shows no soybean yield increase by adding spring manure when following the fall manure moldboard plow two years prior. Also spreading spring manure on the growing twin-rows of rye on the ridge damages some of the rye. The 1994 soybeans averaged over 70 bushels per acre, the highest yield we have ever had and this was the first time soybeans have followed fall manure/moldboard plow practice. Tests in 1995 in field #4C and 4D showed no corn yield decrease from spring manuring on the third year of the C-SB-C-O-H rotation (Figure 10).

Other people involved:
Practical Farmers of Iowa newsletter publishes all of the data from the Thompson farm. Rick Exner, PFI/ISU On-Farm Research Coordinator, handles the statistical work. Gary Huber, PFI/ISU Education Coordinator, brings many 4-H, FFA students and instructors to the farm. All the above people help with the field day and other tours. The major funder for our research work is the Wallace Institute for Alternative Agriculture which publishes a scientific journal. A recent issue had three articles about our alternative practices and our farm was pictured on the cover.

Researchers from Fred Blackmers’ group, ISU Agronomists, funded by the Leopold Center, have taken nitrogen measurements for a manure study on this farm. Doug Karlen, USDA/ARS, National Soil Tilth Lab ahs taken plant samples, yields, soil samples from several fields. Doug Buhler and Keith Kohler, USDA/ARS, NSTL are taking soil and weed seed samples prior to the first plowing done in 25 years and will watch for changes in soil test and weed seed numbers over the next five years.

Iowa State University extension produced a 22 minute video about the farming practices of the Thompson farm called “Walking the Journey Toward Sustainable Agriculture”.

A walk through an exhibit about the sustainability of the Thompson farm is part of the California Museum of Science & Industry traveling exhibit. The exhibit presents solutions to the environmental problems we face today. The 6000 sq. ft. exhibit opens in Los Angeles based museum which has 3 million visitors per year and then will travel to other cities in the United States.


Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.