Deep Placement of Compost
The purpose of this research is to enhance and sustain the effect of sub-soiling beneath the row area by applying composted manure in the sub-soiled zone to prevent the fractured layer from re-compacting. The grant is being used to: a) purchase compost, b) purchase the implements that will be modified to apply the compost, c) offset some of the cost of modification and fabrication, and d) offset some of the cost of a field experiment to evaluate the effectiveness of deep placement of the compost. Benefits derived from the incorporated compost are being evaluated in a replicated field experiment of two years duration. This progress report describes the production of the compost, the equipment that was used to apply the compost, and the first year of the field experiment.
The compost was made under cover in a hoop hog-house in what was essentially a static pile in which straw bedding was added periodically for the hogs over a long period. This was followed by storage outside in a long windrow about 10 to 12 ft. high. It was then brought to the experiment site and further composted with more aggressive turning to accelerate the composting process. Approximately six weeks prior to applying the treatments the compost was spread out to dry so that it could be ground for ease of application. Shortly before application the quantity of compost was judged to be inadequate for the experiment, so it was diluted with composted cattle manure in a ratio of 4:1 (hog manure compost:cattle manure compost).
We benefited from the dry late summer in 2003, which made it possible to spread out the compost on concrete cattle yards to dry. It occasionally had to be piled under cover when the rain chance was high enough. But it was dry for long enough to reduce the moisture content sufficiently to easily pulverize the compost to a very friable state. Prior to spreading the compost out to dry, it was processed through a side-slinger type manure spreader, which ground the compost as was discharged. Well-composted cattle manure was mixed with the hog manure compost in a forage wagon by layering the two composts in the forage wagon and discharging them into a pile. Good vertical mixing of the layers was accomplished in this way. Alternately spreading and piling the compost for periodic rainfall events also helped to blend the compost mixture. It should perhaps be acknowledged that this kind and degree of handling would be prohibitive in normal practice. But the emphasis in this research was to evaluate the agronomic merits of compost application in the proposed manner. Demonstration of agronomic advantages could then be followed by research on the methods of application. The nutrient analysis of the compost mixture on a dry matter basis is as follows:
% Moisture, % Total N, %P2O5, % K2O, %Amm-N, %Org-N, pH
17, 1.33, 1.73, 1.58, 0.148, 1.19, 8.94
Field Experiment and Equipment Used
The field experiment was conducted on a Franklin silt loam soil near Osage, IA. The site was approximately 6 acres. Soil pH was >6.0 and P and K levels in the soil were at or above the optimum levels recommended by Iowa State University. Drainage tile had been installed in the field in 2002. The experiment site drained quite slowly prior to 2002, which made it more prone to soil compaction. The field has a long history of row cropping, but alfalfa/grass hay was established for two years before the experiment began. The site was sprayed with glyphosate (41%) at a rate of 48 oz./ac on September 24. The compost and fertilizers were applied Nov 21, 2003. The experimental treatments are as follows:
Treatment #, Compost rate (T/ac), Sub-soiling Fertilizer, placement
1, 0, No ,Surface
2 ,0, Yes ,Surface
3 ,0, Yes ,Sub-soiled
4 ,3.7 ,Yes, Sub-soiled
5 ,5.5, Yes, Sub-soiled
6 ,11 ,Yes ,Sub-soiled
Treatments 1, 2, and 3 are controls without compost application. Treatment 1 vs. 2 was to evaluate the effect of sub-soiling. Treatment 2 vs. 3 evaluated the effect of fertilizer placement. Treatment 3 vs. 4, 5, and 6 tested the effects of adding compost at different rates into the furrow behind the sub-soiler. The experimental site was quite uniform, so a completely randomized design was used. Each treatment was replicated three times. A random number table was used to assign plot sequence. The low and high compost rates were applied first. There was only enough compost left for two of the three reps of the intermediate rate.
The equipment purchase and modification requirements for sub-soil application of the compost were minimal. A used three-point toolbar was purchased, and two auto-reset sub-soiler units were donated (Photograghs 1 and 2). New shanks and points were purchased for the sub-soiler units. Long and narrow drop-tubes were fabricated and fastened behind each sub-soiler shank. The top dimensions of the drop-tube were 2 inches wide and 10 inches long. Where the drop-tube attached to the sub-soiler shank, the drop-tube extended down to the bottom of the shank (to a depth in the soil of about 15 inches). The bottom of the drop-tube was tapered upward toward the rear at about a 45-degree angle. In this way it was intended that the soil would close behind the drop-tube at different depths along its length as it traveled through the soil, and the material delivered into the drop-tube would be distributed vertically. Funnels were made from sheet steel and attached to the top of each drop-tube.
A hitch was welded onto the right end of the toolbar for a forage wagon to be towed (Photograph 3). The forage wagon carried the compost in the field and was calibrated to deliver it to the sub-soilers at the prescribed rate. The hitch was oriented on the toolbar so that the wheels of the forage wagon would track between rows and the discharge point of the forage wagon would be alongside the sub-soiler units. As the compost came off of the incline web of the forage wagon (Photograph 4) onto the discharge web a portion of the compost was directed to the front of the discharge web using sheet metal (Photograph 5). This better distributed the compost on the discharge web so that it could be evenly divided to the two sub-soiler units. As it was discharged the compost was divided into two pipes, which directed the two streams to their respective sub-soilers (Photographs 6 and 7). A dry fertilizer hopper was mounted on top of the toolbar. Tubes leading from the fertilizer hopper were inserted into the drop-tubes so that fertilizer could be added simultaneous to compost application (Photograph 8). Both the fertilizer hopper auger and the forage wagon were driven by hydraulic orbital motors, which were independently controlled at the tractor so that a constant rate of fertilizer could be maintained while varying the rate of compost application. The rate of discharge of each unit was calibrated to the tractor ground speed to apply the desired rate of fertilizer and compost. An unanticipated complication of the application system was that the wheels of the forage wagon would fall into the ruts made by the sub-soilers in a previous pass. This would result in misalignment of the discharge tubes and the funnels on the sub-soilers. It was necessary to begin application at the center of the plot and work toward the outside so that the wheels of the forage wagon stayed on firm ground. It also became necessary to shift the plot layout so that there was always firm soil for the forage wagon to roll on. This was possible because there were more plots planned for in the experimental design than were used.
Phosphorus, potash, and micronutrients were applied in the fall during compost addition at high enough rates to ensure adequate levels of the applied nutrients to sustain crop growth during both years of the experiment. Because the purpose of the experiment was to evaluate the physical effects of deep placement of the compost, attaining a high level of fertility in all treatments minimized effects due to fertility benefits of compost addition. The fertilizer was a mixture of di-ammonium phosphate, potassium chloride, elemental sulfur, zinc sulfate, and sodium borate (59-150-150-20-10-2;N-P2O5-K2O-S-Zn-B), and was applied at a rate of 700 lb/ac. Fertilizer nutrients were distributed in deep bands through the same openers through which the compost was applied, with the exception of the two controls with and without sub-soiling (Treatments 1 and 2) where the fertilizer was broadcast on the surface.
A high nitrogen fertilizer rate (200 lbs. N/ac as urea) was applied to all treatments on April 17, prior to planting the corn, to assure that N fertility did not limit crop growth. A field cultivator was used for shallow tillage to prepare a seedbed April 29. The plots were planted May 3, 2004 with corn (Pioneer 36R11). A Bt variety of corn was chosen for protection from corn borers that could confound treatment results. The seeding rate was 35,600 seeds/ac. The plant population was 34,500 plants/ac, which was determined by counting the number of plants in 100 ft. of row. Plots were 20 ft. by 500 ft. Each plot consisted of 8 rows. Field operations following planting were carried out using controlled traffic patterns to prevent driving on the rows. To minimize the effects of drainage tile, plots were arranged so that rows ran perpendicular to tile lines. The plots were sprayed with a full-recommended rate of Accent and a half rate of Northstar herbicides on June 8. Weed control was very adequate. Corn grain was harvested with a combine on October 21, and yields were determined using a weigh wagon. The center 6 rows of each 8-row plot were sampled by combining the entire length of the plot. The grain was weighed using a weigh-wagon. Moisture contents and test weights were determined at the time of harvest.
A private laboratory analyzed compost samples. Analysis of variance (ANOVA) was calculated for the data. After the second year of the experiment, all data will be submitted to Iowa State University for statistical analysis. Precipitation data for the 2004 season was taken from the rain gauge on the farm near the experiment site. Temperature data and the 54-year means for both precipitation and temperature were for the weather station in the City of Osage, IA.
Mar, Apr, May ,Jun, Jul, Aug ,Sep ,Total
2004 ,3.8, 3.0 ,12.5 ,2.4 ,12.9, 4.3, 5.2, 44.1
54-yr mean, 2.1, 3.3 ,4.2 ,4.6, 4.6, 4.4, 3.4, 26.6
2004 , 48 ,58, 65 ,70, 64, 66
54-yr mean, 47, 59 ,68 ,72, 70, 62
difference , 1, -1 ,-3 ,-2 ,-6 ,4
The 2004 growing season was unusually wet and cold with more than 12 inches of rain in both May and July. From March through September rainfall was 65% greater than normal. Very early in the growing season it was possible to see faster corn growth over the drainage tile lines in plots that were not sub-soiled. As the soil drained and temperatures warmed the corn growth became more even, and during most of the growing season the only observable differences in corn growth corresponded to somewhat improved growth in treatments with surface-applied fertilizer. By September 1 corn development was well behind schedule because of the cool temperatures, but substantially above normal temperatures in September helped to mature the crop before the killing frost on Oct 2. By the end of the growing season corn growth appeared to be uniformly excellent, and treatment differences could not be observed. Corn yields in the controls (treatments 1-3) did not respond to fertilizer placement or sub-soiling (see table below). Although there appeared to be a small yield response to compost addition, it does not seem to be significant based on a preliminary statistical analysis. However, the unusually wet conditions during the growing season raise questions about the potential for greater response in a more normal or abnormally dry year in which the corn roots would have more incentive to search for moisture and nutrients in the subsoil. Most of the root growth in 2004 may have been confined to the surface where better aeration existed, and even when the weather was drier the rainfall was frequent enough to maintain enough moisture in the surface soil to preclude the need for deep root development. After harvest, the soil was excavated from a row in the high compost treatment. The compost had accumulated largely at the bottom of the furrow that was opened by the sub-soiler and drop-tube at a depth of 11 to 13 inches.
1 ,2, 3 ,mean
Treatment # * bu/ac
1 ,210, 218, 213, 214
2 ,215, 213, 205, 211
3 ,210, 204, 216 ,210
4 ,219, 221, 217, 219
5, 218 ,222 , 220
6 ,210 ,223, 212, 215
* see earlier table for explanation of treatments
Following harvest, strip-tillage was done on the entire plot area in preparation for the 2005 season. Because the quantity of residue was too high to strip-till into in the fall, corn stalks were removed at a rate of about 3T/ac. Additional P and K fertilizer was applied to compensate for nutrient removal in the stalks. Assuming a harvest index for corn of around 0.5, there may have been up to 5T/ac of stalks above the soil line. Since most of the stalks were chopped and raked and only part of the windrow was picked up during baling, allowance was made for a higher rate of nutrient removal between windrows than would be indicated by the 3T/ac rate. Since it is recommended that 4 lbs of P2O5/ac and 40 lbs K2O/ac be applied to replace the nutrients in each ton of stalks removed we added about 20 lb P2O5 and 200 lbs of K2O/ac (43 lb DAP and 333 lb potash/ac) during strip-tillage, which corresponds to a stalk removal rate of 5T/ac. Nitrogen will be applied next spring for the 2005 season, and the plots will be planted to corn again.