S.A. Ebelhar, C.D. Hart and G.K. Robertson 1
Tile drainage provides many benefits to growing crops. Draining wet fields allows fields to warm up faster and be planted earlier, provides better aeration to plant roots, and reduces problems with denitrification losses of N (IL Agronomy Handbook). Earlier planting and better growth associated with drainage leads to increased yields and perhaps even a more efficient use of applied fertilizer N. Tile drainage of claypan and poorly drained soils in southern Illinois is increasing at a rapid rate, even though the effects on yield and environmental issues have yet to be demonstrated. There is little information as to the effects of tile drainage on nitrogen use efficiency and subsequently the impact on nitrates leaving through tile lines. This study should help to determine if N use efficiency is affected by drainage and at what spacings tile should be placed to optimize this efficiency.
The current nitrogen use efficiency numbers for corn in Illinois ranges from 0.8 to 1.2 lb N/bu based on yield goal, previous crop, manure credits and other incidentals. The efficiency for wheat is about 1.0 lb N/bu or higher. But there is little information as to the effects of tile drainage on nitrogen use efficiency and subsequently the impact on nitrates leaving through tile lines. This study should help to determine if N use efficiency is affected by drainage and at what spacings tile should be placed to optimize this efficiency.
Potassium (K) fixation and availability may also be affected by tile drainage. Work by Stucki and Huo (1997) indicated that oxidation and reduction (redox) may play a significant role in the ability of clays (especially smectitic clays) to fix K. In poorly drained soils, one would expect soil near tile lines to be significantly drier that soil between lines, especially if tile lines are greater than 50 ft apart on centers. This would suggest that soil test K levels may be different above or near tile lines versus between tile lines, but to what magnitude. Periodic sampling over tiles and between tiles would provide information on K fixation and availability as related to tiling.
The objectives of this study are to 1) compare the effects of tile drainage systems of 30 ft, 60 ft and 120 ft laterals on soil test P and K levels over time, and 2) determine the effects of tile drainage spacings on nitrogen use efficiency of wheat and corn crops. The goal is to determine if tile drainage alters the fertilizer management of farms in southern Illinois.
A tile drainage study was established in the Spring 2003 on a 52 acre field in Franklin Co., IL. The field was broken into six replications (Reps) of tile spacings of 30 ft, 60 ft and 120 ft randomly assigned within Reps forming a randomized complete block (RCB) design. Treatments were broken into five classes: 1) over tiles on 30 ft spacing, 2) between tiles on 30 ft spacing, 3) over tiles on 60 ft spacing, 4) between tiles on 60 ft spacing, 5) between tiles on 120 ft spacing. Three inch tile lines were placed on grade an average of 30 inches below the soil surface. Tile lines were mapped with GPS (see Figure 1) at the time of installation.
Soybeans were grown in 2003 with wheat planted in the fall of 2003. Nitrogen rate plots were established for wheat in spring 2004 and corn in 2005 and 2006 within each of the five basic drainage treatments replicated five times. Nitrogen rates for wheat were 0, 30, 60, 90 and 120 lb N/acre spring applied treatments. The area was double-cropped with soybean after wheat harvest in 2004. In 2005, corn (Pioneer hybrid 33P67) was planted on April 15 with sidedress N rates applied on May 18. In 2006, corn (Pioneer hybrid 33K40) was planted on April 16 with sidedress N rates applied on May 22. In both years, nitrogen rates on corn were 0, 50, 100, 150 and 200 lb N/acre. Plot size was based on the width of the farmer’s equipment (10 ft for the wheat drill and 15 ft for the corn planter) x 30 ft with the center 5 ft x 30 ft. harvested for yield in 2004 and 2005. In 2006 plot sizes were extended to 80' lengths to allow a combine equipped with a yield monitor and GPS to harvest the entire length and width for yield. The optimum N rate and yield at optimum N for each crop were determined and compared among the five drainage treatments. Nitrogen use efficiency was calculated as the lb N per bu of crop produced.
To address the issue of K fixation, sampling points were identified with GPS markers for each of the 5 drainage treatments. Monthly samples (as possible) were collected to measure soil test P and K levels, soil moisture, and soil temperature. Grain yields and nutrient removal are being monitored along with fertilizer additions to determine nutrient balances and effects on changes in soil test levels over time.
The soil type for this field is almost exclusively Hoyleton silt loam (Fine, smectitic, mesic, Aquertic Hapludalfs), a flat, somewhat poorly drained soil high in shrink-swell type clays with K-fixing potential.
Wheat Results (The detailed listing of wheat results were presented in the 2005 report)
2005 Corn Results
Small plots. Corn yields were about average at this location in 2005 (Table 1). Increasing N rates increased ear-leaf N composition at silking but tile treatment had little effect. As with wheat, rainfall after N application was below the 30-year averages (Figure 2). Increasing N rates increased yields, with a highly significant linear and quadratic response. This allowed us to fit a regression equation (Figure 3) and calculate optimum N rate, yield at optimum N rate, and nitrogen use efficiency (NUE) for each tile treatment (Table 3). There was a significant yield increase where corn was grown directly over the tile lines versus between the tile lines. This could still be associated with the soil disturbance associated with the installation of the tiles, but there in increasing evidence that the tiles are providing a significant benefit to N utilization and corn yields. The corn yield at optimum N was 195 bu/acre over 30' spaced tiles compared to 185 bu/acre over 60' spaced tiles. NEUs for these two treatments were around 0.65 lb N/bu compared to NEUs between tiles of 0.76-1.01. Yields for corn between tiles were significantly lower than yields for corn over tiles.
Whole field. When data were compared over the entire field by passing data through (filtering) 5' buffered zones around the tile treatments, yield differences among tile spacing treatments were insignificant (Table 5). This filtering process is done by taking yield points from within 5' on either side of tile lines or 5' on either side of the halfway points between tile lines. The analysis of this type of data is very complicated because there are many influences on the yields not related to tile treatments. These include surface drainage patterns, surface water flow and accumulations, previous erosion, soil type and elevation. Research in the near future will try to separate the field into management zones based on several of these factors and then determining if tile treatments responses are affected by management zone. Another method of filtering is to pass the data through drainage blocks of 30' vs 60' vs 120' tile spacings. When this was done there were no significant differences among the tile spacings (Table 6).
2006 Corn Results
Small plots. Corn yields were above average at this location in 2006 (Table 2). Increasing N rates increased ear-leaf N composition at silking but tile treatment had little effect, except that the between 60' spacing treatment had unexplainably lower leaf N levels. Rainfall after N application was below the 30-year averages (Figure 2) for much of the growing season, but was not as low as in 2005, but it is unlikely that significant N losses occurred in 2006 due to denitrification (usually associated with waterlogged soils). Increasing N rates increased yields, with a highly significant linear and quadratic response. This allowed us to fit a regression equation (Figure 4) and calculate optimum N rate, yield at optimum N rate, and nitrogen use efficiency (NUE) for each tile treatment (Table 4). There was a significant yield decrease where corn was grown between the 120' tile lines versus between the other tile treatments. This is possibly due to wet soil conditions prior to N application, as there were no significant differences in ear-leaf N levels, indicating that N may not have been in short supply under any of the tile spacing treatments. NUE values for the tile spacing treatments varied slightly, but there were no significant treatment differences, unlike in 2005.
Whole field. When yield data were filtered through 5' buffered zones around the tile treatments, yield differences among tile spacing treatments were insignificant (Table 5), as in 2005. Filtering the yield data through drainage blocks of 30' vs 60' vs 120' tile spacings also produced no significant differences among the tile spacings (Table 6).
Monthly samples. Monthly soil samples are taken when conditions are conducive for sampling (not too dry, ground not frozen, crop not too tall). Differences in soil moisture by volume are determined with Time Domain Reflectometry (TDR). There are times where soil moisture is relatively high and differences among tile treatments are noticeable (Figure 5), mostly in the off-season. In most of these cases the treatments over the tiles have slightly lower soil moisture than those between tiles. Soil pH, P, and K levels have not been significantly affected by tile spacings (soil test K shown in Figure 6). There is a trend of the between 120' spacing to usually have the highest K level but most of the time there is no significant difference among tile treatments for soil test K levels.
There is some indication that higher yields and increased NUE were achieved over tile lines compared to areas between tile lines in small plot research in 2005, but not 2006. It is still too early to speculate on the advantage of tile drainage on a whole field basis. Monthly soil sampling identified periods when moisture and soil test K levels were different above the tiles versus between tiles, but these differences are small and infrequent. This study will continue for several more years.
Table 5. Effects of tile treatments (based on 5' buffers) on corn yields, Benton, 2005-06.
Table 6. .Effects of tile treatments (based on drainage blocks) on corn yields, Benton, 2005-06.
Figure 1. Map of tile lines for field in Franklin Co., Illinois
Figure 2. Rainfall accumulation after corn planting and N application, 2005-06.
Figure 3. Effects of N rates and tile treatments on corn yields, 2005.
Figure 4. Effects of N rates and tile treatments on corn yields, 2006.
Figure 5. Effects of tile treatments on soil moisture as measured by TDR, Benton, 2006.
Figure 6. Effects of tile treatments on soil test K over time, Benton, 2004-06.
1S. A. Ebelhar is an agronomist, Department of Crop Sciences, Univ. of Illinois, C. D. Hart is research specialist, Dept. of Crop Sciences, Univ. of Illinois, and G. K. Robertson is Agronomy Manager, Rubenacker Farms
Stucki, J. W. and D. Huo. 1997. Continued studies on the behavior of potassium in soils. In R. G. Hoeft (ed.) IL Fert. Conf. Proc. pp 1-10.