Illinois
Fertilizer Conference Proceedings
January 26-28, 2006
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S. A. Ebelhar, C. D. Hart and G. K. Robertson1
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
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:
Soybeans were grown in 2003 with wheat planted in the fall of 2003. Nitrogen rate plots were established for wheat in spring 2004 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. Plot size was based on the width of the farmer's equipment (currently 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. The optimum N rate and yield at optimum N for each crop were determined and compared among the five drainage treatments. Nitrogen use efficiency will be 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 will be 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 last year's report; a short synopsis follows:)
Small plots. Wheat yields were very good for this location in 2004. Increasing N rates had a highly significant effect on increasing wheat yields (Table 1). However, there were no significant differences among tile treatments. Flag-leaf N concentrations were also significantly increased with increasing N rates, but test weights were actually reduced slightly with increasing N rates. There was a significant interaction between tile spacings and N rates for flag-leaf N. The 120' foot tile spacing had the lower N concentration with the 30' tile spacing had the higher N concentration. This was an indication of better N availability with closer tile spacings, although there was no difference between the “over tile” versus the “between tile” treatments, and there was no effect on grain yields.
The rainfall after N was applied on March 19 was very sparse with less than four inches of rainfall over an eight-week period. Although there were differences among tile spacing for flag-leaf N, these differences were very small and the rainfall pattern would suggest that there was little N loss experienced by the wheat crop after the time of N application until well into grain fill. This would account for the little difference in yields among the tile treatments. The optimum economic N rate was 84.5 lb N/acre producing an optimum economic yield of 81.9 bu/acre and a nitrogen use efficiency of 1.03 lb N/bu wheat, which is very close to the published efficiency of 1.0 lb N/bu.
Whole field. Yields within 5' on either side of the tile treatments were determined across the whole field and compared to the center 10' between tile treatments. There was a highly significant difference between the 30' tile treatments and the 60' tile treatments (Table 4). The 60' tile treatments had about a three bu/acre yield advantage over the 30' tile spacings.Corn Results
Small plots. Corn yields were about average at this location in 2005 (Table 2). Increasing N rates increased ear-leaf N composition at silking (Figure 2) but tile treatment had little effect. As with wheat, rainfall after N application was below the 30-year averages (Figure 3). 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 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 194 bu/acre over 30' spaced tiles compared to 185 bu/acre over 60' spaced tiles. NEUs for these two treatments were around 0.62 lb N/bu compared to NEUs between tiles of 0.7-0.85. Yields for corn between tiles were significantly lower than yields for corn over tiles.
Whole field. When data are compared over the entire field by passing data through (filtering) 5' buffered zones around the tile treatments, results are 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.
Monthly samples. Monthly soil samples are taken when conditions are conducive for sampling (not too dry or ground not frozen or crop 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 (Figures 5 and 6). In most of these cases the treatments over the tiles have slightly lower soil moisture than those between tiles. After a particularly wet period in November and December of 2004, soil K levels were significantly higher for tile treatments of between 60' spacings and between 120' spacings (Figure 7). There is a trend of the between 120' spacing to always 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 are achieved over tile lines compared to areas between tile lines in small plot research. 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 were small and infrequent. This study will continue for several more years.
Table 4. Effects tile treatments (based on 5' buffers) on wheat yields, Benton, 2004.
Table 5. Effects tile treatments (based on 5' buffers) on corn yields, Benton, 2005
Figure 1. Map of tile lines for field in Franklin Co., Illinois
Figure 2. Effects of N rates and tile treatments on corn ear-leaf N concentrations, 2005.
Figure 3. Rainfall accumulation after corn planting and N application, 2005.
Figure 4. Effects of N rates and tile treatments on corn yields, 2005.
Figure 5. Effects of tile treatments on soil moisture as measured by TDR, Benton, 2004.
Figure 6. Effects of tile treatments on soil moisture as measured by TDR, Benton, 2005.
Figure 7. Effects of tile treatments on soil test K over time, Benton, 2005.
1 S. 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.
