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Fluid Journal : Fluid Journal 1996-1998
2 Fluid Journal Spring 1997 Yield - bu/A ! ! ! ! ! ! ! ! ! ! ! ! ∀∀ ∀ ∀ ∀ ∀∀ ∀ ∀ ∀ ∀ ∀ Inches rainfall 210 180 150 120 90 60 30 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 35 30 25 20 15 10 5 Yield Inches rainfall Figure 1. Correlation between yield and rainfall in non-irrigated corn trials from 1986 to 1996. Powell, Virginia Tech. 1984, GLAI appeared to remain constant during the second stage instead of slowly declining as predicted. The only difference between the two crop years was the addition of boron to the irrigated crop in 1984. This simply confirmed the need for additions of boron if high corn yields were to be achieved. Subsurface fertigation To improve crop production and manage root zone moisture and fertility, a subsurface microirrigation research project was initiated in 1986 at the Virginia Tech Tidewater Agricultural Research and Extension Center in Suffolk, Virginia. Table 1. Soil test levels taken in an Emporia/Uchee soil, Powell, Virginia Tech. Depth pH P K Ca Mg B in ---------ppm---------- 0-6 6.43 44H+ 47M- 475M- 44M- 0.09 6-12 6.40 30H 25L 310L+ 35L+ 0.05 12-18 6.24 3L 35L+ 127L 23L 0.00 18-24 5.63 1L- 49M- 173L 47M- 0.01 H=High;M=Medium;L=Low As shown in Figure 2, drip/trickle tubing was buried 14 to 16 inches below the soil surface below each row (3-foot spacing), below alternate row middles (6-foot spacing), and below each third row (9-foot spacing). Tube spacing was important because it was a large part of the equipment cost per acre. Wider spacing translated into lower installation cost per acre. This type of system has the advantages of low energy cost (10 psi in the field) and 100 percent water efficiency (no water lost to evaporation, runoff, or deep drainage). A properly designed, installed, and managed system of this type will last in excess of 10 years. Ballpark on installation costs is somewhere between $750 and $800 per acre for the 3-foot spacing, provided enough acres are used to justify a pumping station (pump, filter, etc.). Mix critical Average irrigated corn yields for the period 1986 to 1989 (Figure 3) were disappointing, even though they were equal to or greater than non-irrigated yields. Plots were fertilized in the spring with 500 lbs/A 5-lO-30. ZnSO4 was broadcast at the rate of 50 lbs per ton of fertilizer or 12.5 lbs/A over the surface as a dry fertilizer. An additional 200 lbs/A of fluid N as 25-0-0-3S was applied to the crop through the irrigation water in approximately four equal applications at 7- to 10-day intervals, starting five to six weeks after planting with the last application prior to or at silking and tasseling. Where non-irrigated plots equaled average yields of irrigated plots (155 bu/A), we attributed it to an unusually wet season. Some yields of 210 to 220 bu/A were recorded from rows directly above the tubing in the 9-foot tube spacing. From this we concluded that higher overall yields would be achievable with 3-foot and 6-foot tube spacing, providing the mix of water and plant nutrients was proper. Added kick Even higher average irrigated yields were achieved in 1990 to 1993 by again adding boron to the N provided through irrigation water (Figure 3). Boron as Solubor was dissolved in N solution. On some plots, boron was added at the rate of a quarter to half pound per acre on each of the four 7- to 10-day intervals. Yields, especially at the 3- and 6-foot tube spacing, made a significant jump. Yields hit 205 to 260 bu/A in the rows directly above the 9- foot tube spacing. Further fine-tuning In 1994 and 1995, average yield increases were achieved by changing to calcium hypochlorite as a water disinfectant instead of using sodium hypochlorite (Figure 3), which added Ca to the soil instead of Na. Plant
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