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Fluid Journal : Fluid Journal 1993-1995
3 Fluid Journal Late Spring 1997 Every furrow 30" knife spacing Alternate furrow 60" knife spacing 1400 1300 1200 1100 1000 900 800 Lint Yield - lbs/A Nitrogen Fertilizer Placement Figure 3. Influence of nitrogen fertilizer placement on cotton lint yields, 1992. the Missouri project. Improved irrigation scheduling or timely rainfall may eliminate negative yield response to alternate furrow irrigation and accentuate the benefits of potentially improved N-use efficiencies. Fertilizer placement did not affect yield in 1991 or 1992 (Figure 2), indicating that corn can be produced with alternate furrow fertilization management regardless of irrigation effective-ness. The site responded to N fertilization, with grain yield increasing with each additional 60-lb/A N application (Table 1). Plant N and corn growth responded similarly to N applications. Cotton Rainfall at the Delta Research Center in 1992 was uniform and adequate, resulting in no cotton irrigation requirement. Nitrogen placement information showed no statistical yield reduction associated with placing N 60 inches apart in alternate furrows (Figure 3). However, unlike corn, there was a trend toward reduced yields in alternate fur-row (60-inch spacing) N placement compared to every furrow (30-inch spacing) N placement. There was also no difference in the cotton crop's ability to take up N when it was placed 60 inches apart, but like yield, cotton N content tended to be lower when compared to 30-inch knife spaced N. The difference between corn and cotton response to alternate furrow water and N fertilizer placement may be a function of different rooting systems between crops. Cotton has a taproot that may not be able to extract water and nutrients spaced far apart, compared to corn that has a more fibrous root system that may be better suited for wide-spaced nutrients and water. The site responded to N fertilizer with a lint yield increase occurring at each additional 40 lbs/A N increase (Table 1). Methodology Corn was planted both years in Tiptonville silt loam on raised, 30-inch spaced beds at a rate of 27,500 seeds per acre. Planting dates were April 23, 1991 and April 9, 1992. Both seasons, 40 lbs/A of starter N were applied as 32% UAN in a three-inch band on the soil surface directly above the seed. Cotton was planted on May 11, 1992 on raised, 30-inch spaced beds at a rate of 50,000 seeds/A. No starter N was applied on the cotton. All N treatments on corn were knifed at the V-6 growth stage, using UAN. All cotton N treatments (UAN) were knifed at the first square growth stage. Irrigation water treatments were applied via furrow irrigation, using poly-pipe as the water delivery method. Experimental treatments are listed in Table 2. Variables tested for each corn plot included: ear leaf tissue N, plant height, plant biomass, chlorophyll measurement at silking and major yield components. Variables tested for each cotton plot included leaf N, petiole nitrate-N, leaf chlorophyll measurement at first bloom and yield components. Tests not conclusive Improved irrigation scheduling is needed before an alternate furrow irrigation/fertilization system can be developed for corn or cotton produced under mid-Southern growing conditions. It is encouraging that placing N in alternate furrows performed equivalent to every furrow N placement. The potential of the alternate furrow irrigation/fertilization system to reduce inputs and improve N-use efficiency exists, but this was not positively identified during these short studies. This system needs further study, modification and expansion. Researchers and producers at several locations are now experimenting with the alternate furrow management system. Possible modifications and improvements in the system might include a number of areas. 1. Dual knives could be used in the fertilizer furrow to put N closer to corn and especially to cotton roots, as opposed to a single knife in the furrow center. 2. Alternating water furrows during successive irrigations could be employed, starting with the non- fertilized furrow during the first and most leachable irrigation. This system might work best in sandy soils by ensuring that each furrow receives supplemental moisture at some time during the season. This approach would also ensure that N uptake, which is a function of water uptake, would not be depressed as a result of having N placed in a dry soil. 3. Irrigation water and N could be placed in the same furrow while sup-plying no water or N to alternating furrows on extremely droughty soils. This might improve N uptake by ensuring that water and N were taken up simultaneously by the plant. 4. Other fertilizer sources could be explored. 5. On-farm trials and demonstrations could be used to test the system, selecting many soil types, crops and varying environments. Producers considering the alternate furrow irrigation/ fertilizer placement system should do so on a limited acreage basis until they are comfortable about its effectiveness in their operation. Dr. Tracy is assistant professor and Hefner is research associate in the Department of Agronomy at the University of Missouri.
Fluid Journal 1996-1998