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Fluid Journal : Fluid Journal 1999-2001
1 Fluid Journal Winter 2001 Summary: The response of alfalfa to high dose P fertilization has important economic implications. If a producer is able to maximize yields over a six-year period by supplying the fertilizer as a single event, additional profit may be realized because of reduced applica- tion costs. Band (knifed) placement of P provided an additional boost to P responses and to profits. It is important to note that alfalfa yield responses ob- served in this study may be particu- larly adapted to high-yielding envi- ronments (e.g., irrigated production). A A A A Alfalfa is an important forage legume crop in Oklahoma and many other states. It is pre- ferred over other forage legumes due to its highyield potential, protein content, and palatability. The N-fixing capability of alfalfa de- creases the need for nitrogen fertilizer, but places a high demand on the soil for phosphorus (P) and potassium (K). Phosphorus and potassium concentra- tions range from 0.2 to 0.5 percent and 1.0 to 2.0 percent in dry alfalfa forage, respectively. This implies that a field producing 5 tons/A of alfalfa annually removes from soils 46 to 115 lbs/A of P205, plus 120 to 240 lbs/A of K20. quan- tities that must be replenished from fer- tilization or by mineral weathering. Typically, producers supply P annu- ally to meet the needs of the crop and recharge depleted P pools. The objective of this research was to evaluate alfalfa yield response to broad- cast and banded P at high rates. The project was initiated in 1992 and com- pleted in 1998. P response Alfalfa response to P the first year showed a linear increase in yield as P rate was increased, yield being maxi- mized by applying P2O5 at the rate of 600 lbs/A (Figure 1). In the final year of the trial (1998), yield response to the initial 600-lb/A treatment of P2O5 had decreased while plots that had received annual and bi- R.W. Mullen, and Drs. G.V. Johnson, J.F. Stritzke, J.L. Caddel, S.B. Phillips, W.R. Raun Alfalfa Responds To High P Rates, P Banding Oklahoma State University trials show that additional profit may be realized because implement and labor costs are decreased due to fewer applications. ennial P fertilization still showed marked increases in yields above the check (Figure 2). Despite the drop in yield response to the 600-lb/A/6-yr rate of P2O5 late in the experiment, this treatment still yielded the highest of all broadcast P over the six years of the trials (Figure 3). Addi- tionally, subsurface banding of fluid 10- 34-0 (APP) stabilized alfalfa yields over the length of the trial, resulting in the highest yield over the six years of all P- only treatments. Placement/rate/timing The responses in this study support the theory that banding of P increases availability by placing the nutrient closer to plant roots, thus minimizing soil-fertilizer reactions and maintaining P availability for longer periods. Supplying a large amount of incorpo- rated P (600 lbs/A of P205) during alfalfa establishment in a high yielding irri- Table 1. Initial soil test of entire experimental area. NO3-N P KpH ....... ... .... lbs/A ... .......... ... ____________________________ 27.2 30.2 326 6.6 ___________________________ NO3-N-2M KCI extractant; P,K -Mehlich III; pH - 1:1 soil water Table 2. Final soil tests of selected treatments. ___________________________________________________________ Treatment NO3-N P KpH ------------lbs/A---------- Check 7.0 15.5 717 7.2 100 lbs P2O5/A/yr 4.6 77.4 679 6.9 200 lbs P2O5/A/2-yr 5.5 77.6 738 6.9 600 lbs P2O5/A/6-yr 6.2 41.0 708 7.0 200 lbs P2O5/A/2-yr (knifed) 5.8 78.3 693 6.8 600 lbs P2O5 /A/6-yr (knifed) 5.8 25.6 679 7.0 200 lbs P2O5/A/2-yr + 500 lbs K2O/A/yr 5.6 59.8 1,135 6.5 200 lbs P2O5/A/2-yr + 50 lbs S/A/yr 5.3 69.3 648 7.1 ____________________________________________________________ NO3-N-2M KCI extractant; P,K - Mehlich III; pH- 1:1 soil-water All treatment, including check, received 500 lbs/A of K2O in years 1,3 and 5
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