Sign up for email alerts of new Fluid Journal issues!
Fluid Journal : Fluid Journal 1999-2001
2 Fluid Journal Winter 2001 gated environment provides maximum response because plant density is high. As stands age and plant density de- creases, availability of P is lessened by reactions with soil, removal by crop uptake the first two years, and poorer extraction by a less dense root system. Smaller rates applied more frequently are better able to sustain a P-rich envi- ronment that supports higher yields in the sixth year. Kprovidesboost Potassium fertilization also resulted in increased yields over the length of these trials. The rate of 200 lbs/A/2-yr of P205 in conjunction with 500 lbs/A/yr of K2O yielded the highest of all treat- ments over the six years (Figure 4). This response was somewhat surprising since the initial soil test of 326 pp2m K was near the calibrated adequate level (K>350 pp2m), plus the comparison treatment received 1,500 lbs K20 over the six-year period. We might conclude, then, that alfalfa responds to higher levels of available soil K in high-yielding environments. This statistically significant response of about 3 tons/A (value about $240) was from an input of an additional 1,500 lbs K20 (cost about $165), thus merits serious economic consideration. it is possible that lower annual rates (e.g., 25 300 lbs/A of K2O) might have also supported this maximum yield and that the yield difference would have been even larger compared to a no-K control. Sulfur fertilization only slightly affected yield over the six years of the trial. Soil tests Phosphorus. Initial P soil test levels appear in Table 1. Final P soil test levels in the 600-lb/A rate of P2O5 initial treat- ment plots (broadcast and injected) Check Yield Response (tons/A) 4 5 5.61 5.85 6.15 7 6 7 100 lb/A/yr 200 lb/A/2-yr 600 lb/A/6-yr Rate of P O (lb/A) 25 Figure 1. Response of alfalfa to P applications in year one. Check 5 6 7 8 6 6.89 7.14 6.55 100 lb/A/yr 200 lb/A/2-yr 600 lb/A/6-yr Yield Response (tons/A) Rate of P O (lb/A) 25 Figure 2. Response of alfalfa to P applications in 1998. were significantly lower than treatments receiving annual and biennial P applica- tions (Table 2). Soil test P was signifi- cantly lower in the unfertilized check than for all other treatments. Lower P tests on areas receiving banded P may reflect inability to hit P bands with ran- dom sampling. Potassium. As expected, the treatment receiving 500 lbs/A/yr of K2O had the highest K soil test value while other plots receiving only the initial and two subsequent blanket treatments of 500 lbs/A of K2O still had higher than what is commonly considered adequate levels of K in the soil (Table 2). Mullen, and Drs. Johnson, Stritzke, Caddel, Phillips, and Raun are re- searchers at Oklahoma State University Stillwater, Oklahoma. 100 lb/A/yr Yield Response (tons/A) 0 1 2 3 4 3.4 4.2 4.7 5.8 6.8 5 6 7 200 lb/A/2-yr 600 lb/A/6-yr 200 lb(knifed) /A/2-yr 600 lb(Knifed) /A/6-yr Rate of P O (lb/A) 25 Figure 3. Total alfalfa yield increases from P fertilization (minus the check) after six years. 200 lb/A/2-yr +500 lb K 0/A preplant and years3&5 2 200 lb/A/2-yr +50 lb S/A/yr 200 lb/A/2-yr + 500 lb K O/A/yr 2 4 5 6 7 8 9 5.5 6.44 8.53 Yield Response (tons/A) Rate of P O (lb/A) 25 Figure 4. Total alfalfa increases (minus the check) from P, K and S treatments after six ye ars.
Fluid Journal 1996-1998
Fluid Journal 2002-2004