Cowell, L.E.

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University of Saskatchewan Research Archive

- 2 -1.1 Alfalfa Forage Response to Residual P and K Fertilizer L.E. Cowell (Project funded by Agriculture Development Fund through Innovative Acres) IN1RODUCTIQN Alfalfa grown for hay is a major cr~p in Saskatchewan. If properly inoculated, alfalfa will fix its nitrogen (N) requirement from the atmosphere. However, alfalfa has a high phosphorus (P) and potassium (K) requirement which must be taken from soil reserves or added fertilizers. When alfalfa is cut for hay large amounts of nutrients are removed. Fertilization of alfalfa is therefore often essential, but there is a lack of information on the residual availability of fertilizer P and K to alfalfa. Interest from farmers in the Innovative Acres Program initiated a project to measure the long term availability of fertilizer P and K for alfalfa as measured by hay yield and protein content. l\1ETHQDS In 1987 three plots were set out in Innovative Acres cooperator alfalfa fields. Three diverse sites were selected at Porcupine Plain (Gray Luvisol, Whitewood loam assochi.tion), Melville (Black Chemozem, Oxbow loam association) and at Marcelin (Black Chernozem, Meota loamy sand association). At Porcupine Plain the plot was placed on a one year old alfalfa stand. At Melville and Marcelin the plots were laid out before the farmer seeded the field. Unfortunately a severe spring frost killed the alfalfa at Marcelin. Seed placed P had been applied with the barley nurse crop at Porcupine Plain. No nurse crop nor seed placed fertilizer was used at Melville. At each site, 0-0-60 and 11-51-0 fertilizers were broadcast in a split plot design ( 4 blocks) to provide rates of 0, 30, 60 and 120 kg KzO/ha and 0, 25, 50 and 100 kg PzOs/ha. The fertilizer was broadcast in May 1987 using a small fertilizer spreader. Harvest samples of hay were cut in the early bloom stage. The plots were sampled once per year, though the farmers cut and removed hay - 3 -twice each year (including the plot areas). Yields and protein contents were measured for the second (fall) cut at Porcupine Plain in 1987, and for the first spring cut at both sites in 1988 and 1989. Soil samples were taken before fertilizer application in 1987. At harvest in the spring of 1988 and 1989 composite samples were taken from the POKO, POK30, POK60, POK120, KOP25, KOP50 and KOPlOO plots. RESULTS Soil Analyses and Yield Increase Predictions Analysis of soil sampled prior to fertilizer application indicated a deficiency in P and K at Porcupine Plain, but only a slight P deficiency and no need for K at Melville (Tables 1.1.1 and 1.1.2). Available N levels did not change with treatment and remained low due to the high and constant requirement of N by alfalfa. Recommendations for fertilizer N were not made, assuming proper inoculation of the seed and subsequent fixation of atmospheric Nz by the plants. The initial available soil P levels were very low at Porcupine Plain but nearly ·adequate at Melville. Fertilizer P recommendations for the sites were 75 and 25 kg/ha, respectively. In the following years the soil test level of P reflected the amount of fertilizer P originally applied. As a consequence fertilizer recommendations were reduced because of the earlier fertilizer applications. At both sites the level of soil test P was much lower in the third year of the trial than in the second year. Crop uptake reduced the level of available P to the point that large P recommendations would have been made even in the second year at Porcupine Plain and by the third year at Melville. Extracted soil K levels were initially low at Porcupine Plain and remained low in following years despite fertilizer K application. Soil K levels were initially sufficient at Melville. but by the third year were reduced to the point that fertilizer recommendations were made for the plots that received no fertilizer K. Soil test levels did not reflect additions of K fertilizer at either site. - 4 -Table 1.1.1 Soil nutrient analyses and fertilizer recommendations for Porcupine Plain before fertilizer application, and at harvest in 1988 and 1989. · Treatment Composite of site POKO POK30 POK60 POK120 P25KO PSOKO PlOOKO POKO POK30 POK60 POK120 P25KO PSOKO PlOOKO N (0-60cm) 20 11 10 11 10 12 15 14 24 19 16 49 22 28 31 Nutrients (kglha) Recommendedt P N (0.15 em) 1987 (before fertilizer application) 0 8 75 1988 (spring harvest) 0 10 75 0 10 50 0 12 50 0 11 50 0 14 50 0 15 50 0 20 25 1989 (spring harvest) 0 8 75 0 7 75 0 9 75 0 13 50 0 9 75 0 9 75 0 17 25 K (0.15 em) 100 180 150 160 170 140 140 160 110 100 100 100 110 llO 120 llO 60 90 60 60 90 90 60 110 110 110 110 110 110 110 t Recommended fertilizer application rates based on the Saskatchewan Soil Testing Laboratory guidelines - 5 -Table L1.2 Soil nutrient analyses and fertilizer recommendations for Melville site before fertilizer application, and at harvest in 1988 and 1989. Treatment Composite of site POKO POK30 POK60 POK120 P25KO P50KO PlOOKO POKO POK30 POK60 POK120 P25KO PSOKO PlOOKO N (0-60cm) 56 15 21 19 25 20 22 18 15 14 17 17 13 25 15 Recommendedt N 1987 (before 0 Nutrients (kg/ha) p (0-15 em) fertilizer 20 application) 25 1988 (spring harvest) 0 22 0 0 23 0 0 20 25 0 18 25 0 16 25 0 24 0 0 25 0 1989 (spring harvest) 0 9 75 0 9 75 0 8 75 0 11 50 0 10 75 0 14 50 0 11 50 K (0-15 em) 290 230 380 310 330 200 240 220 160 250 260 230 160 180 180 0 0 0 0 0 15 0 0 60 0 0 0 60 60 60 t Recommended fertilizer application rates based on the Saskatchewan Soil Testing Laboratory guidelines - 6 -Hay Yield and Protein Response toP Fertilizer As predlcted by soil testing, hay yield increased with P fertilizer addition at Porcupine Plain (Table L 1.3). The alfalfa was able to utilize residual P fertilizer. For example. total yield was increased by 33%, 60% and 50% in 1987, 1988 and 1989 with the 100 kg P20slha treatment in 1987. Yield was increased in both dry years (1988) and when moisture was adequate (1989). No P x K interaction was measured for the Porcupine Plain yield, nor in any other parameter in this study. P fertilizer also signifi~ candy increased hay protein content in 1988 and 1989, and protein yield in each year. At Melville original soil tests indicated an adequate level of soil P, and there was no yield response to fertilizer Pin 1988 (Table 1.1.4). In 1989 the soil P test levels were low, and a corresponding hay yield increase occurred (Table 1.1.4). Protein yield was increased in 1988 with P addition. A similar trend occurred in 1989, though the response was not significant Hay Yield and Protein Response to K Fertilizer At Porcupine Plain extracted soil K levels were low each year and large fertilizer K recommendations were made. Although a yield response did occur in 1987 and 1988, the response was small and inconsistent and did not occur in 1989 (Table 1.1.3). Protein content of the hay was not increased in any year. No K fertilizer was initially recommended at Melville. In 1989 soil test levels forK were low and a yield increase was measured for K fertilizer addition. Alfalfa uptake and removal of soil K was high enough to induce a K deficiency in the final year. Hay protein content was increased in 1988, perhaps as an early indication of the yield response that would occur the next year. - 7 -Table 1.1.3 Hay yields and protein contents after P and K fertilizer application at Porcupine Plain site. Treatment Hay yield (kglha) Protein(%) Protein yield (kglha) 1987 KO 1919 17.8 344 K30 1682 18.8 316 K60 1761 17.3 305 K120 1999 19.3 385 LSD (0.05) 207 NS 82 PO 1580 17.9 281 P25 1770 18.0 321 P50 1904 17.8 340 P100 2107 19.5 410 LSD (0.05) 153 NS 51 1988 KO 2030 18.1 365 K30 1620 18.3 302 K60 1930 17.9 350 K120 1950 17.9 350 LSD (0.05) 314 NS NS PO 1420 17.6 252 P25 1750 17.4 305 P50 . 2040 17.7 360 PlOO 2320 19.5 452 LSD (0.05) 185 1.49 49 1989 KO 2855 18.4 528 K30 2735 18.3 503 K60 3065 17.1 528 K120 2725 17.9 490 LSD (0.05) NS NS NS PO 2327 17.8 411 P25 2489 17.2 429 P50 3145 17.9 565 PlOO 3420 18.9 642 LSD (0.05) 453 0.86 89 - 8 -Table 1.1.4 Hay yields and protein contents after P and K fertilizer application at Melville site. Treatment Hay yield (kg/ha) Protein(%) Protein yield (kg/ha) 1988 KO 3795 14.9 560 K30 3645 163 600 K60 3980 17.3 685 Kl20 3775 15.6 590 LSD (0.05) NS 0.9 69 PO 3665 15.3 570 P25 3765 15.7 590 P50 3935 16.7 660 PlOO 3835 16.4 625 LSD (0.05) NS NS 63 1989 KO 2458 15.4 377 K30 2925 15.4 440 K60 2911 16.3 476 K120 2737 15.0 407 LSD (0.05) 319 NS 80 PO 2474 15.8 390 P25 2654 14.7 390 P50 2803 16.4 446 P100 3101 15.2 474 LSD (0.05) 166 NS NS Economic Returns to Avplied P and K Fertilizers The economic return to applied fertilizer is of primary concern to the fanner. Costs of fertilizers were approximately $0.70/kg for P20s and $0.18/kg for KzO. Hay prices fluctuated with each year, but an average of $60/tonne could have been achieved over the three years. The plots were sampled only once per year, but two cuts were actually taken by the fanners (including the plot area). Second cut yields were similar to first cut yields according to farmer information. Total yield increase was therefore assumed - 9 -to twice that measured in the single plot harvest. Net return and marginal returns were then calculated for P fertilizer applications (Table 1.1.5). Within three years a large return was realized for the fertilizer dollar at Porcupine Plain. Net returns increased to the PlOO level and marginal returns were high for all fertilizer rates. At Melville, where a yield increase occurred only in the second of two years, net and marginal returns were lower. Returns were still adequate to provide a reasonable marginal return to at least the P50 leveL With added harvest years this return could improve. Response to the added P had not shown signs of reduction after three years at either site. The inconsistent yield response to fertilizer K made any economic evaluation difficult and probably invalid. The investment into K fertilizer would have been of questionable value at either site. l'c .. · Table 1.1.5 Economic return toP fertilizer applications. Site Porcupine Plain Melville Treatment P25 P50 PlOO P25 ' PSO PlOO Yield increase I (kg!ha) 1364 I'\ 3524 5040 560 1198 1374 Net return2 ($/ha) 64 175 230 15 36 10 Marginal retum3 4.5 5.9 4.2 1 Total yield increase for 3 years at Porcupine Plain and 2 years at Melville: assumes two harvests per year. 2 Value of hay yield increase less fertilizer cost. 3 Marginal return = Value of increased yield/cost of fertilizer input. - 10 -CONCLUSIONS AND RECOMMENDATIONS This project has provided several points to consider in P and K fertilization of forage alfalfa. P and K fertilizers obviously have residual value beyond the year of . application and can be broadcast at high rates for long term nutrient management of alfalfa. Soil P analysis was able to accurately predict P deficiencies and fertilizer requirements for alfalfa. Residual fertilizer was detected by soil analysis and fertilizer recommendations reflected the differences. Alfalfa has a high requirement for P and K, and long rotations may develop P and K deficiencies over time, as at Melville. Extracted soil K did not consistently nor accurately predict K requirements. An exception to this was the detection of a K deficiency at Melville in the final year, and an associated yield increase. A yield response to K fertilizer was not initially expected at Melville since this site had a chemozemic Oxbow loam soil, which is not typically K deficient. Residual fertilizer K was not detected by the soil analysis. Economic responses to added P were large and persisted throughout the length of the trial. Fertilizer K would have been a poor investment in this trial, despite predictions of a large K deficiency at Porcupine Plain. Further refinement of the K analysis and for the recommendation ranges for P and K are needed. However, soil testing in each year of an alfalfa rotation would be a valuable tool in detecting nutrient deficiencies. 

Alfalfa forage response to residual P and K fertilizer

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Alfalfa forage response to residual P and K fertilizer

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