In this article, a study is outlined. It was initiated to determine the effects of potash and phosphate fertilization on alfalfa production and it's economic profitability. The methods are presented. The results and discussion follow. The results of this study indicated that producers must test the soil and apply the potash and phosphate to maximize yields of aging alfalfa stands on irrigated course textured, sandy soils

Dodds, D.L.

Hoag, B.K.

Thompson, C.R.

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----- - --Potash and Phosphate Fertilization on Irrigated Alfalfa C.R. Thompson, D.L. Dodds and B.K. Hoag North Dakota has had approximately 210 ,000 irrigated acres annually from 1983 through 1986, of which 65 to 70,000 acres was irrigated hayland (2,7,8 ,9) . Alfalfa may be one of the more profitable crops grown under irrigation in North Dakota beca use of the short growing season and cool climate . MOisture is often the limiting factor in production ' however , with irrigation, fertility becomes limiting . Therefore monitoring fert ility levels on irrigated crops like alfalfa are very important for optimum production . Estimated nutrient use by alfalfa is 11.5 pounds of phosphate P 205 (P) and 60 pounds of potash K20 (K) per ton of forage yield (10) . Bauder et al. reported that irrigated alfalfa at Oakes did not respond to surface applied phosphate and potash . Fer­tilization occurred in the initial harvest year on ly and has harvested for a five-year period (1). Danke et aL reported that phosphate fertilizatio n increas­ed alfalfa yields at Langdon but did not influence yield at Carrington, Minot or Dickinson (3) . Dodds et a!. report preliminary data indicating a lfa lfa stands respond to phosphorus fertilization when the phosphorus level of the soil as indicated by a soil test is 5 pounds or less per acre (4) . Phosphorus and potassium are relatively immobile in the soil (6) . There is increased utilization of phosphorus (P) and potassium (K) when placed in the root zone compared to broadcast surface applied; however, fertilizing established alfalfa may be limited to broadcast surface applicatio n by the average producer, so P and K applied to the surface of ir­rigated alfalfa need to be evaluated for their benefits . METHODS A study was initiated to determine the effects of P and K fertilization on alfalfa production and its economic profitabili­ty . The study was conducted at the Karlsruhe Irrigation Research ite which is located in north central North Dakota . The soil is classified as a Clontarf sandy loam which has approximately 2 feet of sandy loam soil over a medium coarse sand with sand and gravel layers at lower depths . The organic matter ranges from 2.0 to 3.0 percent and the soil pH ranges from 7.5 to 8.0. The water holding capacity of the soil is approximately 4.5 inches in the top 4 feet of soil, which is very suitable for irrigation . Thompson is assistant agronomist and Hoag is superintendent both at the North Central Experiment Station, Minot; Dodds is grassland specialist, Cooperative ExtenSion Seroice . Alfalfa variety DeKalb brand 120, which is winterhardy, bacterial wilt resistant and resistant to phytophthora root rot (5), was seeded at 18 pounds per acre on the study area in June 1982. Eptam at 3.0 pounds per acre was applied preplant incorporated for weed control. An excellent stand was established . One cutting of a lfalfa was harvested in September 1982, but yield was not determined . A randomized complete block design with four replicates was used . Experimental units are 5 x 20 feet of wh ich 3 x 16 feet was harvested for yie ld. A three-cut harvesting system was used with harvests occurring in June, July and August of 1983, 1984, 1985 and 1986. Specific harvest dates are given in Table 1. All fertilizer , 0-0-60 (KCL) and 0-46-0 (tri­ple super phosphate), was applied according to treatment in late April of 1983, 84, '85 and '86. Experimental units were soil sampled in April 1983 and October 1983 '84, '85 and '86 . Soil samples were analyzed by the NDSU soil tes.ting lab. Table 1. Crop water use, water applied and date of forage harvest, Karlsruhe, NO 1983·1986. Crop Growing Water Season Irrig. Harvest Date Year Use Rainfall Applied Cut 1 Cut 2 Cut 3 -----------------­ inches---·-----~----1983 24.00 9.93 18.20 6/17 7/21 8/22 1984 18.79 7.09 14.85 6/13 7/13 8/21 1985 19.67 10.88 12.40 6/12 7/16 8/26 1986 23.24 9.14 14.10 6/10 7/11 8/19 Irrigation water scheduling and application were deter­mined with tensiometers, neutron probes and Jensen­Haase scheduling information for alfalfa. Annual crop water use and water applied are given in Table 1 . RESULTS AND DISCUSSION Initial levels of soil P and K were quite variable among ex­perimentaJ units with P ranging from 8 to 37 pounds per acre and K from 120 to 300 pounds per acre (data are not presented) . When so il testing levels were averaged over replicates by treatment, P ranged from 13 to 16 pounds per acre (Table 2) and K from 164 to 244 pounds per acre (Table 4) . Based o n NDSU soil testing procedures, the 0-6 inch so il depth testing 0-9 pounds per acre of P is rated low, 10-19 medium, 20-29 high and 30+ very high. In contrast, 29 -Table 2. Phosphate Soil Test Results 0 to 6-lnch, Karlsruhe, NO (1983-1986). Treatment 'P' soil test 0 to 6-lnch P2 0 e K20 4/83 10/83 10/84 10185 10/86 Avg. ····_···1blA···--··· -·-·--------..---·-..-·..··-1blA----........... - ...-.-- ­0 0 13.0 5.3 4.3 4.5 5.0 6.4 50 0 16.3 13.3 16.3 15.3 16.0 15.4 0 100 16.0 11.5 6.0 4.5 7.5 9.1 50 100 14.3 9.5 9.0 11.0 11.3 11.0 100 250· 16.3 18.5 27.0 37.5 34.3 26.6 LSD (5%) NS NS 6.9 11.4 5.5 3.7 LSD (5%) YearxTreatment=8.2 *200 Ib K20 applied In 1983. soil testing 0-99 pounds per acre of K is rated low, 100-199 medium , 200-299 high and 300 + very high. Initial soil P and K test levels were medium ranged except the unfertiliz­ed treatment initial K level was high ranged . Phosphorus and K levels in the soil appeared to have an influence on alfalfa yield during the first year of the study. Forage yields by fertility treatments were not significantly dif­ferent under the three-cut management system (Table 5). Alfalfa yields ranged from 4.94 tons of 15 percent moisture forage on the unfertilized treatment of 5.38 tons on the highest fertility treatment the first year of study. Annual soil test levels of P and K indicate fertility levels were influenced by application of fertilizers and alfalfa yields. Phosphorus levels in the 0 to 6-inch soil depth of the unfer­tilized treatment were reduced from 13 to 5.3 pounds per acre the first harvest year and then tended to stabilize (Table 2). Unfertilized treatment K levels fell from 244 to 108 pounds per acre from April 1983 to October 1986 (Table 4) . Unfertilized treatment K levels in the 6-24 inch depth re­mained constant from 90 pounds per acre in 1983 to 73 pounds per acre in 1986 (data not presented). This would indicate that K uptake occurred primarily in the top 6-inch soil layer. Alfalfa yields from the unfertilized treatments have fallen from 4 .94 ton per acre in 1983 to 3.89 ton per acre in 1985 and 4.51 ton per acre in 1986, indicating a shortfall of available soil phosphate and potash (Table 5). The unfertiliz­ed yield of alfalfa increased in 1986 from 1985 yields due to better growing conditions in 1986. Phosphorus levels of the 50 pound per acre P2 0 S treat­ment remained constant over the four-year period (Tables 2 and 3); however, K levels fell significantly from 174 pounds per acre in April 1983 to 100 pounds per acre in October 1986 (Table 4) and yields were reduced from 5.04 to 4.71 ton per acre during the same period (Table 5) indicating a shortfall in K20 availability. Phosphorus levels in the 0 to 6-inch depth on the 100 pounds per acre K20 treatment were reduced significantly from April 1983 to October 1984 with an additional reduc­tion from the 1985 harvest (Table 4). Like the unfertjlized treatment, the 100 pounds per acre K20 treatment alfalfa yield declined from 5.06 to 4 .84 ton per acre from 1983 to 1986, respectively, indicating a shortfall in phosphate availability (Table 5). Table 3. Phosphate Soil Test Results 6 to 24-lnch, Karlsruhe, NO (1983·1986). Treatment 'P' soil test 6 to 24-inch PZ0 6 K20 4/83 10/83 10/84 10/85 10/86 Avg. --------lb/A--·--­ -·-·----·......·-·---1blA.--.. -.------.---------.--­0 0 4.0 2.8 3.3 1.8 3.3 3.0 50 0 4.0 3.8 4.3 3.8 5.3 4.2 0 100 3.8 2.8 2.8 2.0 3.5 3.0 50 100 3.8 3.8 4.0 3.8 4.0 3.9 100 250· 3.3 6.8 10.0 7.0 10.0 7.4 LSD (5%) NS 1.6 2.4 2.1 2.2 0.9 LSD (5%) Year x Treatment = 1.9 . *200 Ib K20 applied in 1983. Table 4. Potassium Soli Test Results 0 to 6·lnch, Karlsruhe, NO (1983-1986). Treatment 'K' soil test 0 to 6·lnch P20 5 K20 4/83 10/83 10184 10/85 10/86 Avg. ...._. -1 blA-·--­ -----·--· ­ -·lb/A·--·.......-·- ­ ------· 0 0 244 103 103 125 108 136 50 0 174 89 96 118 100 115 0 100 164 85 128 178 146 140 50 100 164 115 104 150 133 133 100 250· 175 118 203 215 159 174 LSD (5%) 46 18 73 NS NS 23 LSD (5%) Year x Treatment = 51 *200 Ib K20 applied In 1983. Table 5. Irrigated Alfalfa Forage Yields By Fertilizer Treat· ment, Karlsruhe, NO (1983-1986). Treatment Alfalfa yield 1983 1984 1985 1986 Avg. ----lb/A---·-- ---·----ton/A at 15% H20-·--·_·..·..· ­o 0 4.94 4.63 3.89 4.51 4.49 50 0 5.04 5.11 4.18 4.71 4.76 o 100 5.06 4.85 4.04 4.84 4.69 50 100 5.09 5.33 4.85 5.36 5.16 100 250* 5.38 5.45 5.1 1 5.54 5.37 AVG. 5.10 5.07 4.41 4.99 LSD (5%) NS 0.53 0.35 0.53 0.26 LSD (5%) Year = 0.23 Year x Treatment =NS *200 Ib K20 applied in 1983. When 100 pounds per acre of K20 was appl1ed with 50 pounds per acre PzOs, the soU test levels of P were slightly lower than the 50 pounds per acre P20S treatment alone (Table 2) and the soil test levels of K were generally lower than the 100 pounds K2 0 treatment alone (Table 4) . Alfalfa yields from the 50 pounds P20S + 100 pounds K20 treat­ment were 5.09 to 5.36 ton per acre from 1983 to 1986. respectively, indicating this to be a maintenance level of fer­tilization on this soil type. The yield of forage harvested from this treatment was Significantly greater than the unfertilized, 30 50 pounds P2 0 S and 100 pounds K2 0 treatment yields (Table 5) , indicating improved nutrient use efficiency when crop nutrient needs were in balance . Phosphorus and K levels on the 100 P20 S + 250 1<20 treatment Increased from the fall of 1983 to the fall 1986 in­dicating an excess of nutrients being applied (Tables 2 and 4). The 100 P20 S + 250 K20 treatment produce more alfalfa than all other treatments but was not Significantly greater than the 50 P20 S + 100 K20 treatment (Table 5). Potassium levels from the 6 to 24-inch depth were not in­fluenced by fertiUzer applied or alfalfa yield, indicating that K uptake occurred primarily in the top 6-inch soil layer and that K was not being leached downward into the sandy loam soil (data not presented). Nitrate nitrogen soil tests were similar regardless of fertility treatment. Nitrate nitrogen was quite low ranging from 11 to 26 pounds per acre in the 0 to 24 inch soil depth (data not presented) . Alfalfa yield data were analyzed on the basis of individual cuttings (Figure 1) . June and July cut alfalfa yielded significantly more forage when the P and K combination was applied compared to P or K alone or no fertilizer applied. August cut alfalfa treated with 50 P + 100 K tended to yield more than alfalfa treated with 50 P or 100 K alone and yielded significantly more forage than the unfertilized alfalfa. The increased yield from balanced fertilization occurred at all cuttings; however , the June and July cuttings received most benefit. The dollar returns to fertilizing irrigated alfalfa on coarse textured soil in the Karlsruhe area are provided in Table 6 . This data was calculated by using the average annual forage yield at 15 percent moisture and $46 per ton alfalfa hay (four-year average price) . Costs were P20S at 17.5 cents per pound, K20 at 7 cents per pound and a $3 per acre per year application charge . Returns to fertilizer were negative in 1983, the first year of the study (Table 6) . The negative returns resulted when June Cutting July Cutting August Cutting Figure 1. Influence of Fertilizer Treatment on Irrigated Alfalfa Yield by Cutting. Karlsruhe 1983·1986. 31 Table 6. Fertilizer Cost and Return Summary by Treatment and Year, Karlsruhe. NO (1983·1986). Treatment 	 Return/acre P20S K20 1983 1984 1985 1986 Total ·--··-··--1 bl A -------­ ..------------.----.----$-----.--.----~-----.---0 0 227 213 179 207 826 50 0 220 223 181 205 829 0 100 223 213 176 213 825 50 100 215 226 204 228 873 100 250· 213 213 197 217 840 *200 tbs K~O applied in 1983. average soil P levels were medium and K levels were medium to high as determined by soil test. Summation of the annual returns by fertilizer treatment indicate a four-year return above fertilizer and application costs of $47 per acre when a combination of 50 pounds P20 S and 100 pounds K20 was applied per acre annually. This treatment was far more economical than other treatments which Indicates the need for P and K applications when soil tests are low . SUMMARY The results of this study indicate that producers must soil test and apply P20 S and K20 to maximize yields of aging alfalfa stands on irrigated coarse textured sandy soils in the Karlsruhe area . A maintenance level of P205 and K20 should be applied annually or by the second production year on irrigated alfalfa when soil test levels are in the low­medium to low range, P less than 10 and K less than 100 pounds per acre . LITERATURE CITED 1. 	 Bauder, J .W., and A. Bauer. 1978. Irrigated Alfalfa Forage Production on a Well-Drained Sandy Loam at Oakes, North Dakota. North Dakota Farm Research Bimonthly Bulletin 36(2) :19-24. 2 . 	Burbank, W.E. 1984. 1983 Irrigation Survey - North Dakota . lrrigation Journal 34(1) . 3. 	 Danke, W.c., and L.J. Swenson . 1974. Soil Test Values and Alfalfa and/or Grass Response to Fertilizer. Annual report, Dept. of ~oils , North Dakota Agri. Exp. Station . 4 . 	Dodds, D.L., D.W. Meyer and B. Rice. 1983. Alfalfa Management tn North Dakota . North Dakota Coop . Ext. Service, Circular R-571 (Revised) . 5. 	Dodds, D.L., D.W. Meyer. 1985. Alfalfa Variety Selection . Nroht Dakota Coop. Ext. SerVice, Circular R-681 (Revised). 6. 	 Follett, R.H., L.S . Murphy , and H.L. Donahue . 1981. Fer­tilizers and Soil Amendments. Prentice-Hall lnc. Englewood Cliffs , New Jersey. P . 89-100, 160-170. 7 . 	Lundstrom, D.R. 1985. 1984 lITigation Survey - North Dakota. Irrigation Journal 35(1) :29. 8 . 	Lundstrom , D.R. 1986. 1985 Irrigation Survey - North Dakota. Irrigation Journal 36(1) :25. 9 . 	Lundstrom , D.R. 1987. 1986 Irrigation Survey - North Dakota. Irrigation Journal 37(1) :23. 10 . 	Rhykerd . C.L. , and C .J . Overdahl. 1982. Nutrition and Fertilizer Use. In C.H. Hanson (ed .) Alfalfa Science and Technology. Agronomy 15:445-449. American Society Agronomy, Madison Wisconsin . 1.90 1.80 o 'X,.. "#-	 1.70 It),... -; <I: 	 1.60 C o ~ 1.50 1.40 LSD 5% 0.14I

Potash and Phosphate Fertilization on Irrigated Alfalfa

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