The article concerns both the attrition of soil nutrients and the replacement thereof. Soils inherently contain only a finite quantity of nutrients. When more nutrients are removed than are being replaced, soil eventually becomes depleted. Data from a study in this paper indicated that in North Dakota, plant nutrients are not being replaced in quantities large enough to replace all of the nutrients being removed by crops

Dahnke, W. C.

Johnson, A.

Swenson, L.J.

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Crop Nutrient Removal$ vs . Fertilizer Additions in North Dakota W. C . Dahnke, L.J. Swenson and A. Joh nson North Dako ta has an agricultural system in which large amounts of plant nutrients are exported from the state in marke ted crops . The retation between the amount of nutrients exported from the state, soil test levels, and the amount of commercial fertilizer applied can give insight into potential soil fertility problems. North Dakota Crop Production Small grains a re grown on about 70 percent of the cropped land in North Dakota (Table 1). The acreage of land used in the production of sunflower has increased fro m about 120,000 acres in 1971 to over a million acres at the present time . Most of these products and the nutrients they contain are exported from the state when they are marketed. About 17 percent of the crop land in North Dakota is use d for the production of hay However, unlike small grains and sunflowers , most of the hay produced remains in the state Table 1. Average harvested acres (000 acres) of the major crops grown In North Dakota between 1971·1980.· Crop Area 000 acres Wheat (all) Sunflower Oats Barley Sugarbeets Potatoes Flax Corn (grain) Corn (si lage) Edible beans Hay (all) Soybeans 9,650 1,1 60 1,260 2,070 130 120 570 220 300 130 3,330 180 TOTAL 19,110 ·From: North Dakota Crop and Livestock Statistics, Dept. of Agric. Economics, NDSU and USDA Economics, Statistics and Cooperative Service. Dahnke is profess or, Swenson is an Instructor and Johnson is research technician, Departmen t 0/ So il Science . and is used as cattle feed. Consequently, some of the nutrients contained in hay are returned to the land in the form of ma nure. O ther crops such as flax , corn , potatoes , sugarbeets and beans are grown on approximately 9 percent of the crop land. Nutrient Removal by Crops vs. Fertilizer Additions Harvested crops remove tremendous a mounts of nutrients from North Dakota soils each year. The nutrients removed in the greatest quantity are nitrogen (N), phosphorus (P) and potassium (K). The amount of these nutrients removed per harvested unit (bushel, to n , etc.) are given in Table 2. These data were multiplied by the average production of the major crops in North Dakota to determine the amount of N, P and K removed (Table 3) . Approximate­ly 400,000 tons of N, 60,000 tons of P (140,000 tons of P20 5) and 150 ,000 tons of K (180,000 tons of K20) are removed from the soils of North Dakota each year. About half of the Nand P are from land planted to wheat. Table 2. Nutrient removal per harvested unit of major crops grown in North Dakota. Harvested Nutrient Crop Unit N P K .. ·Ib/harvested un it" --­Wheat (al\) bu 1.60 0.25 0 .20 Sunflower (all) cwt 2.90 0.50 0 .60 Oats bu 0.65 0.11 0 .16 Barley bu 1.1 0 0.18 0.30 Sugarbeets ton 4.17 0.25 6.90 Potatoes cwt 0 .30 0.09 0.50 Flax bu 2.00 0.37 0 .62 Corn (grain) bu 0.90 0.15 0 .20 Corn (si lage) ton 6.67 1.16 5.40 Ed ible beans cwt 6.66 0.58 1.94 Hay (aU) ton 28.00 4.40 32.00 Soybeans bu 3 .20 0.36 1.16 · Sunflower data from M.S. thesis of Allen A. Faulkner enti tled, "Effect of Plant Density and Fertility Treatment on the Uptake of N, P & K by Sunflower" 1977. Other data from various publicat ions of the American Potash Institute. 8 Table 3. Average production (1970·1 980) and nutrient removal of the major crops grown in North Dakota. Nutrient Removal Crop Production* N P [P20S] K [K2O] 000 ····· ..... ·.·.000 tons .............. Wheat (all) 255,000 bu 204 32 [73] 26 [31] Sunflower (all) 13,800 cwt 20 7 [7] 4 [5] Oats 61,500 bu 20 3 [7] 5 [6] Barley 85,500 bu 47 8 [18] 13 [16] Sugarbeets 2,025 tons 4 0.3 [0.7] 7 [8] Potatoes 19,200 cwt 3 1 [2] 5 [6] Flax 6,000 bu 6 1 [2] 2 [2] Corn (grain) 14,600 bu 7 1 [2] 1 [1] Corn (silage) 1,690 tons 6 1 [2] 5 [6] Edible beans 5,000 cwt 17 1 [2] 5 [6] Hay (all) 4,500 tons 66 10 [23] 76 [91] Soybeans 3,500 bu 6 1 [2] 2 [2] TOTAL 406 62 [142] 151 [181] •Data from North Dakota Crop and Livestock Statistics, Dept. of Agricultural Economics, NDSU and USDA EconomiCS, Statistical and Cooperative Service. Potassium Soil tests and experience have shown that the soils of North Dakota are well supplied with potassium, except for a few sandy soils. From the standpOint of balanced plant nutri· tion and economics , potassium fertilization should not be of great concern on many soils at the present time. Since only 4 percent of the soils in North Dakota have K soil test levels of medium or below (1) (Table 4), only about 6,000 tons of K fertilizer are needed each year to replace the potaSSium removed by crops . Presently about 22,000 tons of potassium fertilizers are being applied annually to our soils (2) . This is more than enough to maintain potassium soil test levels, provided the fertil izer is being applied to the soils that need it. Table 4. Summary of soil test phosphorus and potaSSium levels for North Dakota. Soil test category Phosphorus Potassium •••••••••••••••••••••• % ...................... Low Medium High Very hig h 20 44 23 13 o 4 15 81 Phosphorus North Dakota farmers are doing a very good job of main· taining the P levels in their fie lds . Approximately 62,000 tons of P are re moved by crops each year and about 50,000 tons or 81 percent of the P removed is being replaced as fer­tilizer. On the average this is good . Hopefully most of the fertilizer is being applied to low testing fie lds and not to those already testing very high. Nitrogen While significant losses of P and K only occur through crop removal and erosion, N balances are more d ifficult to determine. Nitrogen can be gained or lost from a soil in various ways. Nitrogen gains occur through atmospheric fix· ation and when legumes are included in a crop rotation. Losses of N can be a result of denitrification , leaching or volatilization. When a soil is in sod or some other type of no·tillage crop­ping system, organic matter levels tend to increase. Cultiva· tion Qf these soils promotes the mineralization of this organic matter and a subsequent increase in available nitrogen to plant growth. Each year these soils are cultivated , the amount of organiC matter mineralized becomes less. At some point in time, the amount of nitrogen released each year will become relatively constant assuming nitrogen has not been added as fertilizer. The length of time required for this to occur depends on the amount and type of organic matter which was present originally . Most soils in North Dakota have been cultivated long enough so that the amount of nitrogen released from soil humus each year is rather constant. In the western quarter of the state about 30 pounds of N per acre are released each year and in the eastern quarter it is about 55 pounds per acre . At present the amount of mineralization is probably more related to the amount of crop residue and its nitrogen content. The use of nitrogen fertilizer in North Dakota has greatly increased in recent years. In 1970 approximately 100,000 tons of N were applied. This level increased to 300,000 tons in 1982 (2). The amount of N which is removed by crops each year is 400,000 tons (Table 3). As a result, the reserve supply of N in our soils is decreasing . Nitrogen deficient crops are commonly observed. Table 5. Crop nutrient removal versus nutrients applied In commercial fertilizer (1982)* In North Dakota. Nutrient N .... ···--·--000 tons -.---. Removal Addition Percentage added 406 300 74 62 [142] 50 [114] 81 151 [181] 22 [28] 12 'Sunflower data from M.S. thesis of Allen A. Faulkner en titled, "Effect of Plant DenSity and Fertility Treatment on the Uptake of N, P & K by Sunflower" 1977. Other data from various publications of the American Potash Institute. Summary Soils inherently contain only a finite quantity of nutrients . When more nutrients are removed than are being replaced, soil eventually becomes depleted . Data from th is study in· dicate that in North Dakota, plant nutrients are not being replaced in quantities large enough to replace all of the nutrients being removed by crops (Table 5) . 9 The difference between re moval and replacement is not serious with potassium, as the level in most of the state's so ils is very h igh . O n the average, North Dakota soils are medium in nitrogen and p hosphorus. These nutrients are . not being added in amounts large enough to replace the amount being removed by harvested crops. As a result , yields are below potential simply because of a lack of nutrients . The systematic use of soil testing is a valuable tool for the manage ment of soil fertility . Knowledge of the nutrient levels in each field will help avoid the application of fertilizer when it is not needed and will determine the amount of fer ­tilizer to apply to different soils. Knowledgeable use of plant nutrien ts on whea t in North Dakota will often resu lt in a return of five dollars for every dollar in vested in fert ilize r. References 1. 	 Dahnke, W.e., LJ . Swenson , Arlyce Johnson and Adeline Klein. 1982. Summary of soil fertility levels for No rth Dakota: 1972-1981. Bulletin No. 51 2 , North Dakota Agric . Expt. Sta ., Fargo , ND 58105. 2. 	 Hargett , Norman L and Janice T. Berry . 1983. 1982 fertilizer summary data . [SSN .0146 .1850, National Fertilizer Develop­ment Center, Tennessee Valley Authority , Muscle Shoals, AL 35660. 

Crop Nutrient Removals vs. Fertilizer Additions in North Dakota

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