CIRCULAR 152 MARCH 1966 Spacing and Rates of Nitrogen for CORN !FR3,mcvFS Ni 1 ; AGRICULTURAL EXPERIMENT STATION AUBURN UNIVERSITY E. V. Smith, Director Auburn, Alabama SUMMARY OF RESULTS AND SPACING-NITROGEN RECOMMENDATIONS Close spacing and high rates of nitrogen are management practices that are essential for production of high yields of corn in Alabama. Since each of these practices affects value of the other, both must be followed for highest possible returns, as shown by results of experiments at several locations of Auburn University Agricultural Experiment Station System. Averages of data from 18 experiments show that 9-inch spacing in 42-inch rows (16,600 plants per acre) produced more corn than wider spacings tested. Since there is usually about a 15 per cent loss of stand between planting and maturity, getting the correct population requires planting at 8 inches in 42-inch rows and at 9 inches in 86-inch rows. For most locations in Alabama, 90 to 120' pounds of nitrogen per acre is the recommended rate, based on the experiments reported. In the Sand Mountain area, rates of 120 to 150, pounds are recommended. Choices of actual rate within the ranges suggested should be made on the basis of anticipated yield. When conditions are favorable for production to surpass 75 bushels per acre, the higher rates will usually be profitable. Spacing and Rates of Nitrogen for Corn C. E. SCARSBROOK, Professor, Agronomy and Soils J. T. COPE, JR., Professor, Agronomy and Soils ORN YIELDS are the product of many factors, such as fertility, variety, and management. Two of the most important management decisions to be made by corn growers concern drill spacing (plant population) and rate of nitrogen fertilization. These two factors must be considered together because each affects results obtained from the other. Using high rates of fertilization without adequate plant population can be a waste of fertilizer. High plant populations will not increase yield unless there are sufficient plant nutrients. Nitrogen recommendations cannot be made for individual fields as can recommendations for phosphorus and potassium, which are based on soil test. There is no satisfactory chemical test to determine capacity of a soil to supply nitrogen for a growing crop. Alabama soils have a low capacity to hold reserves of available nitrogen. For crops like corn, nitrogen must be applied annually near the time it can be used by the growing plant. Although the nitrogen supplying power of Alabama soils is low, it does vary. Because of this and the variation in yield from year to year and from field to field, average yield response is the logical basis for determining amounts of nitrogen to be used. Nitrogen experiments that show the yields from a range of nitrogen rates at many locations during a period of several years provide the best estimate of the most efficient rate. HOW THE STUDY WAS MADE Experiments on spacing and rates of nitrogen were begun in 1961 at the Brewton, Monroeville, and Prattville experiment fields and in 1962 at the Gulf Coast (Fairhope) and Sand Mountain (Crossville) substations. Spacings used were 9, 12, 18, and 24 inches in 42-inch rows. These represented populations of 16,600, 12,400, 8,400, and 6,200, respectively, Table 1. Corn was planted thick and thinned to the desired stand when about 3 to 4 weeks old. C TABLE 1. PLANT POPULATIONS AS RELATED TO Row SPACINGS Row WIDTH AND DRILL Row width 36 38 40 42 inches inches inches inches Plants per acre at four drill spacings 24 inches 18 inches 12 inches 9 inches Number Number Number Number 7,300 9,700 14,500 19,400 9,200 6,900 13,800 18,300 6,500 17,400 13,100 8,900 16,600 12,400 8,400 6,200 Rates of nitrogen were 60, 90, 120, and 150 pounds per acre for all spacings.. One treatment received no nitrogen and was spaced at 24 inches. All plots were fertilized with 54 pounds of P (120 pounds of P2 0s) and 98 pounds of K (120 pounds of K 2 0) per acre. In another series of experiments at seven locations, the same nitrogen rates were used with constant spacing of approximately 9 to 12 inches in the drill. These were conducted at the Tennessee Valley (Belle Mina), Sand Mountain (Crossville), Upper Coastal Plain (Winfield), and Wiregrass (Headland) substations and at the Brewton, Monroeville, and Prattville experiment fields. Fertilization rate for all plots was 27 pounds of P (60 pounds of P 20 5 ) and 66 pounds of K (80 pounds of K 2 0) per acre. Ammonium nitrate was the source of nitrogen in all experiments. It was put on in two applications - 30 pounds of nitrogen at planting and the remainder sidedressed just ahead of the last cultivation when corn was 18 to 24 inches high. Varieties recommended by Auburn University were planted at each location. Soil types were: Decatur clay loam at Belle Mina, Kalmia fine sandy loam at Brewton, Hartselle fine sandy loam at Crossville, Marlboro fine sandy loam at Fairhope, Norfolk fine sandy loam at Headland, Magnolia fine sandy loam at Monroeville, Greenville sandy clay at Prattville, and Savannah very fine sandy loam at Winfield. RESULTS OBTAINED AND WHAT THEY MEAN Average yields from five locations in the nitrogen and spacing experiment show that the 9-inch spacing produced about 3 bushels more corn per acre than the 12-inch spacing at the 90-, 120-, and 150-pound rates of nitrogen, Figure 1. Yields at the 9-inch spacing were 3 to 9 bushels more than from 12-inch spacings at three of the five locations, Table 2. At the other two locations, 9- and 12-inch spacings made about the same yield. Close spacing did not increase yields at the 60-pound nitrogen rate. The 9- or 12-inch spacings gave much higher yields than the 18- or 24-inch spacings at all locations. Close spacing did not decrease yields in the most unfavorable years of the experiments. Spacing effects were similar in the best years and poorest years, Figure 2, although yields exceeded 100 bushels in the best years and dropped to the 60-bushel range during poorest years. No extreme droughts were encountered during the 4 years. With no nitrogen applied [4] Z 80 U IoL 70 0 -J 9 12 18 241 inn in. 9 12 18 24 in. in. in in 9 12 18 24 in. in. in. ir. 5 12 18 24 in, in. in. in 50-- 60 90 120 150 NITROGEN APPLIED, Ib./A FIG. 1. Corn yields from rates of nitrogen and spacing experiments in 1961-64 are shown by the graph. Yields given ore averages of five test locations. bushelsi~ pcr acre ili 1)est 8 eatx. 01).01iii biy spatin lt8it(It lx fathe Hg apar111t ini liii I oxx . Lii i 1. It is eui) by l1)1.11111 i thicek av1 ag (I.lp('1)121i54' an d thini (2orn should to t speifiedl xtau iiI. To o)itaii this I)1 bi pliantedi aboit1I5 pci cenlt thi eke! to tot all I\ 121 ,c~ of dixises or othier ealiex. [lii eorce 9-initl spuii~ig uiiii at the 111p1nthad il li-tlii Atithe :3. xxe Culll ' l ate S xxb i ii (( )ith x. ix dr Sut ith i12 etiom o iltro i11 xiV iHIiiIat i xaill. aS2 i d ltl txp il eli x \Icre iex liii al buhealsi Coaspit Subsi itiat in i app)l lied \ as ii4 I A\t b)oth tihl 9- and 12-ineh spacinigs there wasaxlii axetalgi inicreaxe of TABLE 2. CORN YIELDS FROM DIFFERENT NITROGEN RATES AT DRILL SPACINGS, FIVE TEST LOCATIONS DIFFERENT Spacing in 42-inch rows Per acre yields Sand Gulf Monroe- PrattBrewton, Coast, Mountain, Average ville, 4 years 4 ville, years 4 years 3 years 3 years Bushels Bushels Bushels Bushels Bushels Bushels 49 65 74 73 75 63 77 77 82 67 74 83 86 65 73 84 92 44 64 66 73 74 66 72 77 85 68 75 81 86 65 76 78 86 28 49 52 54 54 49 56 58 62 51 56 59 66 49 59 64 62 54 69 73 76 78 71 74 79 79 69 78 83 84 72 77 83 86 36 63 74 70 69 76 80 88 86 76 82 100 97 77 88 102 106 42 62 67 69 70 64 71 75 78 No nitrogen 24 inches60 lb. nitrogen 24 inches 18 inches12 inches 9 inches 90 lb. nitrogen 24 inches18 inches----- ---12 inches--------9 inches .-------120 lb. nitrogen 24 inches _-------18 12 inches 9 inches --------- --------- inches .-------- 66 72 80 83 65 74 81 85 150 lb. nitrogen 24 inches----- 18 inches----- ---12 inches.----------. 9 inches .----- --. bushels of corn when the nitrogen rate was changed from 60 to 90 pounds per acre. Figure 1. The 120-pound rate produced about 5 bushels more than the 90-pound rate, but the increase from more than 120 pounds was small. Assuming that the price of corn is such that 1 bushel is equal in 90-pound value to 10 pounds of nitrogen, the choice between the 120rates is close at most locations. The higher rate might be profitable if moisture is sufficient for high yields, but the lower rates proved more profitable in less favorable years of the experiment, Figure 2. However, the high rates of nitrogen did not decrease yields even in the most and favorable un- years. How spacing and nitrogen affected lodging of corn was determined in the experiments at Prattvile and Fairhope by counting the lodged stalks. Lodging was never serious at either location. Corn stalks were smaller in the high population treatments and would be more susceptible to lodging in case of high wind or extended wet conditions in the fall. [6] BEST YEARS 120 100 80 60 40 a 20 0 z 0 ______ POOREST YEARS ____ 0 LL120 100 Wu >80 60 40 20 0 9 12 18 24 in. in. in. in. 9 12182421824 in. in. in. in. in. in. in. in. in. in. in. in. 60 90 120 150 NITROGEN APPLIED, Ib./A I FIG. 2. Close spacing did not decrease yields even in most unfavorable years, as shown by this comparison of yields between best and poorest test years. [7] BREWTON 140 120 100 PRATTVILLE AVERAGE - - 60 40 20 0 0 30 60 90 120 150 0 30 60 90 120 150 POUNDS NITROGEN PER ACRE FIG. 3. Yield response to nitrogen rates varied widely among locations, as illustrated by these 3-year average yields at the seven test locations.