Legume Rotations-Crop Yields and Nitrogen Fixation

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It is well known that legumes have beneficial effects on succeeding crops.The benefit has been attributed • to nitrogen fixation and improved soil physical conditions.Legumes such as alfalfa and red clover also provide high quality forage rich in protein, so little if any protein supplement is needed in livestock rations.Nitrogenous fertil izers at a relatively ch-eap price gave farmers an alternative source of nitrogen for grain production.
This report compa res legume rotations with continuous grain production w ith •and w ithout nitrogen fe rtilization at the Cornbe lt Experiment Field in northeastern Kansas to determine legume effects on cereals grown in rotation.

Results and Discussion
Response to nitrogen was marked in continuous corn and the CCO sequence (Table 1).The data suggest that corn after red clover requires less than 80 pounds of nitrogen for optimum yield, and corn following two years of alfalfa requires no added nitrogen.The reduced yield of corn the first year after alfalfa makes it impossible to evaluate the nitrogen replacement value of alfalfa.Corn yields after red clover compared with continuous-corn yields suggest that red clover was equal to about 70 pounds of nitrogen per acre.
Residual nitrogen from preceding crops in the rotation had little influence on yields of alfalfa and red clover.First year alfalfa yields exceeded red clover yields but were lower than second year alfalfa yields.
Income from the various cropping systems is of major importance.Average yearly gross returns per acre are shown in Table 2.With yields around 90 bushels per acre, continuous corn and 80 pounds per acre of nitrogen should give highest net returns.
Low yields of oats and low prices for oats suggest excluding them as a cash crop from commercial crop production in northeastern Kansas.
Eighty pounds per acre of nitrogen increased gross income $26.60 from continuous corn compared with corn in the CCOAA rotation with no nitrogen.Such an increase would permit paying up to 33 cents per pound for 80 pounds of nitrogen on continuous corn and break even assuming no adjustment for differences in production costs.However, the increased yield would involve higher handling costs so the 33 cents is somewhat high.Shifts in crop prices would change gross income from that shown in Table 2. Shifts in fertilizer prices and other production costs would change net income, which is the important figure to farmers.One  .14 in 1963, $1.20 in 1964, 1965,  and 1966, $1.l0 in 1967, and $1.07 in 1968.Oats per bushel: $ .78 in 1962, $ .75 in 1963 and 1965 through 1968,  and $ .72 in 1964.Red dover per ton: $14.20 in 1962, $ 21.00 in 1963, $18.00 in 1964  and 1965, $20.00 in 1966 and 1967, and $ 12.00 in 1968.i lfalfa per ton: $16.00 in 1962, $15.62 in 1963\ $20.00 in 1964 and  1966, $18.00 in 1965 and 1968, and $25.00In 967.
must also recognize that individual farming systems often include livestock that need forages.When the experiment ended, soil s amples were taken to l 0 feet deep from two rep I ications of continuous corn and from corn plots planted in 1968 in the CCOAA sequences and analyzed for inorganic nitrogen (Table 3) 1 The greater accumulation of inorganic nitrogen in the 160pound nitrogen fertilizer plots over the 80-pound nitrogen plots shows the 160 pound rate to be excessive for yields obtained.Less inorganic nitrogen in the CCOAA rotation soils probably resulted from no nitrogen being applied to the alfalfa in the rotation and to alfalfa removing nitrogen.

Table 1 : Crop yields as influenced by crop sequence and added nitrogen fertilizer, 7-year averages, 1962 through 1968. Crop sequence and Yields-bu/acre and tons/ acre! nitrogen ratel 1st yr 2nd yr Pounds per acre cotn c orn oats clo ver
1. Nitrogen rates were 0, 40, and 90 pounds per acre for oats and 0 1 80. and 160 for corn.Red clover and aHalft'! received no nitrogen fertilizer, .2.

Yie lds of co rn and oats corrected to 15V2o/O moisture, Hay yields are air dry weights.
3. No hoy yields were obtained for red clover and first year alfalfa in 1965 as stands were not established in 1964.They were reseeded in the fall of 1964 and again In April, 1965.

Table 3 : Inorganic nitrogen in soil profile after corn in two cropping systems. 1 Crop sequence and nitrogen r;ate Lbs/acrtl of ac-cumulated inorganic nittogen 2
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