Studies in central and northern Illinois at 4 locations and 12 location‐years were conducted with 5 rates of N applied in the fall and as spring‐preplant. Sidedress N was also included at 1 of the 4 locations for 4 years. Relative efficiency of the times of application was calculated by dividing the corn (Zea mays L.) yield increase from a given rate of N added at one time by the yield increase from the same rate of N applied at another time. At the Carthage and Hartsburg locations the 3‐year average relative efficiencies of fall‐ versus spring‐applied N are about 0.8 and 0.9 (fall was 80 and 90% as effective as spring) at N rates of 67 and 134 kg/ha, respectively. Fall and spring N were about equally effective at 201 and 268 kg/ha of N. There was generally little yield response to N rates greater than 201 kg/ha at Carthage and Hartsburg. Fall and spring N gave similar corn yields for all rates of N at Urbana. For the 4‐year average at DeKalb, sidedress N was the most effective, spring N was intermediate, and fall‐applied N was the least effective. The difference between spring and sidedress N was less than that between fall and spring N. There was considerable year‐to‐year variation in relative efficiency. The importance of the time at which conditions suitable for N loss occur is discussed.
The objective of this research was to determine the effect on soybean (Glycine max (L.) Merrill) yields of N added at different rates by different times and methods of application, as direct and residual, and as inorganic and organic sources. A number of studies were conducted over a period of several years at 10 field locations in Illinois. Nitrogen at rates up to 360 kg/ha added for corn (Zea mays L.) the preceding year had no effect on soybean yields. Neither were soybean yields increased by organic sources of N such as manure or alfalfa (Medicago sativa L.), or by combinations of organic and inorganic sources. Fertilizer N added for soybean as plow‐down, disked‐in, and side‐dressed at early flowering and at pod filling did not increase yields. Nitrogen added for soybeans planted on four dates did not increase yields. High rates of N (1800 and 1440 kg/ha), broadcast and disked‐in in the spring, decreased yield due to germination and seedling injury. Considering all the studies, yields were significantly increased in only 3 out of 133 instances and these occurred at high, uneconomical rates of N fertilizer. It is concluded that N available to the plant is not the growth factor that presently limits soybean yields in Illinois.
Experiments were conducted on Zanesville, Elliott, and Muscatine soils to determine the relative efficiency, with respect to corn yields, of broadcast P as compared to banded P. The 16 fertilizer treatments consisted of 4 rates of banded P and 4 rates of broadcast P in factorial combinations. Yields from each of the 3 soils were used to calculate a multiple regression equation for each soil. The equation is of a quadratic form, and it expresses the relation between yield and rates of banded and broadcast P. The regression equations account for 77 to 88% of the variation in yield. The largest yield increases from added P were 1287, 1474, and 873 pounds of corn per acre for the Zanesville, Elliott, and Muscatine soils, respectively. With all the P either banded or broadcast, the relative efficiency of broadcast P ranged from 0.49 to 1.23 for the 3 soils For a given soil, the relative efficiency of broadcast P varied with rate. At 35.2 pounds of P added per acre, higher yields were obtained on Zanesville and Elliott soils if a combination of banded and broadcast application were used than if all the P was added either banded or broadcast. Banding all the P gave higher yields than the other application methods if 17.6 and 8.8 pounds of P per acre were added. Yields from the Muscatine soil were not dependent on whether all the P was drilled, broadcast, or applied by a combination of both methods.
The use of nitrapyrin as a nitrification inhibitor of ammonium fertilizers applied to corn (Zea mays L.) has gained widespread interest. Even though initial nitrification rates are usually decreased by nitrapyrin, its use does not always result in increased grain yield. To evaluate the effects of nitrapyrin applied with anhydrous ammonia on yield and N uptake of corn grown on poorly drained soils, field studies were conducted in Illinois at Urbana, Brownstown, and DeKalb. The soil at Urbana and DeKalb was Typic Haplaquoll and Mollic Albaqualf at Brownstown. Anhydrous ammonia was applied with and without nitrapyrin in the fall and spring. Nitrapyrin and N rates ranged from 0 to 1.12 and 0 to 268 kg/ha, respectively. The addition of nitrapyrin had varied effects on N concentration in the plant tissue and on grain and total dry matter yield; however, these effects were not consistent among N rates, locations, or years. At Urbana, the addition of nitrapyrin increased the N concentration in the plant tissue at the fifth‐leaf growth stage in 1975 by as much as 7% and in the ear leaf at silk in 1976 by as much as 6%, when comparing within N rates and seasons of application. The N concentration in the grain and stover was reduced by as much as 8 and 27%, respectively, by the addition of nitrapyrin at low rates of N. At DeKalb in 1975, nitrapyrin did not affect N in the plant tissue. In 1976, applications of nitrapyrin with fall‐applied N increased N in the ear leaf up to 20% over fall‐applied N without nitrapyrin, and increased it up to the concentration found for spring‐N applications with or without nitrapyrin. At Brownstown in 1975, plants did not respond either to applied N or nitrapyrin. In 1976, plants responded to nitrapyrin, but adverse weather resulted in data that did not follow expected trends. Grain and stover‐yield increases could not be attributed to applied nitrapyrin when N was applied at levels required for maximum economical yield. Soil moisture during both years was not favorable, however, for N losses that would occur normally through leaching and denitrification.
Reduced stands after planting may force maize (Zea mays L.) producers to consider the feasibility of replanting. The objective of this research was to develop guidelines for replanting decisions based on planting date, hybrid maturity class, population density, and plant distribution. Maize was planted at central and northern Illinois locations in 3 successive years. In each experiment adapted and early season hybrids were planted at three dates ranging from late April through early June. Plots were thinned to final densities of 30,890; 41,180; 51,480; and 61,780 plants/ha. The three lower densities were distributed uniformly within the row, with small gaps ranging from 0.42 to 0.85 m long, and with large gaps 1.5 m long. Adapted hybrids tended to yield more than early season hybrids when planted before 20 May, but the overall effects of hybrid maturity class were minor. Regression analysis indicated that the optimum planting date was near 6 May, and planting either 2 weeks before or after 6 May reduced yields by less than 5%. However, a rapid decrease in yield due to planting date occurred when planting was delayed past 20 May. Averaged across environments, the interaction of planting date with density and plant distribution was not significant. Before mid May the major factors to consider in replant situations are density and plant distribution within the row. After mid May, calendar date increases in importance. A model for uniformly spaced plants is presented that predicts yield on the basis of planting date and population density. Compared to uniform spacing within the row, small gaps reduced yield by an average of 1.9% while large gaps reduced yield by 5.4%.
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