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.

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.

Goatsrue is a member of the Fabaceae family, native to Europe and western Asia. It contains the toxic alkaloid galegine. The objective of the study was to describe galegine concentration in aboveground goatsrue plant parts and total galegine pools over phenological growth stages. Twenty goatsrue plants at four locations were selected and a stalk was harvested from each at five stages of phenological development and separated into parts. Plant parts were freeze-dried, ground, and analyzed with liquid chromatography/mass spectrometry. Galegine concentration was significantly different in plant tissues; reproductive tissues had the highest levels of galegine (7 mg g−1), followed by leaf (4 mg g−1) and finally stem (1 mg g−1) tissues. Galegine concentration and pools varied over plant tissues and phenological growth stages. Galegine pools (dry weight by concentration) or the total amount of galegine per stalk were lowest at the vegetative growth stage (2 mg stalk−1) and increased until reaching a maximum at the immature pod stage (91 mg stalk−1). The pools decreased nearly in half (48 mg stalk−1) by the mature seed stage. Like galegine pools, galegine concentration also reached a maximum at the immature pod stage (4 mg g−1), and decreased by nearly half by the mature seed stage (2 mg g−1). The increased levels of galegine pools at immature pod stage corresponds with the time of meadow hay harvest, implying that goatsrue is potentially most toxic at the phenological stage when it is likely to be harvested as a contaminant in meadow hay.

Goatsrue is an introduced perennial plant which has proven to have great invasive potential, leading to its classification as a noxious weed in many states and at the federal level. Very little research has been done on its basic biology. Physical dormancy of mature goatsrue seed was tested through scarification with sulfuric acid for up to 60 min resulting in 100% germination. Comparison of dormancy for 26-yr-old and 6-mo-old goatsrue seed indicated that aged seeds had reduced dormancy levels compared to newly harvested seeds. Maximum germination was similar among the 6-mo old and 26-yr-old seed lots, suggesting no loss of viability had occurred in seed stored dry for 26 yr. Goatsrue seedling emergence was inversely related to burial depth, and decreased as burial depth increased. Emergence of seed buried at 0.5 to 3.0 cm soil depth was 93 to 87%, respectively, and no emergence occurred from 12 and 14 cm. When the soil seed bank of five goatsrue-infested areas was sampled, the largest density of seeds found was 74,609 seeds m−2 while the lowest was 14,832 seeds m−2. Viability and dormancy of seeds recovered from the soil seed bank survey ranged from 91 to 100% and 80 to 93%, respectively. Management, which reduces the soil seed bank and controls emerging seedlings, is as essential as control of mature goatsrue plants in order to avoid seedling establishment and reinvasion of a location.