B. E. Johnson

SEED TREATMENT, SEEDING RATE, AND CULTIVAR EFFECTS ON IRON DEFICIENCY CHLOROSIS OF SOYBEAN

Iron (Fe) deficiency chlorosis of soybean (Glycine max L. Merr.) is a common problem in the North Central United States. The objectives of these studies were to determine the effectiveness of seed treatment, seeding rate, and cultivar on the severity of chlorosis and yield of soybean grown in wide (76-cm) rows. A study in 1998 showed an early-season reduction in chlorosis when the seed of a susceptible variety (‘Glacier’) was treated with FeEDDHA, but not with Fe citrate. Studies in 1999 showed increases in leaf chlorophyll, crop height, and yield, as seeding rate of Glacier soybean was increased. Studies in 2000 compared the effectiveness of cultivar selection (Glacier, Council, Traill), seeding rate (370,000 versus 740,000 seed ha−1), and FeEDDHA seed treatment (0 versus 0.56 kg ha−1) on chlorosis severity and yield. Cultivar selection was the most effective tool in reducing chlorosis. Chlorosis was the lowest, and yields the highest with the most resistant cultivar, Traill, followed by the moderately resistant cultivar, Council. Increased seeding rate reduced chlorosis of all cultivars and increased the yield of Traill and Glacier. FeEDDHA seed treatment reduced chlorosis at the 2–3 trifoliolate and increased yield at one site. Cultivar selection was the most effective tool for reducing chlorosis, but increased seeding rates gave additional reduction in chlorosis. Chlorosis reduction by 0.56 kg ha−1 of FeEDDHA was short-lived. Higher rates may be needed.

Effect of ammonium thilosulfate and dicyandiamide on residual ammonium in fertilizer bands

Abstract Ammonium thiosulfate (ATS, 12–0–0–26S) and dicyandiamide (DCD, 66–0–0) are fertilizer products that also inhibit nitrification. It has also been proposed that ATS can improve the nitrification inhibition properties of DCD. The purpose of this research was to compare the effects of ATS, DCD, and ATS/DCD mixtures on the nitrification of banded urea solution or urea‐ammonium nitrate (UAN) under laboratory, field microplot, and field conditions. The laboratory study demonstrated that adding 8.7% (vol vol‐1) ATS to a urea solution inhibited nitrification by 68%. Inhibition of nitrification was greater with ATS + DCD than with DCD alone. Some nitrite accumulated when ATS was added, but little or no nitrite accumulated when both ATS and DCD were present In field microplot studies, the addition of ATS to urea solution significantly (P ≤ 0.10) increased residual soil ammonium levels over urea alone at six of 11 trials. ATS was usually a less effective nitrification inhibitor than was DCD, and ATS + DCD ou...

Greenhouse Evaluation of Controlled-Release Iron Fertilizers for Soybean

Abstract Iron (Fe) deficiency chlorosis is a widespread problem for soybean [Glycine max L.(Merr.)] production in the North Central region of the United States. Fertilization options are limited due to the high cost of soil-applied chelates, and inconsistent crop response to foliar sprays. The objective of this study was to evaluate the response of soybean to several inorganic and organic Fe sources applied alone or coated with Polyon® organic polymers. Three greenhouse experiments were performed, using an alkaline Ulen sandy loam soil. Chlorosis was severe in all three experiments. Most of the products tested, such as uncoated ferrous sulfate, polymer-coated ferrous sulfate, or polymer-coated urea-ferrous sulfate, gave small increases in leaf chlorophyll content at the unifoliate or first trifoliolate stage, but not at the second or third trifoliolate stages. The most dramatic increases in leaf chlorophyll content and dry matter production were observed when the soil was amended with uncoated FeEDDHA or with a polymer-coated mixture of ferrous sulfate, ammonium sulfate, and citric acid. It was concluded that polymer-coated ferrous sulfate-ammonium sulfate-citric acid deserves further evaluation.

Method for determination of ureides in soybean tissues.

The ureides allantoin and allantoic acid are important transport compounds of fixed nitrogen from soybean (Glycine max L. Merr.) nodules to the plant tops. The objective of this research was to develop a colorimetric method for determination of ureides in soybean tissues. The 2,3-butanedione monoxime-thiosemicarbazide (BDM-TSC) method for urea was adapted for ureide analysis by adding an alkaline hydrolysis step and converting allantoin to allantoate before determination as urea. Water extracts of soybean tissue samples containing a wide range of ureide concentrations were analyzed by the proposed method and two alternative procedures. The alternative procedures included a volumetric method based on urease and a colorimetric method for ureide-derived glyoxylic acid. The proposed method was highly correlated (r = 0.99) to the two alternative methods. The proposed method was easier to perform than the two alternative methods and should be adaptable for use by microplate methods.

Preliminary evaluation of the soil application value of crambe meal.

Crambe (Crambe abyssinica L.) is a specialty oilseed crop. By‐product crambe meal has a high glucosinolate content, restricting its use for animal feed. The purpose of this study was to evaluate crambe meal for various types of soil application. When incubated with soil, crambe meal mineralized more slowly than soybean meal, with an average of 38% of the added nitrogen (N) from crambe meal appearing as mineral N after 12 weeks of incubation, compared with 57% for soybean (Glycine max L. Merr.) meal. Sulfur mineralization from crambe meal was rapid. Bioassays indicated no phytotoxicity to seedlings from crambe meal. In a second experiment, high rates of crambe meal inhibited the nitrification of urea added to soil, but this effect was short‐lived. In a third experiment, crambe meal–ferrous sulfate mixtures applied to calcareous soil partially alleviated iron deficiency chlorosis of soybean, but the response was less than observed with iron–ethylenediaminedi(o‐hydroxyphenylacetic) acid.

Effect of urea pellet size and dicyandiamide on residual ammonium in field microplots

Abstract Nitrification of urea can be slowed by adding a nitrification inhibitor or by fertilizer localization. The purpose of this research was to compare the effects of urea pellet size (0.01, 0.1, and 1.0 g) and level of dicyandiamide (DCD) addition (0, 1, 2, 5, and 10% of N as DCD‐N) on residual ammonium in field microplots. Trials were conducted at ten locations in North Dakota during 1988 and 1989. Adding DCD to 0.01 g urea pellets slowed nitrification at all locations and the lower rates of DCD (1–2% of N as DCD‐N) often performed as well as higher rates. Increasing urea pellet size to 1.0 g was more effective in inhibiting nitrification than adding DCD to 0.01 g pellets. Increased pellet size plus addition of DCD led to a very slow nitrification. A 1.0 g urea pellet containing 1–2% of N as DCD‐N should be a practical fertilizer formulation where a very slow nitrification is required.

EVALUATION OF SOYBEAN CULTIVARS FOR RESISTANCE TO IRON DEFICIENCY CHLOROSIS IN ROWS VERSUS HILLS

Selection of a resistant cultivar is the most practical control measure for iron deficiency chlorosis in soybean (Glycine max L. Merr.). Plant breeders routinely evaluate cultivars for chlorosis resistance in hill plots, but this procedure may overestimate the chlorosis resistance of a cultivar. The objective of this research was to compare the chlorosis scores of soybean cultivars differing in chlorosis resistance, planted in conventional 76-cm rows, or with two, four, or eight plants per hill. In both 2001 and 2002, it was estimated that three plants per hill would give average chlorosis scores most similar to that observed in 76-cm rows. The highest overall precision was given with row plots, and the lowest with two plants per hill. Hill plots are more space-efficient than row plantings, but are much more easily lost due to animal predation.