Recently killed cover crops often interfere with crop seedling growth. Controlled‐environment and field studies were conducted to characterize the nature and persistence of cover crop interference with sorghum [Sorghum bicolor (L.) Moench] seedling growth and to test several seed‐zone management practices that might alleviate detrimental effects. Germination, root and shoot length, and disease incidence of sorghum germinated at 25°C for 5 d in soil collected 2, 4, 7, 14, 23, and 32 d after killing cover crops indicated legume cover crops were more detrimental to seedling growth than were nonlegumes. Surface residues, subsurface residues, and residue leachates contributed to the deleterious effects. Seedling shoot disease incidence of 50% persisted through 32 d when legume residues were mixed into soil or placed on top of soil at planting, but disappeared by 7 to 14 d if residues were removed. Pathogenic organisms isolated from lesions on seedlings indicated legume cover crops increased damage due to Rhizoctonia solani Kühn. In a no‐till field study, stand density was reduced 15% and aboveground seedling dry weight was reduced 45%, from 85 to 45 mg plant−1 28 d after planting, when sorghum was planted 1 d after killing crimson clover (Trifolium incarnatum L.) compared with planting 21 d or longer after killing. Insecticide, activated charcoal, or CaO2 seed coating improved sorghum stand density 15%, but did not affect seedling size. In‐furrow fungicide drench had no effect on stand density, but phytotoxic effects of the fungicide reduced shoot and root growth rates in both field and controlled‐environment studies. Residue removal combined with selected in‐furrow treatments may allow the interval between cover‐crop killing and successful no‐till planting to be reduced to less than 7 d.

Crop residues left on the soil surface after harvest are effective in reducing erosion; however, when subjected to rainfall‐leaching, the residues are a significant source of soluble nutrients to agricultural runoff. Nutrient leaching from crop residues as a function of rainfall intensity, and residue loading rate, was studied in a series of laboratory experiments under controlled conditions. Using a multiple‐intensity rainfall simulator corn (Zea mays L.) stover placed on a nylon screen at an equivalent field loading rate of 10 t ha−1, was subjected to simulated rainfall at intensities of 6, 12, 25, 51, and 99 mm h−1. In another series of experiments, simulated rainfall was applied at 25 mm h−1 to four stover loading rates of 5, 7, 10, and 15 t ha−1. In both experiments, leachate was sampled as a function of time and analyzed for PO4‐P, NH4‐N, NO3‐N, and total organic carbon (TOC). Nutrient concentrations and losses were generally greater at the lower rainfall intensities and higher stover loading rates. In each study, nutrient concentrations decreased hyperbolically with either time or cumulative leachate volume. For all loading rates and rainfall intensities, nutrient amounts (kg ha−1) leached from the stover followed the order C ≫N = P; however, the amounts of N as (NH4‐N + NO3‐N) or C leached were ≤1.5% of total nutrient in residue compared with 2.8 to 6.0% of total nutrient in residue for P. Stover exposed to field conditions over time showed leaching kinetics similar to freshly collected residues.

Knowledge of nutrients leached from crop residues will aid in understanding nutrient cycling in agricultural systems and in the development of small watershed chemical transport models. Using a multiple‐intensity rainfall simulator, wheat straw residue (Triticum aestivum L.) was subjected to 25.4 mm simulated rainfall at intensities of 7, 12, 25, 53, and 105 mm h−1. The wheat straw loading rate was 4500 kg ha−1. Runoff was sampled as a function of time and analyzed for PO43−‐P, NH4+‐N, NO3−‐N, and organic carbon (OC). Except for NO3−‐N, nutrient concentrations and losses were greater at the lower rainfall intensities. At each intensity, PO43−‐P, NH4+‐N, and OC concentrations in runoff from the wheat straw increased rapidly to maximum values and then decreased with time. After maximum nutrient concentrations were reached, a power function, Y = aXb, best described the relationship of nutrient concentrations with time, whereas a hyperbolic equation of the form Y = 1/(a + bX) best described the relationship of nutrient concentrations with runoff. The quantity (kg ha−1) of nutrients leached from the wheat straw followed the order C > P > N as (NH4+‐N + NO3−‐N). Amounts of N as (NH4+‐N + NO3−‐N) and C leached from the wheat straw were ≤ 1% of the nutrient content compared with 80 to 140 g kg−1 for P. This study also indicates that the variability in both the leachability and nutrient content of crop residues from different sources will be important, factors in the development of crop residue leaching models.

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Ips typographus populations were screened for 3 enzyme-loci, Aat-2, Amy-2 and Est-2. These three loci showed between 8 and 18 alleles. An additional electromorph was observed by a braconid parasitoid. The allozymes pattern and the mode of inheritance of the alleles were proved. Aut-2 had 8, Amy-1 had 14 and Est-2 had 18 alleles, therefore the statistical procedures were calculated for each locus individually. Two multivariatic methods proved the degree of relationship of the 9 Austrian I. typographus populations. The genetic similarity between six populations, infesting natural Pzcea d i e s stands, supports the hypothesis that they have emerged from the Dinaric Alps parallel to the host migration after the glacial period. Three populations are infesting artifical planted hosts and are suggested to have immigrated secondarly.