The effect of crop residue incorporation date on soil inorganic nitrogen, nitrate leaching and nitrogen mineralization

 Delaying cultivation and incorporation of arable crop residues may delay the release of NO₃ ^– and hence reduce leaching. The objective of this study was to investigate the effect of timing of cultivation on the mineralization and leaching of NO₃ ^– from an arable crop residue. Overwinter N leaching and periodic measurements of soil inorganic N were combined to estimate net N mineralized after ploughing a crop residue into a free-draining loamy sand soil in central England on six dates from June 1994 to January 1995. The crop residue was whole green barley with approximately 2% N. N leaching in the two following winters was increased by the addition of crop residues. Early residue application also tended to increase N leached in the first winter, largely as a consequence of relatively large losses early in the drainage period. Thus, early incorporation of crop residues presents a greater leaching risk. The amount of N leached in the second (drier) winter was similar for all dates of incorporation. At the end of the first winter, inorganic N derived from the crop residue was greatest for earlier additions: June (40% N applied) > September (30% N applied) > August (20% N applied) > October (19% N applied) > November (11% N applied) > January (3% N applied). However, at the end of the experiment, there was no evidence that the residues which had mineralized least by the end of the first winter had, to any significant degree, caught up, and this was confirmed by the parameters of the equation for first-order decomposition in thermal time. These results indicate that the effect of temperature, particularly in the early stages of residue mineralization, is complex and interacts with other soil processes in terms of the fate of the N mineralized. Received: 19 July 1999     

Low protein provision during the first year of life,but not during foetal life,affects metabolic traits,organ mass development and growth in male mink (Neovison vison)

Low protein provision in utero and post‐partum may induce metabolic disorders in adulthood. Studies in mink have mainly focused on short‐term consequences of low protein provision in utero whereas the long‐term responses to low protein (LP) provision in metabolically programmed mink are unknown. We investigated whether low protein provision in utero affects the long‐term response to adequate (AP) or LP provision after weaning in male mink. Eighty‐six male mink were exposed to low (19% of ME from CP; crude protein) or adequate (31% of ME from CP) protein provision in utero, and to LP (~20% of ME from CP) or AP (30–42% of ME from CP) provision post‐weaning. Being metabolically programmed by low protein provision in utero did not affect the response to post‐weaning diets. Dietary protein content in the LP feed after weaning was below requirements; evidenced by lower nitrogen retention (p < 0.001) preventing LP mink from attaining their growth potential (p < 0.02). LP mink had a lower liver, pancreas and kidney weight (p < 0.05) as well as lower plasma IGF‐1 concentrations at 8 and 25 (p < 0.05) weeks, and a higher incidence of hepatic lipidosis at 25 weeks (p < 0.05). Furthermore, LP mink had a higher body fat (p < 0.05) and lower body CP content (p < 0.05) at 50 weeks of age. It is concluded that some effects of low protein provision in utero can be alleviated by an adequate nutrient supply post‐partum. However, long‐term exposure to low protein provision in mink reduces their growth potential and induces transient hepatic lipidosis and modified body composition.     

Heritability estimates and response to selection for growth of Nile tilapia (Oreochromis niloticus) in low-input earthen ponds

This study presents results of two generations of selection (G₁ and G₂) for growth of Nile tilapia. The selection environment consisted of earthen ponds which were fertilized daily with 50 kg dry matter (dm)/ha chicken manure. No supplementary feeds were provided. In total, 6429 fully pedigreed experimental fish were included in the analysis. Survival till harvest was highly variable ranging from 35% to 77% and was affected by initial weight, pond, and age effects. Body weight at harvest (BW) increased from a mean of 67.4 g in the grandparental (unselected) population (G₀) to 129.5 g in G₂ was affected by initial weight, pond, sex and age effects. Generations were discrete and therefore genetic parameters were estimated separately for each year. Heritability estimates for BW ranged from 0.38 to 0.60, and the heritability for survival ranged from 0.03 to 0.14. The estimated selection response was 23.4 g (34.7%) between G₀ and G₁ and 13.0 g (14.9%) between G₁ and G₂. These results demonstrate the feasibility of selection for growth of Nile tilapia in low-input environments.     

Patterns in seabird distribution west of Scotland

The distribution of seabirds west of Scotland was studied relative to water masses in August 1988. Surface salinity was used to indicate the ship's position relative to the water masses described in the literature. Comparisons were made between seabird densities in Inshore Water, the Northern Coastal Current, the Southern Coastal Current and Atlantic/Hebridean Water. Seabird density varied with water mass; some species distributions suggested strong habitat associations. Water masses represent marine habitats, with different physical regimes supporting different marine life; patterns in bird distribution are likely to reflect prey distribution and availability. Manx shearwaters Puffinus puffinus, razorbills Alca torda, guillemots Uria aalge, and kittiwakes Rissa tridactyla were found mostly in Inshore Water, with lower densities in the Northern and Southern Coastal Current water. Only trace numbers of these species occurred in Atlantic/Hebridean Water. Storm petrels Hydrobates pelagicus, fulmars Fulmarus glacialis and puffins Fratercula arctica were found in very low densities in Inshore Water, and were dispersed in higher densities throughout the more oceanic areas. These data suggest that in late summer the Inshore Water of southwestern Scotland has the highest densities of seabirds potentially vulnerable in the event of an oil incident.     

Fish species redundancy in estuaries: A major conservation concern in temperate estuaries under global change pressures

1. Fish assemblages in estuaries have a much lower species richness (number of taxa) when compared with the combined numbers of freshwater and marine species from adjacent aquatic ecosystems. This is primarily because of the relatively harsh and fluctuating physico-chemical conditions in estuaries compared with the more stable freshwater and marine environments.
2. A comprehensive fish survey of estuaries in South Africa is used as a basis to determine fish species richness in subtropical, warm temperate, and cool temperate systems along the coast, and to assess the degree of redundancy in the different biogeographic regions.
3. In general, only one or two species belonging to each of the detritivorous, piscivorous, zoobenthivorous, and zooplanktivorous fish guilds are numerically well represented in the larger cool temperate estuaries, but between four and 10 species in each of these guilds are usually recorded in the larger subtropical estuaries.
4. Although the overall low redundancy of fish species groups in estuaries has already been formally recognized in the literature, this short note highlights the sensitivity of certain trophic guilds in temperate South African estuaries to any form of redundancy, a characteristic that may be equally applicable, based on declining species richness with increasing latitude, to temperate estuaries in other parts of the world.

     

Identifying resistance in wild and ornamental cherry towards bacterial canker caused by Pseudomonas syringae

Bacterial canker is a major disease of stone fruits and is a critical limiting factor to sweet cherry (Prunus avium) production worldwide. One important strategy for disease control is the development of resistant varieties. Partial varietal resistance in sweet cherry is discernible using shoot or whole tree inoculations; however, these quantitative differences in resistance are not evident in detached leaf assays. To identify novel sources of resistance to canker, we used a rapid leaf pathogenicity test to screen a range of wild cherry, ornamental Prunus species and sweet cherry × ornamental cherry hybrids with the canker pathogens, Pseudomonas syringae pvs syringae, morsprunorum races 1 and 2, and avii. Several Prunus accessions exhibited limited symptom development following inoculation with each of the pathogens, and this resistance extended to 16 P. syringae strains pathogenic on sweet cherry and plum. Resistance was associated with reduced bacterial multiplication after inoculation, a phenotype similar to that of commercial sweet cherry towards nonhost strains of P. syringae. Progeny resulting from a cross of a resistant ornamental species Prunus incisa with susceptible sweet cherry (P. avium) exhibited resistance indicating it is an inherited trait. Identification of accessions with resistance to the major bacterial canker pathogens is the first step towards characterizing the underlying genetic mechanisms of resistance and introducing these traits into commercial germplasm.     

Evaluation of sprinkler application of fungicides for control of potato early blight in Colorado

Sprinkler application of four fungicides, Du-Ter 47.5% W.P. (0.70 kg/ha), Difolatan 4F (3.51 1/ha), Bravo W-75 (1.68 kg/ha) and Bravo 500 (1.17 1/ha, 1.761/ha and 2.341/ha) were evaluated in Colorado for control of potato early blight caused byAlternaria solani (Ellis & G. Martin) L.R. Jones and Grout and compared to the conventional method of airplane application. Fungicides applied through center pivot irrigation systems generally achieved disease control equal to airplane application. Application of fungicides through both center pivot sprinklers and by airplane effectively reduced early blight infection. Control of early blight by airplane or sprinkler application of fungicides significantly (P = 0.05) increased potato yields in 1978. In other years (1977, 1979 and 1980) fungicide applications which reduced disease severity generally increased tuber yields but the increases were not significant when compared to the control.     

The effect of storage environment on the infection of potato tubers byAlternaria solani

Manipulation of storage environment to provide favorable conditions for wound healing immediately after harvest reducedAlternaria solani tuber infection. Prestorage of tubers at 15.6°C for three weeks before final storage at 10°C normally maintained for commercial storage of potato chip stocks resulted in fewer and smaller lesions than constant storage at 10°C or 4.4°C or prestorage for varying periods at these temperatures. Prestorage of potatoes at a low temperature (4.4°C) for 1–3 months resulted in moreA. solani infection suggesting that low temperatures may inhibit the wound healing process more than they reduce rates ofA. solani infection or disease development. Variations in relative humidities above 75% did not have an appreciable effect on the wound healing process nor onA. solani infection.