A comparative study of the physical, chemical and microbiological status of soils, as influenced by conventional and reduced tillage

Historically, shifts to reduced and no-tillage management for production of crops were fostered by needs to decrease soil erosion and loss of organic matter, reduce fuel and labour costs and conserve soil water, as compared with conventional fallow tillage management. Recent interest in maintaining soil quality has been stimulated by a renewed awareness of the importance of soil condition to both the sustainability of agricultural production systems and environmental quality (Doran and Parkin, 1996). The aim of this project was to determine the impact on the physical, chemical and microbiological status of the soil of conventional and reduced tillage. It has been suggested that the reduced soil disturbance associated with the tine cultivator improves soil structure, increases nutrient content in the top 10cm of soil, increases microbial activity and improves physical characteristics. From this study it was determined that the environmental benefits linked to reduced tillage in literature, did not develop in the first two years of this programmes implementation. The results of this study determined that soil nutrients did not increase in concentration in the top 10 cm of soil under reduced cultivation. The only exception was exchangeable potassium. As potassium is not a mobile nutrient its movement is dependent on soil disturbance, therefore under reduced cultivation its concentration was allowed to accumulate in the upper horizon of the soil profile. Microbial activity was greater in the conventionally tilled treatments, as determined by total aerobic bacterial numbers. This could be due to the increased rates of soil aeration in this treatment. Numbers of aerobic bacteria were greater in the conventional tillage treatments at both incubation temperatures of 22 and 32° C. The physical characteristics of the soil determined, indicate that below the depth of soil cultivation, cone penetration resistance increases. Therefore the reduced cultivation treatments would be more prone to soil compaction, higher in the soil profile.

An assessment of biological and population parameters of the Common whelk, Buccinum undatum (L.) in the region of the North West Irish whelk fishery

The Common whelk, Buccinum undatum (L.) is a conspicuous benthic scavenger in Irish waters, and is a valuable fisheries resource in South East Ireland. B. undatum is fished in many parts of its range, and previous studies have shown that certain life history parameters, which vary with location, make this species vulnerable to overexploitation. This makes research into each exploited stock essential to ensure sustainable fisheries management of the species. In 2003, interest in B. undatum as a complementary species in the inshore fishery east of the Inishowen Peninsula, North West Ireland, initiated investigation into fisheries related biological and population aspects of the species in this region. The current study presents estimates of spatial variation and density of the stock, size at age and growth rates, size and age at onset of sexual maturity, and timing of reproductive events in the region of the North West Irish whelk fishery for the period of June 2003 to May 2004. Analysis of variance of the total shell length of whelk landings to the fishery was conducted over spatial scales of fishing pot, fishing string and landings to vessels. Landings varied significantly in shell length at the spatial scale at which whelks are attracted to baited pots, but did not vary significantly over larger spatial scales. Depletion estimates of stock density from fisheries derived Catch per Unit Effort data and a mark re-capture experiment estimate 0.134 - 0.227 whelks per m2. Two independent methods of age determination found similar growth logistics functions for B. undatum.Modal analysis of length frequency distribution of landings to the fishery estimated symptotic length, Leo = 151.64 mm and Brody growth coefficient, K = 0.04. Analysis of the striae in individual opercula, where each stria was found to represent annual growth, estimated Loo = 137.73 mm and K = 0.12. Common whelks in the region of the North West Irish whelk fishery grow slowly and are long-lived, with 19 opercula striae recorded in one individual. Onset of sexual maturity is late, and no sex-specific differences in size or age at maturity were determined in the present study. Males were found to achieve sexual maturity at 83.30 ± 10.77 mm, and 8.9 - 11.1 years of age, and females at 82.62 ± 10.68 mm and 8.8 to 11.1 years of age. Systematic observations of reproductive events, including histological changes to the female ovary and male testis, and changes in the size and mass of body components, suggest that breeding occurred between the autumn and winter months of October and December 2003. Biological aspects of B. undatum in the study region are compared with previous studies from other regions, and discussed in relation to sustainable management of the fishery.