THE POTASSIUM STATUS OF SIX LOESSIAL SOILS OF CANTERBURY, NEW ZEALAND, IN RELATION TO RAINFALL AND RATE OF LOESS ACCUMULATION

A selection of greywacke-derived loessial soils in Canterbury, New Zealand, was examined to test the hypothesis that soil K status is a function of soil-forming factors. Soils were selected such that factors besides loess accumulation and rainfall were relatively constant and the effects of each variable could be isolated. Soil K status was evaluated by plant, chemical, and X-ray diffraction techniques. With increasing rainfall and decreasing rate of loess accumulation soil K status decreased; there was a concurrent decrease in illite and increase in interstratified mineral content of the clay fraction.     

Drop-cone penetration in situ and on minimally disturbed soil cores

Drop-cone penetration was measured both in situ and on minimally disturbed cores at a selection of soil matric potentials for four soils. The drop-cone penetration/water content relation was linear in situ and, if results for very low water contents were excluded, for the cores. The slope of the line for the field data was much greater than for the core data and this raises doubts about the value of other than in situ measurements of soil strength for predicting field behaviour. Vane shear strength is negatively correlated with in situ drop-cone penetration. The drop-cone test is a useful strength test for small volumes of soil, but care must be taken in selecting the mass of the cone as this affects the volume of soil which will influence the test results.     

Root Extraction Force Measurements for Sitka Spruce

Extraction force and displacement were measured on roots pulledhorizontally from the sides of a pit made in the soil afterremoval of the tree and the bulk of its root system. Measurementswere made on a brown earth and a deep peat, in 24- and 27- year-oldcrops respectively. The brown earth soil was drier and moredeeply rooted than the peat, but the root diameter at the pulledend, the length of root extracted and the root displacementat maximum extraction force were each similar on both soils.Extraction force was related to the root cross-sectional areaat the pulled end and regressions showed that roots requiredsignificantly more force for extraction on the peat than onthe brown earth. However, the difference was small, and anydifferences in tree stability between the two sites would haveto be explained by other features of the anchorage. Data arealso presented on effects of root morphology and depth on extractionforce.     

Seasonal variation in in vitro digestibility and structural carbohydrate content of some commonly grazed plants of blanket bog

Oven- and freeze-dried samples of the separated green material of Trichophorum caespitosum, Molinia caerulea, Eriophorum vaginatum, Erio-phorum angustifolium, Juncus acutiflorus and J. squarrosus collected in May, July and September were analysed for dry matter digestibility (DMD) using an in vitro procedure and for structural carbohydrate content. Results were affected by method of drying, oven-dried (45°C) samples in general giving lower estimates of quality than freeze-dried samples. Low DMD values were obtained for J. squarrosus for all sampling dates. The remaining species had DMD values above 60 in May; some maintained these levels until July but all had low values by September. A comparison was made between in vitro DMD and predicted DMD using the data from the structural carbohydrate analyses and the summative equation of Van Soest (1965a). Two species, J. acutiflorus and J. squarrosus, showed poor agreement between values obtained by the two methods. The other species showed good agreement between values in May and July but poor agreement in September. The data are discussed in relation to the quality and seasonal patterns of growth of species of hill vegetation.     

Disease signs reported in south-eastern Australian dairy cattle while grazing Brassica species

Objective
To estimate the relative frequency of various disease signs in dairy cattle fed brassicas in south-eastern Australia, to estimate the incidence of disease signs within affected groups and to identify risk factors for commonly reported signs in brassica-fed dairy cows.
Design
A case series study and a case-control study.
Procedures
Case data was collected using an incident reporting system. Herd managers and veterinarians recorded details about disease incidents in brassica-fed dairy cattle in summer and autumn 1995 using a standard questionnaire. Potential risk factors for photosensitisation were assessed using a case-control study.
Results
Disease signs were reported in 66 groups of brassica-fed dairy cattle. Photosensitisation and bloat were the more frequently reported signs. While high incidences were reported in some groups, the incidence of disease signs was low within most affected groups. Photosensitisation occurred more frequently among groups of cows fed brassica crops treated with nitrogenous fertilisers or which were low yielding. Risks of other disease signs were greatest while the first one quarter of the crop was grazed.
Conclusions
In the study population, most disease outbreaks occurring in brassica-fed cattle were of low incidence. However, some high incidence outbreaks occurred. Results from this study suggest that important risk factors exist for disease signs in brassica-fed dairy cattle. Further studies are required if these risk factors are to be fully identified. This would allow the development of preventative strategies for high incidence disease outbreaks while feeding brassicas to dairy cattle.     

PLASTIC LIMIT DETERMINATION USING A DROP-CONE PENETROMETER

The drop-cone method, in which a 30° cone of mass 80 g is allowed to sink into a soil sample at a selection of moisture contents, was used to determine the moisture content/cone penetration curve in the region of the plastic limit for eighteen soils. The moisture content corresponding to the minimum of the curve is shown to be always numerically less than, but to correlate closely with, the plastic limit. It is suggested that the plastic limit be redefined as the moisture content corresponding to the minimum of the moisture content/cone penetration curve, with the advantages that the test is more closely related to soil behaviour, less subjective, at least as reproducible as the Casagrande test and may be carried out simultaneously with the liquid limit test.