Browsing by Author "Baker, Christopher John"
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- ItemAn approach to a field drainage problem by laboratory examination of selected properties of undisturbed soil cores : thesis presented at Massey University of Manawatu in part fulfilment of the requirements for the degree of Master of Agricutural Science(Massey University, 1964) Baker, Christopher JohnFor many years, soil drainage investigators, from a practical view point, have had to content themselves with expert appraisal of certain direct and indirect soil and environmental characteristics in order to ascertain the cause of a particular drainage problem. In a great many instances, observations of vegetative composition, topography and general soil type, aided by aerial photography and local experience, give completely adequate information. Normally, derivation of conclusions from such observations is based on well established principles, and the recognition of general broad classes of the cause of mal-drainage conditions. Such classes may be grouped as; (I) where infiltration capacity of a soil is inadequate to deal with the amount of water supplied to the surface, because of topography, abnormal rainfall, or through inherent inability of the soil to transmit water internally, (II) where the groundwater table rises to a height detrimental to vegetative survival and/or soil structure, or where its presence hinders the function of a free draining subsoil, end (III) where a similar situation exists, due to a perched or elevated ground-water table. The allocation of a particular drainage problem to one or more of these broad classes is not usually difficult, but identification of causal processes within classes presents quite another problem. Often, drainage investigators have been content to evolve general treatments for each class, and, as a basic rule, such procedures have, more often than not, proved reasonably effective. However, with the increasing intensification of pastoral and agricultural farming, the fundamental causes of individual mal-drainage conditions must be positively identified and rectified within the broadly classified groups.
- ItemAn investigation into the techniques of direct drilling seeds into undisturbed, sprayed pasture : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand(Massey University, 1976) Baker, Christopher JohnMethods of evaluating the techniques and equipment used for direct drilling of seeds into untilled soils were reviewed and developed. Field tests were used to highlight seedling establishment problems and were complimented by a tillage bin technique which sought to isolate variables such as climate, soil type and soil moisture regime. The tillage bin technique involved collecting half-tonne undisturbed blocks of turf in open ended steel bins using a special turf cutting machine. These tillage bins were subjected to a common climate and moisture supply by placing them beneath transparent rain canopies and applying water artificially. Drilling utilized a support bed on which several bins were placed end to end and which was straddled by a moving gantry and tool testing apparatus operating on rails alongside. This facility allowed close visual appraisal to be made of the action of coulters and seed deposition and was operated at speeds which were infinitely variable, within limits. Seed metering was precisely controlled and selected coulter forces and soil physical properties were measured with the apparatus. Turf blocks, in their tillage bins, were returned to the rain protection canopies after drilling for plant response studies. Soil cover over the seed appeared to be important in promoting seedling emergence. Field covering devices were evaluated and a bar harrow was developed and adopted as a standard covering procedure. The importance of covering the seed appeared to be more pronounced with large seeds such as maize and barley than with smaller seeds such as lucerne. A strong relationship between visual scoring of the amount and type of cover, and seedling emergence data was established. This favoured covering media with a predominance of unbroken dead pasture mulch, compared with loose soil and rubble. The performances of a range of drill coulters operating at slow speeds in association with the bar harrow, were compared in terms of plant responses under soil moisture stress. An experimental chisel coulter was developed to obviate the noted shortcomings of some of these existing coulters. In contrast to the "V" shaped grooves left by most coulters, the chisel confined most of its soil disturbance to sub surface layers, with a narrow opening at the surface. With all coulters, seed germination appeared to be less affected by coulter design than seedling emergence because of sub surface mortality of seedlings. In this respect clear seedling emergence responses favoured the chisel coulter. Maximum wheat seedling emergence with the chisel coulter assembly was 77%, which was significantly greater than hoe and triple disc coulters with 27% and 26% respectively. As the initial soil moisture level was raised in other experiments the magnitude of these differences decreased but the order of ranking remained. A 22% comparative decrease in initial soil moisture content was necessary to reduce the performance of the chisel coulter to a similar level to that of the hoe and triple disc coulters. Difficulty was experienced in accurately monitoring in-groove soil moisture regimes, but irrigation responses and gravimetric determinations of sub samples suggested that the ability of grooves to retain available soil moisture was a critical factor in the plant emergence responses. Soil temperatures appeared not to be greatly affected by coulter type in these experiments although the in-groove minimum temperature with the chisel coulter was significantly higher than the hoe and triple disc coulters in one experiment. Observation of the modes of action of coulters showed that the chisel and hoe coulters produced some upward soil heaving while the triple disc appeared to operate with a downward and outward wedging action in the soil. An increase in soil density under the groove resulted from passage of the triple disc coulter but no effect on density was seen with the chisel or hoe coulters. The down forces required for 38 mm penetration of all coulters tested, appeared also to be closely related to their modes of action and relatively insensitive to soil moisture content in the stress range. In this respect the triple disc required 1.4 times more force than the dished disc coulter and from 2.3 to 4.6 times more force than a range of 4 other coulters. Field tests of the wear rates of chisel coulters constructed of various steel based materials, with and without hardening treatments, suggested a number of preferred treatments but could not establish any difference in wear rate from coulters operating in the tractor wheel marks compared with those operating in unmarked soil.