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    Tillage and no-tillage effects on physical characteristics of a silt loam under 5 years of continuous oats-maize crop rotation : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Agricultural Engineering, Institute of Technology and Engineering, Massey University
    (Massey University, 2000) Viegas, Edmundo da Silva Soares
    Conservation tillage is one of the conserving practices recognized worldwide despite its empirical benefits still largely undergoing continuous research. This research is part of a sequence of studies carried out at Massey University tillage trial. The soil type is Ohakea silt loam representing youngest yellow-grey earth with poor natural drainage on fine texture material, and topsoil moderately to strong acid enleached soils. Selected soil physical properties under different tillage systems i.e. no-tillage (NT), moldboard plough (MP) and permanent pasture (PP) (as control) were measured and compared. The important soil properties considered were soil aggregate stability, soil penetration resistance, water infiltration rate, soil bulk density, soil water content, crop dry matter, water runoff and leachate and soil pH (H2O), total C and N. Results from both the field and laboratory experiments suggested that 5 years of continuous no-tillage have improved soil characteristics relative to conventional tillage. Soil penetration resistance was significantly lower in the MP plots soon after cultivation and at the early oats growing season, compared to the NT and PP plots. However, this trend was reversed within six months, following winter grazing and spring fallow when soil was recompacted. Bulk density measured during early oats growing season indicated a remarkably higher density at the top 0-5 cm soil layer under the NT compared to the MP treatment suggesting that NT plots' soils were more compacted at the time of planting and had lower total porosity than soils in the MP plots. On the other hand, water infiltration rates measured over one year period indicated an average value significantly higher under the NT and PP treatments than the MP plots. These results suggest that macropore continuity, water-filled porosity and other hydraulic properties were improved under NT. A substantially higher level (11%) of water content was found in the NT plots compared to that in the MP plot. These suggested that although the NT soils were more resistant to penetration and had high levels of bulk density, these soils retained more water. These further suggested that the water-filled porosity under the NT soil was higher, thus helped increase the water availability for plant growth. The results also demonstrated that the NT soil produced comparable winter oats and summer maize DM to those under MP treatment. Regression analysis results indicated, not unexpectedly, a strong linear relationship between bulk density and soil penetration resistance with R2 values of 0.97, 0.99, and 0.73 for the PP, MP, and NT treatments respectively. Similar analyses between soil water content and soil penetration resistance demonstrated a strong, moderate, and no correlations under the NT, MP and PP treatments respectively. The NT soils were substantially more stable than the MP soils but were similar to the PP soils. The surface soil (0-10 cm soil depth) water-stable aggregates remaining on sieve for the PP, MP, and NT were 75.2, 26.2 and 70.8% respectively. The macroaggregates (> 2 mm diameter) made up a large proportion of the pasture soil (54.7%) and the untilled soil (37.4%), whereas the ploughed soils had macroaggregates at 4.8%. The ploughed soil was consisted of 73.8% of 0.5 mm water-stable aggregates. Prolonged sieving for 60 minutes also confirmed the above results that the detachment of soils by water in the continuously ploughed land was much easier as compared to the NT and PP management. Thus making the MP soils most vulnerable to water erosion. Runoff and leachete experiments had produced rather inconclusive results as compared to the results on the same plots three years ago. However the trend was obvious that the MP treatment had caused more surface runoff than the other two treatments. By contrast, water runoff was lower in NT plots, which was also reflected by the occurrence of more water leaching under this treatment compared to the MP treatment. The NT soils were relatively more acidic (lower pH) both at 0-10 and 10-20 cm soil layers. Both the MP and NT had resulted in a marked decline in total C level compared to PP at the 0-10 cm soil layer. The decline of total C content after 5 years of continuous double cropping in the 0-20 cm soil layer was about 12% in the MP plots and 2.65% in the NT plots. At the 10-20 cm soil depth, total C and N showed no differences among all treatments. Total N at the 0-10 cm soil layer was significantly lower under MP treatment compared to the other two treatments.
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    Selected soil physical properties and their affects [i.e. effects] on cereal yields in the Manawatu-Rangitikei region, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Soil Science at Massey University
    (Massey University, 1986) Grealish, Gerard John
    The Manawatu-Kairanga-Rangitikei region is now a major cropping district in New Zealand. Expansion and intensification has led to a need for more specific information on soil physical properties and how these properties interact with crop yield and soil management. Soil physical properties largely determine the rooting depth and available water storage capacity of a soil-crop system. Compacted subsoils (1.5-1.7 Mg/m3), low saturated hydraulic conductivity (0-10 mm/hr), and poor aeration (0-5% large pores) were the probable causes restricting root depth in the six high terrace soils (Kiwitea mottled, Marton, Tokomaru silt loams) investigated. The two river plain soils (Kairanga silt loams) gave results vhich indicated a more suitable rooting environment than the high terrace soils. Restricted rooting depth led to low (65-80mm) total available water contents (TAWC) for the high terrace soils and higher, but more variable, TAWC (80-116mm) for the Kairanga soils. A simple soil water balance model allowed soil water storage and climate to be integrated to estimate periods of moisture stress. In the year of this study (1985/86) there was a range in moisture stress days (0-27 days) dependant on soil type. However, there was no correlation between the computed number of moisture stress days and crop yield. This was due to an unusual wet spring-summer growth season. Thus other factors, probably related directly and indirectly to poor drainage and aeration, affected yield more than moisture stress. Extended to different climatic seasons, the model predicted that 25-64 moisture stress days would occur in a drier season, depending on soil type. This is predicted to cause a 40% and 20% reduction in yield due to moisture stress for the high terrace soils and a Kairanga soil respectively.
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    Effect of organic crop rotation on soil fertility : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Soil Science, Massey University
    (Massey University, 1995) Sutassanamalee, Angsana
    Studies of soil nutrient fertility status of the organic and conventional plots at the Flock House cropping and organic units, Bulls, were undertaken to investigate the effects of organic crop rotation system on soil chemical fertility. Soil samples (0-75 mm, 75-150 mm, 150-300 mm depths) were collected from two organic plots lying adjacent to conventional plots of identical soil type (Manawatu silt loam) in Autumn and Spring. The crop rotation plots were established in 1988. Soil samples were analysed for total C, total N, mineralizable N, extractable P (Olsen), exchangeable K, CEC and pH. Earthworm surface casts collected from the surface of these plots were also analysed for exchangeable K and CEC. Results of this study showed that after seven years of conversion to organic management, there were significant quantitative increases in the soil nutrient levels at topsoil depth 0-75 mm. Organic plot number 3 (OP3), now under clover based pasture showed higher percent of organic C and N than the organic plot under continuous cultivation (OP5) and conventional plot (CP8). Mineralizable N was significantly higher in the soil of OP3 and the mean topsoil (0-75 mm) value increased from 104 to 139 μg g-1 (67%) from Autumn to Spring collected soils. Crop rotation under continuous cultivation resulted in decrease of mineralizable N from 90 to 30 μg g-1 (150%) from Spring to Autumn collected soils at depth 0-75 mm. Extractable soil P (Olsen) remained significantly high in CP8 in both Autumn and Spring seasons. Soil Ca and Mg were significantly higher in the organic plots during Autumn but there was no significant difference observed in Spring collected soils. Exchangeable K levels were similar under both organic and conventional management system and generally showed higher amounts at topsoil (0-75 mm) as a result of mixing with earthworm surface casts which contained appreciably high amounts of K, Ca and Mg. Soil CEC was generally higher in organic plots. Surface casting by earthworm was significantly higher (> 1000 casts m-2) in OP3 as compared to 380 casts m-2 and 300 casts m-2 in OP5 and CP8 respectively. This coincided with greater a cation nutrient status observed in the Spring collected soil samples. Organic management under different crop rotation system resulted in significantly variable levels of soil nutrient fertility. Seven years of crop rotation under the organic system was sufficient to maintain sustainable levels of soil nutrient fertility.
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    Farm management and soil quality : an investigation into the effects of conventional and organic crop rotation systems on soil quality indicators : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Agricultural Science in Soil Science at Massey University
    (Massey University, 1995) Steensel, Frank van
    The physical and biological properties of soil from the pasture phase of organic and conventional crop rotation systems were compared. At the same time, a similar comparison was made of soil from the crop phase versus soil of the pasture phase of organic plots. A search was started for a new biological indicator of soil quality. The potential use of the relative abundance of fluorescent pseudomonad bacteria in rhizosphere soil and on the rhizoplane of plants in conventional and organic plots was explored. Soil respiration was also evaluated as an indicator of soil quality. Several soil amendments including earthworm casts, rhizosphere soil, compost material and biodynamic "preparation 500" were examined for their effect. The research has concluded that; 1. The pasture phase of organic crop rotation had superior soil quality to the similar pasture phase of the conventional plot. 2. Though recently cultivated, the pasture phase of the organic rotation system was able to restore appropriate levels of soil quality. 3. The relative abundance of fluorescent soil pseudomonad bacteria was greater in soil from the organic plot. 4.Based on soil respiration activity, none of the organic amendments were able to show a stimulation of soil biological activity in soil from organic or conventional crop rotation plots.