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    Inrteractions [sic] between farm effluent application methods, tillage practices and soil nutrients : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Agricultural Engineering at Massey University, Palmerston North, New Zealand
    (Massey University, 1998) Hoang, Son
    Land disposal of liquid effluent has benefits for the environment and is economically viable. Firstly, it can reduce nutrient levels from wastes polluting waterways. Secondly, the land application of effluent has been the most common treatment method because it can provide some necessary nutrients for plant growth. In New Zealand, land application of farm liquid effluent is a common method for disposing agricultural wastes. However, there is little comparative information about nutrient recycling in soils treated with effluent using surface application or subsurface injection. A field trial was conducted to examine the effect of tillage on the transformation of nutrient added through dairyshed effluent. Liquid effluent was either injected at 10 cm depth or broadcast on the surface at the Massey University long-term tillage experiments which include permanent pasture, and crops sown with no-till and conventional tillage as main treatments. In the first experiment, raw dairyshed liquid effluent was applied in August 1997 at the rate of 120 m 3 ha -1 (30 kg N ha -1 equivalent). This was considered as a low rate of application. In the second experiment starting in December 1997, the application was at the rate of 600 m 3 ha -1 (150 kg N ha -1 ). At this rate, although the hydraulic loading was considered as a high rate, the nutrient loading was considered optimum. Soil samples were collected before application, after one week, one month, and two months of application, at two depths: 0-10 cm and 10-20 cm and the samples were analysed for total N, total P, NO 3 - , NH 4 + , exchangeable K, available Olsen-P. Throughout the experiments, interactions between nutrient status, methods of application and different tillage practices were analysed. In the case of injection method, soil samples were taken both in the centre of the injected row and 10cm horizontally away from the centre of row. At the low rate of application (first experiment), soil nitrogen and phosphorus status did not change significantly for up to two months after application. Soil ammonium concentration reduced immediately after one week then reduced slowly. Nitrate concentration reduced slowly during the first month and significantly reduced during the second month after application. Exchangeable K and Olsen-P were not significantly different among treatments. At the high rate of application (second experiment), levels of soil nitrogen and phosphorus reduced slightly after two months of application. Nitrate concentration in the soil increased in the first month, but steadily reduced during the second month. On the other hand, ammonium concentration reduced gradually over a period of two months. Ammonium in injected plots was higher than that in the broadcast plots. Pasture retained more ammonium concentration compared with no-till and conventional tillage plots. Moreover, nitrate content in the injection plots was similar to that in the broadcast. This may be related to low rainfall during the experiment period that may have restricted the denitrification and reduced nitrate losses through leaching. Generally, there was higher content of exchangeable K and available P in soil which resulted from effluent application. Method of effluent application had no effects on K and P concentrations. Overall, there was an increase in nutrients in soil after application of liquid effluent, especially at the topsoil. There was a greater retention of nutrients in no-till soil than the conventionally tilled soil. Subsoil injection of effluent allowed higher level of nutrient retention than the surface broadcast method. This may be due to reduced nitrogen losses caused by volatilization of ammonium.
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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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    The effects of tillage practices on soil microbial biomass and CO2 emission : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Agricultural Engineering at Institute of Technology and Engineering, Massey University
    (Massey University, 1998) Aslam, Tehseen
    Conversion of permanent pasture land to forage crop rotation by conventional tillage and reversion to pasture, for recovery of nutrients is a common practice in New Zealand. Because of their effects on soil physical, chemical and biological degradation, and the extent to which these soil management practices are sustainable is not fully known. To evaluate short- and long-term impact of tillage induced changes in soil physical, chemical and biological properties, a quad replicated field experiment was established at Massey University, Turitea campus in 1995. Permanent pasture land was converted to a double crop rotation using conventional (CT) and no-tillage (NT) practices on the Ohakea silt loam soil. The overall aim of this research programme is to develop a sustainable land use management for pasture-based arable cropping to suit local farming conditions. The present study investigated the effects of CT and NT practices on soil biological status and CO2 emission. The test crops were summer fodder maize (Zea mays L.) and winter oats (Avena sativa). An adjacent permanent pasture (PP) was used as a control. Soil samples were collected at 0-100 mm in summer, 0-50 and 50-100 mm depths in autumn and winter before or after crop harvest. The 'fresh' field moist, sieved samples were used for the measurement of microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP) and basal soil respiration. Earthworm population and biomass were extrusion with formaldehyde. Field CO2 emission was measured at 3-4 weeks interval for one year. After two years of continuous cropping, overall nutrients status (organic C, total N and total P) in NT remained similar to that in PP. In CT the nutrient levels were significantly lower. Earthworm population and live mass were also significantly lower in CT as compared to PP and NT treatments. However, there was no differences in plant establishment, crop dry matter yield, soil temperature and soil pH (0-100 mm depth) between the two tillage (NT and CT) systems. Higher levels of MBC, MBN and MBP were found in NT as compared with CT at 0-100 mm depth throughout the three seasons studied. When samples were analysed separately from two depths i.e. 0-50 and 50-100 mm, the microbial biomass contents were higher in surface soil (0-50 mm depth) as compared with 50-100 mm depth. Microbial biomass contents at 50-100 mm layer did not differ significantly among the three treatments. At 0-100 mm depth, MBC declined by 29%, MBN by 32% and MBP by 33% with two years (4 crops) of CT. Such a decline in microbial biomass is an early indication of future decline in soil organic matter. Soil organic matter (total C) had also declined by 22% (from 35,316 to 27,608 kg ha-1) with CT. No such decline occurred either in MBC, MBN and MBP or organic matter with NT. Basal soil respiration data indicated that microbial biomass activity in CT was 38% lower than in NT at 0-50 mm depth. However, at 50-100 mm depth, the activity was 25% higher in CT as compared with NT. Metabolic quotient (qCO2) did not differ among the three treatments at 0-50 and 50-100 mm soil depths. Field CO2 emission from PP was significantly higher as compared to NT and CT treatments. The two tillage practices did not influence the CO2 emission measured both shortly after tillage and during crop growth period. The annual estimated carbon loss through CO2 emission was 34 t C ha-1 year-1 in PP, 24 t C ha-1 year in NT and 21 t C hayear in CT treatment. Field CO emission was generally higher in summer and autumn as compared to winter and spring. Overall, this study, which spanned two cropping seasons, clearly showed that 2 years cropping with CT resulted in a decline in soil biological status and organic matter. The decline in soil biological status is likely to affect crop yields in CT over the longer period. Conversely, NT cropping was efficient in sustaining soil biological status and organic matter. NT had similar influence on soil biological status as clover based PP during a short-period. Therefore, it is concluded that NT may be used as an effective tool to enhance soil productivity while promoting agricultural sustainability.