Browsing by Author "Aslam, Tehseen"

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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.
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    Investigations on growth and P uptake characteristics of maize and sweet corn as influenced by soil P status : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Ph. D.) (Plant & soil science), Institute of Natural Resources, Massey University, Palmerston North, New Zealand
    (Massey University, 2005) Aslam, Tehseen
    Despite being different cultivars of the same plant species (Zea mays L.), maize and sweet corn have contrasting P fertiliser recommendations in New Zealand, that are reflected in different target Olsen P values of 10-15 mg P/kg soil for optimum maize growth and 26-35 mg P/kg soil for optimum sweet corn growth. Three key hypotheses were developed in this study to explain why these differences may exist: i) maize and sweet corn differ in their responsiveness to P fertiliser i.e. maize is more internally P efficient and requires less P than sweet corn to grow, ii) both cultivars differ in external P efficiency i.e. their ability to take P up from soil iii) both cultivars differ in external P efficiency because they have different root system structure. Two field experiments evaluated the growth and yield responses of maize and sweet to different rates of P fertiliser application. The first experiment was conducted in Hawke's Bay (2001-02) and second in the Manawatu (2002-03) with P application rates of 0, 100 and 200 kg P/ha in the Hawke's Bay and 0, 15 and 70 kg P/ha in the Manawatu. Both experiments were conducted on soils of low available P status. The Olsen P test values of 13 mg P/kg soil in the Hawke's Bay and 11 mg P/kg soil in the Manawatu were far below the recommended values for sweet corn (25-35 mg P/kg soil). In both experiments and across all P treatments maize produced significantly higher dry matter yields than sweet corn during all sampling stages. In the Hawke's Bay experiment at 100 days after sowing (DAS), the maize (87719 plants/ha, 20.9 t/ha) produced 43% more dry matter than sweet corn (71124 plants/ha, 14.6 t/ha), whereas, in the Manawatu experiment (140 DAS), maize (71124 plants/ha, 15.2 t/ha) had a 39% higher dry matter yield than sweet corn (71124 plants/ha, 10.9 t/ha). In both the field experiments, the sweet corn fresh cob yield of 27 and 28 t/ha in the Hawke's Bay and the Manawatu regions and maize grain yields of 16 and 10 t/ha, respectively, were within the range of the reported commercial yields for each region. In both experiments, the P fertiliser application raised the soil P status (Olsen P test values) but caused no significant increases in either maize or sweet corn yields (total dry matter, sweet corn fresh cob or maize grain). Commercially viable yields of both cultivars were able to be achieved without P fertiliser application with Olsen P soil test in the range of 10-15 mg P/kg soil. Sweet corn reached harvestable maturity at 115 DAS in the Hawke's Bay and 140 DAS in the Manawatu experiments. By this time maize had produced 4-6 t/ha more total dry matter yield than sweet corn, yet maize and sweet corn had achieved similar total P uptake (32-37 kg P/ha at 100 DAS in the Hawke's Bay and 18-19 kg P/ha at 140 DAS in the Manawatu). At silking (after 75 DAS in the Hawke's Bay and approximately 110 DAS in the Manawatu), both cultivar's total leaf P concentrations (0.21-0.25%) were within the sufficiency range values for maize crops in New Zealand (0.18-0.33 %). Maize, however was more internally P efficient growing more dry matter per unit P taken up, which was more noticeable in the drier season. Fertiliser P application increased P uptake with both cultivars under moist conditions in the Hawke's Bay experiment (2001-02). However, the dry conditions in the Manawatu (2002-03) limited P uptake as well as restricted dry matter yields with both cultivars. Further, there were no significant differences between maize and sweet corn P uptake efficiency (kg P/kg root) despite significant differences in the root system structure (biomass) for both cultivars at all stages, which lead to different temporal patterns of P uptake. The lack of maize yield response to fertiliser P in both field experiments is consistent with the New Zealand recommendations for growing a maize grain crop (because soil Olsen P was in the range of 10-15 mg P/kg). However, the lack of sweet corn yield response in both field experiments does not support the New Zealand recommendations for growing sweet corn (which assume optimal Olsen P values are 26-35 mg P/kg).