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Identifying characteristics and drivers of the maize value chain in Shan State, Myanmar : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Agribusiness at Massey University, Palmerston North, New Zealand
(Massey University, 2023) Htoo, Kyan
As an agrarian country, Myanmar’s economy largely relies on the agriculture sector. Maize is the second most important cereal crop after rice in Myanmar in terms of growing area and export volume and value. Maize is not a staple food crop, but is grown primarily for export and domestic poultry production. Shan State is the most important region for maize in Myanmar, and about 50% of the total maize growing area is in this State. It was expected that the maize-growing areas continue to increase as there were no better alternative crops for maize farmers in Southern Shan State, despite challenges such as the unpredictable dominant export market and price fluctuations. However, there had been little knowledge of why there was a robust growth of maize amid the challenges. A single case study approach was applied to explore the characteristics of the maize value chain and the factors influencing the chain. In this study, the qualitative method was used to learn how and why the maize value chain in Shan State was performing as it did. In this respect, semi-structured interviews were used to explore the answers to those questions. Taunggyi township, a major maize township in Southern Shan State, was selected as the primary research area, whereas other types of actors from other townships throughout the chain were also selected to be interviewed as research participants. For example, exporters from Muse in Northern Shan State exporting maize to China via cross-border trade, key informants from Muse Commodity Exchange Centre, an exporter from Yangon who dealt with overseas exports, and an exporter from Yangon who exports maize to Thailand via cross-border trade were interviewed. Purposive and snowballing sampling methods were applied to select participants. The thematic analysis method was used to analyse the collected data. Despite price fluctuations, maize farmers were willing to continue to grow and increase the area of maize grown because of the certainty of the market for maize and the relative uncertainty of markets for other potential alternative crops. In addition, maize had a relatively low labour demand, easy access to improved varieties of maize and limited access to improved varieties of other alternative crops, easy access to credit, mechanization, and suitability for large-scale production. Therefore, the growth of maize production is likely to continue in the foreseeable future. The price farmers received for maize fluctuated significantly, yet remained relatively high compared to other crops, and remained certain. The Shan State maize market relied strongly on an unstable dominant export market which accounted for close to 90% of Myanmar maize exported to the Chinese market. In the 2018-2019 season (at the time of data collection) the border trade with China stalled in large part due to policies of the Chinese Government, and there was an expectation that market access would resume. During the period when access to the dominant export market was stopped, the demand for maize was stabilised through domestic maize buyers buffering the stock of maize and because of the emergence of an alternative export market. This provided maize farmers with the certainty of market. Furthermore, an international company, which has a significant stake in the maize value chain in Myanmar influenced the access to the alternative export market. Informal relationships were dominant between the actors throughout the maize value chain in Shan State. Most transactions between the actors were informal and based on reciprocity. Local wholesalers provided credit to farmers who sold their maize to the wholesaler. Most large-scale farmers stored maize at their wholesalers’ storage houses. Both informal and formal agreements existed between wholesalers and feed factories and/or exporters. However, if there was a risk associated with a formal contract, particularly due to price fluctuation, wholesalers helped each other to mitigate the risk in an informal way based on their social relationships. Even the transactions between foreign buyers and the exporters from cross-border trade were made mainly through informal agreements. Only formal agreements were used for the transactions between foreign buyers and the exporters from the emerging and relatively small overseas trade. Informal relationships reduced risks, transaction costs, and the amount of investment capital in trading maize. There was a tremendous growth of maize in Myanmar over a couple of decades despite a lack of Government support. There was no Government policy specific to the maize sector, whereas there were general policies or rules and regulations for the whole agriculture sector, which probably had impacts on the maize industry. This was probably because maize is not a staple food crop in Myanmar like rice. Moreover, there were no formal quality standards for maize. However, despite some issues, transactions of maize were carried out quite smoothly because the domestic and international cross-border markets, which were major markets for Myanmar maize, did not necessarily require it, except for overseas export markets. This study identified some important potential areas to be improved by policy interventions. First, formal quality standards should be set for the stable market access of the maize sector. Second, the formal banking sector should practice flexible repayment schedules for better convenience for the farmers. Moreover, the formal banking sector should focus on small-scale farmers as they had more difficult access to informal credit than large-scale farmers. Third, the Myanmar Government should take account of a policy, which facilitates the improvement of infrastructures such as roads, drying machines, and storage facilities for reducing transaction costs and improving the quality of maize. In this way, the Government policy will support the sustainable development of the maize sector.
Comparison of maize silage and traditional forage crops in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Manawatū Campus, New Zealand
(Massey University, 2022) Thant, Aung Myo
Cattle wintering systems using crops including grazing kale, swede, and fodder beet crops in situ have resulted in soil and water quality deterioration. Nitrate leaching is the most common problem due to the high deposition of urine N driven by excess N intake. Alternative cropping systems offer a potential solution to reduce these environmental problems while maintaining or maximising productivity. We proposed maize silage as an alternative crop because it has high yield potential, flexible feeding requirements, compliments the nutritive value of pasture, and is potentially suitable for more regions in New Zealand in the future due to climate change. However, research needs to determine whether maize silage yield, feed quality and potential nitrate losses during production and utilisation means it is a viable alternative to in situ grazed forage crops in these areas. Field experiments were conducted at Massey University, Tokoroa and Kiwitea to determine forage yield and feed quality, management effects and site differences in 2018/19 and 2019/20. Crop yields and forage N content were utilised to simulate urine N loads from the feeding of these forage crops. The excreted N loads were analysed in APSIM (Agricultural Production Systems sIMulator) to predict nitrate leaching losses. Maize produced significantly higher yields compared with the winter forage crops at all Massey University trials while producing competitive yields at Tokoroa and Kiwitea. Yields ranged from 10,940 to 30,417 kg DM/ha for maize whilst wide and lower yield ranges were observed for the winter forage crops (4,579 to 22,928 kg DM/ha). Irrigation increased yields of forage crops by 29-63%. Similarly, nitrogen fertiliser increased yield by 30%, on average. The faster canopy development of maize has the advantage of intercepting more radiation in summer and suppressing weeds, contributing to greater growth and yield despite a shorter crop season. All forage crops produced forage with good metabolisable energy content (MJ/kg DM); higher values in swede (10.1-14.5) and fodder beet (10.8-14.9) whereas intermediate values in kale (8.9-12.7) and maize (9.9-12.2). However, maize was the highest energy-yielding crop, ranging from about 200-316 GJ/ha while other crops varied from 34 to 217 GJ/ha. Protein content in kale (7.5-16.6% DM) and swede (11.4-18.2% DM) were adequate for non-lactating cows whereas maize (5.4-9.2% DM) and fodder beet (7.6-11.2% DM) were lower than recommended protein levels for dairy cows but offering an opportunity to reduce urinary N excretion. Maize also had recommended fibre content. With higher sugar contents, swede and fodder beet were poor in fibre sources, potentially prone to rumen acidosis unless considered mixed diet with high fibre feed. APSIM modelling indicated that maize would produce the lowest urine N output while swede the highest in simulated feeding. Accordingly, N loads/ha was higher for winter forage crops especially when good yields were produced. When common feeding practices were considered, i.e., off-paddock maize feeding (no urine N deposition) and on-paddock grazing of winter forage crops (high urine N deposition), simulated nitrate losses from maize cropping systems were the lowest. Predicted nitrate losses were 21 and 32 kg N/ha for maize under irrigated and non-irrigated conditions. A ryegrass cover crop further reduced simulated nitrate losses by 20-30%. Predicted nitrate losses for fodder beet, kale, and swede crops were 126, 162, 154 kg N/ha under irrigated conditions and 72, 201, 199 kg N/ha under non-irrigated conditions, respectively in grazing systems.
Predicting spatiotemporal yield variability to aid arable precision agriculture in New Zealand : a case study of maize-grain crop production in the Waikato region : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Agriculture and Horticulture at Massey University, Palmerston North, New Zealand
(Massey University, 2020) Jiang, Guopeng
Precision agriculture attempts to manage within-field spatial variability by applying suitable inputs at the appropriate time, place, and amount. To achieve this, delineation of field-specific management zones (MZs), representing significantly different yield potentials are required. To date, the effectiveness of utilising MZs in New Zealand has potentially been limited due to a lack of emphasis on the interactions between spatiotemporal factors such as soil texture, crop yield, and rainfall. To fill this research gap, this thesis aims to improve the process of delineating MZs by modelling spatiotemporal interactions between spatial crop yield and other complementary factors. Data was collected from five non-irrigated field sites in the Waikato region, based on the availability of several years of maize harvest data. To remove potential yield measurement errors and improve the accuracy of spatial interpolation for yield mapping, a customised filtering algorithm was developed. A supervised machine-learning approach for predicting spatial yield was then developed using several prediction models (stepwise multiple linear regression, feedforward neural network, CART decision tree, random forest, Cubist regression, and XGBoost). To provide insights into managing spatiotemporal yield variability, predictor importance analysis was conducted to identify important yield predictors. The spatial filtering method reduced the root mean squared errors of kriging interpolation for all available years (2014, 2015, 2017 and 2018) in a tested site, suggesting that the method developed in R programme was effective for improving the accuracy of the yield maps. For predicting spatial yield, random forest produced the highest prediction accuracies (R² = 0.08 - 0.50), followed by XGBoost (R² = 0.06 - 0.39). Temporal variables (solar radiation, growing degree days (GDD) and rainfall) were proven to be salient yield predictors. This research demonstrates the viability of these models to predict subfield spatial yield, using input data that is inexpensive and readily available to arable farms in New Zealand. The novel approach employed by this thesis may provide opportunities to improve arable farming input-use efficiency and reduce its environmental impact.
Growth response to temperature of two maize (Zea mays L.) hybrids with differing levels of cold tolerance : a thesis presented in partial fulfillment of the requirements for the degree of Master of Agricultural Science in Plant Science (Seed Technology), Massey University
(Massey University, 1993) Mukumbuta, Mwangala Stephen
Low temperatures are a hazard to maize production especially in high altitude and high latitude areas (Eagles, 1979; Hardacre and Eagles, 1986) where it may cause substantial yield reductions through its accumulated effect on vegetative and reprodutive growth. Cold tolerant cultivars with rapid emergence and growth at low temperatures have been identified in highland tropical genotypes and are being developed in New Zealand (Eagles, 1979; Hardacre and Eagles, 1986). Growth of one such hybrid A665 x NZlA was compared in this study to that of an established hybrid, A665 x H99, but identified as of warm weather at two field and one glass house environments. The hybrids were planted in the field on 26th October and 26th November, 1991, and in the glass house on 30th April, 1992. Glass house grown plants were later transferred to two controlled temperature environments set at 28/22°C and 16/6°C during the grain filling period. Both hybrids had comparable high percentage laboratory germination. However A665 x NZlA emerged earlier than A665 x H99 at all plantings, though only significantly so at the October planting were mean temperatures were lowest ( < 15°C). Seedling emergence rates did not differ significantly. Seedling dry weights at about 7 weeks after planting were highest in the glass house planting where mean temperatures were highest (19°C) and lowest in the October planting, where temperatures the lowest. A665 x H99 had faster leaf growths than A665 x NZlA at all plantings although differences were not significant between the hybrids. Across plantings the hybrids had their greatest leaf appearance rates and leaf area growth rates in the November planting where temperatures were the highest and their lowest rates in the glass house where the photoperiod was longest (14 hrs). Maximum leaf area and leaf area index were however attained in the October planting where although temperatures were lowest and hence suppressed leaf growth, the extended growth periods resulted in larger leaf areas and leaf area indices. The lowest leaf areas and leaf area indices were obtained in the glass house primarily because the plants there were much smaller than those in the field. Days to anthesis did not differ significantly between the hybrids though A665 x NZlA reached mid-silk earlier than A665 x H99 at all plantings. Across plantings the hybrids reached mid-silk earliest in the November planting and latest in the glass house planting where temperatures were highest and the photoperiod longest, respectively. At anthesis total plant dry weights (TPDWT) at all plantiIJ.gs did not differ significantly between the hybrids. Across plantings the TPDWT were highest in the October planting and lowest in the glass house where temperatures were lowest and highest, respectively. During the reproductive period A665 x H99 still maintained a larger but non significant TPDWT than A665 x NZlA in the field plantings. At both temperatures (28/22°C and 16/6°C) in the controlled temperature environments, A665 x H99 had significantly greater TPDWT than A665 x NZlA. These temperatures did not influence the coefficients of growth, which must already have been established during the first 30 days of grain growth prior to moving plants from the glass house. A665 x H99 had significantly greater cob and grain growths than A665 x NZ1A in the October and glass house plantings where mean temperatures were higher (> 16°C) during the early reproductive period and the onset of the linear dry matter accumulation phase. In the November planting where mean temperatures were low (< 16°C) during the early phase of reproduction and then further declined, cob and grain growth of the hybrids did not differ significantly. However the cob and grain growths of A665 x H99 were more retarded than those of A665 x NZlA. In the October planting and at 28/22°C where the hybrids had time to reach physiological maturity days, to physiological maturity and the duration of the grain filling period did not differ significantly between the hybrids. A665 x H99 had greater final crop grain yield than A665 x NZlA in the environments where temperatures were higher during the reproductive growth (October and glass house plantings). In the November planting where temperatures were lower A665 x NZlA yielded higher though only slightly. Across plantings grain yields were highest in the October planting where temperatures were the highest during grain growth, and lowest in the controlled environments which was mainly a reflection of the small plant size. The main yield component which was different between the hybrids was total grain number. A665 x H99 had more total grains than A665 x NZIA at all plantings and these differences were significant so in the October and glass house plantings.
The growth and yield of maize (Zea mays L.) and soyabeans (Glycine max. (L) Merrill) grown as intercrops : a thesis presented in partial fulfilment of the requirement for the degree of Master of Agricultural Science in Plant Science at Massey University
(Massey University, 1986) Kamarudin, Yusoff
The effect of plant population maize (Zea mays L.) cultivar (Pioneer 3901) and AMT and Matara cultivars of soyabeans (Glucine max (L) Merill) grown together in an intercropping system was studied. In the experiment three rows of maize were sown at populations of 6, 8, 10 plants/m2 and three rows of soyabeans were planted between the rows of maize at either 50 or 75 plants/m2 replacing one of the three rows of maize. Plants were sampled for vegetative analysis during the growth of the crops and at final harvest. Total dry matter, grain yield and the components of yield and leaf area index were determined. Grain yield of maize increased from 794 to 1522 g/m 2 as the population of maize increased. However the yield of the maize was not affected by either the cultivar or the populations of the soyabeans grown among it. Grain yield and the component of yield of the intercropped soyabeans were not affected when population of maize in the mixture was increased. Matara produced higher yields than AMT when grown with maize and this was associated with production of more grain per plant and larger seeds. As the plant population of the soyabeans was increased the grain yield of Matara increased and up to 336.9 g/m2 was obtained, however the yield of AMT was not affected by a similar increase in plant population, possibily Matara had greater temporal difference and was more competative than AMT when grown in the mixture. Three methods were used to evaluate the yield of intercropped plots. These were the seed yield summed for both crops, Land Equivalent Ratio (LER) and a yield ratio based on maize. Although the results obtained depended on the method used all the three methods indicated intercropping could be more advantageous than growing maize and soya beans as pure stands. All the three methods indicated that the highest yield was obtained when the highest population of maize was combined with the highest population of soyabeans. Higher yields were obtained when Matara rather than AMT was grown in the intercropped plots.
Quantitative genetics of maize (Zea mays L.) during seedling establishment under cool conditions : a thesis presented in partial fulfillment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University
(Massey University, 1992) Chozin, Mohammad
Two experiments were conducted to study cool tolerance in maize (Zea mays L.). The first experiment was carried out under controlled environment to evaluate several genotypes from five synthetic populations which are currently being used to develop hybrid maize for better adaptation to New Zealand climate and to study the qualitative inheritance of maize seedling growth under cool conditions. In this study, diurnal temperature of 16 °C day/6 °C night was used and characters related to seedling growth were examined. The second experiment conducted to study the effect of temperature on maize during its early growth and to examine whether the initial seed constitution and germination characteristics could be used as selection criteria for improvement of the subsequent seedling growth. Eleven physical, chemical, and morphological characters were measured. The growth was studied in germinators under two temperature regimes of 25/20 and 16/6 °C. The genotypic variation was highly significant for all nine characters examined in the first experiment. For the three repeatedly measured characters (i.e. chlorophyll content, shoot and root dry masses), the genotype x time interaction effect was significant. In the second experiment, the variation due to genotypic difference was highly significant only for the initial seed constitution characters and the amount of ion leakage during the early hours of germination process. It was non significant for the time to germinate, seedling growth rates, and seedling growth functions. The variation due to the difference of temperature regimes was significant for the time to germinate and seedling growth but not the growth functions. The genotypes of synthetic line NZS3 showed the best performance for general combining ability (GCA) for almost all characters studied in the first experiment. From all genotypes evaluated, however, only few of them consistently showed good GCA over the characters. Four of the characters studied in the first experiment had moderate to high narrow sense heritabilities, namely total leaves at 50 days after planting (82 %), chlorophyll content (46 %), anthocyanin (69%), and leaf area (62 %). In the second experiment, the estimated broad sense heritabilities observed ranged from very low to very high over all characters. The high broad sense heritabilities were recorded on most of the initial seed constitution characters, the conductivity of ion leakage, and the growth rates of root (length) and shoot (dry mass). Both the phenotypic and genotypic correlation coefficients between pairs are in good agreement and followed the same direction. Amongst the characters examined in the first experiment only time to achieve second mature leaf, total leaf number at 50 day after planting, chlorophyll content, leaf area had considerable correlations to the dry masses. In the second experiment a good correlation with growth rate was observed for the seed weight, nitrogen and maltose contents.
The effects of drying methods and storage conditions on pea seed (Pisum sativum L.) quality and the relationship between high temperature drying and maize seed (Zea mays L.) stress cracks : this thesis presented in fulfilment of the requirements for the degree of Master of Applied Science (Agricultural Engineering) in the Institute of Technology and Engineering, Massey University, New Zealand
(Massey University, 1998) Thuy, Nguyen Xuan
High temperature and high relative humidity adversely affect the quality of seeds, and are features of tropical climate. Seed drying and storage are being used increasingly in developing countries to improve seed storage and quality. This study was undertaken to evaluate a range of seed drying methods and storage conditions with the view to selecting an appropriate method(s) for use in tropical countries. Pea (Pisum sativum L.) seeds at three initial seed moisture content (m.c.) of 23.8, 18.0 and 14.5% were dried to 10% seed m.c. before storage. The performances of four different drying methods: artificial dryer (Kiwi Mini) set at 30°C or 45°C, natural sun drying, and in-bin natural ventilation drying were evaluated. Natural sun drying, and in-bin natural ventilation drying were conducted from March to May, 1997, when mean temperature and relative humidity during sunny days were 17°C and 60% respectively. The dried seeds were stored under two conditions: open storage at 20.5°0 and 55% relative humidity (r.h.), and closed storage at 25°C and 90% r.h. for 20, 40, and 60 days. Time and energy consumed for drying by the different methods were determined to compare the drying efficiency when combined with quality of the seed. Deterioration of the seed due to storage conditions and drying methods used was determined by assessing their effects on seed germination, abnormal seedlings, dead seed, hollow heart percentages, and conductivity. Seed samples dried by the Kiwi Mini dryer set at 45°C took 7 hours and those set at 30°C took 17 hours. It took 54 hours with natural in-bin ventilation drying, while sun drying took 37 hours. However, energy consumed when drying seeds at 30°C was 17 kWh, which was more than twice that at 45°C. Seed germination was not significantly different between drying methods, but averaged only 75% because of sprouting damage of the crop prior to harvest. Germinations after open and closed storage for 20 days did not differ, although some differences appeared after 40 days of storage. However, open and closed storage for 60 days significantly reduced seed germination to 54 and 33% respectively. Because seeds are heat-sensitive, drying air temperature and drying rate are particularly important to avoid internal seed breakage, cracking and splitting, fungal growth, and loss of germination and vigour. Selected studies have shown that seed can be dried at high temperature for a short time, followed by tempering to re-distribute moisture and temperature inside the seed, thus reducing the percentage of cracking. Thus, a second experiment was conducted with maize (Zea mays L) to study the impact on seed viability of high temperature drying followed by tempering. Maize at 28.5% initial seed m.c. was dried at 60°C for short periods of 5, 10, 15, 20, or 25 minutes, followed by tempering for 45 minutes at either 30°C or 21°C. This cycle was repeated until maize seeds were dried to 13.0% m.c.. The percentage of cracked seeds, germination immediately after drying, and after an accelerated ageing test, did not differ between 30°C and 21°C tempering. Drying exposure times of up to 10 minutes per cycle at 60°C caused vertical cracks in up to 50% of seeds, but seed germination remained over 90% and seed vigour was also maintained. The percentage of seeds with stress cracks due to high temperature drying (5 - 25 minute cycles) at 60°C followed by tempering had polynomial relationships with seed germination and vigour. Seeds dried at the same temperature without tempering had their germination reduced from 99 to 20%.
Effect of cultivation on maize response to nitrogen fertilizer : a thesis presented in partial fulfillment of the requirements for the degree of Master in Applied Science in Soil Science, Institute of Natural Resources, Massey University, Palmerston North, New Zealand
(Massey University, 2000) Munir, Sulhadiana
Continuous cultivation of arable soils results in the decline of 'soil quality' in terms of structural degradation and nutrient depletion. It decreases soil organic matter content, induces the leaching and gaseous losses of N through enhanced nitrification and denitrification, resulting in the depletion of nitrogen content of the soils. This will affect N availability, soil moisture retention, soil aeration and the activity of soil microorganisms. The objective of this study is to examine the effect of cultivation on the response of maize to N fertiliser. A glass house experiment was conducted using four soils. The soils included a permanent pasture soil and three maize / barley grown soils which have been cultivated for 6, 17 and 34 years. Maize plants were grown at six levels of N applied as urea (0 - 500 kg N/ha). The dry matter yield response to N application indicated higher maize growth for the pasture soil than for the cultivated soils at all levels of N application. Even at the highest level of N application (500 kg N/ha) the maize dry matter yield for the cultivated soil did not reach that for the unfertilised pasture soil. This indicates that N alone was not limiting the dry matter yield among the cultivated soils. It was hypothesised that the differences in the physical conditions among these soils may also be responsible for differences in dry matter yield. In the second experiment, pasture and the 34 year cultivated soils were incubated with poultry manure for eight weeks. The addition of poultry manure was to improve the physical conditions of the soil. A glasshouse experiment was then conducted to examine the effect of poultry manure addition on the growth of maize at five levels of N (0-400 kg N/ha) applied as urea. There was a clear visual indication of an improvement in the structure of the cultivated soil due to the incorporation of poultry manure. Addition of poultry manure increased the dry matter yields of maize plants both in the cultivated and the pasture soils. The dry matter yield of plants in the cultivated soils (in the presence of manure addition) was higher than the pasture soils at low levels of N application and similar yields were obtained at the higher rates of N application. Oxygen diffusion rate (ODR) values were higher for the pasture soil than the cultivated soil. The addition of poultry manure in the initial stages, however, decreased the ODR values in both soils which is attributed to the increased consumption of oxygen by the easily decomposable organic carbon in the poultry manure. With increasing time after incubation the ODR values slowly increased in the poultry manure treated soils indicating an improvement in soil structure. The study clearly demonstrated that the impact of cultivation on maize yield was partly due to poor soil physical conditions.
Effects of nitrogen fertiliser on the growth, development and yield of maize (Zea mays L.) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Science
(Massey University, 1974) Thom, Errol Ross
Maize has been grown in New Zealand for over a century. The traditional grain growing district has been Gisborne, where suitable environmental conditions prevail. Over recent years there has been a rapid expansion of maize production for grain, silage and greenfeed. For example, in the 1970/71 season (NZMAF estimates), 12,000 hectares of maize was grown for grain while in 1962/63 only about 3,000 hectares were grown; in the 1971/72 season 18,600 hectares were involved in grain production. Respective estimates for the 1972/73 and 1973/74 seasons were 16,300 and 17,800 hectares. Furthermore maize growing has now extended far beyond Gisborne with the Waikato, Bay of Plenty and Hawkes' Bay districts being regarded as major grain producing areas of New Zealand. Further south in the Manawatu and Canterbury high yielding crops of maize are also being grown for silage and greenfeed under suitable environmental conditions. Along with the upsurge in maize growing in these districts there has been the need for more agronomic information (Gooding, 1972) on the yield response, in terms of grain and total dry matter production; on the appropriate rate of nitrogen application and on the timing of the application for maximum response under the prevailing environmental conditions. With more maize being utilised in intensive animal production enterprises (Jagusch and Hollard, 1974) the quality of the dry matter produced assumes greater importance.
Effects of seed vigour on seed production and quality in Zea mays L. cv. illini gold : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Sciences in Seed Technology at Massey University
(Massey University, 1993) Mashauri, Isaka M
Some of the consequences of seed deterioration can be a reduction in field emergence and stand establishment, retarded plant growth and reduced seed yield. From the available literature it is not clear whether the reported lower seed yields are solely a consequence of lower population density resulting from low vigour seed and hence poor emergence, or are a result of poor individual performance of plants grown from low vigour seed. Two high vigour seed lots of shrunken-2 super sweet corn (Zea mays L.) cv. Illini Gold were artificially aged to obtain differential vigour levels (high and low vigour seed lots). These seed lots were then used to study the effects of seed vigour on field emergence and emergence rate, vegetative and reproductive growth and development, and seed yield and quality. The quality of unaged and aged seed lots was judged by the use of standard germination, health and vigour tests. This last category included seedling growth and evaluation tests, eg seedling growth test; stress tests, eg cold germination, soil cold test, complex stress vigour test (CSVT) and soak germination test; and biochemical tests, eg electroconductivity, respiration and tetrazolium tests. The two high vigour seed lots differed significantly (P < 0.05) in thousand seed weight and mechanical damage levels, but not in their germination and vigour performance. However, both these seed lots were heavily infected by Fusarium subglutinans. The internally-borne Fusarium subglutinans survived the high temperature employed during the artificial ageing treatment, and was able to cause severe damage in the deteriorated seed lots. Aged seed lots demonstrated a decrease in germination and vigour as illustrated by a slower rate of seedling growth and accumulation of dry weight, an increase in electroconductivity leakage, a decrease in respiratory oxygen uptake and an increase in respiratory quotients. Interestingly, however, the performance of these seed lots in the soil cold test, cold gemination test, and low temperature respiration test, did not differ significantly from that of the unaged seed lots, presumably because the activity of the seed-borne Fusarium subglutinans was reduced by low temperature (10°C or less). This cultivar has some cold tolerance and exposing seed lots to low temperature did not cause the extent of physiological disorder expected, possibly because of adaptive protection mechanisms that allowed the seeds to undertake some cellular repair. Field emergence and emergence rates were poor but did not differ significantly between high and low vigour seed lots over three spring sowings at the same site, probably because the environment exerted little stress, but more probably because the effects of both seed-borne and soil-borne Fusarium spp on chemically untreated seeds masked any other seed quality differences. As a consequence, no seed quality test was significantly related to field emergence, with the exception of the CSVT which was significantly (P < 0.05) correlated with field emergence for the November sowing. A greater (P < 0.05) loss of plants from low vigour seed lots due to post emergence damping-off and seedling blight caused by seed-borne and soil-borne pathogens was recorded in the October and December sowings, with the result that plant population was significantly reduced when compared to that of high vigour lots. While the reason for this increased loss was not explained conclusively, it is possible that seedlings produced from low vigour seeds were less able to withstand the fungal attack. However, in plants which survived there were no differences in heterotrophic plant growth as demonstrated by similarities in leaf, stem and plant dry weight at the 3rd leaf stage for all seed lots within any one sowing date. Significant sowing date effects were recorded, however, during autotrophic growth (5th leaf stage), the performance of high vigour seed lots (measured as leaf, stem and plant dry weight) was significantly (P < 0.05) superior to that of low vigour seed lots. However, these differences decreased as the plants grew and were no longer present at the 7th leaf stage, because plants from low vigour seed lots had produced thicker tillers. From silking on, no significant differences among populations were recorded as grain filling rate and days to maximum grain dry weight did not differ. However, for the two sowings (October and December) when plant population differed significantly, plants grown from the low vigour seed lots significantly (P < 0.05) outyielded those grown from high vigour seed lots because the former compensated for lost plants by producing more tillers and hence reproductive parts. The seed vigour status of the parent did not affect the seed vigour of the progeny as demonstrated by similarities in seed quality, vigour and field performance among seed lots of freshly harvested seeds. However, seed quality differed with sowing date, with seed harvested from the November and December sowings having a significantly (P < 0.05) lower quality than that from the October sowing. These results should be treated with caution, because seed quality from all harvests was poor, due to heavy infection of seeds by Fusarium species and also damage incurred during drying. The performance of the original seed lots after storage for 14 months showed that the high vigour seed lots had a significantly (P < 0.05) higher germinability, vigour and field performance in comparison with their pre-storage performance because the occurrence and activity of Fusarium subglutinans which was rampant in unstored seed lots, decrease considerably following storage. Although seed-borne pathogens also decreased in low vigour seed lots after storage, the deterioration originally induced by the accelerated ageing had increased. For stored seed lots, a significant relationship existed between field emergence and both the standard germination and cold germination tests. The results from both the laboratory tests and field trials were confounded by Fusarium subglutinans and other fungi. This work should be repeated in the absence of particularly seed-borne pathogens before any definite conclusions can be drawn.

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