exam questions Flashcards
List five (5) key scientific or technological advances that contributed to the Grassland Revolution in New Zealand.
Introduction of fertiliser/aerial topdressing
Soil deficiencies were corrected. First was the use of superphosphate & potash (volcanic soils) which improved pasture growth. Cobalt & Selenium deficiencies were corrected & resulted in improved animal health/production. Molybdenum and sulphur (& phosphate) increased legume production therefore improving pasture production.
Introduction of electric fences/rotational grazing
Electrical fencing allowed better pasture utilisation management practices & allowed better feed conservation therefore overall pasture quality was improved & stocking rates went up.
Development of a truly perennial ryegrass & high-performing white clover Previously ryegrasses were a mix that spanned a range of life cycle behaviour from annual to short-lived perennial to long-lived perennial. A truly perennial ryegrass and a vigorous, high yielding white clover that had an ability to respond to phosphate topdressing were isolated
The introduction of the NZ seed certification scheme
The Seed Certification Scheme allowed cultivars to remain pure when multiplied over several generations, thus preserving the breeders’ improvements for the benefit of pasture production. Also it contributed to reducing unwanted & noxious weeds from establishing in new areas.
Oversowing
The ability to establish improved pasture species & cultivars onto existing vegetation,
allowed pasture production improvements to occur, especially in hill country often by aerial spread.
grass tiller can be said to be made up of a co-ordinated or linked series of phytomers in different stages of development. Explain further the meaning of the words “phytomer” and “linked series” in this statement. Inclusion of a diagram with your answer is recommended.
A phytomer is the basic modular unit of the grass tiller, each phytomer consisting of a leaf, a node, an axillary bud, & joined to the next phytomer by internode tissue. Perhaps 20 or more phytomers in a linked series comprise the tiller axis. Each phytomer is more developmentally advanced and follows a general pattern of leaf primordium forming; leaf emerges; tiller bud may activate to become a daughter tiller, leaf dies, root initiation, root growth & persistence for a time, death (refer diagram). The root cycle lasts longer than the leaf cycle. Thus each phytomer has programmed senescence built in, with new phytomers constantly being added for the life of the tiller
Write brief notes on mutualism and herbivory.
Mutualism: this is the relationship formed between two organisms that is beneficial to each other. An example is the clover & rhizobium relationship whereby clover provides the bacteria with a food source & protection/a place to live. Rhizobium then fix atmospheric N2 to plant available nitrogen (NH4+) which can then be used for the growth of the clover plant. Another example is the mychorrhizal & grass association of which the fungal hyphae act as an extension of the roots for improved water & phosphorous uptake and the plant provides the mychorrhizal fungiwith a food source & place to live.
Herbivory: This is a relationship which is beneficial to one & neutral to the other. An example is livestock grazing grass where the animal benefits from the energy intake of which grass pasture is not harmed due to mechanisms being located below defoliation level to ensure regrowth. The animal also returns some nutrients back to the grass through excrement.
Briefly explain why perennial weeds are less likely to be controlled by cultivation than annual weeds.
Perennial weeds have specialised structures such as rhizomes, creeping roots, stolons, taproots & bulbils which have an accumulated food reserve. After distribution of the vegetative part of the plant the root material can remain in the soil & new plantlets can develop from the carbohydrate reserves in the structures. Perennial structures can easily survive being cut up, in fact this often results in the wider distribution of the weed, e.g. docks may be distributed even further around a paddock after cultivation, as the root pieces can survive burial. In contrast, annual weeds develop/establish from seeds as all their energy goes into rapid spring growth & seed development, rather than developing root structures as perennials do. Perennials can also establish in a dense crop/pasture due to their structures. Again in contrast, annuals require bare ground & light stimuli.
Outline any five (5) physical, climatic or cultural features that make Canterbury an ideal seed production province.
- Canterbury is located close to a port (Lyttleton) which is important for the movement & export of seed.
- Canterbury has a temperate climate with relatively low rainfall (~600 mm) & good sunshine hours. This is important to reduce disease pressure & to allow for maximum levels of photosynthesis.
- Canterbury land contour is relatively flat making conditions easy to plant & harvest for machinery access
- Canterbury has good access to irrigation which provides timely applications of water at important stages of seed production
- Canterbury has suitable soil types for seed production.
Compare the agronomic characteristics of early and late maturing maize hybrids.
Late maturing maize hybrids have longer growth periods, therefore intercept more radiation & produce higher yielding crops. Late maturing hybrids however run the risk of not reaching maturity before killing autumn frosts resulting in high moisture crops, low yield, prolonged drying period, low crop quality & frosts lowering grain yield & overall yield. Early maturing hybrids reach maturity earlier; however, have lower yields due to a shorter growth duration. This hybrid, however, runs a much lower risk of not reaching maturity & is more suitable to districts with lower thermal time.
There are three ways in which insect sex pheromones are used in insect pest management: monitoring; trap and kill; and mating disruption. Briefly describe each of these three.
Monitoring = sex pheromones are used to entice insects so they are able to be collected & monitored to gauge species numbers in a particular area so as to time insecticide sprays to maximum effect. In addition they can be used in research.
Trap & kill = sex pheromones are put into insect traps in order to entice insects in. Once they are inside the trap they are unable to escape. This is done as a way to control problem insects in certain areas by decreasing their numbers. Mating disruption = sex pheromones are placed on tree branches or placed spatially around. By having large numbers of pheromones in the air, insects find it difficult to follow a single scent to locate a partner. By disrupting their mating cycle, insect numbers can be controlled as they are unable to come together to breed.
What is site index and why is it important to foresters?
Site index is the mean height of the 100 largest diameter trees at 20 years of age of Pinus radiata. Site index is usually independent of management & more dependent on the environment such as rainfall, temperature & soil fertility. Site index indicates final yield of trees on a site, making it important to foresters.
The seed quality of a seed lot can be assessed by a range of standardised tests in a seed lab. Two of these are commonly referred to as (analytical) purity and germination. Explain what is meant by these two (2) terms and also what constitutes a high quality seed lot.
Analytical purity involves the identification and quantifying of pure seed, weed seed & inert matter. The higher the analytical purity, the higher the quality of the seed lot. The NZ seed certification scheme requires an analytical purity of typically 97-99%, depending on certification class & a weed seed population is required to be no higher than in the range of 0.3-0.7%, again depending on certification class. Certain weed seeds are considered to be noxious such as nodding thistle, yellow gromwell & wild oat which results in automatic rejection of the seed lot. These weeds are particularly undesirable because they are difficult to eradicate & have the potential to cause significant costs to control them. Analytical purity is also very important to seed exporters as certain weed seeds are prohibited in many countries & have the potential to cause significant economic cost & damage. Weed identification is also very important for region to region trade of which some weeds may be particularly undesirable if they have not already established in that area. Some weeds however, are of less concern to end users as they already exist in a vast majority countries or are easily controlled or present no major threat to the system they will be used in. Analytical purity is particularly important to organic growers who do not use herbicides to control weeds.
Germination, tests the ability of the seed to establish all essential structures required for subsequent growth. The test is conducted under controlled & ideal conditions in the lab. Tests are performed under these conditions so that test results are constant no matter where the test is performed (e.g. different country), and also that reproducible results can be achieved if a re-test is required within a period of about 6 months. Thus the maximum field emergence under ideal climatic conditions is predicted. The germination test categorises seeds into four different categories: normal seedlings which have all the correct structures for continued growth; abnormal seedlings which are damaged or malformed in some way; hardseeds which are impermeable to water (characteristic of many legumes) and remainder which are dead or deeply dormant seeds. The germination capabilities of a seed lot is used to determine management practices such as sowing rate, however this test does have some limitations. Field emergence often returns substantially different results to the germination test results as this test does not take into consideration that optimal conditions are seldom met in the field and effect of seed deterioration over time. A high quality herbage seed lot would have a germination result of 90% or greater.
Discuss the influence of the environment and management on the physiological determinants of grain yield.
The physiological determinants of grain yield include radiation interception, radiation utilisation, growth duration & dry matter partitioning of which are all determined by both the environment & management practices.
Radiation interception is what ultimately determines crop growth. Radiation is required for photosynthesis, therefore the production of dry matter. The higher the radiation interception, the higher the plant growth & therefore production of high yield. Lead Area index (LAI) of a crop determines the amount of radiation a crop can intercept. LAI is the leaf area in relation to total ground area, therefore a high LAI means a high radiation interception. Radiation interception is the ultimate aim of crop management. Management practices such as sowing rate are important for rapid crop establishment & early canopy closure resulting in maximum radiation interception from an early stage. Disease & pest control are very important in terms of maintaining green leaf area therefore maximising radiation interception. Temperature can significantly affect radiation interception as it slows leaf elongation & tends to encourage greater root growth.
Radiation utilisation is maximized in unstressed healthy plants. Environmental factors such as water deficit put stress on plants and can result in the stomata of the leaf closing in order to conserve water and photosynthesis therefore ceases due to CO2 not being able to enter thus radiation utilisation is very poor. This can be prevented by management practices such as irrigation which maintains high transpiration rates, high photosynthetic rates and therefore efficient plant growth. Temperature can significantly affect radiation utilisation as plant growth will cease once temperature reaches the plant threshold.
Growth duration: a long growth duration results in maximum radiation interception therefore high yields. High yields can be achieved by selecting later maturing hybrids or planting crops earlier has initial growth takes longer due to lower temperatures and shorter days. Growth duration can be limited by the environment by water deficit which can cause early leaf senescence and then shorten the post anthesis/dry matter partitioning stage resulting in lower growth period, therefore lower overall yields. Management practices such as sowing high densities can also result in competition for light and therefore early canopy senescence. This means that management needs to base sowing rates around early canopy closure but at the same time prolonged growth periods/delayed leaf senescence (death). Irrigation should also be used to maintain long growth periods and prevention of leaf/plant death. Disease and pest control is very important for maintaining healthy long growing plants.
Dry matter partitioning is determined by the growth duration post-anthesis. Post-anthesis growth duration contributes 70-90% of grain yield while pre- anthesis contributes to 10 to 30% of grain yield. Pre-anthesis is characterised by dry matter accumulation of leaf, stem, roots and ears of which pre-anthesis growth sets the potential for overall high dry matter partitioning. The LAI sets the potential grain yield in radiation interception capabilities, pre-anthesis also determines potential grains/unit area. Post-anthesis growth duration is essential for successful dry matter partitioning and this growth duration can be severely affected by water deficit. Water deficit post-anthesis can result in early canopy senescence (death) and therefore dry matter partitioning is severely affected & can result in poor grain yields.
Overall management practices are aimed at making the most of the environmental resources. Management of radiation interception, radiation utilisation, the growth duration of the crop & dry matter partitioning can result in a high crop yield
Discuss net blotch of barley. Be sure to mention the symptoms and signs, how it survives, where the primary infection in a new crop comes from and control options.
Symptoms and signs of net blotch include the following: brown round to oval- shaped necrotic lesions on the plant. These are typically 1 mm wide & up to 25 mm long. Lesions may appear as both longitudinal & traverse along leaf margins, giving a characteristic net pattern. Lesions may also appear on the seed head later on. In resistant varieties, net blotch may appear as small pinhead brown lesions. Plants may appear stunted.
Netblotch survives between crops as fungal spores, it could be harboured on crop residues or debris. An important source of infection for the crop is if seeds are direct drilled into crop residues, which previously harboured the fungal disease.
The primary infection comes from contaminated seeds. As the seeds germinate, the coleoptile & first leaves become infected. From here, the fungi can spread higher up the plant & to neighbouring plants in secondary infections during moist weather in particular.
Control options for net blotch include seed treatments, fungicide sprays & resistant cultivars & crop hygiene (so deep ploughing or burning destroys inoculum).
Outline the determinants of Pinus radiata log values and briefly discuss the influence of forest management on each.
Small end diameter is an important determinant of the value of Pinus radiata logs, as it influences the recovery of sown timber from a log. The small end diameter determines the number of full length boards that can be cut from the log. The more full length boards that can be cut from the log, the more valuable it is. Small end diameters are graded P1 (40 cm diameter) or P2 (30 cm diameter) for clearwood logs, with P1 logs being worth more than P2.
The stocking rate of Pinus radiate influences the small end diameter of logs. A higher stocking rate will usually mean the small end diameter is less because the competition between trees for nutrients & water is greater so the trees grow less.
Another important determinant of value is the amount of clearwood in the log. Clearwood is the wood in the log which is free of knots. Clearwood is most valuable as it has a wider range of end uses because it is stronger than wood containing knots & is more pleasing to look at. The amount of clearwood in a log can be influenced by both pruning & thinning. When the branches of the trees are pruned will determine the size of the defect core – diameter over stumps. The smaller the diameter over stumps is, in relation to the diameter of the log, the more clearwood there will be. Thinning combined with pruning will help to increase the size of the defect core because by removing some trees there is less competition and more available nutrients for tree growth. The final important determinant of Pinus radiate logs is the presence and size of the knots. Knots weaken the wood and make it less valuable. The larger the knots, the weaker the timber (maximum knot size is important for timber used for framing), therefore the larger the knots, the less valuable the timber is. Logs with knots are graded either L1 or L2 for small knots and S1 for large knots.
As mentioned earlier, knots can be prevented by pruning of trees during the first 5-10 years of the tree’s life.
If the stand of trees is only thinned but not pruned then there will be knots in the logs.
Stands which are neither thinned nor pruned will have low yields, no clearwood and large knots. The wood from a stand like this is only usable for pulp & is of the lowest value.
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The pastures in New Zealand are:
(E) based mainly on species from Europe.
The 1860-1910 wheat boom in the South Island resulted in:
approximately 250,000 ha ploughed and sown to wheat;
The grassland revolution (1920-1970) included the introduction of:
aerial application of phosphate fertilisers;
The storage organ of a monocotyledon wheat grain is the:
endosperm;
Which of the following yield components is altered depending on the extent of tillering in a grain plant, e.g. barley?
ears/plant;
Phytochrome is a protein pigment in plants which:
- is involved in day length and light/shade responses
- causes a burst of tillering in grasses after grazing events.
The relationship between thermal time (TT) and pasture production (PP) is:
positive and direct: when TT increases, PP also increases;
Which of the following nutrients is directly involved in stomata opening?
potassium;
When Rhizobium bacteria infect legumes they:
form a mutualistic association;
Fruit thinning has the following effect on an individual tree:
the fruit that is left on the tree will grow to a larger size;
A plant competitor is a plant:
specialised at capturing resources;
The function of a white clover stolon is to:
(A) increase the survival probability of an individual plant;
(B) allow an increase in the area explored by an individual plant; (C) keep the growing points under defoliation height;
An example of a perennial weed with a rhizome is:
yarrow
A weed that is a winter annual:
is often not very tolerant of droughts;
When a crop plant falls over during the growing season, thus reducing light interception and therefore seed yield, it is said to be:
lodged
In the context of white clover seed production, which of the following is not normally practiced:
adding nitrogen and phosphate fertilisers at sowing to improve seed yields;
Incoming solar radiation is 10 MJ/m2/day. A crop intercepts 90% of this energy and converts it to dry matter at a rate of 1 gram/MJ. What is the daily crop growth rate in kg/ha?
90
