Agriculture and Environment最新文献

Seedlings of two half-sib families of American sycamore were exposed to 0.05 ppm O₃, 0.10 ppm NO₂, and/or 0.14 ppm SO₂ for 6 h/day for 28 consecutive days. The treatments were O₃, NO₂, SO₂ (each used alone), O₃ + SO₂, O₃ +NO₂, and O₃ + NO₂ SO₂. Significant growth suppressions were noted for both families when exposed to O₃ + SO₂ or O₃ + SO₂ + NO₂. The O₃ + SO₂ treatment had a more significant effect than O₃ alone, and adding NO₂ to the O₃ + SO₂ treatment further suppressed height growth significantly. A 45% and 34% growth suppression was observed for the two families (16-Syc-19 and 16-Syc-23), respectively, in response to the three pollutants in combination. The height growth of both families was significantly suppressed by O₃ alone in some cases. Both families exhibited significant height growth recovery 2 weeks after removal of the pollutant stress. Pollution-induced foliar injury was never evident on the seedlings.

We have conducted some experiments aimed to help the introduction in new habitats of Hedysarum coronarium L., a legume of high potential for animal nutrition. A survey was first undertaken to examine whether H. coronarium is nodulated and mycorrhizal in its natural growing area. Pot experiments were then set up to assess the feasibility of field inoculation in soils (new habitats) previously studied for some of their physical, chemical and biological (microbial) characteristics. Finally, a field experiment was carried out in a selected soil.

Rhizobium and the VA mycorrhizal fungus were both successfully established in the rhizosphere of H. coronarium growing in the field. They stimulated the yield of plant material and the nutrient uptake by the plants beyond that achieved by adding a standard dose of a compound N-P-K fertilizer.

Results of computer simulation concerning transport, nonlinear adsorption, and fixation of orthophosphate in soil, based on a physico-mathematical model discussed in Part I, are presented. The consequences of application of excessive amounts of phosphate and the influence on long-term effects of fixation rate, adsorption isotherm, time of application, and equilibrium concentration were investigated. The fixation rate was found to have the greatest influence on depth of penetration. In the limiting case of very high fixation rates it was shown that the analytical solutions derived in Part I can be used to predict rate of penetration.

This paper discusses how the context of agricultural research in North America is shaped by the structure of agricultural production, by agricultural policy, and by the nature of agricultural research institutions. Our principal concerns are: (1) the historical influences of agricultural research on the structure of agricultural production and on resource management in North American agriculture, and (2) the constraints on agricultural research institutions in developing technologies which will facilitate the husbanding of agroecosystems. We argue that the autonomous role of agricultural research in shaping the structure of agriculture and in causing degradation of agricultural resources is often overestimated; for example, the principal dynamics of change in North American agriculture were apparent well before the surge of productivity-oriented agricultural research after World War II. We also suggest that the nature of North American agricultural structure and historical and contemporary agricultural policies have decidedly influenced the context of agricultural research and have led to a number of major barriers to more beneficent management of agricultural resources. The distinctive characteristics of North American agricultural research institutions are emphasized, particularly those characteristics such as the decentralized nature of agricultural research in conjunction with the often invisible power of professional scientific organizations that limit the ability of research institutions to develop innovative approaches to agricultural resource management. Nonetheless, we argue that the major burden of environmental protection in agriculture cannot be placed on agricultural research institutions, since these institutions will have relatively little leverage over the key forces — the nature of agricultural structure and deleterious public agricultural policies — which lead to degradation of agroecosystems.

A computer simulation model of the migration of orthophosphate in soils was applied to undisturbed soil columns treated with amounts of pig slurry up to the equivalent of 1000 t of wet slurry per ha. The kinetic parameters and adsorption data necessary in filling in the model were obtained from long-term batch phosphate fixation experiments. Computer simulation predicted a somewhat greater mobility of phosphate than was found in soil columns. The causes of this discrepancy are discussed. The necessity of taking into account the mineralisation of organic phosphorus is shown. The direct contribution of organic P in pig slurry to P-mobility in the soil was found to be negligible.

Agricultural Remote Sensing at the Macaulay Institute for Soil Research is examined in three parts. The first and second outline the historical development of the remote sensing facility and its present applications. Since 1975 an automated system, linking photogrammetric and remote sensing techniques, has been developed. This system now allows resource and land use/land cover mapping to be carried out from combined aerial and satellite information. A peatland resource map of Lewis and North Harris, and a land cover map of N.E. Scotland are used as specific examples. The third part deals with future developments in remote sensing techniques and information sources, and their implications for agricultural problems. Possible relationships between crop spectra and crop yields, diseases and nutrient deficiencies are highlighted. The discussion emphasises the crucial role of ground studies in establishing the value of spectral data acquired from high altitudes.

A physico-mathematical model describing convective and diffusive transport, nonlinear reversible adsorption, and irreversible fixation is formulated. The rate of fixation is assumed to be proportional to the amounts of mobile phosphate above an equilibrium level and to the amount of Al + Fe available for binding phosphate. The finite fixation capacity implies that, with a continuous supply of phosphate at the soil surface, all fixation occurs in a front moving downward at a certain velocity and having a constant shape. The fixation front separates a transmission zone near the soil surface in which all available aluminum and iron has been used and a zone in which the equilibrium values prevail. If the fixation capacity were unlimited then all fixation would occur in a zone near the soil surface. In the absence of fixation, the model reduces to one dealt with extensively in the literature.

In tropical lowlands, agriculture is largely controlled by rainfall conditions. In these areas, most elements of climate, and particularly temperatures, are very uniform both over place and time, but rainfall is much more variable. Lack of sufficient rainfall is the main limiting factor in agriculture in most tropical areas. Long-term predictions, expected from agroclimatologist, should be mainly concerned with rainfall, but the irregularity of this element makes this a difficult task.

Therefore an obvious need exists for methods to quantify rainfall variability in relation to agriculture. These methods should be simple, so that they can be used wherever necessary without the use of a computer. Peninsular Malaysia offers favourable conditions for the study and application of these methods.

Annual rainfall totals present a picture of endless variations, with no clear trend or cycles. The seasonal rainfall distribution is much more regular, as large-scale weather patterns are frequently controlled by the monsoonal wind systems. Agricultural conditions determined by seasonal rainfall can be described most conviniently by probability figures. When these are related to crop water needs, as is done in the Agricultural Rainfall Index, the risk of droughts can be indicated accurately enough for most agroclimatic purposes. The proper selection of crops and correct timing of planting can also be decided by this method.

The irregularity of rainfall from day to day affects the growth and yields of many crops, particularly those with shallow root systems. Even during seasons which are generally considered favourable for crop production, temporary shortages or surpluses of rainfall occur often. To obtain estimates of these effects a daily water-balance model is introduced. Risks are indicated by the number of days with severe moisture stress and by the amount of surplus rain water. A comparison with a more sophisticated computer programme shows the validity and accuracy of the model.

The use of insecticides has created environments which have favoured the development of resistance in many species that have been exposed to them. Exposure to insecticides has also brought about the development of resistance in some non-pest species (Section 1). However, because of the suddenness of the spread of resistance in many instances, it may bring about a concomitant erosion of genetic variability (Section 2); this process has been called the hitch-hiking effect. The extent of the erosion of variability that may be expected in a particular instance has been shown to depend on the extent and distribution of exposure to the pollutant, the genetic parameters of the species population and the genetic nature of the resistance factor (Section 3).

Genetic analyses have been carried out in a number of cases, and pest resistance to insecticides seems usually to be attributable to a gene at one locus. If the cases of resistance which have been investigated are typical, then hitch-hiking effects may be expected in some instances and not in others (Section 4).

The development of the technique of gel electrophoresis has enabled estimates to be made of the genetic variability of species populations. It is therefore now possible to investigate directly whether pollution has eroded genetic variability in particular instances. This seems to have been investigated in only one case, although estimates of genetic variability have been made for over 250 species populations and instances of pollution could easily be investigated using available techniques (Section 5).

It is suggested that electrophoretic analyses of genetic variability should be incorporated into pollution monitoring programmes and carried out in polluted and control environments on the same individuals for which measurements of pollutant concentrations are taken (Section 6).