Showing papers in "Advances in Agronomy in 1987"

Cereal–Legume Intercropping Systems

Abstract: Publisher Summary This chapter describes the various aspects of cereal-legume intercropping systems Intercropping is the growing of two or more crop species simultaneously in the same field during a growing season The intercropping of legumes with cereals offers scope for developing energy-efficient and sustainable agriculture The main types of intercropping include mixed intercropping, row intercropping, and strip intercropping Crop combinations differ with geographical location and there may be intercropping of tree crops, intercropping of tree and field crops, or intercropping of field crops Combinations of crops are determined primarily by the length of the growing season and the adaptation of crops to particular environments Different indices have been suggested for evaluating productivity and efficiency per unit area of land of cereal-legume intercrop systems These include comparisons of absolute yields, protein yields, caloric equivalent, and in economic terms, gross returns from intercrops and sole crops Differences in competitive ability affect the relative performance of component crops and thus the land equivalent ratio values of different cereal-legume intercrop systems It is found that phosphorus is a major nutrient that determines the production potential of most grain legumes usually intercropped with cereals

Genotypic variation in crop plant root systems

Abstract: Publisher Summary This chapter elaborates the genotypic variation in crop plant root systems. Genetic improvement of crop species, however, requires knowledge of intraspecies variability in significant root parameters and its genetic control. Ecological studies provide many examples of plant root systems, adapted to cope with variability in major edaphic environmental factors such as temperature and water. Vertical distribution of root dry matter illustrated that some species were better adapted to rooting in the shallow soil near the surface while others exploited crevices in the underlying limestone. It is found that many landraces of rice adapted to rain-fed culture exhibit substantially larger root systems with some large-diameter roots extending into the plow pan and deeper soil levels. Rain-fed agricultural ecosystems range from no-input mixed cropping of shifting cultivators on marginal soils to complex soil, water, and fertility management systems rivaling irrigated areas in production. It is found that when root pruning was performed in the field to simulate stress or mechanical damage to nodal roots, the inbreds with early vigorous seminal root development showed less reduction in height and ear weight. The analysis of means and variances indicated considerable heritable variation from crosses between tall and semidwarf height groups.

The Impact of Soil and Fertilizer Phosphorus on the Environment

Abstract: Publisher Summary This chapter describes the impact of soil and fertilizer phosphorus on the environment. Phosphorus in the form of phosphate (P) is essential for plant growth and its application to agricultural land often improves crop production. Production per unit area is increased with fertilizer P. The increased plant cover that is possible with proper use of fertilizer can reduce soil erosion from the cultivated area. Addition of phosphorus to fish ponds may also increase fish production. Potentially toxic chemical elements may be introduced into the food chain by adding P fertilizer to the soil. Increase in the amounts of soluble and particulate P transported in surface runoff have been measured after the application of fertilizer P. Phosphorus losses in surface runoff may be reduced by incorporating fertilizer material into the surface soil, away from the zone of extraction and detachment, and by using conservation or minimum tillage methods to reduce soil erosion. The detachment and transport of particulate phosphorus is also elaborated.

Speciation, Cytogenetics, and Utilization of Arachis Species

Abstract: Utilization of wild species for improvement of cultivated forms has been investigated since Faircloth made the first interspecific hybrids in 1717. Many wild species have been of value in crop improvement for a large number of traits (Harlan, 1976; Hawkes, 1977; Stalker, 1980a; Hadley and Openshaw, 1980). However, in leguminous oilseeds, utilization of species germplasm has proven difficult, in large part because of barriers to interspecific hybridization between species (Smartt, 1979). Further, sterility often restricts introgression from wild to cultivated accessions even when initial hybridization is possible. Interspecific hybridization is also difficult among the peanut species in the genus Arachis, but breeding populations derived from crossing A . hypogaea L. with related species are currently being evaluated for farmer use (Moss, 1985b). Four species of Arachis have been cultivated, including two diploids (2n = 2x = 20: A . villosulicarpa Hoehne and A . repens Handro) and two tetraploids (2n = 4x = 40: A . glabrata Benth. and A . hypogaea). Arachis villosulicarpa has only been cultivated by Indians in the northwestern part of the Brazilian state of Mato Grosso (Gregory et al., 1973). Arachis repens and A . glabrata have been grown in different parts of South America as forages or as ground covers in urban areas. Arachis glabrata has also been selected for forage qualities in Florida, where recent cultivar releases have been made (Prine et al., 1981). However, A . hypogaea is the only species which is cultivated extensively for commercial production of seeds and oil.

Uptake of Mineral Nutrients and Crop Growth: The Use of Flowing Nutrient Solutions

Abstract: Publisher Summary This chapter elaborates the use of flowing nutrient solutions for uptake of mineral nutrients and crop growth. The strength of the technique of flowing solution culture is that it provides precise control of nutrient concentrations at, or very close to, the root surface. When the system is automated, the concentrations can be kept constant and also very low. Monitoring provides a continuous record of nutrient addition; therefore, of nutrient uptake by roots of whole plants from known nutrient concentration. It is observed that nonrecirculating nutrient solutions flow past the plant roots and then to waste. In such systems the supply of nutrients is sometimes controlled by adjusting the flow rate of the solution through the roots, and uptake is measured by analysis of the waste solution and/or plant analysis. The Hurley system has been used to investigate the conditions that determine nutrient uptake rates, and the effects of nutrient solution composition on the growth and composition of plants. It is found that the response of nutrient uptake to root zone temperature depends on the plant species, the nutrient ion, and the period over which the measurements are made.

Reclamation of Acidic Mined Lands in Humid Areas

Abstract: Publisher Summary This chapter elaborates the reclamation of acidic mined lands in humid areas. A primary objective in plans for achieving satisfactory reclamation is to establish a permanent vegetative cover. Establishment of vegetation on abandoned mined lands is often hindered by low availability of plant nutrients and soil moisture, and by unstable slopes due to hilly terrain. Spoilbanks consist of a heterogeneous mixture of the overburden strata. The composition of the overburden material and the type of mining and reclamation will thus have a large influence on the physical properties found at the surface of a given spoilbank. Acidic mined lands exhibit reduced biological activity compared to undisturbed soils. Biological activity is important for the breakdown of litter so that plant nutrients can be released and recycled within the ecosystem, and for improving soil physical properties. Covering spoil with topsoil can be used to establish vegetation. It is found that when topsoil is used to cover toxic spoil, the nutrient status can be determined by a soil test. Based on this information, the approximate quantity of nutrients required for good plant growth can be calculated. Large quantities of sewage sludge have also been used to establish vegetation on toxic spoils. The seeding and management of amendment-treated spoil are also described.

Mineral nutrition of linseed and fiber flax

Abstract: Publisher Summary This chapter describes the mineral nutrition of linseed and fiber flax. Flax is a temperate winter-growing annual ranging in height from 20 cm to over 100 cm depending on the cultivar. Seedling establishment is slow at the low temperatures experienced in winter in the Australian wheat belt, and the small seedling competes poorly with weeds. In Australia, linseed competes with temperate cereals, especially wheat, for a place in rotations based on subterranean clover pasture, and it also competes with rapeseed as a winter oilseed crop. Most of the reported research on the nutrition of linseed and fiber flax concerns N and P and, to a lesser extent, K. There is also a considerable, but often restricted, range of information on other nutrients. It is found that flax seeds are also very sensitive to P fertilizer, and yields are generally reduced by the application of more than 5 kg/ha of water-soluble orthophosphate P fertilizer placed with seeds, as it suppresses germination. It is observed that application of P fertilizer to linseed may increase seed oil concentration but usually it does not alter the iodine value of the oil.

Water and Quality Loss During Field Drying of Hay

Abstract: Publisher Summary This chapter discusses the water and quality loss during field drying of hay The objective of haymaking is to conserve the yield and nutritional value of fresh-cut forage by drying it as quickly as possible to a level at which the activity of microbial decomposers is halted The moisture content theoretically required to prevent microbial activity is 10–12%, but in practice, dry hay is baled and stored at from 15– 20% moisture, which incurs low but acceptable levels of microbial damage Rate of water loss during field drying of cut hay typically declines exponentially, such that each additional percentage drop in moisture content requires progressively more time Heavy, high-moisture hay, particularly if composed of juvenile, leafy tissues rather than stiff, reproductive stems, tends to compact or settle under its own weight, reducing air circulation within the windrow, and increasing boundary layer resistance Predictive models of forage drying have identified irradiance as having the greatest influence on both alfalfa and grass drying rate, with other significant contributions from the drying potential of the environment, expressed as potential evapotranspiration or vapor pressure deficit, soil moisture, and windrow density It is found that practical methods of facilitating water loss from cut hay include growing grasses and legumes in mixture to lessen the impact of the slower drying legumes

Biotechnology Applications in Weed Management: Now and in the Future

Abstract: Publisher Summary This chapter examines the applications of biotechnology in the field of weed management. The concept of deliberately using organisms to control a pest constitutes the fundamental basis of all biological pest control systems. The bioherbicide approach employs the massive, usually annual, release of a biocontrol agent into specific weed-infested fields to infect and kill susceptible weeds. The concept of using fungi, bacteria, and even viruses as bioherbicides is biologically feasible with several host-pathogen combinations. The potential commercialization of a microbial phytopathogenic agent is dependent greatly on whether this microbe possesses properties that allow it to be handled like a chemical herbicide or not. Utilization of innovative approaches for large-scale production and stabilization under field conditions has resulted in the commercialization and registration of two fungi as mycoherbicides. Pathogen strain improvement may be also achieved by mutagenesis induced either by irradiation or by chemical treatment. This approach seems particularly promising for the selection of strains of bioherbicides that are tolerant to chemical pesticides. Increased activity of a target enzyme is a mechanism that may confer resistance to selected herbicides. The genetic manipulation of crop tolerance to herbicides is also elaborated.

Application of cell and tissue culture techniques for the genetic improvement of sorghum, Sorghum bicolor (L.) Moench: progress and potential.

Abstract: Publisher Summary This chapter describes the progress and potential of application of cell and tissue culture techniques for the genetic improvement of sorghum, Sorghum Bicolor (L.) . In sorghum, as with most grasses, primarily very young tissue temporally close to a meristematic state has proven responsive in culture. The embryogenesis from cultured immature inflorescences of several sorghum cultivars and hybrids including CK-60, Regular Hegari, Plainsman, WAC692, G522DR, FS302, and G83F is reported. All entries except Regular Hegari produced plants, although the hybrid G522DR was superior in culture response. The embryogenic responses of CS3541 and Regular Hegari were negatively correlated with inflorescence length, while MN1500 demonstrated a positive correlation. It is found that the MN1500 yielded more callus per unit length of inflorescence than CS3541. In order to determine whether cell and tissue culture techniques are viable tools for creating useful variability in sorghum, it is necessary to use established, agronomically important lines and evaluate them in terms of agronomic characteristics. It is suggested that useful variability may be identified and incorporated more easily in traditional sorghum breeding programs.