Showing papers in "Advances in Agronomy in 1986"

Application of Geostatistics to Spatial Studies of Soil Properties

Abstract: Publisher Summary This chapter reviews some of the traditional methods of describing soil variability, discusses geostatistical approaches to quantifying spatial dependence and their use for interpolation under different kinds of spatial variation, and identifies some future applications of geostatistics to spatial studies in soil and agronomic research. Recognition of the importance of spatial variability on land use has led to the study of soil heterogeneity, ranging from a global scale to changes in structural and chemical composition of soil minerals on a microscale. Soil classification and soil survey have traditionally been the most practical approaches to grouping similar and separating different soils on a regional scale. Variability of properties within soil mapping units and within smaller sampling units—such as fields, experimental plots, or pedons, is acknowledged and has been described by classical statistical methods. Developments in statistical theory enable spatial relationships among sample values to be quantified and used for interpolation of values at unsampled locations. These developments are based on the theory of regionalized variables. This theory takes into account both the structured and random characteristics of spatially distributed variables to provide quantitative tools for their description and optimal, unbiased estimation. Geostatistical analysis of spatial variability is applied to estimation of ore reserves in the mining industry, water resources research, soil science, and archaeology.

Reflectance properties of soils

Abstract: Publisher Summary This chapter discusses the reflectance properties of soils. In delineating differences among soils and in describing the characteristics of a soil profile, color is one of the most useful attributes for documenting these differences. Soil visible reflectance, or color, is a differentiating characteristic for many classes in all modern soil classification systems and is an essential part of the definitions for both surface and subsurface diagnostic horizons. The chapter includes instrumentation for reflectance measurements. Instruments that are used to measure the reflectance of soil are divided into two broad classes—namely, spectroradiometers and multiband radiometers. Multiband radiometers contain several optical filters to define the spectral bandpasses. These spectral bandpasses are selected to sample discrete portions of the optical spectrum, e.g., the Landsat multispectral scanner or the thematic mapper bands. The character of reflected light from a soil surface depends on the nature of the surface and the intensity and spectral quality of the radiation incident upon the surface. The soil surface may be irradiated by direct sunlight, scattered skylight, and thermal radiation from the surroundings.

Crop Water Deficits: A Decade of Progress

Abstract: Publisher Summary This chapter describes the various aspects of crop water deficits. The water status of a crop plant is usually defined in terms of its water content, water potential, or the components of water potential. The simplicity of measuring water content led to its early adoption, but the diurnal and seasonal changes in dry weight make comparisons of water content at different times of day or during the season unsatisfactory. Water deficits develop inevitably as a consequence of water loss from the leaf as the stomata open to allow the uptake of carbon dioxide from the atmosphere for photosynthesis. There have been developments in both direct and indirect methods of measuring water deficits that have resulted in considerable progress in the field. The use of infrared thermometry for the measurement of crop water deficits and the use of in situ psychrometers for the measurement of water potential respectively is elaborated. It is found that the identification of the root as the site of sensing soil water deficits does not eliminate the role of turgor pressure as the transducer of water deficits, but moves the emphasis from leaf to the root. It is observed that at the whole crop level, the water use efficiency will depend not only on the transpiration efficiency of the leaves, but also on the water loss from the soil and the optimization of yield per unit of water used.

Agronomy of White Clover

Abstract: Publisher Summary This chapter focuses on agronomy of white clover (Triflium repens L.). White clover is the most important pasture legume in temperate zones of the world. It is of value because of its wide climatic range, the high nutritional quality and digestibility of its herbage, and the significant contribution it makes to the economy of grass/white clover pastures by fixation of atmospheric nitrogen, especially in the absence of fertilizer nitrogen. White clover is normally described as a creeping, much-branched perennial. White clover grows on roadside verges and in natural pastures throughout the world where climatic and soil conditions are suitable, but it is seeded deliberately in pastures mainly in North America, New Zealand, and northern Europe. White clover is used principally as a component of mixed grass/clover swards, which are usually grazed in situ. It is not grown in monoculture because of the difficulties of keeping such swards weed free, low annual herbage production, its short growing season, and concern about bloat and possible reproductive problems in grazing livestock. In the European Economic Community (EEC) countries, about 3,000 tons of white clover seed is used each year, of which the United Kingdom sows about one-third. This chapter is based largely on work in northwestern Europe and New Zealand, but literature on work from other countries is also cited where relevant.

Crop simulation models in agronomic systems.

Abstract: Publisher Summary This chapter discusses some crop simulation models in agronomic systems. Many crop models or parts of crop models have been built to help the researcher and students understand the operation of some part of an agronomic cropping system, for example, soil water flow, stomata1 control, or fertilizer nutrient movement. In addition to understanding various parts of agronomic systems, the modelers want to see what can be expected to happen if some change is made in that system. Field tests are very expensive, especially as the numbers of variables and/or treatments increase, and years of results are needed. A proven model of the system helps to evaluate these treatments and indicates which ones could be expected to give the desired results. The cotton model, GOSSYM, has been widely validated. GOSSYM has been used in a user-friendly form on a PC microcomputer as a tool for on-farm management decisions pertaining to nitrogen fertilizer applications, irrigation scheduling, and timing of harvest-aid chemicals. By combining GOSSYM with an expert system program, COMAX, the on-farm management decisions have been run in several combinations to give the user an optimal plan for fertilizer and irrigation scheduling.

The influence of soil structure on water movement, crop root growth, and water uptake

Abstract: Publisher Summary This chapter focuses on the role of the soil structure (the soil–pore system) through which both water and roots move. The principle reason for concentrating on soil structure is that, of the soil's intrinsic physical properties, it is the one most easily, frequently, and widely altered, particularly by cultivation. The transmission porosity is responsible for rapid water movement and provides pre-existing channels for root growth. Disruption or lack of, transmission pores is common in cultivated soil. This leads to impeded water flow and root growth within the profile. Structural instability is frequently encountered at the surface of tilled soils. It gives rise to crusting and translocation of clay into the subsoil. Crusting can reduce the infiltration rate by up to two orders of magnitude. Organic matter accumulation at the soil surface, by conservation tillage practices, provides the most cost-effective remedy. Crop roots have been studied less than crop canopies, but it appears that considerable inter-and intra-specific variation exists in such properties as maximum rooting depth, lateral branch production, xylem vessel diameter, and root hair length. Mechanical impedance and transient waterlogging are structurally related causes of restriction to root development in arable soils. There is evidence that loosening of zones of high strength improves crop–water relations.

Agronomic Value of Unacidulated and Partially Acidulated Phosphate Rocks Indigenous to the Tropics

Abstract: Publisher Summary This chapter evaluates the degree to which phosphate rocks (PR) and partially acidulated phosphate rocks (PAPR) are suitable for use in tropical agriculture. Considerable research has been conducted in search of alternative means of supplying phosphorus (P) for crop production in tropical soils. The use of PR combined with soluble forms of P, such as PAPR, represents a highly efficient means of utilizing indigenous PR resources. The research on these combinations throughout Latin America, Africa, and Asia has shown that the response curves for products with only 40– 50% of the phosphorus applied in a water-soluble form are similar to those of highly soluble phosphorus fertilizers, thus suggesting that both the soluble and insoluble fractions contribute to the plant response. This approach offers expanded opportunities for utilizing indigenous resources that possess properties unsuited for production of fully acidulated products and for use with soils and crops where PR alone is unreliable. This is especially the case in soils characterized by high phosphorus retention capacity, where the soluble fraction of the fertilizer treatment is relied upon only for the early stages of growth and the unacidulated fraction continues to dissolve during the longer term.

Reaction of Anions and Cations with Variable-Charge Soils

Abstract: Publisher Summary This chapter outlines models that provide a consistent explanation of many seemingly disparate observations The models describe bulk behavior from a consideration of molecular behavior They involve two principles of modeling: one is the principle of sufficiency, and the other is the principle of hierarchies The term “variable charge” is used to describe those constituents whose charge varies with the pH of the soil solution The charge is also affected by the amount of reaction with anions and cations that has occurred Important variable-charge constituents of soils are the oxides of iron, aluminium, titanium, and manganese The variable-charge constituents may be contrasted with the “fixed-charge” constituents, mostly the crystalline clay minerals that develop a negative charge as a result of lattice substitutions The chapter determines that the surfaces with which ions react are large relative to the ions that they can be regarded as planes The reactions of a diverse range of ions with soil are described by three rules The first is that there is an initial reaction between a variable-charge surface and certain of the ions in solution—that is, reaction is between charged surfaces and charged particles The second is that the soil surfaces are heterogeneous And the third rule is that the initial surface reaction is followed by a diffusive penetration, the rate of which is modified by electrostatic effects

Genetics and Physiology of Vernalization Response in Wheat

Abstract: Publisher Summary This chapter describes the genetics and physiology of vernalization response in wheat Vernalization is generally considered to be affected by temperatures of 10°C or less, although the upper limit has not been critically established It is generally considered that the weaker the vernalization response, the higher the vernalizing temperature necessary for maximum rate of vernalization The vernalization process in partially devernalized seeds has been shown to be more rapid than in plants receiving just an original vernalization treatment An important aspect of the vernalization process in wheat is the change in response of plants as they age It is found that wheat was responsive to vernalization in 2- to 44-day-old plants, but the older the plant was, the shorter was the period of cold treatment necessary for vernalization to be satisfied It is observed that spring wheat has little or no vernalization response and a winter wheat has a strong response The use of intervarietal chromosome substitution lines in hexaploid wheat has facilitated the location to specific chromosome of genes that influence vernalization response The interactions between genes for growth habit or vernalization response are also elaborated

Kinetics of Ionic Reactions in Clay Minerals and Soils

Abstract: Publisher Summary This chapter discusses the principles of kinetics to clay minerals and soils and reviews present literature dealing with the kinetics of elemental reactions in these systems. Chemical kinetics deal with chemical reaction rates and these rates are explained in the chapter in terms of reaction mechanisms. There are two salient reasons for studying the rates of chemical reactions: first to predict how quickly a reaction mixture moves to its equilibrium state, and to reveal reaction mechanisms. One should realize that the rate law is determined by experimentation and it cannot be inferred by simply examining the overall chemical reaction equation. A number of equations have been employed to describe the kinetics of reactions in clay minerals and soils. These have included the first-order, Elovich, parabolic diffusion, zero–order, second–order, and two–constant rate equations. Data based on the kinetics of ion exchange in pure clay systems is used by soil chemists for many years to model kinetic reactions in heterogeneous soil systems. Vermiculite, montmorillonite, kaolinite, and hydrous mica vary drastically in their preferences, in ion binding affinities, and in types of ion exchange reactions. Soil systems are typically composed of complex mixtures of clay minerals, noncrystalline components, oxides, hydroxides, and organic matter. The inevitable interaction of these various components creates a heterogeneous exchange complex that makes the kinetics of ionic exchange in these systems difficult to study.

Urea Transformations and Fertilizer Efficiency in Soil

Abstract: Publisher Summary This chapter discusses urea transformations and fertilizer efficiency in soil. Urea has less tendency to coalesce and compact than ammonium nitrate, is less corrosive than other nitrogen fertilizers, and is suitable as a carrier for a number of herbicides. Much of the urea in the United States is applied as urea ammonium nitrate solution prepared by combination of urea with ammonium nitrate. Although urea is frequently equivalent to other nitrogenous fertilizers poor crop responses to urea have frequently been observed. The rapid hydrolysis of urea in the soil can result in high soil pH values and high ammonium ion concentrations, which are conducive to the accumulation of ammonia. The major problems observed in urea fertilization are the loss of volatile ammonia gas and ammonia toxicity to germinating seedling. This chapter discusses environmental, chemical, and physical soil conditions, which must be considered in regard to controlling urea transformations in the field. It also elaborates studies that have directly measured urea transformations in the field or under simulated field conditions. New classes of urease inhibitors that may improve the efficiency of urea under field conditions are also described.

Lupin Crop as an Alternative Source of Protein

Abstract: Publisher Summary This chapter analyzes the lupin crop as an alternative source of protein. Lupin is considered one of the legumes with the greatest future potential because of its high protein content, even in a wild state, and because of its adaptation to poor soils and dry climates. The wild species of Lupinus are distributed in two large areas: The Mediterranean and the Western Hemisphere. The Mediterranean zone ranges from southern Europe to the highlands in northern and eastern Africa. The range in the Americas includes the western part of North and South America, and excludes the tropical lowlands and the Amazonian basin. Cultivated lupins appear in agricultural production in diverse forms and for very different purposes: Grain production and forage in crop rotation, green manure, soil conservation, agroforestry, and also as a permanent pasture for livestock. Lupins not cultivated for grain are usually ploughed in as green manure, or used alone or mixed with cereals or grasses as fodder. Lupin also plays a role in the fight against erosion in soil establishment and afforestation in numerous areas of the world. This chapter discusses the role of legumes in protein production. Botany and ecology of lupin is also described.

Conversion of Tropical Rainforest: Agronomic Potential and Ecological Consequences

Abstract: Publisher Summary This chapter describes the agronomic potential and ecological consequences of conversion of tropical rainforest. Tropical rainforest refers to the climax vegetation of the lowland humid tropics where there is either a short period of water deficit or none at all. Tropical rainforest is confined to the equatorial region and is a very diverse and complex ecosystem. Soil is an integral element of the rainforest ecosystem and is as much influenced by the vegetation as the vegetation itself is influenced by the soil. Soils supporting tropical rainforests are usually old, highly weathered, and excessively leached. Estimates of forest conversion in the Brazilian Amazon, in tropical Africa, and in the tropics are presented. Possible local effects of deforestation on biophysical environments are explained. Major effects are on microclimate, water and energy balance, nutrient capital with disruption in pathways of various nutrient elements, soil, flora and fauna composition and activity. Deforestation for intensive land use is an important factor in forest conversion. Methods of deforestation vary widely depending on the intended cropping systems, and soil and crop management methods. It is suggested that forest conversion for plantation crops should also be preferably done by manual, and slash and burn methods.

An Evaluation of Computational Methods for Field Uniformity Studies

Abstract: Publisher Summary This chapter presents an evaluation of computational methods for field uniformity studies. Soil variability is a familiar problem to agricultural scientists, who must constantly deal with cumulative effects of microvariation, which can easily mask treatment differences. A precision experimental field is a land area, in which the plot size and soil variability have been minimized for a specific crop or soil physical/chemical treatment. The statistical methods used to estimate existing field uniformity include field plot and frequency analysis, auto and spatial correlation with spectral analysis, and semivariograms and kriging analysis. The choice of plot size has been recognized as important for efficient and economic experimentation. Systematic variability is a gradual or marked change in soil properties as a function of landform, geomorphic elements and soil-forming factors, or soil management by man. The mean, standard deviation, and coefficients of skewness and kurtosis at their 5% significance level are shown for the chi-square nonparametric test indicated for both columns and rows of the cotton seed example. The standard deviation of row data appears less variable than column data. It is found that the use of various geostatistical techniques to evaluate field plot uniformity depends upon available techniques, which weight each sample according to its distance from the point being estimated.

Sources of Temperate Maize Germplasm and Potential Usefulness in Tropical and Subtropical Environments

Abstract: Publisher Summary This chapter examines the sources of temperate maize germplasm and potential usefulness in tropical and subtropical environments. Success in maize breeding depends on the identification and utilization of useful genetic variability within the crop. The nature and diversity of varieties of maize vary tremendously around the world. Much of the genetic variability has been collected and utilized through the breeding efforts of the CIMMYT, through various public regional and national breeding programs, and through private commercial maize breeding programs. A series of crosses between S1 families from this pool with temperate and tropical testers is being made in Mexico. CIMMYT has been improving a number of maize populations for resistance to several major diseases of corn including, downy mildew, maize streak virus, corn stunt, ear and stalk rots, and several leaf blights. The isozyme data shows that the most successful sources of elite United States germplasm each encompass relatively wide range of genetic diversity. Development of inbreds and hybrids from among these contrasting pools of diversity has provided a rich source of highly productive germplasm. The combinations of United States temperate and tropical or subtropical germplasm are also elaborated.

Weeds and Weed Management in Upland Rice

Abstract: Publisher Summary This chapter develops weed control research programs for upland rice to look for herbicides that are efficient and safe and that can be integrated with existing control methods. Upland rice is grown under a wide range of management intensities, varying from shifting cultivation—as in Malaysia—to highly mechanized systems, as in Brazil. It provides information on the weed flora of the world's upland rice that is useful for describing the ecology and habitat of weeds and for planning appropriate weed control. Upland rice grows under varying edaphic and climatic situations in India. The chapter focuses on distribution pattern of weeds in upland rice. Weed distribution in upland rice is influenced by several environmental and management factors. The type and number of weeds growing with preceding crops, weeding treatments, and soil moisture content before and after crop establishment determined the weed flora. The chapter discusses several weed control methods in upland rice—such as, cultural control, mechanical weed control, and biological weed control.

Enhancing Nitrogen Fixation by Use of Pesticides: A Review

Abstract: Publisher Summary This chapter highlights that the harmful predators, grazers, or competitors can be controlled by pesticides Several methods are used to obtain isolates of microorganisms that are resistant to the chemicals that are introduced for the control of predators or possible competitors that affect the nitrogen fixers For fixation of nitrogen, Rhizobium must colonize the rhizosphere of its host legume, free-living nitrogen-fixing bacteria must grow around the roots of nonlegumes, and blue–green algae must multiply in fields of lowland rice Biological controls may affect free-living nitrogen-fixing bacteria in the root zone of nonlegumes Grazing by ostracods and cladocerans reduces the extent of colonization of flooded soils by blue-green algae Few attempts have been made to favor the inoculum organism in some selective way The inoculums strain is added to the seed, the floodwater, or sometimes the soil, and in the absence of means of selective stimulation, large inocula are used The chapter determines that the biotic stress is reduced or overcome, and the introduced nitrogen fixer has a selective advantage in the heterogeneous community in which its establishment is aimed

Gaseous hydrocarbons in soil

Abstract: Publisher Summary This chapter discusses the formation, transformation, and importance of gaseous hydrocarbons. The aeration status is an important parameter influencing the production of gaseous hydrocarbons. Under anaerobic conditions or conditions with restricted aeration, methane is the most important hydrocarbon, followed by ethylene, ethane, and propane. The methane concentration is highest in soils with pH near neutral. Ethylene formation is enhanced by the presence of high levels of organic matter. Methane and especially ethylene, when produced in sufficient quantities, can cause crop damage. The chapter focuses on environmental factors that affect the evolution of gaseous hydrocarbons in soil. Because the gaseous hydrocarbons in soil are produced by biological processes, mostly occurring under anaerobic conditions, any factor affecting the physical, chemical, and biological characteristics of the soil have an influence on the production and evolution of these gases. Moisture is required for the activity of microorganisms, and within certain limits the activity increases with moisture content. The chapter provides sampling and analysis of the gaseous hydrocarbons. Dissolved gases are determined by equilibrating a water sample of known volume with a known volume of inert or noninterfering gas in a sealed bottle and sampling the gas phase with a hypodermic syringe.

Rice-based cropping systems and their development in China

Abstract: Publisher Summary This chapter focuses on the major environmental factors, such as temperature, rainfall, soil, and population that influence crop production Rice is grown in the tropic, subtropic, temperate, and subtemperate zones in China, and on plains, basins, hilly regions, and plateaus Temperature is the most important environmental factor that affects rice-based cropping systems in China Referring to natural conditions and specialties of rice production in different localities, the rice-cropping areas of China are divided into six belts These divisions of rice belts are discussed in the chapter Several problems in multiple-cropping systems, such as growing season stress, deterioration of soil physical and chemical properties, pest problems, and stress in labor utilization are also discussed in the chapter High cropping intensity brought about obvious changes in insect fauna and the population dynamics of major insect pests The yellow stem borer, striped rice stem borer, and rice plant skipper were the major insect pests of rice in China Because these problems had occurred, readjustments of rice-based cropping systems were started in 1978 The cropping intensity in some places has been reduced and the problems have been solved to a certain extent, but grain production has also decreased