eChapters

Herbicide Mixtures

A mixture of two or more herbicides could be more effective for controlling different weed species. In horticultural and plantation crops, weed free situation is needed during the entire year over several years. In such situations, herbicides are to be rotated to take care of all the species of weeds. A mixture of herbicides, due to chemical reaction, may enhance or reduce the efûciency of one or more compounds. Hence, knowledge of herbicides interactions is essential for efûcient use of herbicides in weed control.

Mode of Action

The term mode of action refers to the sequence of events from absorption into plants to plant death. The mode of action of the herbicide influences how the herbicide is applied. For example, contact herbicides that disrupt cell membranes, such as acifluorfen (Blazer) or paraquat (Gramoxone Extra), need to be applied post emergence to leaf tissue in order to be effective. Seedling growth inhibitors, such as trifluralin (Treflan) and alachlor (Lasso), need to be applied to the soil to effectively control newly germinated seedlings.

To be effective, herbicides must 1) adequately contact plants; 2) be absorbed by plants; 3) move within the plants to the site of action, without being deactivated; and 4) reach toxic levels at the site of action. The application method used, whether pre-plant incorporated, pre-emergence, or postemergence, determines whether the herbicide will contact germinating seedlings, roots, shoots, or leaves of plants.

Mode of Action of Herbicides

Herbicides perform a vital role in the management of weeds. As the name indicates, herbicides are chemicals that kill or control vegetation. Although the ultimate effect of most herbicides is the same (usually death of weed), the way they control weeds is vastly different. Physiologists use the term mode of action to describe the way the herbicides affect weeds. It includes the entire sequence of events that occur from the time the weed absorbs the herbicide to the final plant response (usually death). The term mode of action is the broad term under which all aspects of herbicidal action including the mechanism of action is included, while the mechanism of action refers to only the biochemical and biophysical responses of plants that appeared to be associated with herbicidal action.

Thus, mode of action includes absorption, translocation to an active site, inhibition of a specific biochemical reaction, degradation or breakdown of the herbicide in the plant and soil and the effect of the herbicide on plant growth and physiology.

Although two herbicides may differ chemically, they may still possess the same mode of action example trifluralin (a dinitroaniles herbicide) and propanamide (an amide herbicide) are inhibitors of microtubule/spindle apparatus. Each herbicide family (class or group) has a primary site of action which may be different in its action from others example sulfonylureas herbicides are ALS or AHAS inhibitors while glyphosate and sulfosate are ESPS inhibitors. Some may have more than one site of action, but the mostinhibitory of these will be affected first. The other site(s) may be considered secondary. Fluometuron, a urea group herbicides act by inhibiting photosynthesis at photosystem II and carotenoid biosynthesis.

Herbicide Application

Generally, herbicides are applied in the form of solution or granules. Of the two, spraying solutions of herbicides formulated as wettable powders, soluble powders and emulsifiable and solution concentrates is more common. When herbicides are formulated as granular or encapsulated materials, they are applied by hand or with the help of a granular applicator.

History on Classification of Herbicides

Copper sulphate (CuSO₄) was the earliest inorganic salt used as selective herbicide for controlling dicot weeds in cereal crops during 1896 in France, Germany, and USA. Sulphuric acid (H₂SO₄) was used as herbicide in cereals during 1909. In selective killing action depends on the fact that it runs off the leaves of the cereals and scorches rough surfaces of certain seeds. Sodium chlorate (NaClO₃) under the name mort-herbs is used in France for killing deep rooted perennials. Another non-selective herbicide, ammonium sulphamate (NH₄SO₃NH₂) was introduced in 1945 as ammate for the control of woody plants. Organic herbicides are more effective and selective.

Classification of Herbicides

Classification of herbicides is modified periodically as and when new herbicides are developed. Herbicides are classiûed based on their method of use (soil and foliage applied), mode of action (systemic or translocated and non-systemic or contact herbicide) and chemical key structure (aliphatic-aromatic, dinitrophenal, etc. Some herbicide molecules contain more than one classifying key structure and they are put into the group most likely to be contributing activity.

Any approved herbicide is known by three names: common name, chemical name and trade name. Common name of herbicide is a technically accepted abbreviation of its chemical name. Chemical name reads out its full molecular structure. Trade names refer to their formulations offered by the chemical companies for the consumers.

Herbicide History and Development

Common salt, ash, smelter waste, and like cheap materials have been used for centuries to control weeds on roadsides, fence rows, and pathways. But Chemical weed killing was born in 1896 when Bonnet, a French grape grower, observed that the Bordeaux mixture which he used against downy mildew of grape turned the leaves of Sinapis arvensis (a weed) black. Soon it was found that copper sulphate present in the Bordeaux mixture was responsible for its weed killing effect. Further tests in France, Germany, and U.S.A. established that copper sulphate could indeed be used for selective control of broadleaf weeds in small grains; wheat, barley, and oat. Between 1896 and 1908, several other inorganic salts, as also sulphuric acid, were found selective to small grain cereals. Of these, in Europe, a 6 to 10 per cent solution of sulphuric acid continued for considerable time as a satisfactory herbicide for broadleaf weed control in cereals, but it corroded the containers and sprayers. In the U.S.A., salts like sodium chlorate, carbon bisulphide, sodium arsenite, kainite, and calcium cyanamide were developed for non-selective eradication of perennial weeds, particularly, Convolvulus arvensis ‘field bind weed’ and Cirsium arvense ‘Canada thistle‘. In Hawaii, sodium arsenite solution was found highly effective for weed control in sugarcane plantations. Between 1930 and 1940, some boron compounds, thiocyanates, dinitro phenols (DNC and DNBP), ammonium sulphate, and certain mineral salts were developed in the west for selective and non-selective weed control. DNC and DNBP wereused extensively in Europe in small grains for broadleaf weed control, even though these chemicals dyed the hands and clothes of the users to yellow colour, almost permanently. Further milestones in weed control were introduction of organic chemical, 2-methyl-4, 6-dinitrophenoll (DMOC), in 1932 and discovery of hormone type selective weed killers. Selective residual chemicals such as substituted phenyl ureas and triazines, and non-residual chemicals diquat and paraquat are more recent discoveries.

The discovery of the herbicidal activity of 2, 4-D (2, 4-dichlorophenoxyacetic acid) first synthesized in 1941, triggered the development of modern herbicide technology. 2, 4-D proved to be an outstanding herbicide.

Integrated Method of Weed Management

Definition

1. An integrated weed management may be defined as the combination of two or more weed-control methods at low input levels to reduce weed competition in a given cropping system below the economical threshold level. It has proved to be a valuable concept in a few cases, though much is still to be done to extend it to the small farmers’ level.
2. When more than one method is employed for controlling weeds, it is termed as integrated method weed management.

FAO Definition

It is a method whereby all economically, ecologically and toxicologically justifiable methods are employed to keep the harmful organisms below the threshold level of economic damage, keeping in the foreground the conscious employment of natural limiting factors.

IWM is the rational use of direct and indirect control methods to provide cost-effective weed control. Such an approach is the most attractive alternative from agronomic, economic and ecological point of view.

Methods of Weed Control

Prevention, eradication and control are the fundamental principles of weed control.First basic step is to prevent the infestation of a weed(s) in a locality in order to avoid their further spread. If one fails in preventing spread of weeds, eradication step must be adopted. Eradication is limited on a very small scale and adopted only when suitable methods of complete weed removal are available as eradication is cent per cent control of weeds alongwith its root system and other propagative parts. Further, if one fails in prevention and eradication techniques then different weed control methods must be strictly followed in which the objective is to bring down the weed population (with any method) to a level that economical crop yields are possible. The aim of each weed control method is to achieve reasonable good control of weeds. Following methods for controlling weeds are very common:

Preventive Methods

Try to prevent spread of weed seeds/vegetative parts with the adoption of following preventive techniques.

Weed monitoring is conducted to detect significant weed problems, rank them for relative severity and sort them by management type annuals, biennials, perennials, grasses and broadleaves. Weed monitoring provides information to tailor weed management efforts that reduce the impact of the weeds. The primary objective of weed survey and mapping is to accurately identify and delineate land with populations of unwanted plants. These surveys are conducted so that scientists and managers can predict those areas potentially subject to weed invasion; understand the biology of the invasion process and determine means by which weeds spread; develop, implement and evaluate weed management plans; assess the economic impact of weed invasion and increase public awareness, education and weed management efforts. Weed survey information is collected and compiled into maps showing the distribution and severity of infestation. Weed monitoring involves repetitive surveys to track weed populations over time. A standardized system of weed surveying and mapping is necessary to provide consistently reliable information that can be compared from year to year. Further, a standardized system allows weed survey data to be incorporated into a state wide weed survey database for the production of state wide noxious weed maps.

Weed Ecology

Ecology is the study of reciprocal relationship between organisms and their environments. The ecology of weed is thus concerned with growth characteristics and adaptations that enable weeds to exploit the ecological niches left open in those environments altered by man for his use and the survival mechanisms where by weeds persist in such environments. In simple words weed ecology is reciprocal relationship of weeds with their environments. Weeds grow voluntarily in all crops raised by human beings since ancient ecology of weeds is divided into two categories (types).

1. Weed Auto Ecology

It is study of only one population i.e. how an individual species in a population interacts with its environment at all stages of its life cycle. So, in case of auto ecology competition within same species (intraspecific) or with crop plants (inter specific competition) is studied.

2. Weed Synecology

The study of relationships between communities of different weed species with their environment is called weed synecology. Different weed species grow in certain combinations and in specific patterns in the ûeld. The population of different weed species interact with the external environmental conditions and among themselves. Weed communities differ from field to field and crop to crop in the same locality. The community character is dynamic and changes in form and composition of weed flora takes place in course of time due to some external and internal factors prevailing in the community. This process is called ecological succession. With the passage of time there will be series of changes in the composition of weed community which ultimately results in stable community. This is termed as climax community.

Weed Biology

Weed biology is the study of the establishment, growth, reproduction, and life cycles of weed species and weed societies/vegetation. Weed biology is an integrated science with the aim of minimizing the negative effects, as well as using and developing the positive effects, of weeds.

Life Cycle - Based on life cycle weeds are classified as annuals, biennials or perennials.

Annuals

Annuals complete their life cycle from seed in less than one year. There are two types: summer and winter annuals. Summer annuals germinate in the spring, mature, produce flowers and seeds and die before fall. Winter annuals germinate in the fall, overwinter in a seedling or rosette stage, mature, produce flowers and seeds, and die in the spring or early summer. Because of the seedling stage, annual weeds are generally easy to control. There are usually few annual weeds present in low bush blueberry fields.

Biennials

Biennials generally complete their life cycle over two years. The first year the seeds germinate and form a basal cluster of leaves and a tap root. The plant overwinters in this stage. During the second year the weed produces a flower stalk, sets seed and dies. Examples of biennial weed are evening primrose and wild carrot.

The association of weeds with field crops was started when ancient man started cultivating plants as crops commercially. However, type of weed flora went on shifting with the passage of time, due to changing climatic conditions, cropping pattern, agronomic practices, crop cultivars etc. When crops are cultivated invariably a variety of volunteer undesirable vegetation come up simultaneously which competes with the crop for all growth factors viz., nutrients, soil moisture light, space etc.

Definition of Weed

Weed is a plant that originates under a natural environment and in response to imposed and natural environments, evolved and continues to do so as an interfering associate with our desired plant and activities.

Weed is a plant growing out of place. They are unwanted not useful, persistent and prolific, effectively competing with the beneficial and desirable crop plants for space, nutrients, sunlight, and water, interfere with agricultural operations and thereby reducing the yield and quality of produce.

Weeds are unwanted and undeserved plants that interfere with the utilization of the land and water resources and thus adversely affect crop production and human welfare. Thus a plant out of its place or a plant growing where it is not desired is a weed. This definition was given by Buchholtz in 1967. E.g. Bajra is a weed in pulse, pulse is a weed in bajra, tomato is a weed in brinjal field. Weed is defined as the unwanted, undesirable plant growing out of their proper place which interfere with the utilization of natural resources, prolific, persistent, competitive, harmful and even poisonous in nature and can grow in adverse climatic conditions (Jethro Tull: Father of Weed Science).

Weediness: Weediness is defined as the state or condition of a field, flower beds, lawns and so forth in which there is an abundance of weeds.

Weeds are plants that are unwanted in a given situation and may be harmful, dangerous or economically detrimental. Weeds are a serious threat to primary production and biodiversity. They reduce farm and forest productivity, displace native species and contribute significantly to land and water degradation. The costs of weeds to the natural environment are also high, with weed invasion being ranked second only to habitat loss in causing biodiversity decline.

Introduction

Considering the accountable post-harvest losses which is approximately 30-35 percent, food processing becomes an extremely important sector for preventing the losses and feeding the growing population. The Indian food industry is poised for huge growth, as currently valued at US$ 1.3 billion with compound annual growth rate of 20 per cent per year, increasing its contribution to world food trade every year. In India, the food sector has emerged as a high-growth and high-profit sector due to its immense potential for value addition, particularly within the food processing industry. Increasing population of the country and high cost of fuels have also created a demand for new alternate sources of energies for post-harvest processing of foods. Solar food processing technologies may become a viable option that provides good quality foods at low or no additional fuel costs. The energy policy of the developing countries now focuses on the clean renewable energy to create a further reduction of the petroleum import and to alter the utilization of petroleum energy toward the utilization of solar energy. It is an interesting fact that most of the developing countries fall in the climatic zone where the insolation is considerably higher than the world average of 3.82 kWh m-2 (Majumdar 2015). The daily horizontal insolation of India is approximately 5.80 kWh m-2 (Visavale 2009, Visavale et al. 2011). Solar dyers are an alternative to traditional drying technique and a contribution towards the solution of the problems of the open sun drying from perspective of renewable and clean energy. The International Energy Agency (IEA) declared in its 2011 solar energy perspectives executive summary (SEP 2011): “Solar energy offers a clean, climate-friendly, very abundant and inexhaustible energy resource to mankind, relatively wellspread over the globe. Its availability is greater in warm and sunny countries that will experience most of the world’s population and economic growth over the next decades.

Introduction

The thermal performance of a building refers to the process of modeling the energy transfer between a building and its surroundings. For a conditioned building, it estimates the heating and cooling load and hence, the sizing and selection of HVAC equipment can be correctly made. For a non-conditioned building, it calculates temperature variation inside the building over a specified time and helps one to estimate the duration of uncomfortable periods. These quantifications enable one to determine the effectiveness of the design of a building and help in evolving improved designs for realizing energy efficient buildings with comfortable indoor conditions. The lack of proper quantification is one of the reasons why passive solar architecture is not popular among architects. Clients would like to know how much energy might be saved, or the temperature reduced to justify any additional expense or design change. Architects too need to know the relative performance of buildings to choose a suitable alternative. Thus, knowledge of the methods of estimating the performance of buildings is essential to the design of passive solar buildings.

Introduction

As the most of the conventional resources are depleting and can last only for about a few 30 to 50 years. Scientists worldwide are looking for alternative energy resources and they have come to an agreement that solar energy can provide much of our energy needs in the future. The major challenge before them is to store this energy. The radiation falling on the earth surface can be tapped and stored in no of ways. However, the most efficient way is done through the latent heat storage through PCM. The PCM has many added advantages i.e. high energy density, isothermal behavior, non-polluting and low cost. Nowadays, it gaining popularity worldwide and now seen as the most efficient way of thermal energy storage. There is a large number of PCM at use i.e. organic, inorganic, eutectic and salt hydrates. Their utilization depends on the user’s requirement technological constraints. They also serve the purpose of energy availability at night beside the uninterrupted supply during the day. They are seen as the materials for ensuring the environmental sustainability

Introduction

Solar energy could be converted to electricity both through thermal route and photovoltaic cells but the latter is more advantageous as it has no moving part, it doesn’t require water, a rare commodity specifically in arid regions. Moreover, the maintenance of PV systems is easy, it can be installed right at the place of utility, the system is modular and these are reliable having life more than twenty years and of course eco-friendly.

In photovoltaic cells, generally known as solar cells, charge carriers are generated by the incoming irradiance (energy greater than band gap) and these are separated and swept away by an internal electric field, which is created by either making metal semiconductors contact (Schottky barrier) or p-n junction or MIS (Metal Insulator Semiconductor) or SIS (Semiconductor Insulator Semiconductor) devices. The height of potential barrier at the junction determines the voltage and the flowing charge carriers contribute to the current when connected externally. The choice of material depends on its band gap, absorption coefficient, diffusion length, mobility of charge carriers, ease in contact formation, type of junction with thermal and electronic compatibility, availability of material, toxicity and several other fabricational opto-electronic and practical aspects. PV cells based on single crystal and polycrystalline silicon, amorphous silicon, CdS, CdTe, CuInGaSe, InP, GaAs etc. have been much studied. PV modules of efficiency above 16% on silicon and 10% on CdTe, CuInGaSe and 8-9 % on amorphous silicon are commercially available. Dye sensitized TiO₂ devices have also been receiving more attention with coloured panels for windows. Organic semiconductors are explored and more recently perovskite solar cell has been studied. Flexible solar cell panels based on thin film devices are in use. The applications have gone from solar lighting to operation of pumps, small and medium size equipment, stand alone and grid connected solar power plants, roof top and building integrated PV and now even energizing cars and aero planes. With technological advancement and enhanced production (233 GW in 2015) the cost of commercially available PV modules, which used to be high at one time has been brought down from 30 $/Wp in seventies to about $0.5/Wp at present.

Life cycle cost analysis

Economics of solar energy devices can be calculated through life cycle cost (LCC) analysis. Total life cycle cost of a device is comprised of capital cost, maintenance cost, replacement costs for damagaed components and operational cost. Before adding these above costs, all future costs (C) are converted to present worth considering the relative rate of inflation (i) and discount rate (d).

Where, PW is the present worth of any future cost, i is the relative rate of inflation and d is the discount rate per year and n is the time period in years. Relative rate of inflation accounts for the escalted increase or decrease in prices of a commodity in comparison to general inflation rate. For any commodity, if the price escalation is expected as per the general inflation rate then relative rate of inflation is considered zero. In general case, relative rate of inflation is considered zero. Discount rate accounts the real value of money in future and in most of the economies of the world it is about 8-12%, and therefore 10% is considered in most analyis. The discount rate also refers to the interest rate used in discounted cash flow (DCF) analysis to determine the present value of future cash flows. The discount rate in DCF analysis takes into account not just the time value of money, but also the risk or uncertainty of future cash flows; the greater the uncertainty of future cash flows, the higher the discount rate. A discount rate of 10 % per year would mean that in real terms it makes no difference to a farmer whether he has ? 100 now or ? 110 in one year’s time. Conversely, a cost of ? 110 one year from now has a present worth of ? 100. For a future single cost in n^th year, the present worth of that cost is calculated using Eq (1). However, for future multiple payments, costs are to be converted to present worth for each year and then needs to be cumulated. For calculation of annualized life cycle cost (ALCC) of solar devices, annuity factor (AF) needs to be calculated for a period of life cycle of the device as follows:

Introduction

Cultivation of crops in greenhouse or protected structure has been increased tremendously in recent times and also has been spread from temperate regions to the warmer regions of tropics and subtropics. Plentiful technologies have been developed for heating the inside environment of greenhouse for optimum plant growth (Sethi et al. 2013). However, in hot arid areas, cultivation in greenhouse is very difficult as the temperature reaches to a very high level to sustain plant growth (Pek and Hayles 2004, Saran et al. 2010). Under such situation requirement for cooling the greenhouse microclimate environment is the necessity, but is very energy and water intensive. Hence, in such regions, reduction of air temperature inside the greenhouse or the regulation of temperature closer to the ambient temperature during summer is necessary for successful crop production. A typical diurnal variation of temperature and global solar radiation during late winter months inside a shade net structure has been plotted in Fig. 18.1. It has been found that global solar radiation has been decreased to almost 1/3 of the radiation received outside by using 75% shade net cover. The temperature inside structure during morning time has also been found higher than outside temperature and in summer such increase is expected to be much higher.

Therefore, cooling is considered as the basic necessity for greenhouse crop production in tropical and subtropical regions to overcome the problems of high temperatures during summer months. Development of suitable cooling system that provides congenial microclimate for crop growth is a difficult task as the design is closely related to the local environmental conditions. Different cooling techniques for greenhouse crop cultivation may be found in Kumar et al. (2009). Fan pad cooling system has been widely used for greenhouse cultivation however, requires large amount of water during evaporation based cooling. Since water resources are becoming scarce in future such fan-pad cooling system may not be viable in future specifically in hot arid region.

Introduction

Agricultural produce are being sun dried since ages as the first step to preserve the product for future consumption. It is still practised being most inexpensive over mechanical and other advanced drying systems. The most prevailing disadvantage of open sun drying is the quality losses due to insect infestation, enzymatic reactions, microorganism growth, and mycotoxin development. On the other side, sun drying is also a highly labor intensive and time consuming process prone to theft and damage by birds. It also suffers with the lack of process control and treatment uniformity (Bansal and Garg 1987, Bansal, 1987).

To overcome these disadvantages several types of solar dryers have been developed over the years (Ekechukwu and Norton 1999). These dryer may be identified into three group namely active, passive and hybrid. As regards their structural arrangement three generic subclasses were also identified: direct-modes (the solar-energy collection unit is an integral part of the entire drying system), indirect-modes (the solar collector and the drying chamber are separate units) and mixed-modes solar dryers. Natural convection solar dryers have become more suitable for rural sector and remote areas, as they work on single energy option and do not require any other external energy source (Pangavhane et al. 2002).

Introduction

For optimum use of harvested rain water in surface reservoir like farm ponds or tankas, small sized solar PV pumping systems with 1 hp AC and DC motor were experimentally tested at research farms of ICAR-Central Arid Zone Research Institute, Jodhpur (Fig. 16.1). Total suction head in both pumps was about 5 m. Among two installed pumps, the system with AC pump consisted of 1400 Wp (200 Wp × 7) whereas the DC pump consisted of PV array of 920 Wp (230Wp × 4). Each PV panel of AC solar pump was connected in series, which was further connected with an inverter to generate AC output of about 220-240 volt and 4-4.2 ampere. In case of DC solar pump, panels are connected in parallel to generate DC output of 40-50 volt and 15-20 ampere.

Introduction

Agriculture has been the back bone of Indian economy and culture and it will be continued to remain as such for a long time in future. Parallel to this, energy security of a country is also very important and efforts have been given on renewable energy utilization since the fossil fuel based energy is depleting at a very fast rate. In agricultural fields, considerable amount of energy is used to do different field activities e.g. ploughing, irrigation through pumps, intercultural operations, spraying of agricultural chemicals for plant protection, harvesting, post-harvest processing etc. Therefore, there is also need to replace the conventional energy source with renewable sources to operate above mentioned agricultural activities.

Approximately, 35% of the crop production is damaged if pest and diseases are not controlled at right time. Uniform spraying of liquid formulations throughout the crop field is very important for effective control of pest and diseases. Using sprayer, liquid pesticide formulations are generally broken down to minute droplets of effective size for uniform distribution over a large surface area. Different types of sprayers are used in agricultural field based on different requirements.