Mechanical cropping

Byrne PF, McMullen MD, Wiseman BR, Snook ME, Musket TA, et al. (1998) Maize silk may-sin concentration and com earworm antibiosis QTLs and genetic mechanisms. Crop Sci 38 461 71. 

Phthalide. In a 1 litre bolt-head flask stir 90 g. of a high quality zinc powder to a thick paste with a solution of 0 5 g. of crystallised copper sulphate in 20 ml. of water (this serves to activate the zinc), and then add 165 ml. of 20 per cent, sodium hydroxide solution. Cool the flask in an ice bath to 5°, stir the contents mechanically, and add 73-5 g. of phthalimide in small portions at such a rate that the temperature does not rise above 8° (about 30 minutes are required for the addition). Continue the stirring for half an hour, dilute with 200 ml. of water, warm on a water bath imtil the evolution of ammonia ceases (about 3 hours), and concentrate to a volume of about 200 ml. by distillation vmder reduced pressure (tig. 11,37, 1). Filter, and render the flltrate acid to Congo red paper with concentrated hydrochloric acid (about 75 ml. are required). Much of the phthalide separates as an oil, but, in order to complete the lactonisation of the hydroxymethylbenzoic acid, boil for an hour transfer while hot to a beaker. The oil solidifles on cooling to a hard red-brown cake. Leave overnight in an ice chest or refrigerator, and than filter at the pump. The crude phthalide contains much sodium chloride. RecrystaUise it in 10 g. portions from 750 ml. of water use the mother liquor from the first crop for the recrystaUisation of the subsequent portion. Filter each portion while hot, cool in ice below 5°, filter and wash with small quantities of ice-cold water. Dry in the air upon filter paper. The yield of phthalide (transparent plates), m.p. 72-73°, is 47 g. 

Chemical, cultural, and mechanical weed control practices have been relatively successful ia reducing yield losses from weeds (448). However, herbicide-resistant weed populations, soil erosion, pesticide persistence ia the environment, and other problems associated with technologies used (ca 1993) to control weeds have raised concerns for the long-term efficacy and sustainability of herbicide-dependent crop production practices (449). These concerns, coupled with ever-increasing demands for food and fiber, contribute to the need for innovative weed management strategies (450). 

Nonchemical or traditional practices, such as weed seed removal, optimal crop seeding rates, crop selection, enhanced crop competitiveness, crop rotation, and mechanical weed control are all important components of an effective weed management program (458,459). In the context of modern intensive chemical herbicide appHcation, nonchemical practices may even represent an innovative approach to weed management and should receive careful consideration. 

Many factors affect the mechanisms and kinetics of sorption and transport processes. For instance, differences in the chemical stmcture and properties, ie, ionizahility, solubiUty in water, vapor pressure, and polarity, between pesticides affect their behavior in the environment through effects on sorption and transport processes. Differences in soil properties, ie, pH and percentage of organic carbon and clay contents, and soil conditions, ie, moisture content and landscape position climatic conditions, ie, temperature, precipitation, and radiation and cultural practices, ie, crop and tillage, can all modify the behavior of the pesticide in soils. Persistence of a pesticide in soil is a consequence of a complex interaction of processes. Because the persistence of a pesticide can govern its availabiUty and efficacy for pest control, as weU as its potential for adverse environmental impacts, knowledge of the basic processes is necessary if the benefits of the pesticide ate to be maximized. 

Harvesting. Except for the cotton gin, the introduction of the mechanical harvester has probably had a greater effect on cotton production than any other single event. Commercial mechanical harvesters were introduced into the United States after World War 11. By 1955, about 23% of the cotton was mechanically harvested. That value had increased to 85% by 1965. In the early 1990s more than 99% of the U.S. cotton crop was mechanically harvested, although cotton was stiH hand harvested in some other countries. 

B. Diethyl aminomalonate hydrochloride. The crude diethyl aminomalonate is diluted with 80 ml. of dry ether and filtered to remove a small amount of white solid. The filtrate is collected in a 250-ml. Erlenmeyer flask and cooled in an ice bath. Dry hydrogen chloride is passed just over the solution while it is being stirred mechanically (Note 6). The fine white crystals which precipitate are collected by suction filtration and washed three times with a total of 60 ml. of dry ether (Note 7). The filtrate and washings are treated again with hydrogen chloride, and a second crop of diethyl aminomalonate hydrochloride is collected and washed as before. This process is repeated until no further precipitation results from passing hydrogen chloride into the solution. A total of 16.5-17.4 g. (78-82% yield based on diethyl malonate) of diethyl aminomalonate hydrochloride, m.p. 162-163°, is obtained. Recrystallization from alcohol-ether affords a purer product, 164-165°. 

Diethyl-p-nitrobenzyl-phthalimidomalonate (70 g) and sodium carbonate (70 g) in water (700 ml) were refluxed overnight with mechanical stirring (to avoid bumping). The clear brown solution was acidified with hydrochloric acid and refluxing and stirring were continued for a further 40 minutes. The mixture was cooled and the colorless precipitate (31 g) collected. A second crop (18.5 g) was obtained on evaporation of the mother liquors. Crystallization from aqueous ethanol gave the compound N-carboxybenzoyl-p-nitro-DL-phenylalanine as small needles, MP 198° to 200°C. 

Between 1935 and 1960 outputs per man-hour of labor increased about 4.5 times, and crop production per hectare of crop-land almost doubled. Inputs of labor were decreased by 50 percent, inputs of land remained relatively stable, but inputs of non-real-estate capital inputs were nearly tripled. Among these capital inputs, those of seed, feed, and livestock purchased increased by about four times, and those of mechanical power and machinery by more than 2.5 times. 

In addition, naturally growing plants resist plant pathogen and Insect attack because resistance develops over time via natural selection (35). Also, most natural and crop plants have, as a part of their basic physical and chemical makeup, a wide array of mechanisms that help them resist pest attack. These Include chemical toxicants, repellents, altered plant nutrients, hairiness, thorns, and diverse combinations of these (35). 

Early in the century the amount of energy output in the form of food was about equal to the commercial energy input to the crop and livestock. That was before electricity, natural gas, and petroleum products were available to the farm. Now at least 10 kcal of commercial energy is used for each kcal of food energy produced. This change has occurred as a result of mechanization, irrigation, and consumer demand for low fat foods and for precooked and prepared foods. 

The techniques of molecular biology have particular potential for rapidly introducing small numbers of single genes. Unfortunately there is strong evidence that the complex compensation mechanisms that exist in plants, and the interactions between different whole-plant and biochemical responses to stress, will make the direct improvement of environmental stress tolerance in crop plants by genetic engineering rather more difficult... 

Flowers, T.J. Yeo, A.R. (1989). Effects of salinity on plant growth and crop yields. In Biochemical and Physiological Mechanisms Associated with Environmental Stress Tolerance in Plants, ed. J. Cherry. Berlin Springer-Verlag, (in press). 

Yijin X. and Caiyaun P., Block and star-hlock copolymers by mechanism transformation. 3. S-(PTHF-PSt)4 and S-(PTHF-PSt-PMMA)4 from living CROP to ATRP, Macromolecules, 33, 4750, 2000. Feldthusen J., Ivan B., and Mueller A.H.E., Synthesis of linear and star-shaped block copolymers of isobutylene and methacrylates hy combination of living cationic and anionic polymerizations. Macromolecules, 31, 578, 1998. 

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