Factors influencing yield

Every continent, except Antarctica, grows com 40% of the present world crop is produced in the United States. In the 1987—1988 crop year, 12 states (Iowa, HI., Nebr., Minn., Ind., Ohio, Wis., Mo., S. Dak., Mich., Kans., and Tex. in order of production) produced 157.5 million metric tons (6.2 biUion bushels) that was 88% of the United States and 36% of the world s crop (66). Yield is influenced by many factors, including climate, pest control, planting density, and fertilization. Yield in the United States has increased from about 1.5 metric tons /hectare in the 1930s to about 7.5 metric tons /hectare. In 1985, a test plot produced 23.2 metric tons /hectare and yields approaching 40 metric tons /hectare are considered possible com is the most productive of the principal food crops. 

The theoretical yield is approached by the firefly reaction, discussed later, which is reported to have of 88% (5). In practice, however, most chemiluminescent reactions are inefficient, withQc values on the order of 1% or much less. The factors influencing yields can be discussed in terms of a generalized three-step chemiluminescent mechanism (6) ... 

Evans (1951) described land potential and measured it in terms of sustained yield of oats. The determining factors influencing yield were, as we have seen, soil type and climate, particularly rainfall. He then went on to calculate whether a particular farmer was achieving the optimal output, or whether he was under-achieving, or exploiting his land by over-production in the one case he was making less money than he could have and in the other case productivity would have quickly fallen as the soil lost both structure and nutrients. 

Amon D. I., and Hoagland, D. R., 1940, Crop production in artificial solutions and soils with special references to factor influencing yield and absorption of inorganic nutrients, Soil Sci. 50 463-471. 

Factors influencing the choice of synthetic routes to pyrimidines depend very much upon the substitution pattern of the desired product. For pyrimidines unsubstituted at the 4- and 6-positions, a two-component ring synthesis reaction involving a 1,3-dialdehyde and a urea or amidine derivative is the most straightforward route, but only if the dialdehyde is readily available. For example, synthesis of 2-chloro-5-(2-pyridyl)pyrimidine 989, an intermediate in the synthesis of a selective PDE-V inhibitor, was achieved in two steps in 40% overall yield by condensation of 2-(2-pyridyl)malondialdehyde 987 with methylurea, followed by demethylation/chlorination of the pyrimidinone 988 with a mixture of POCI3 and PCls <20070PD237>. 

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