Increasing World Food Supplies Through Greater Crop Production
By the intelligent and widespread use of fertilizers along with other improvements in farming methods, food production in the underdeveloped countries could be expanded for a long time to come at a faster rate than that at which populations are likely to rise. No new discoveries are required, but governments must be prepared to spend much money and effort on development work, particularly in the provision of adequate advisory services.
World Population and World Food Supplies
THERE is an old Egyptian saying that whoever has once drunk of the waters of the Nile will want to go back and drink them again. I do not know if that has ever been said of the waters of the Tyne but it is certainly true that the British Association always welcomes an invitation to Newcastle. This is our fifth visit ; to no other city have we been more often.
The correlation of easily soluble phosphorus in soils with responses of crops to dressings of phosphate fertilizers
When sufficient numbers of soils are examined empirical determination of easily soluble soil phosphate can be used to forecast crop responses to fertilizer dressings. Correlations between soil analyses and crop behaviour fail for individual soils and the causes have been examined. 
 
 
 
Dilute acids dissolve relatively large quantities of phosphate from some soils where crops respond to phosphate fertilizers owing to (1) dissolution of iron and aluminium phosphates, which are useless to crops, (2) use of too much solvent, (3) use of an unsuitable solvent and (4) dissolution of phosphate from the interior of particles of calcium carbonate in calcareous soils. 
 
 
 
Other soils contain very little phosphate soluble in dilute acid but, nevertheless, crops grown on them do not respond to phosphate fertilizers. In such cases crop growth may be limited by some other factor, such as drought. Phosphate dissolved by dilute acids is immediately reprecipitated by some soils; the extent of such reactions may be estimated by repeated extractions in the presence of added phosphate. Most mineral soils in eastern England fix very little phosphate during acid extraction, but fen soils and ferruginous soils may fix considerable amounts. 
 
 
 
Changes in the amounts of soil phosphate that are soluble in dilute acid may occur when air-dried soils are stored. Such changes are accentuated by incubating moist soils with or without calcium hydroxide. Incubation experiments may be used to forecast increases in dilute-acid-soluble phosphate that occur during the growing period of a crop and changes which occur in easily soluble phosphate when acid soils are limed. Incubation with lime was used to measure reserves of soil phosphorus that were easily converted into forms soluble in dilute acids; such measurements were more satisfactory than simple extraction with dilute acid in relating crop responses and soil-phosphorus status in one group of field experiments.