CAROTENOIDS 



excess. ^ ^ ' Deficiency of iron reduces production in Swiss chard and 

 pineapple, ^ * but apparently has no effect on lettuce ; ^ •" Lo ^ ^ • 

 claimed that addition of nickel sulphate to the soil had some positive 

 effect on the carotene content of plants. 



Powers, 12 in a short report has claimed that the addition of boron 

 to the soil in Oregon resulted in a 30 per cent, increase in the carotenoid 

 content of lucerne (alfalfa) ; Beeson ^ ^ claims to have confirmed this, 

 but full details of these investigations are still awaited. 



PHYSICO-CHEMICAL PROPERTIES OF SOIL AND 

 CAROTENOID PRODUCTION 



Wynd and Noggle^^i [^ ^n important study broke new ground in 

 relating carotenoid formation in oat and rye leaves to the physico- 

 chemical characteristics of the soil ; they confirmed that the nitrogen 

 content of the soil is the most important single factor. The base 

 exchange capacity and percentage loss on ignition of the soil appears to 

 affect carotene production but probably only because in base-saturated 

 soils these values parallel the nitrogen content of the soils ; similar 

 considerations make it difficult to decide whether phosphorus, calcium, 

 magnesium, CO" 3, or pH are important per se, although later work 

 suggests that the amount of replaceable magnesium is important. ^ ° • 

 With regard to pH it has been claimed that increasing the soil pH 

 increases carotene production, ^ ^ and that carotene formation in cress 

 grown in water culture was '* rather closely " related to the pH of the 

 cell sap. ^ ® * 



The important distinction to be drawn between yield and concen- 

 tration is emphasised by Wynd and Noggle. A rich soil with a high 

 degree of base saturation will produce a high yield of dry matter con- 

 taining a high percentage of carotene, whereas soils with lower degrees 

 of base saturation may produce a low yield of dry matter containing 

 an equally high percentage of carotene. The dependence of yield on 

 dry matter has been confirmed, 1 0, 1 2 2 ^nd this agrees with the 

 earlier observation of Barnes ' ' and the more recent work of Hunter, 

 Kelley and Somers ® ^ that soil moisture has no effect on the carotene 

 concentration of carrots when based on dry weights, but that on a wet 

 weight basis the concentration was inversely proportional to the soil 

 moisture owing to higher moisture content of the carrots grown on 

 damp soils. This probably explains the claim that soil moisture influ- 

 ences the " colour " of carrots. ^^3 Drought per se has no great effect 

 on carotene production. ^ ^ * 



78 



