PLANT NUTRIENTS AND THEIR ABSORPTION 117 



tion, rather than the presence of specific calcium or manganese compounds, 

 is responsible for the formation of iron hydroxide. 



Pineapples grown in Hawaii on the black manganese soils of the island of 

 Oahu suffer from chlorosis. This condition is recognized by yellowing of the 

 leaves, stunted red or pink fruits, many of which crack open and decay and 

 other toxic effects. ^^^ Other crops grown on these manganese soils suffer 

 similarly, especially corn, pigeon peas, cowpeas and rice. On the other hand, 

 sugar cane is less sensitive and certain weeds such as the sow thistle, Waltheria 

 americana and Crotalaria sp., show no effects from manganese. ^"^ The difference 

 between these two types of plants was revealed by ash analyses. Those to 

 which the soil is toxic have less iron in their ash when grown on manganiferous 

 soils than when grown on ordinarj^ soils. The ash of the weeds growing wild on 

 the manganese soils without apparent ill effects showed no decrease in iron, con- 

 taining even more than when grown on other soils. ^'^ 



The other elements in the ash showed no such significant variation, though 

 in practically every instance the absorption of manganese was increased on the 

 manganese soil and with it the absorption of calcium. 



The unhealthy growth on the manganese soil thus appears to be due 

 to a lack of available iron. The plants suffered from iron starvation in 

 spite of the 10 to 30 per cent, of iron, oxide in the manganese soils. 



Applications of iron sulphate to the soil, at rates varying from 500 to 

 3000 pounds to the acre, were unsuccessful in preventing chlorosis; 

 but less than 50 pounds of iron sulphate per acre sprayed on the leaves 

 effected a prompt cure.^^ This is of particular interest for it shows that 

 pineapple leaves can absorb enough iron to cure chlorosis, though the 

 roots are not able to do so under the circumstances. It has been found 

 that the chlorosis of many coniferous seedlings growing on a calcareous 

 soil can be remedied by spraying with a 1 per cent, solution of iron sulphate 

 and this treatment has become a regular practice in certain nurseries. ^'^ 

 An interesting treatment more or less generally and successfully used 

 in France and Germany for the cure of chlorosis in grape vines^*^ 

 consists in brushing the cut surfaces of pruned vines with a concentrated 

 solution of ferrous sulphate. Filling, with a soluble iron salt, holes bored 

 in chlorotic trees frequently has been tried in New Mexico and generally 

 with satisfactory results. ^^^ 



From this discussion of the effects of calcium and manganese on 

 iron, it is evident that fertilization may be of value, not only for adding 

 plant nutrients to the soil, but also under certain conditions, for rendering 

 soluble and available to the plant, nutrients that though present are 

 unavailable. Conversely, ill advised fertilization may change mineral 

 elements that are present from a soluble to an insoluble form and there- 

 fore make them unavailable to the plant. Through this effect liming has 

 led to chlorosis of the pineapple in Porto Rico.^^ It would be of interest 

 to know the results following direct attempts to change the reaction of the 



