Vol. XV. No. 377. 



THE AGRICULTURAL NEWS 



327 



GREEN DRESSING TRIALS IN DOMINICA. 



Reference to the reports of the Dominica Agricultural 

 Department will show that during the last few years a large 

 number of plants have been tried at the Experiment Station, 

 with the -view of finding out those that are most likely to 

 prove of value under Dominica conditions. 



Cajanus indicxis, the pigeon pea, is so well known that 

 no description need be given of its cultivation and habit of 

 growth. 



Below will be found a list of some 

 with: — 



Horse bean {Canavalii ensiformis) 



„ ijladiata 

 Tephrosia Candida 



„ Hooleriana, var. amcena 



„ Vogelii 



Indigofera suffruticosa 



, Anil 



Jerusalem pea {Phaseoltis trmervis) 

 Chick pea {Cicer arietinum) 

 Cluster bean (('pamopiis Psoraloides) 

 Bengal „ {Stizolobtum dterrimum) 

 Lyon ,, ., nivenm 



Pigeon pea {Cajanus indicus) 

 Clitoria cajanifolia 

 Soy bean (Glycine hispida) 

 Rounceval pea ( Vigna unguiculata) 



With two or three exceptions the various species grew 

 well, producing a large quantity of green material. Those 

 that years of experience have shown to give the best 

 results are: — 



The Horse bean (Ganavalia ensiformis) 

 Tephrosia Candida 



,. Hool-eriana, var. amwna 



Bengal bean (Stizolohium aterri?num) 

 Pigeon pea (Cajanus indicus) 



Canavalia ensiformis, the horse bean, is the best all- 

 round cover that we have. The seed is large and germinates 

 readily. Planted at the beginning of the wet sea.son it 

 keeps on growing for four to six months, covering the ground 

 with a low (2 to 3 feet) undergrowth which keeps the soil 

 free of weeds. The plants form a large number of root 

 nodules, thus adding to the soil a very considerable quantity 

 of nitrogen; and on decaying, the foliage forms valuable 

 mulching material. They may be sown in rows 3 feet apart 

 and about 6 inches apart in the row. They will require to be 

 weeded once or twice. The plant is a weak climber. 



Tephrosia Candida has been under cultivation for several 

 years and can be strongly recommended. The seeds, however, 

 are very small and should be sown with the rains; the plants 

 need careful nursing in the early stages; they must not be 

 sown too deeply. Once established, ' they grow 6 to 7 feet 

 high and keep the ground free of weeds for about two years. 



Tephrosia Hookeriana, var. a)/((««a,is similar to former, 

 but grows to a height of 2 to 3 feet. 



Stizololjium, aterrimur.i, commonly known as the Bengal 

 bean, whilst forming a dense growth and a large quantity 

 of green manure, and keeping the ground clean for 

 a lengthy period, cannot, owing to its strong vine-like 

 growth, be grown amongst trees such as limes, cacao and 

 coco-nuts, unless care is taken to keep the vines cut back 

 from the trees at intervals. If this precaution be taken, 

 then several species of Stizolobium could be employed for 

 the production of mulch. 



In spite of the efforts which have been made by the 

 Department, by examole and in other ways, to popularize 

 the growing of green dressings, it cannot be said that the 

 of those experimented practice has been taken up on estates to any considerable 

 extent. With one or two exceptions, the growing of green 

 dressings never enters into estate practice in Dominica. This 

 is to be regretted, for it is recognized as being one of the 

 chief methods of improving the condition of the soil. With 

 the heavy rainfall and the action of the hot tropical sun, 

 the decay of humus in the soil is rapid, and needs continuous 

 replacing if the fertility of the soil is to be maintained and 

 increa,sed. Furthermore, the growing of green dressings 

 would prevent to a large extent the wash of surface soil 

 which is to be seen going on all over the island, and would 

 also add materially to the nitrogen content of the soil. 



On the other hand, established lime fields in Dominica 

 are so covered in, that but very little vegetation will grow 

 under the shade of the trees, and furthermore, even if they 

 did, there would be the difficulty of picking up the lime 

 crop. Under these circumstances, it is necessary to procure 

 plant food from outside. Whether, under these conditions 

 it would be remunerative to grow crops on waste land to be 

 carried on to the fields at the right season, has not yet been 

 demonstrated Ettbrts to solve this problem are being made 

 at the Lime experiment station, where ravines and such places 

 are planted up with lemon grass (Cymhopogon citratus) 

 and the Nicaragua shade tree {Gliricidia maculata). Data 

 as to the tonnage per acre obtainable from such places with 

 these plants may be available in a year or two. There cvre 

 acres of such land on most estates in Dominica which could 

 be utilized for this purpose. 



The above remarks on green dressings hold good, there- 

 fore, only in the case of young cultivation, and when 

 the trees are widely planted and have not yet filled in. 



Transformations in the Sweet Potato.— The 



following is a summary to a paper on this subject in the 

 Journal of Agricidtural, Research, Vol. V, No. 13: From the 

 data given in this paper it appears that in the carbohydrate 

 transformations in stored sweet potatoes, starch is first con- 

 verted to reducing sugars and cane sugar is synthesized from 

 the reducing sugar. The rates of starch hydrolysis and of 

 sugar synthesis in a general way conform to the Van't Hoff 

 temperature rule for rates of chemical reactions. At high 

 temperatures the reactions are rapid at first, but soon become 

 slower and approach an end point. At low temperatures the 

 rates are slower and the end point is so shifted as to permit 

 a greater concentration of sugar. The reactions are 

 continuous. 



In the growing sweet potato the concentration of sugar 

 remains comparatively low. The extensive conversion of 

 starch into sugar appears to be inhibited by the activity of 

 the vines. When the vines are destroyed and the flow of 

 materials to the roots is thus interrupted, the carbohydrate 

 transformations characteristic of stored sweet potatoes are 

 begun, even if the roots are left in the ground. 



