406 



THE AGRICULTURAL NEWS. 



December 28, 1918. 



DEMERARA SJGAR-CANE MANURIAL 

 EXPERIMENTS IN 1917 



I'rot'essor J. I). Harrison, C.MG., iJirector of Agri- 

 culture, an 1 Mr. R. Ward, Agricultural Superintendent, con- 

 tribute an interesting paper on the above subject to the /tiirr- 

 tia/of the Board of Agriculture of British Guiana, October 

 191t<. These experiments were carried out on the experi- 

 mental fields of the Board of Agriculture, Botanic Gardens, 

 where the rainfall for the year was 9 'J '22 inches. 



One half of the south field, after lying fallow from cane 

 cultivation for two years, was placed under cultivation in 

 June 1916. At the commencement of the fallow period 

 Bengal beans {Stizo/u/'ium ati-rrimum) were sown throughout 

 the field; the beans however did not spring well, nor did they 

 produce a satisfactory cover, and the land was purposely 

 allowed to become covered with a spontaneously growing 

 mixed herbage consisting largely of indigenous or naturalized 

 leguminous plants. The herbage was cut and forke.t in 

 twice each year during the period the land remained fallow. 

 Thirteen varieties of Demerara seedlings were planted in the 

 fields. A table is given of the average yield of these vari- 

 eties in tons of cane and of indicated sugar per acre, together 

 with the average gravity and purity of the expressed juice. 

 From this table it appears that D. 118 takes the first place, 

 with an average yield of 3.31 tons of cane pe'- acre, and an 

 indicated yield of sugar per acre of 3-78 tons. 



The plots were either unmanured, or received 40 lb. or 

 60 B). of nitrogen per acre in the form of sulphate of 

 ammonia. 



As a rule the increased manuring with sulphate of 

 ammonia did not result favourably, although the lower 

 application gave a comparatively large increase both in tons 

 of cane and indicated sugar per acre. It is suggested that 

 this was doubtless due to prevalent weather conditions, the 

 period of actual growth not being long enough to allow of 

 the complete utilization of the larger quantities of the 

 manure. 



Alternate half-plots of this variety vrere dressed with 

 superphosphate of lime. The results given in tabular form 

 show that the mean gain by the application of superphos- 

 phate of lime to plots not manured with sulphate of ammonia 

 was 17 tons of cane per acre, whilst on plots manured with 

 sulphate of ammonia as well it was 11 ton. It is not 

 considered that, at the usual price of superphosphate of lime, 

 the increase due to the manuring would pay the cost of the 

 application. 



Owing to the increasing scarcity of sulphate of ammonia, 

 it is necessary for cane planters to seek for other sources of 

 nitrogen. For this purpose experiments were made in mulch- 

 ing plots heavily with rice straw, large quantities of which are 

 readily available in British Guiana. It was considered that 

 such applications of the straw would conduce to beneficial 

 effects for three reasons: (1) because of its direct nian- 

 urial action by the addition of nitrogen, phosphoric acid, 

 lime and pota-nh to the soil; ('!) because of its action in 

 preventing the development of weeds, especially grasses; 

 (3) by the large amount of woody fibre not immediately 

 decomposable added to the soil, which would gradually 

 render the surface soil lighter, and hence of better tilth. 



With regard to the first reason, it is computed that an 

 application of 12 tons of rice straw per acre adds to the soil 

 the following quantities of the more important constituents 

 of plant food: nitrogen, from 70 Bb. to 94 lb.; phosphoric 

 anyhdride, 32 Bb. ; potash, from 214 lb. to 231 11». ; lime, from 

 32 lb. to 38 Bt). 



With regard to the second reason, the surface dressings 

 of rice straw have a marked efl'ect in keeping down the growth 

 of weeds, if the straw is spread fairly thickly ovi-r the land in 

 which are young cane.", or before planting it in canes. In 

 the experiments the plots dressed with rice straw remained 

 comparatively free from weed.s, especially grasses, while plots 

 not receiving any straw dressing became covered with a thick 

 (growth of such weeds. 



The third benefit will teed to increase after the land has 

 received several dressings of the straw. The result of experi- 

 ments with three varieties showed an average increase of cane 

 per acre of 2 8 tons on plots treated with 2.j,000 ft), of rice 

 straw per acre over those receiving no rice straw. It is stated, 

 therefore, that from the results ol this first year's compara- 

 tive trials, it is evident that it is worth the while of sugar 

 planters in British Guiana to make large scale trials with any 

 rice straw which may be available, remembering always that 

 the full advantage of mulching with rice straw will not be 

 apparent until repeated for several crops 



Professor Harrison has pointed out on several occasions 

 that although the soils in British (iuiana are extremely rich 

 in potash, there is always a possibility that sugar cane cul- 

 tivation long continued without any break may result in the 

 readily available potash of the soil being the first soil con- 

 stituent to show signs of commencing depletion. .\ series 

 of plots was arranged to be manured with sulphate of 

 potash at the rate of 150 lb. per acre in addition to the 

 usual nitrogenous manuring. 



From the tables given as to the results of this experi- 

 ment, it would appear that the gains due to the applicntion of 

 sulphate of potash in the above amount per acre were 2 6 

 tons of cane per acre, and '42 per cent, of saccharose. 



These results indicate that when the supply of immedi- 

 ately available potash in the soil has become somewhat 

 depleted, the nitrogenous dressings, as well as the readily 

 available nitrogen of the soil, cannot exert their fu'.l effect 

 unless aided by aiiplications of potash salts. 



DOWN THE ISLANDS. 



ITEMS OF LOCAL INTEREST. 



.sr i.u<i.\. During the month of November plant dis- 

 tribution included the following: lime plant.s, 2,500; gruftel 

 mango, 2; budded orange,4 1 ; grape fruit,G;decorativeand orna- 

 mental plants, 39; cassava cutting.s, 60,000; potato cuttings, 

 20,000; also SO packets of vegetable seeds. Regarding staple 

 crops, iMr. Brooks, the Agricultural Superintendent, mentions 

 that the reaping of the cacao and lime crops continues, while 

 that of the sugar crop has commenced A leaflet containing 

 notes on drainage was issued for general di.stribution, while 

 one giving notes on the general im[)rovemcnt of cacao planta- 

 tions in St i.ucia is now in the press. IJoth of these were 

 prepared by the Agricultural Superintendent The rainfall 

 during the month recorded at the Botanic (iardens, Castries 

 was f.S2 inches; the record at the Agricultural and Botanic 

 Station, (Jhoi.seul, was 4-24 inches. 



.\NTiou.A. According to notes of interest forwarded by 

 Mr. T. Jackson, Superintendent of Agriculture, plant distri- 

 bution during the month of November included the following: 

 bay plants, S98; coco-nut. 103; lime plants, 66; miscel- 

 laneous decorative, ■t'd The cane crop continues to improve 

 and the preparation of land for next year's cane crop i.s well 

 under way. The reaping of the cotton crop is in full swing 



