358 



TEE AGRICCLTURAL hlWS. 



November 15, 1919. 



MANURIAL VALUE OF COTTON BUSH. 



The ti-illowini:; results hii\e bt'cii xbtauR'd in St. 

 Kitts by Mr. K K. Kelsick, Khfeiui'al Assistant in the 

 Atiriciilturul Dcparlinent. ThebC results will appear 

 in due course in the Repoit on the Agricultural 

 Department for 1!>1.S-19, but owing to their particular 

 iiiterest, it h.is been decided to publish them at; once in 

 the Ayricultwi'al Neiv^, without waiting for the 

 -appearance of the reponr- 



The practice of burning the remains of cotton plants 



left on thy land after reaping has been, and »tilt is a general 



■ one in the cotton-crowing islands in the West Indies, with 'the 



-exception of St Kitts, where the bushes have always been 



buried under the banks. 



The reason for burning, which is enforced by law in a'l 

 West Indian cotton -jirouing it-lands except St. Kitts and 

 Nevis, was the eradicauiu of insect and fungoid pests, but 

 in a paper by the Agricultural Superintendent, St. Kitts- 

 Nevis, 'Notes on the destruction of cotton bushes by burning' 

 ( /F«/ Indian Bii/Ittht, Vi.l. XV, p. 319), it vat pointed out 

 that at La Guerite Experiment Station, where cotton was 

 grown continufiusly, burying the bushes had been done 

 instead of burning for -^ome ye.ir.-i, with no increase of disease, 

 and a change from burning to burying was strongly 

 advocated- 



The following notes have been written to show 

 te what extent the fertility of the soil is being depleted in 

 those islands where cotton bush is destroyed by burning. 



In 1918 the bush remaining on the no-manure nnd 

 pen-manure plots of the cotton manurial experiments was 

 weighed after the crop had bei n reaped, with the following 

 results : — 



No ra.anure. Ten manure. 



Series 1 ir.9.'; lb. 334. V ft. 



„ •-' 14S' „ 254 „ 



Mean IS'ti „ 244| „ 



Per acre 6,140" „ 9,780,, 



This amount of organic material might be considered 

 i«mall, but in tropical countries where the decay of organic 

 matter is very rapid and the supply of organic manures 

 usually inadequate, any material which will help to maintain 

 the humus content of the soil is valuable It will therefore 

 be seen that by burning the bushes there is an appreciable 

 loss of useful material every year. 



The amount of nitrogon, phosphoric acid, and potash 

 present in an average sample of this material was determined, 

 ^nd the following figures obtained : — 



Nitrogen 2'16 percent. 



Phosphoric acid 140 „ „ (on air dry material) 

 Potash 2-3.3 „ „ 



The.se figures, show that the bush has a high manurial 

 value, and although some consideration must be given to the 

 fact that it is returned t^ the land in a very undecomposed 

 state, yet its value as a supp'y of potential plant food cannot 

 be questioned. 



The amount of manurial cnnstituenta remove<l annually 

 from land yielding at thp rate of 1,000 ft), of seed-cotton per 

 acre would be al>out as follows; — 



Nitrogen 26 '33 ft), per acre 



Phosphoric acid 12 67 ., ,, „ 



Potash 11 '96 „ „ „ 



In computing these fiaures u.se has been made of the 

 figures givin in the //..v/ Imliivi Bultclin, Vol. V, p. 'JL'-5, 

 /or the compotiticn of Sea Island coltouseed. 



The amount of manorial constituents returned to the soil 

 by burying the remains of the plants would be about as follws: 

 Niirogeii 1719 lb. per acre 



Pijosphonc acid 1I1'44 „ ,, ,, 



Potash 1S7T ,, „ ., 



It will therefore be seen that the amounts of uiUogen, 

 ph )sphoric acid, and potash returned to the .soil by burying 

 the old plants are greatly in excess of those removed in the 

 seed and lint. 



Consideration of the foregoing facts makes it evident 

 that the practice of burning remains of cotton plants is 

 detrimental to the fertility of the land- In the first place 

 there is th-» loss of an, appreciable amount of orga&ic material, 

 so essential for main:aining the fertility of tropical soils; and 

 secondly, the land is deprived of a valuable supply of nitrogen. 

 The continuation of the practice must eventually lead to 

 a state of unproductiveness, especially in the case of light 

 soils, unle.ss ample supplies of organic manures are available 

 for a[)pliiatiou to the land. 



NEW PACTS CONCERNING HEVEA 

 RUBBER. 



In the following extract;, taken from the Jndui 

 Rubber Journal for August 2, 1919, two .subjects are 

 dealt with; in|the first paragraph the subject is the effect 

 on the tree of change in tapping surface ; in the second, 

 laticifeious vessels in Hevea, and their structure. 



It has been frequently contended that much of the 

 variability in plantation rubber is due to the difterence 

 not only in thn age of bark tapped, but to the differences 

 in intensity of tapping- The effect of a change in tapping 

 surface on latex and rubber has been discussed by 

 Dr. O. De Vries in the April issue of the ArchieJ Voor de 

 Rubber CuUiiiir. It is obvious that wheu a new tapping 

 surface lepresents an area which has been rested for 

 some time, latex extracted tlierefrom wi 1 show a high 

 percentage of caoutchouc- There is bound to be a great 

 difference in the composition of latex from the first cut 

 on a rubber tree, and that obtained from the first cut on 

 primary bark of a tree, say, ten years old- There is also 

 a further effect when a change of tapping surface is 

 accompanied by n change of dipping ---ystem ; undfi- such 

 condition^ there is bound to be a wide variation in the 

 composition ot the latex collected. Dr. De Vries shows 

 that the percentage of caoutchouc in latex obtained from 

 old and new surfaces varied from 20 7 to 261 per cent., 

 and similarly the time of curing varied from 101 to 110. 



The exact area drained by one or more tapping lines on 

 Hevea trees has never yet been determined- It is clear, how- 

 ever, thot a tapping cut will drain an area only if there is 

 an intimate connexion between the vessels containing latex. 

 It may have been forgotten by many people that the latex 

 vessels of Hevea are formed as a result of the breaking dowa 

 of normal cells; time is therefore necessary before communi- 

 cation between the ves.sels can lie well established. Dr. \V. II. 

 Arisz has given a further communication on the structure 

 of the vessels in the April issue of the .journal already men- 

 tioned- He finds after having examined the bark on tree.s 

 varying from five to ten years old, that the various concentric 

 layers of latex vessels in the stem are connected with each 

 other. He also finds that vessels frequently .show douMe 

 bifurcations which render the communication ■ f one series of 

 ve^.sels with another more complete; ihese ( ariioular vessels 

 often reach a great length. At the bft.se of Hevea trees tbej-a 



