October, 1909.] 



Miscellaneous. 



sulphates and phosphates of calcium 

 (lime), magnesium, potash and iron, but 

 they absorb them in different proportions 

 depending on the family or order to 

 which the plant belongs. 



One point must be borne in mind, that 

 if one of those constituents is absent no 

 plant can grow ; they are all necessary 

 for the building up of plant tissues, and 

 one constituent cannot displace another 

 in this work. 



Under normal conditions they are all 

 present in the soil, but sometimes there 

 is a deficiency of one or more of them, 

 and those deficient are usually the 

 nitiates, the phosphates, the potash or 

 the lime, hence in manures those form 

 the principal constituents. 



In all questions relating to manuring 

 it is imperative to remember that the 

 size of any crop is determined by the 

 constituent of plant food present in 

 least amount. For example, if an acre 

 of ground contain a surplus of all the 

 above constituents and less nitrogen 

 than that required for a maximum crop, 

 the return would be in proportion to the 

 nitrogen present, as the plants could 

 not utilise the surplus of other con- 

 stituents when it had no nitrogen to 

 combine with them. 



In Great Britain, as every one knows, 

 crops are grown in rotation, and as 

 different crops use different proportions 

 of the essential plant-food constituents 

 in the soil, there is little fear of soil 

 exhaustion. Under those conditions the 

 land is producing a crop, and at the 

 same time recuperating in the consti- 

 tuents required for the following crop 

 by the natural agencies of soil decay. 



This may be explained by making a 

 comparison of the amounts in pounds of 

 nitrogen, phosphoric acid and potash 

 removed by crops of Cotton, Corn, and 

 Wheat :— 



Crop, 



Nitro- 

 gen. 



Phos- 

 phoric 

 Acid. 



Po- 

 tash, 



To- 

 tals, 



Cotton — 

 190 lbs. Lint 

 414 lbs. Seed 



•65 

 12-95 



•19 

 5'26 



•87 

 4-84 





Total ... 



13-57 



5-45 



5-71 



24-73 



Corn — 



29-4 bus. Grain 



Stalks . . 



32-14 

 41-60 



12-36 

 11-60 



7'06 

 56*00 





Total ... 



73>74 



23-96 



63'06 



160-76 



Wheat - 



13'95 bus. Grain ... 



fctraw ... 



19-55 

 13-57 



7*44 

 2 '76 



5-10 

 11-73 





Total .. 



33-12 



10-20 



10 83 



60-35 



From the above it is seen that Wheat 

 requires more than twice and Corn 

 nearly seven times as much plant food 

 as Cotton. 



It will be noticed in all three crops 

 that nitrogen is absorbed in the largest 

 quantities. Green manuring is the 

 least expensive manner in which to 

 restore this nitrogen to the soil. 



In Nyasaland Maize and Millets are the 

 most extensively cultivated of all the 

 crops, and it is seen that this class of 

 crop is especially exhaustive of nitrogen. 



On the rich lands adjoining the 

 Shire, those crops can be grown for 

 many years on the same soil, but in 

 the Highlands, the crop soon degener- 

 ates in yield, and every few years the 

 native requires to clear new land. 



It is a known fact that no soil when 

 subjected to heavy washing will retain 

 soluble nitrogen if there is drainage 

 the low river lands are not washed by 

 percolating water to the same extent 

 as the highlands, where every shower 

 washes the soil to the valleys, especially 

 in the case of light gravel or rocky soil. 



There is only one way of fixing nitro- 

 gen on sloping soils, and that is by 

 covering the soil with vegetation ; dur- 

 ing life this vegetation absorbs the 

 soluble nitrogen, and on death forms a 

 covering of vegetable debris which 

 decomposes slowly, and prevents soil 

 washing, by acting as an absorbing 

 and evaporating layer on the surface- 

 In the tropics it is imposible to grow 

 crops in rotation, as the cost of trans- 

 port and freight makes it prohibitive 

 to cultivate many of the short-lived 

 crops ; and the more valuable crops, 

 such as Coffee, Rubber, Tea and Coco- 

 nuts, require several years before reach- 

 ing maturity. 



For many years it has been the 

 practice to clean-weed all those plants, 

 irrespective of the situations and clima- 

 tic conditions under which they are 

 growing. Every planter knows that if 

 weeds are allowed to grow, returns are 

 small and quality poor with all crops. 

 It is not the intention of this article to 

 advise the complete abandoning of 

 clean weeding, as with many crops, 

 such as Cotton, clean weeding is an 

 absolute necessity, but with other tropi- 

 cal crops green manuring is more profit- 

 able. 



Reasons for Green Manuring. 

 On sloping elevated ground it is 

 always noticeable that plants growing 

 at the bottom of the hills are stronger 

 than those at the top, and is accounted 

 for by the nitrogen from the top of 

 the hills being washed to the lowest 

 level, 



