96 CHAPTER VI 



then be ploughed into the soil, there is placed in the soil a large amount of 

 nitrogen obtained from the air. 



Green manuring is practised most extensively in Mauritius and in 

 Louisiana, and also to an increasing extent in Hawaii and Cuba. In 

 Louisiana, after plant cane and first ratoons have been grown, the land 

 is sown with cow peas {Vigna unguiculata) , using from one to three bushels 

 per acre ; in August or September the peas are ploughed in and cane planted 

 in October. According to Stubbs, the crop of cow peas above ground is 

 often removed as fodder for cattle, planters who do this holding that the roots 

 supply sufficient nitrogen for the crop, but Stubbs states that when the green 

 crop is ploughed in, an average increase over plant and first ratoon cane of 

 7-42 tons per acre is obtained over that secured when the green crop is 

 removed for fodder ; the amount of nitrogen afforded by a crop of cow peas 

 is, according to Stubbs, about 100 lbs. per acre. 



In Mauritius there are four crops used as green manures : — i. The Pois 

 d'Achery [Phaseolus lunatus). 2. The Pois Muscat.* 3. Pigeon Pea 

 {Cajanus indicus). 4. Indigo sauvage {Tephrosia Candida). 



The first two are pea vines growing in dense thick matted masses. The 

 pigeon pea is a shrub growing to a height of four or six feet ; the indigo 

 sauvage is also a shrub, but of rather more robust habit. The system generally 

 followed is to grow cane up to third ratoons ; the land is then planted with 

 one or other of the above crops, the time during which it is rested under the 

 leguminous crop being from one to three years, dependent on the land 

 available. Where land sufficient for one year's rest only is available, the 

 pois muscat is generally grown ; the pois d' Achery is generally allowed to 

 grow for two years, and the pigeon pea and indigo for three or four. All 

 four crops are planted from seed, which is sown about 15 to 18 inches apart. 

 Where no land can be spared to rest, one or other of the above crops is occa- 

 sionally sown between the rows of cane, and after a few months' growth cut 

 down and buried. 



Although the benefits of green manuring are undoubted, it must be 

 remembered that the expenses connected with it are not small, and very 

 possibly where virgin soil can be had in abundance it may for a time be more 

 economical continually to take in new land than to renew the fertility of old. 

 The benefits of green manuring are most pronounced on estates which have 

 continually to plant on the same soil , such estates are found in Mauritius, 

 Barbados, and other small islands. 



Besides placing in the soil a supply of readily available nitrogen, green 

 manuring has other advantages. 



1. The advantages of a rotation are obtained. 



2. The deep tap-roots of leguminous plants bring available plant food 

 from the subsoil to the surface soil. 



3. The ill effects of a naked fallow are avoided. 



4. The interposition of a crop other than cane will act as a prophylactic 

 towards fungus diseases and attacks of insects, for if the habitat of these 

 parasites be removed for any length of time it must result in their diminution 

 or disappearance from lack of food. 



*The legumes known generally as " velvet beans " and in various parts of the world as Mauritius beans 

 Bengal beans or Florida beans, were formerly put in the genus Mucuna. Following Bort, Bulletin 141, U.S. 

 Dept. of Agrw. Bur. of Plant Indus., they are to be placed in the genus Stizolobium. The Florida bean is classed, 

 as S. deeringiamim and has small marbled seeds ; the Mauritius bean, S. aUtrimum, has black seeds ; the Lyon 

 velvet bean, S. niveum, has ashy seeds, and the Brazilian velvet bean, S. pachylobium, has black and white seeds. 

 Some systematists would not admit these distinctions as being specific, and the beans as grown in Mauritius have 

 black, white and marbled seeds, to the writer's knowledge. 



