18 



THE AGKICULTURAL NEWS. 



Jaxuary 27, 1917. 



give beneficial results, in such a way, and to such 

 a degree, as to result in the conversion of the organic 

 nitrogen of the green manure into nitrate, and the 

 breaking down of the cellulose and ligniiied tissues so 

 .as to result in the addition of humus to the supply 

 already in the soil. 



It was found that the most complete breaking 

 ■down and subsequent nitrification of the plant tissues 

 was obtained by providing an excess of moisture 

 accompanied by anaerobicf conditions during the first 

 stage, followed by a second one of less moisture and 

 semi-anaerobic conditions. The method adopted was 

 to dig pits at the sides of the fields previous to cutting 

 the green crops, this being done during the rains, the 

 pits filled with water; the cut crop was placed in the 

 ^its and left there tor periods varied experimentally 

 -from twenty-four to forty-eight hours, removed from 

 the pits, stacked in heaps, and allowed to ferment for 

 varying periods of time, after which the rotted manure 

 was applied to the soil. Later experiments, however, 

 have shown that owing to the loss of free nitrogen that 

 may occur, it is perhaps advisable to omit altogether 

 the preliminary steeping in water, and commence the 

 preparation of the fermented manure by stacking in 

 heaps, moistening with water, plastering the outsides 

 with clay (kept moist to prevent cracking), and allowing 

 fermentation to proceed as before, without the loss of 

 nitrogen. 



It was found that more complete fermentation 

 could be obtained by inoculaoing the heaps with 

 impure cultures of cellulose-destroying bacteria, obtaioed 

 ■simply by making a water extract of fresh cow dung. 



An important point to bear in mind in connexion 

 ■with the fermentation of green manure is that during the 

 preliminary anaerobic stage, tn.-cins are formed which act 

 injuriously upon plant growth. It is therefore neces- 

 sary to interpose an aerobic stage between the prelim- 

 .inary anaerobic one and the final application to the 

 soil, not only to promote nitrification, but to insure the 

 oxidation and destruction of the toxins produced. 



It may be that where a green dressing is ploughed 

 into a heavy soil containing an abundance of moisture, 

 or where persistent rains follow the application of the 

 manure, an anaerobic condition is produced which leads 

 to the production of toxins. 



tAerobic fermentation is tliat kind of fermentation wliieh 

 proceeds in the presence of air: anaerobic fermentation can only 

 pr-iceed in the alisence of air. A.-- used witli reference to the 

 deoouiposition of green dressing.s and allied manures, the.^e terms 

 -are only proximate, .-^ince under the conditi(jns referred to, 

 complete aerobisin or anaerobism i.^ nnpossible. 



The results of plot experiments with fermented 

 green manure in India indicate that it has a much 

 quicker action than unfermented manure, and very 

 considerable increases in the yield of oats (grain) and 

 tobacco are recorded. The following are the figures 

 obtained in the oats experiment: — 



Grain, Straw, 



ft), per acre. lb. per acre. 

 Control plot (.^-acre) 88.5 2,820 



Sunn hemp (Crotalaria 



ju'ncpa){.^\-&cTe) 91)0 2,83.5 



Fermented Sunn hemp 1,540 2,970 



In the case of the tobacco experiments the prepa- 

 ration of the manure under anaerobic conditions was 

 not carried out in time to allow its application to the 

 soil sufficiently early to avoid toxic effects. The plots. 

 therefore, treated with manure fermented under aerobic 

 conditions (in loose heaps without a covering of wet 

 clay), gave better results. Nevertheless, even the 

 anaerobically fermented manure gave very considerable 

 increases. 



Hutchinson, in discussing the results obtained, 

 raises the point as to whether dn ordinary estate practice, 

 green manures are always applied at the rate per acre 

 likely to do most good to the particular soil or crop it 

 is desired to benefit. The usual procedure is to grow 

 a green dressing on a certain area and turn it in 

 irrespective of the above consideration. In some cases 

 more than is produced, and in other cases less than is 

 produced, would exert the maximum benefit. This 

 seems a point worth investigating. Obviously the 

 fermentation method allows of such regulation of the 

 amounts applied, as also does the process of green 

 mulching that has been found so beneficial to cacao 

 and limes in the West Indies. 



The Indian work would appear to indicate that 

 after the application of green mulch to ihe surface of 

 the soil round cacao.trees, some sort of aerobic fermenta- 

 tion will take place. It is a question whether 

 anaerobically fermented green stuff spread around the 

 trees might not show quicker results, more in accord- 

 ance with the action of certain chemical manures. 



Enough has bi'in said to indicate the sort of green- 

 manuring problems that need to be attacked in the 

 West Indies. In concluding it may be noted as being 

 of particular West Indian interest, that in India 

 attention is being given to the possibility of fermenting 

 sugar-cane stumps and trash by the method that has 

 been described in this article. In most of the sugar- 

 cane districts of India the stools have to be collected 

 and burnt before a succeeding crop can be grown. It 



