CROPS 151 



Hay making'. — When green forage has to be preserved for 

 the winter or future use it is either made into hay or into 

 ensilage. Hay-making consists essentially in drying the plants 

 by exposure to sun and air to a sufficient extent to prevent 

 excessive fermentation when the material is bulked together. 

 The most important change is the removal of water. Ordinary 

 meadow grass contains nearly 75 per cent, of water, while the 

 hay from it will contain about 15 or 16 per cent. The yield 

 of hay from a given weight of grass must obviously vary 

 greatly ; it will usually be between 30 and 40 per cent. The 

 plants should always be cut while flowering, for if left longer 

 the resulting hay will be poorer in albuminoids and ash, 

 though richer in carbohydrates and crude fibre. 



Grass and other green plants are always well supplied with 

 micro-organisms, which at once attack the sap as soon as the 

 grass is cut, producing carbon dioxide and promoting oxidation^ 

 with its resulting evolution of heat. If the green material 

 be spread out the heat is quickly dissipated and 'no rise of 

 temperature occurs, and as the water evaporates the activity of 

 the micro-organisms is soon checked ; but if the green vege- 

 table matter be piled together in large masses, so as to prevent 

 the escape of heat by convection currents, the temperature 

 rises and the processes of fermentation proceed more and more 

 rapidly. The rise of temperature may be so great as to start 

 direct chemical oxidation and finally to set fire to the material. 

 Such an occurrence is often observed when imperfectly dried 

 hay is collected in stacks or barns. The presence of too much 

 moisture is one of the most powerful causes tending to set up 

 dangerous heating of haystacks. Thorough drying of the hay 

 is obviously the best method of minimising the risk, but this 

 is open to the objection that the proper aroma, flavour and 

 colour of hay is not produced unless a certain amount of 

 fermentation occur in the stack. If somewhat green hay has 

 to be stacked, danger of overheating may be lessened either 

 by mixing salt with it or by allowing free ventilation in 

 the stack. The first method checks fermentation, and so 



