THE SOIL AND ITS EFFECT OX PLANT GROWTH. I7 



portion of straw to urine, and that if this is exceeded wastage 

 results. If the straw is insufticient for the nitrogen in the urine, 

 nitrogen is lost ; if the straw is in excess, the manure will not 

 make properly, and the soil derives less benefit than it should. 

 Experiments have shown that i ton of straw can be used for 

 every 100 lbs. of digestible protein fed to the animals. As a rule, 

 however, the excretions are too concentrated, and some added 

 water is necessary. When these proportions are maintained, 

 satisfactory rotting of the straw proceeds rapidly, and the losses 

 of nitrogen are at a minimum. Made under such conditions, 

 manure at Rothamsted has rotted down to half its weight without 

 loss of nitrogen. 



Green Manuring. 

 A further method of increasing the all-important supply of 

 organic matter on the farm is by the use of green manures. 

 Attempts were made to develop this method at Rothamsted 

 in 1914 and 1915, but as the only implements then available 

 were those worked by horses it was rarely found possible to sow 

 a catch crop, and without this, green manuring is hardly an 

 economic possibility. The position is, however, entirely altered 

 by the introduction of the tractor. Experiments in green 

 manuring were started by the Royal Horticultural Society at 

 Wisley is 1919, and are still going on at that centre. Work on 

 somewhat similar lines has been in progress at Woburn for several 

 years. The experiments at Rothamsted have only recently been 

 re-commenced, and the results from all three centres, when avail- 

 able for comparison, should be of the greatest use, for each centre 

 represents a different set of soil and climatic conditions. Wisley 

 has a dry climate and very light soil ; Woburn, with a rather 

 moist climate, has a rather heavier but still light soil ; at Rotham- 

 sted the climate is somewhat similar to Woburn, but the soil is 

 a loamy cla}'. The object of the whole series of experiments 

 is to find out what are the best crops to grow as green manure 

 under different conditions of soil and climate. The experiments 

 at Wisley are on small plots, mainly for the benefit of the market 

 gardener ; at Woburn and Rothamsted, trials on a larger scale, 

 more applicable to farming practice, are being conducted. In 

 all three cases, however, the main lines of investigation are the 

 same, and for the purpose of this report it will be sufficient to 

 indicate the type of experiment in progress at Rothamsted. 

 Leguminous and non-leguminous green crops of various kinds 

 are sown in early autumn, immediately after harvest, and are 

 allowed to grow on, in one case until early winter, and in the 

 other throughout the winter. They are ploughed in, and are 



