LOSS OF XITKATKS IN WKT \( TIMX- -':; 



crop (p. 63) that \]\v incTeascd crop alter fallow i> .ilmost 

 wholly dependent oil t lie retention in llic soil of tlir nitrates 

 thus formed in the sunnner. Should a ucl autimm ;nid eariv 

 winter succeed, the nitrates ar(> \\aslied so tar dnwn in ih,. 

 subsoil as to be out of reach of the ei-o|), which tlnn -Imw- a 

 very small return for the previous sunniiei- fallow inu. 



The rapidity with which nitritieation may take place after 

 harvest is also noticeable in the table. There is plentx of 

 evidence that for three months or so before the reinoxal of the 

 wheat crop the soil in which it is growinjj; is [tiactieallv fr-r 

 from nitrates, but if rain falls when the «j;r()imd has l)eeii 

 broken up after harvest the conditions l)ecome extremely 

 favom-able to nitrification, because the soil is warm and wdl 

 aerated by stirring, and possesses a suitable degree of moisture. 

 Hence heavy autumnal rains, before the land is again occui)ied 

 by a crop to take up the nitrates, may easily result in serious 

 loss to the land, and some quick-growing covering ci-op like 

 mustard is valuable, because it seizes upon the ready formed 

 nitrates. At a later date the nitrogenous compounds the 

 mustard has formed from the nitrates, which would otiierwise 

 have been washed away, are returned to the land, either by 

 being ploughed in or fed off, and become available on their 

 decay for the nutrition of the succeeding crop. Imcu a free 

 growth of weeds on the stubl)le will diminisli the los> of 

 nitrates to the land. 



IV. — Nitrates in Manured and Cian'i'ii) Soils. 



In several instances, as, for example, in the Broa«lltalk field 

 in 1893, soil samples have been drawn to depths of 1» feet, 

 and the distribution of the nitrates in the successive 1» inches 

 determined. Table LXXVIIT. shows the results for certain 

 of the plots sampled in Octolier of that year, after a very dry 

 summer yielding a crop mucli Ix'low the average, and als.» alter 

 a fall of about 4! Indies of rain between harvest and thr time 

 of sampling. 



