Albert Howard 38' 



III. Soil-Temperature. 



Although soil- temperature is such an important factor in the dis- 

 tribution of the crops of India, both as regards season and the areas in 

 which they occur, nevertheless but little attention has been paid to this 

 growth factor in considering the incidence of disease. In India, the 

 higher limit of temperature most frequently affects growth and in 

 studying the crops of cold countries like wheat, which can only just be 

 grown in India, this is one of the factors which frequently deserves 

 attention. 



White ants and ivheat seedlings. One of the difficulties in wheat 

 cultivation in Bihar and the eastern districts of the United Provinces is 

 to establish the crop. If sown a few days too early, the seed germinates 

 but the seedlings are rapidly destroyed by Termites, whole fields dis- 

 appearing in a few days. The trouble became of some importance a few 

 years ago in Bihar as it interfered with the raising of seed of the new 

 Pusa wheats on some of the private seed farms 1 . The disease was par- 

 ticularly serious in years when the rains ceased early and when the last 

 monsoon showers of early October, known locally as the Lathia, were 

 not received. In such seasons, the advent of the cold weather is always 

 postponed and the cool westerly breezes which normally set in about 

 the middle of October are delayed till nearly the end of the month. The 

 sowing time for wheat in Bihar in years when there is a good Lathia is 

 just after the middle of the month and no trouble with white ants need 

 then be feared. When, however, these sowing rains fail, nearly all the 

 fields are destroyed by Termites. More damage occurs on low-lying 

 damp heavy soil than on the higher and dryer areas. Examination of 

 the root-system during the attack shows extensive discolouration of the 

 new primary roots and of the first internode. Only in rare cases is there 

 any formation of the secondary system. Before tillering can take place, 

 the first internode is devoured by the white ants and the plants wither. 

 A possible explanation of the trouble appeared to be a high soil-tem- 

 perature which subsequent investigation seemed to confirm. In several 

 seasons when the late rains failed, a comparison was made between 

 sowings on Oct. 15th and others twelve days later. In addition to the 

 delay, the furrows in the second case were left open for two or three 

 days so as to cool the soil by evaporation. The early sowings were in 

 every case destroyed by Termites, while in the later ones the damage 

 was negligible and normal root-development and growth took place. 



1 Agr. Joum e of India, xi, p. 351. 



