17B Lime Requirements of Neiv Zealand Soils 



good aeration, and by inference, with higher temperatures^, have less 

 organic matter, soluble or otherwise, than those of the Terrace Lands. 

 Observations recorded by Hilgard in his volume on Soils in the 

 Humid and Arid Regions illustrate the same phenomenon of the rapid 

 oxidation of organic matter in dry soils, as the following figures gleaned 

 from the Tables on pp. 136, 137 of the 1910 reprint of this work will 

 show. 



Average percentage of humus in 41 soils of the arid region 0-91 

 Average percentage of humus in 15 sub-irrigated arid soils 1-06 

 Average percentage of humus in 24 soils under humid con- 

 ditions 4-58 



From these considerations it appears probable that the excessive 

 acidity of the soils of the Southland Terrace Lands as compared with 

 those of the River Flats, and with those of Canterbury, is due mainly 

 to the lack of natural under-drainage which in this wet district causes 

 the retention of an excessive amount of water, the presence of which 

 retards the oxidation of organic matter and encourages the accumulation 

 of "sour" humus. 



Summary and Conclusion. 



1. The Hutchinson-MacLennan method for determining the Hme 

 requirements of soils, when practised under suitable standard conditions, 

 gives more rehable indications than are obtainable by the ordinary 

 methods of chemical analysis. 



2. The method gives indications which appear to be uniformly in 

 excess of the actual requirement of the soil for lime as judged by 

 economic standards: hence a correcting value seems advisable. 



3. The correcting value for the soils of Canterbury Plains is about 

 0-10%. 



4. The greater acidity and higher hme requirement of soils of the 

 Southland Plains appears to be due to a combination of lack of natural 



^ In this connection it is important to note that the only localities in Southland where 

 wheat can be grown successfully are Bayswater in the basin of the Aparima river and the 

 Dipton Flat of the Oreti river valley. In other parts the wheat is almost always destroyed 

 by frost. That this is due to differences in temperature of soil and overlying air, there 

 can be little doubt. Damage to wheat by frost is very rare in Canterbury, but last season 

 a severe frost (10 to 14 degrees) caught the plants just when they were ready for fertilisation 

 and totally ruined crops over areas estimated at 12,000 acres (see N. Z. Journal of 

 Agriculture, January, 1916). 



