322 Agricultural Gazette of N.S.W. [May 3, 1920. 



a slightly later maturity is observed in the maize fertilised with it. Wheii 

 a later planting than usual takes place in cold districts, tlieii it would be 

 advisable to apply superphosphate alone at seeding, in spite of all other 

 considerations. 



Residual Effect of Fertilisers. 



Although the amount of fertiliser usually applied to maize contains less 

 plant food than is removed from the soil by the average ci'op, there is reason 

 to believe that there is some residual effect from the fertilisers applied. In 

 other words, we may expect some increase in the second or third years after 

 application (though by no means as great as the increase during the first year). 

 The establishment of this fact is the basis of the complaint by tenant farmers 

 already refen-ed to. 



Nitrogen is the chief element lost from the soil by leaching, and though 

 .•,oils have the power of fixing ammonia salts to some extent, even these are 

 converted fairly rapidly into nitrates dux'ing favourable summer conditions, 

 and the soil then has no power over their retention, except when growing 

 crops are making use of them. The loss from leaching is, of course, greater 

 in districts of heavy rainfall and from sandy soils ; and when these conditioiis 

 are heightened it will be seen that a cover crop of some kind is an economical 

 method of saving nitrogen. It will be apparent, therefore, that nitrogenous 

 fertilisers like sulphate of ammonia and nitrate of soda are not likely to 

 have any residual effect. Phosphatic and potash fertilisers lose but little of 

 their plant food from the soil by leaching under ordinary conditions, though 

 potash is lost to some extent from sandy soils under heavy rainfall. Fairly 

 large quantities of lime are also removed from the soil in drainage or seepage 

 waters. It is, however, chiefly from phosphatic fertilisers and organic 

 nitrogenous manures like blood, bone, &c., that we can expect some residual 

 value— even though the amounts of plant food supplied by these fertilisers is 

 less than that removed by the crops from the soil, for the crops depend more 

 or less on the plant food which is naturally contained in the soil and what 

 part of this is made available. 



Experiments are now in progress in this State to determine the residual 

 effect of superphosphate on maize soils, but in the meantime the experience 

 of other countries is worth quoting. 



In Ohio* it was found that 51 per cent, of the increase from chemical 

 fertilisers was realised in the crop to which the fertiliser was applied and 

 49 per cent, in the crops which followed, the incnvised yields extending for 

 four years afterwards from a single application. 



In Rhodesia,"!' on red soils, an increase of 46 bushels per acre was 

 obtained as an aggregate of three seasons from one dressing of fertiliser 

 costing 20s., practically no increase over the unmanured plot being obtained 

 beyond the third year. 



* Ohio Mon. Bull, vol. 2, No. 2 (February, 1917). 

 t Rhodesia Agr. Jour., August, 1917. 



