On Irrigation. 467 



is best suited to irrigated lands. Eye-grass ought to be extensively, 

 and perhaps exclusively, grown on soils adapted for irrigation, in 

 order that the soluble matters, as soon as they become available, may 

 be elaborated into vegetable produce, and that good food, after being 

 produced on the land, may not be aftervrards washed away. Do, however, 

 what v/e will, we cannot prevent altogether the waste of a great deal of 

 fertilising matters in the drainage of irrigated fields. This is a great 

 fact, well known to those v/ho have seen the irrigated meadows on Lord 

 liatherton's estate at Teddesley, in Stailbrdshirc. I have strong reason 

 for believing that drainage-water is occasionally more useful for irriga- 

 tion than the natural spring-waters of the locality. 



On highly-manm-ed fields we cannot doubt that water, in jiassing 

 through the land, actually takes out more than it imparts to the soil. 

 It is quite true that in other instances the water itself conveys food to 

 the land ; but when the land is highly-manured, or if the soluble 

 matters are, as in the case of sewage, brought on the land in great 

 abundance, a great deal of fertilising matter will pass away in the 

 di'ainage-water. In proof of this I may mention two analyses of 

 water, that I find in the third Eeport of the Commission which sat to 

 inquire into the best mode of distributing the sewage of towns. That 

 Keport states, at page 18, that the sewage, when applied to the soil, con- 

 tained in solution 44-87 grains per gallon of soluble matter ; the drainage 

 from the soil contained 37*o2 ; thus showing that a considerable 

 quantity of soluble matter is retained in the sewage. It is true that 

 most of the ammonia has been absorbed (or transformed), for the 5*74 

 grains originally present in the sewage became reduced to 1 grain ; 

 still there is 1 grain in a gallon left. What is of yet greater im- 

 portance is this fact, — ^that whilst the sewage contains no nitric acid, 

 the drainage contains no less than 4 and a fraction per cent, derived 

 from nitrogenous matter, or even from ammonia ; for I believe that 

 ammonia is capable of oxydation, and of being la,rgely converted into 

 nitric acid, which is perhaps the very best form in vi'hich it can be pre- 

 sented to the growing plant. 



In several drinking- v/aters, fitted rather for irrigation, I have 

 foTind a large proportion of nitric acid — indeed the presence of 

 appreciable amounts of nitric acid can be detected in all natural 

 springs. We have very scanty information upon this subject, 

 which is one that I should like thoroughly to investigate. I should 

 like to ascertain what quantity of v/atcr goes on to the land in 

 the natural rainfall, or the natiu-al springs that are made to fiow 

 over it ; what quantity passes out of the drain in the drainage- 

 water, because the settlement of this question will throw light upon 

 the exhaustion of soils, of which we Iiave heard so much. It is im- 

 possible to restore to the land with ])rofit all that we take out of it. The 

 natural sources of loss are far greater than those occasioned in oiu* 

 fields by the removal of the produce. Perhaps it will clear oiu' ideas 

 en the subjects of exhaustion and j)ermanent deterioration of our fields 

 if this subject is tlioroughly investigated. I therefore purpose to go 

 tlioroughly into it, and examine not only the waters that are best fitted 

 for irrigation, but also the drainage-water : and I stand in need of 



