MANURES

Te Aroha News, Volume V, Issue 239, 28 January 1888, Page 5

MANURES-

Pkom a Beries of articles on the " Growth of Wheat and its products in the 3k fill," by Mr, J. J. , Willis, superintendent of Messrs Lawes and Gilbert's Bothamste'd Experimental Farm, we quote as follows :—: — The experiments at Rothamsted clearly show that mineral manures alone, though applied, in the most soluble form, scarcely increase the produce of wheat at all ; that is, they do not enable the wheat plant in any material degree to assimilate more nitrogen and carbon from atmospheric sources than when it was grown on the practically exhausted, un manured land. In the following table will be found tho produce for four periods of eight years each, and foy the total period of thirty- two years ; and for comparison, there i 3 also cjiven the produce of the unmanured plot over the same periods. Table showing the A verage Produce oj Dressed Wheat and total Produce (Grain and 8lraio ) -per acre without Manure, and on the Plot lohich kai receivedmixedmiverals alone Jor a period of thirty-two years — over Jour periods of eight years each, and over the total period.

During the first eight years of the experiments (1844-51) the plot which afterwards received mixed minerals alone received salts of ammonia as well as mineral manure, and the average produce of wheat during those eight seaeons was twenty-nine bushels per acre, or nearly twelve bushels annually in excess of the produce on the unmanured plot ; while during the first eight years of the mixed minerals without the ammonium salts (1852-59) the average produce was nineteen bushels per acre only, or about three bushels more than the permanently unman ured produce. In the second period of eight years, for which • the results are given ill) the table, the produce of the mineral plot amounted to fifteen and onefourth bushels per acre, as against thirteen and a-half bushels grown on the unmanured plot, a difference of one bushel and threefourths iin favour of the mixed minerals. In the third period of eight years the produce from tho minerals was fourteen bushels per acre, and in the last period enumerated, it was twelve and five eighths, or an increase of one bushel and an eighth over the plot without manure. The who'e period of thirty-two years has thus given an average of fifteen and a quarter bushels of wheat with minerals alone, as againet thirteen and an eighth, bushel without any manure at all; and if we take the average produce of the unmanured plot for forty yearß, the yield of -wheat has been fourteen bushels per acre. The application, therefore, of a very liberal supply of mineral ingredients has only been competent to increase the yield of wheat by one bushel and a quarter per acre per annum. The , average total produce (grain and ■traw),of the mixed minerals plot, for the thirty-two years, amounted to two thousand four hundred and twenty-one pounds, and that of the unmanured plot to two thousand and ninety pounds, a difference of three hundred and thirty-one pounds in favour of the minerals. The amount of nitrogen in this three hundred and thirty -one pounds would be not more than three pounds. This represents the whole of the nitrogen which the wheat upon an acre of land, though furnished with an abundance of minerals, has beon able to obtain from the soil and atmosphere, in excess of that in the wheat grown without manure. In order to explain the causes which have produced these crops, it will be necessary to show what has taken place in the soil ; but before doing so, it may be well to giyre a slight review of the crops themselves. We find the two crops running a parallel course, showing great differences in their { yield as the seasons are favourable or otherwise, but rarely differing from each other more than from three or four bushes per i acre. The yield in both is slowly declining, for we find that during the first eight years the unmanured produce gave in two separate years a crop of twenty bushels of wheat | per acre, and the mineral manured plot on threB occasions exceeding a crop of twenty bushels per aero. For the last twenty-four years neither plot has given a produce of twenty bushels, and it eeems hardly possible that, without some change in the manures applied, a crop of this amount can ever be grown again. The Rothamsted Soil— like a great many cultivated soils- contains a large amount of the mineral food of plants ; it also" contains organic nitrogen, that is to say, nitrogen in combination with carbon, the residue of previous vegetation. This organic nitrogen does not appear to be available directly as food for the 'wheat plant, but every year a certain amount of it is converted into nitric acid, which' combines with the lime in the soil. In this state it is very soluble in water, is readily washed out of the soil by heavy rains, and, further, is a most important and essential food of the wheat plant. The' amount of nitric acid formed each year will vary, the formation being most rapid in the hottest weather, provided the soil is sufficiently moist. The amount of nitric acid which the wheat crop can take up will also 'vary, and in cold and wet winters much will be washod beyond the reach of the roots bf the growing crop. These facts, which are of universal application, euable us to oxplain some of the causes which tend to the production of "good" or "bad " crops of wheat. Analyses of the soil of these two plots made at 1 different times, show 1 that both have lost a large amount of organic nitrogen ; and that, in the first nineinches from t tne surface, the mineral manured soil has lost rather the most. '"The" total loss, of nitrogen over a given area is larger than, the amount of. tnat'subVtJance removed in, the crops, a,ud the^ reasqn XK f or will be f.p,und in an e;xanimation of the drainage ,waters, for except when ,'tjhG crop is. in full yigonr. of. growth, the 'drainage water always contains nitric acid. '"lt "vyill' be sufficient here, to, state that prtbetwenty-eigb-t to jth'irty-t wo poiinds^ qf' nitrogen * available >per\ acre each, yeo(r,-frpitij€he soil," seed, , 'rain, etc., Lawes and Gilbert" estimate ( thaA ojriy ab^ut^Wothijrda are reiriov'od in the crop,,,^nd, that one-third goes into the drains, and is ipßtv ?• Trie're'wEa rather more" nitric acid formed ia the soil Avhich received* minerals, and M cdnsequehioa crofr'was- slightly iriicre^sedi) <but *the evident is' distinct and conclusive as ' regards "the y fety '.sniall effect iwhftah followed *the large applications'* of mineral (plant fbodsfH<On -tlie ui(m'anure'cl < soil 6Jbe> minerals tilths disposft^qf 'thVcVo'p 1 iwej-e^q^ito-BUfljcieiit' to^utilise^ther tf hole' of

ft the nitric ,acid available ; ip faot the result obtained with ammonium salts alone, show that the' available' minerals are competent? to grow a mucb larger crop than that actually produced on* the unmanured plot. .Further, as very little, more nitric acid was liberated on the mineral plot — and the crop ,\vas unable to obtain nitrogen from the atmosphere —we have a produce very slightly Sn excess of that grown without manure. ' By the aid of these results we thus more readily arrive at an explanation of the fact that on some «oils — more especially the newly-cultivated prairie soils of the United States— a largo increase in the wheat crop frequently follows the application of mineral manures, or even gypsum alone, fcfoils rich in organic matter may yield an increased amount of nitric acid by the application of phosphates and potash, but in all cases the source of the nitrogen is the soil j and the loss by the unmanured soil of perhaps from eight hundred to one thousand pounds of nitrogen per acre during the forty years is a fact of the greatest importance.

Db w JESSED HEAT. Total Produce, Grain and sstkaw. PERIODS. II 11l w °> P I Busn Bush. Lbs. Lns. 8 Yrs, 1852-59 8 „ 1860-67 8 „ 1868-75 8 „ 1876-83 161 13J 12i 10i 19 151 14 124 2736 2183 1833 1610 3191 2450 2144 1899 32 „ 1852-83 40 „ 1844 83 13J 14 15i 2090 2244 2421 ....