110 



THE AGPJCULTUEAL NEWS 



April 7, 1917. 



A NEW SYSTEM OP MULCHING. 



(ireen-iuanunng probleins formed ihe subject of 

 an editorial in a recent, issue of the AgriculturaL News 

 (January 27), and in connexion with what was said 

 concerning the fermentation of green dressings in the 

 field, the following- snmmarv of liulletin No. 499, United 

 States Department oi Agriculture, will prove extremely 

 interesting. It is also suggestive in connexion with 

 the usual West Indian method of mulching: — 



Mottle-leaf of citrus trees is characterized by yellowi.sh 

 spots or blotches on the leaves, and by a i-eduction in the 

 size of the leaves and the density of the foliage. In it.s 

 -advanced stages it results in a marked reduction in yield, 

 and in the size and quality of the fruit. No fungus or 

 bacterium has yet been found to be causally associated with 

 this trouble. 



Work carried out by the writers in 1914 and reported in 

 another paper showed that half of the mottling in about 120 

 orange groves, in the Riverside, lledlands, Itialto, and High- 

 land districts of California was as.sociated with a low 

 hunuis content of the soil. Evidence was also secured which 

 indicated that inadequate irrigation might be responsible in 

 part for the development of mottle-leaf. 



The pre.>-ent paper is concerned with field experiments 

 relating to the irrigation of orange.s and the use of organic 

 fertilizers, and deals particularly with a new method of citrus 

 culture, the mulched-basin system, in which low dikes are 

 thrown up so as to form large shallow irrigation basins 

 near each tree, and each basin is heavily mulched with 

 alfalfa hay, bean straw, manure, or sonie other organic 

 material. The basin makes it possible to supply each tree 

 with water in accordance with its needs, while the water 

 carries with it to the feeding-root system the plant food 

 extracted from the disintegrating mulch. 



The system of furrow irrigation and clean cultivation 

 in common use in citric districts in California tends to 

 promote the r.irmation of a plowaole, or incipient hardpan, 

 below the surface mulch, varying in thickne.ss from .'' inches 

 to 2 feet; leads to excessive accumulations of soluble plant- 

 food sub.stances, especially nitrates, at the surface of the soil, 

 where they remain until washed down by the winter rains: 

 and fails to conserve the soil moisture sufhciently to prevent 

 the trees from wilting frequently during the summer months. 



The mulched-basin system was found to conserve the 

 soil moisture bettei than anj other system of soil treatment 

 compaied with it, and niuio of the basined trees on either 

 light or heavy soils willed, "ndcr all the other cultural 

 methods euijiloyed, wilting occurred at some period during 

 the summer on both liiht ami heavy soils. 



Available soil moisture below the third foot did nut 

 prevent orange trees fi.n:: wilting if the moisture content 

 in the first 3 feet of soil fell below the wilting coefficient. 



With the amount of irrigation water ordinarily available 

 in these districts (1 niirer's inch to 4 or 5 acres) cover croiis 

 <if barley or sweet clc":r can not be grown tluring the 

 summer months in grr.vfs on either heavy or light soil 

 without causing the wilting of the orange trees 



Circular trenches dug aiound orange trees, filled with 

 manure or alfalfa, and covered with dirt, did not remain open 

 sufficiently after the second irrigation to distribute the 

 irrii;ation water adequat- 'y. 



In the clay-loam soils of the type constituting the 

 Victoria area, the Literal mriv inent of moisture is very slight. 

 In such soils the furrow .system of irrigation is adequate 

 unless a largo number of furrows are used, including furrow.s 

 Under the trees. 



Moisture determinations in groves in which alfalfa was 

 being grown as a permanent cover crop .=ho-.v that the 

 irrigation water never penetrated deep enough into the soil 

 to ensuie an adequate moisture r.upply for the orange trees. 



For a basin having an area of 1.50 square feet, the 

 experiments indicate that approximately l-501h. of alfalfa or 

 15 to 20 cubic feet of stable manure will be required each 

 year to maintain an eii'ective mulch. 



It is not possible with the water ordinarily available 

 to grow mulching material between the basins sufficient lo 

 maintain a .satisfactory mulch on the basins. C'over crops, 

 however, can be grown between the basins on winter 

 rainfall to supply part of the mulch, and where water is 

 available in the summer it can be used for the same purpose. 



Orange trees on clay-loam soil, such as the Victoria 

 soil, responded more quickly to the mulched-basin system 

 than trees similarly treated on light soils, because the heavier 

 .soils under the furrow method of irrigation do not absorb 

 moisture as rapidly as lighter soils. Mulched-basin tiees 

 on clay-loam soils showed a marked response to the treat- 

 ment in three months, while basined trees on light soils 

 required from six to twelve months to show a growth 

 superior to that obtained with furrow irrigation and clean 

 cultivation. The mulched basin is not satisfactory on 

 heavy gumbo soil. 



The .set of fruit was very light throughout the River- 

 side district in 191.5, owing apparently to cold weather 

 following the bloom. In the Sunny Mountain tract, where 

 the mulched basins were first installed in 19i;i, the average 

 number of oranges per tree on the check trees in 191.5 

 was 116, while on the mulched-basin trees the average 

 number of oranges per tree was 281, or two and one- 

 half times as many as on the check trees. The 

 quality of the fruit on basined trees was also superior 

 to that on the unbasined trees. In the Victoria tract 

 in 1916, the alfalfa-mulched trees averaged 483 oranges, 

 the manure mulched trees 242 oranges, and the check trees 

 1S2 oranges. In the Eureka tract where the mulched basins 

 had been installed the preceding autumn, the alfalfa-mulched 

 trees carried, on the average, 550 oranges, an increise of 

 thirty-three oranges per tree over the average yield of these 

 trees for the preceding six years. Exjieriments in this tract 

 with other mulching materials showed a decrease in yield 

 during the first season, due in part at least to the fact that 

 the new root system below the basins was not established at 

 the time the first buds were set. 



The new leaf growth on the basined trcc^ was less 

 mottled than the new growth on the unbasined trees after 

 sufficient time had elapsed for the mulched-basin system to 

 produce response in the tree growth. 



The new leaves on the basined trees were larger and 

 darker in colour, and had a belter texture than those on the 

 unbasined trees, especially on heavy soil. 



The new growth of rootlets under the mulch in the 

 basins was very much greater than in the check treatments, the 

 .soil in the basins beii.g filled with rootlets tc within about 

 2 inches of the surface. 



Great numbers of earthworms were often foun<l in the 

 basins under the nudch, and their burrows honeycombed the 

 entire soil mass. The worms helped to incorporate the organic 

 material with the soil, while their burrows facilitate the 

 absorption of water in heavy soils. 



No soil crust of any kind has been found in the basins 

 where the lunlch eonii)letely covered the soil surface. A 

 complete mulch must be maintained at all times, however, to 

 prevent the surface from crusting. 



