Crop Response to Methods of Surface Water Distribution

Comparative studies of irrigation methods in relation to crop response was carried out in 1973-1974. Of the two methods of irrigation evaluated, zig-zag Currow method gave well marked yield responses compared to standard furrows. Thc yields obiained under this method of irrigation was well marked in high moisture response crops. Another feature observed in zig-zag furrows was that the yields in different sections of the furrows are more uniform compared to standard furrows.


Introduction
The irrigation mcthods can bc broadly classified into three types:-viz.Sul-IBcc irrigation, Sub-surface irrigation and Overhead irrigation.Surface irrigation may be either flood irrigation or furrow irrigation.The latter in turn is of thc following sub-types : i .Standard furro\vs: Wherc the watcr front advanccs along tllc direction of thc grade.
ii. Zig-zag fwows: Where the watcr front advances alternately along and against the grade and where the exact geometry of the furrow zig-zags usually tends to depend on the slope, gradient and the spacing of the crop. ...

111.
Corrugations: Where the water front advances down the natural slop:: in furrows which are invariably less than 200 ft in length.
iv. Improved corrugations: Where the water front advances down the natural slope in caref~~lly shaped up furrows along the complete length of the field (evcn if the field is several miles long) with the use of gated pipes.
?he present study is concerned wit11 the standard furrow method and tl~c zig-zag furrow method and is an attempt to evaluate certain aspects of the relative irrigation efficiency of the two methods.
The standard furrow method, which in fact is widespread in Sri Lanka, involves comparative disadvantages such as high labour requirements and low efficiency of watcr use. it could also contribute to excessive soil erosion and loss of Irrigation water through run-off.The zig-zag furrow method, on the other hand, which is less frequent in occurrence in Sri Lanka and, where it occurs, is largely confined to irrigating perennial crops.possesses the advantages of low labour inputs and greater efficiency in water use.The lack of popularity of the zig-zsg method in the country is probably due to thc fact that it is alien to conventional practices of surface irrigation.
In Sri Lanka, emphasis on Irrigated highland cultivation urlginalcd with the irrigation projects, developed in the recent past.Uda Walawe, one of such projects, where 63,000 acres of rolling land with natural slopes of 2.5 -3.5 percent is developed to a grade of 0.5 percent.In this project with the limited availability of water, irrigation was carried out in rotational basis using standard furrows widely.The above combination always results in considerable I-educlion of crop yield due to improper irrigation and high labour requirements.Therefore the feasibility of adopting zig-zag method, to suit the cultivation of annual crops under the existing "Land System" was examincd because of its low labour require-tl~ents.This method also facilitates increased water application per unit area of land.
It 1s the author's colitention that the principal significance of the present study lies in the fact that increasing attention is being paid to the production of subsidiary ficld crops (ic.crops other than paddy) under irrigated conditions in the Dry Zone of Sri Lanka and the consequent nzed to determine ths efficls OF the different types of irrigation possible upon crop yields.Thc crops selectcd for the experiment-Cotton, Chillies and Soyabeans-are among the major crops currently recommended in the programines of diversification of irrigated agriculture in Sri Lanka.

Materials and Methods
The experiments upon which this paper is based, were col~ducted at the Research Centre, Eraminiyaya, Angunukolapellessa, and were commenced in the Maha scason of 1972173 and were continued in the Yala season of 1973 and 1974.
Results of the study of Maha 1972173, confined to chilli and.colton provided preliminary evidence that the zig-zag furrow method is supzrior, in both yield and crop performance, to the standard furrow method.They also indicated that, in the for.mermethod, 20 ft furrow segments were superior t o longer furrow segments.
Based on this preliminary findings, a more comprcl~ensivc comparative study of the two metl~ods was undertaken, once again with chillies and cotton, during the Yala season of 1973, in an experiment laid out in a split-plot design in sub plots of 400 sq ft, replicated three times having methods of irrigation as the main treatment and the three stream sizes, 10 g.p.m., 15 g.p.m. and 20 g.p.m. as the sub treatments (see Figure 7).During the Yala season of 1974, tile experiment was repeated Crop Xcsponse to Methock of S t / i j ~~c Water Distribution 7.
with soyabeans.This was also conducted in split-plot design and was replicated 5 times, with variation in the method of irrigation as the main treatment and variation in strean1 size as the sub-treatment.
In the experiments of 1973 and 1974, the total length of furrow was fixed at 200 ft.The ridges were spaced 2 it apart with an average height of 8 inches.The furrow segments were 20 ft in length.The crop spacings were 2 ' ~ 1' for cotton and chilli and 2' x 3' for soyabeans.
Soil conditions at the location of the experiments were as follows: Soil : Low.

1.5" pcr hour
: 1.5" per foot.: 0.5 percent : 2.5 percent Thc crop management and plant care were carried out in accordancc with the standard recomniendations of the Department of Agriculture.The irrigation frequencies were fixed at once in four days, five days, and seven days for soyabeans, chillies, and cotton respectivelq .The irrigation was carried out as per treatment throughout the crop season and the time to irrigate each treatment was recorded.At harvest, the yield data were taken, dividing the full length of the furrow into four sections of 50' each.This was for the purpose or comparing yields along the different scctions of the furrow

Results
The results of the experimci~ts are presented in Tablcs 1, 2 and 3 and are illustrated graphically in Figures 1 to 5. 111 overall terms, the results make it clear that the significant variations in the crop responses correlate only with variations of the main treatment (zig-zag method vs standard furro~v mcthod) and not with differences in the sub-treatment (ie.strcam size).
The data tabulated in Table 1 show that, under thc zig-zag furrow method wliilc overall yield levels were significantly highel-than under the standard f ~~r r o w     method, the yields obtained 111 different sections of tlre furrow were also more unirorm (see Figure 1).It should further be noted (Columns 5 -8, Table I) that the deviations of yicld in different segments of the furrow El-om the mean yield are greater in the standard furrow method than in tlie zig-sag method.
There is some variation among the different crops jn respect of the generallzatrons made above.For, as Table 2 (which contains data on the mean yields under different treatments and the percentage differences in the yield and the zig-zag furrows and standard furrows) indicate, in thc case of tlie high ~iioisture response crops (chilli and soyabean) the difference in their performance under the two iri-ipation systcins is greater than in the case of thc low moisture response crop (cotton).
The total.volunzes of water received under the different treatments are shown in Table 3.The data here indicate that greater qua:l:ities of water could bc fed into the furrow through the zig-zag method.This is a contributory caust for the higher yields obtained specially in the case of the high moisture response crops.As shown in the Figurc 6 due to the fact that in the zig-zag furrow the water rront advances against the grade and iills the inclinations of the furrow in its alternate segments, the volume of water made available for infiltration becomes greater.The exact measurements in this regard are presented i n Colu~nn 5 of Table 3 Thc histograi~lic represcntatlon or Figure 5 s~llista~ltiates the results refcrrcd lo abovc in the sense that the deviations of the yield in thc standard furrow are shown to be higher than those of the zig-zag furrow.Apart from this, another interesting feature borne out by the histograins is that, as the stream sizc is illci eased.the differences in the performance of the crops under the two methods diminish, thus indicating possibilities of improper irrigation under both methods.

Discussions and Conclrlsions
'The resulls presented above eslablisl~ that the crop response undcr the zig-my furrow method is superior to that of the standard furrow method.The bigher yields obtained and the uniforillity of the yields along the furrow of thc zig-'zag method could be attributed either equal coiltact time between soil and water in cvery section of the furrow and thus to uniform watcr infiltr~tion or, alteniatively, to uniformity OF water distribution which results from the flow of mates from high intake areas 10 low intake areas.
The cause of water front advancement in zig-zag furrows is shown in Figurc 6.A s stated earlier, in this method the water has to advance against the gradc in alternate f ~~r r o w segments, filling the inclination of the i'urrow.This process c'sviously permits a longer contact time and facilitates thc infiltration volume of water.In standard furrows, on the other hand, the water front does not change direction once the water is let into tlie furrow.Furthermore, here the total quantity of water fed into the furrow depends on stream size, length of furrow and grade of the furrow.Normally, the water tends to gush down the grade lowering the infiltration time.
One of the econoilllc implications of adopting the practice of zig-zag furrow method, as mentioned before, is the low labour input inherent to its largc scale application.Provided the availability of water is not a limiting factor, irrigation under this method could be carried out sin~ultaneously in a number of zig-zag furrows, either by siphoning from field ditches or by supplying water through buricd pipes.The time required for irrigating all zig-zag furrows is the time needed to irrigate one zig-zag furrow, depending, of course, on variables such as stream size and soil conditions.In contrast, under tlie standard furrow method, water supply to each furrow has to be carried out consecutively, which process obviously requires more labour and more time.
Yct another advantage of the zig-zag furrow method of irrigation is that It facilitates a substantial reduction of uneven irrigation, which in fact, is an ei-ror factor even in experimental plots.Water supply in the furrows, either througl~ buried pipes or by siphoning enables uniform irrigation, provided the land preparation is done uniformly.Furthermore, since the zig-zag furrow method permits greater contact time between soil and water, it overcomes the problems of the "sealing effect" (ie. the formation of an impermeable soil crust on the furrow bed) which characteristically inhibits infiltration of water.
The foregoing discussion leads us to the conclusion that in rcspect of the principal criteria which should be considered in the choice of irrigation technique, the zig-zag furrow is superior to the standard furrow method.The latter is, of course, the inore widespread in the cultivation of higliland crops, at present, even though it entails a series of problems sucll as over-irrigation and/or under-irrigation, higher labour inputs and lower infiltration of water to the soil.In practical application by the farmers, the standard furrow method also involves other problems that relate to difficulties of estimating the optimum length of thc furrow and the size of the stream.The overall beneficial effect of the zig-zag furrow method of irrigation appears more pronounced in the case of high moisture responsc crops.
The author wishes to place on record his indebtedness to Dr. I. P. S. Dias, Deputy General Manager (Agricultural Research) for his co-operaticn in conducting the experiments.A special word of thanks is also due to Mr. M. G. Sugathadasa, Field Assistant, Division of Irrigation Agronomy, Research Centre, Eranliniyaya for the invaluable assistancs he extended to conduct the above experiments.

TAELE 1 .
Mean yields in pounds per acre and deviation of yields from the mean 1:alue 113 different sections of furrow CT 2. Shon4ng the yidd under zig-zag method as a percentage of yreld

TABLE 3 .
The