524 SOIL SECTION

Dr. R. K. Tandon observed that the results obtained in the permanent manurial trials at Shahjahanpur did not tend to support Dr. Sen's statement regarding N:P balance.

Dr. Rege stated that sugarcane being a long-term crop continues t o absorb nutrients for a period of about 4 to 6 months of its growth. The deficiency or adequacy of phosphate as indicated by the chemical analysis of soils was not likely to give a clear indication regarding resporrse to the applied phosphates. During its long period of growth the unavailable phosphate in tho soil becomes available t o the crop, thus masking the efTect of the applied phosphates.

Mr. Mohan Rao described that phosphate applications didnot show any response, while spraying of dilute solutions of ammonium sulphate on leaves led t o encouraging results. ,

In the absence of the author Dr. A.J. Mangelsdorf presented the following paper.

Paper

THE USE OF AQUA AMMONIA IN THE HAWAIIAN SUGAR INDUSTRY

ROGER P. HUMBERT AND A.S. AYRES

Experiment Station, H. S. P. A. , Horzolulz~, Hawaii

The Hawaiian sugar industry has supplied its nitrogen requirements largely from ammonium sulphate since the middle 1930's. The first major change in nitrogen fertilizers since that time is currently taking place. Ammonia dissolved in water, commonly known as "aqua ammonia", is rapidly replacing the other forms of nitrogen fertilizer used. Substantial savings in cost of material, cost of handling and cost of application have resulted in a relatively rapid shift to aqua ammonia.

The first bulk shipment of aqua ammonia arrived in Hawaii in December, 1953. In 1954, 47 percent of the 15,196 tons of nitrogen purchased by the 28 plantations was aqua ammonia. The bulk of the aqua ammonia has been used on irrigated lands where it has largely supplanted other carriers of nitrogen. It is applied both in irrigation water and by injection equipment.

APPLICATION I N IRRIGPiTION WATER

It has long been recognized that poor distribution of water in furrow irrigation resulted in uneven application of fertilizer dispersed in the irrigation water. Intensive studies were initiated in 1951 to evaluate the various systems of irrigation used on Hawaiian sugar plantations. The sh~rtcomin~s'of these systems ,with respect to specific types of soil and length and grade of line were investigated by means of radioactive materials and tracer techniques. These studies ( I ) have brought about modifications of lengths and grades of lines and volumes of water, resulting in better distribution of water. Good distribution of water is obtainable under long line systems of irrigation in relatively impervious soils. In highly permeable soils, it is impossible to obtain a good distribution of water and still keep erosion losses to a minimum. The objectives of these studies were

R.P. HUMBERT,-A.S. AYRES

t i learn where reasonably satisfactory water distribution was being obtained and to encourage the application of aqua ammonia in irrigation water in these areas. Where water distribution was poor, application of aqua ammonia in irrigation water was discouraged.

Fig. 1. Ewa Planation Company's 32,000 gallon storage tank and a small 1,800 gallon field tank below the materials carrier being

Problems in the handling of aqua ammonia have been properly engineered. Aqua ammonia, prepared from anhydrous ammonia, containing 20-21 percent nitrogen, is pumped into tankers and shipped to Hawaiian ports. From the tankers it is pumped into large storage tanlts and transported in tank trucks to the

Fig. 2. Aqua ammonia field tanks designed for handling and distribution to the fields by a materials

carrier. Courtesy Ewa Plantation Company.

526 SOIL SECTION

plantation storage facilities. Figure 1 shows Ewa Plantation's 32,000 gallon storage tank and below the materials carrier an 1,800 gallon field tank being filled with aqua ammonia. Filling the tanlts is a push-button operation. A special gauge automatically shuts off the flow from the storage to the field tank when the latter is full. Figure 2 shows field tanks specially designed for efficient handling by a materials carrier. When applied to the irrigation water, as shownin Figure 3, the aqua ammonia first passes through a metering box whose calibrated dispensing valves assure delivery of the exact amount desired.

Fig. 3. Application of aqua ammonia in irrigation water at Ewa Plantation Company. Automatic controls regulate the fl0.u from ihe portable field tank to the distribution ditch. Courtesy Ewa Pianrarlcn Ccmpany.

Qffective distribution of nitrogen in the irrigation water down furrows 200 to 400 feet in length poses additional problems. To ensure optimum yields, adequate but not excessive amounts of nitrogen must be fed to each section of line. Inadequate nitrogen lowers cane tonnage, while excessive iiitrogell results in higher cane tonnage accompanied by poor juice quality and lower sugar yields. The difficulties encountered in attaining a satisfactory distribution, of llitrogell from aqua ammonia are not only associated with the peculiar physical and chemical properties of ammonia but are also inherent in the mechanics of

A

spreading water in furrow systems of irrigation. ,

WETHOPS O F STUDY

Field and laboratory studies were initiated to determine the reasons for poor distribution in furrow irrigation and to study losses from volatilizatioil

R.P. HUMBERT, A.S. AYRES 529

on different plantations with variations in rates of water flow and amounts of aqua ammonia. Water was applied to the furrows through calibrated Parshall flumes. A recording device provided a continuous record of water input. Ammonia was added to the irrigation water through a calibrated orifice at a constant head. Mixing flumes were used to ensure satisfactory blending of water and ammonia. Ammonia was applied at rates ranging from 4 0 to 100 pounds nitrogen per acre.

Stations for sampling the water were established at 50-foot intervals down the furrow, the first station being located at the point where the ammoniated water left the mixing flume. Samples were taksn at each station at regular intervals throughout the irrigation.

Early in the study, samples representing various periods of flow were analysed separately in order to determine the constancy in concentration of ammonium at a particular station. Subsequently, a single composited sample was obtained at each station. Final samples were placed in tightly closed bottles for transport to the laboratory. Upon arrival, the samples were immediately treated with sufficient sulphuric acid to arrest nitrificatioil and possible loss by volatilization.

To establ.is11 the profile distribution of ilitrogen soil samples were taken in various increments to a depth of three feet, until preliminary data indicated that shallower safl~pling was satisfactoty. The samples representing the entire width of wetted furrow were taken immediately following the infiltration of the ammoniated water into the soil. The wet soil samples were placed in tightly covered moisture cans for transport to the laboratory. The samples were always analysed within 24 hours, ar_d prior to analysis were kept at a temperature of about 10" C to minimize nitrification.

EXPERIMENTAL RESULTS I Ammonia concentration in relation to distance $"om flume. Ammonia

concentration at any point down the furrow does not vary significantly during the period of irrigation. Table I shows the data from six f~~r rows at two rates of ammoilia application, with the applicatio~l time divided into four parts.

TABLE I 1 AMMONIUM IN IRRIGATION WATER IN RELATION TO PERIOD

OF FLOW-IN PPM NITROGEN

Period Of Line 1 ~ i n e 3 Line 5 Line 2 Line 4 flow Line 6

Minutes 50' 50' 100' 50' 100' 50' 100' 150' 50' 100' 50' 100' 150'

0-20 25 24 23 23 23 45 43 42 56 57 52 46 44 3 9 20-40 25 29 28 23 23 46 41 41 63 60 51 51 49 4 1

! 40-60 31 26 26 22 23 55 52 51 55 56 53 50 47 42

I 60-80 2 5 24 26 24 24 43 45 44 52 54 59 51 51 40 Average 26 26 26 23 23 47 46 45 56 57 54 50 48

SOIL SECTION

Absorption of nitrogen from ammoniated irrigation water by the soil. The depth of ammonium penetration from aqua ammonia applied in irrigation water is of great practical importance. In dry irrigated lands, the soil surface is alternately wet and dry. This condition limits the extension of cane roots to the soil surface, thus temporarily placing the ammonia fixed at the surface out of reach. Profile distribution studies show that the aqua ammonia applied in irrigation water is held near th'e surface of the soil. In some soils the entire application is contained in the top three inches, with the bulk of the nitrogen in the surface inch. The results of studies on three widely-separated soils are shown in Tables I1 and 111.

TABLE 11

PROFILE DISTRIBUTION OF N RESULTING FROM AQUA AMMONIA APPLIED IN IRRIGATION WATER

Lahaina Family-HC & S Lahaina Family-Waialua

Distance Distance from head N from head

of line Dcpth Recovered"

*Mean values for three replications.

TABLE I11

PROFILE DISTRIBUTION OF N RESULTING FROM AQUA AMMONIA APPLIED IN IRRIGATICN WATER

Molokai Family-Waipio Substation At 25'" At 100'" At 175'"

0'- 1 53.2 0-1 1-3 26.6 1-3 3-6 10.4 3-6 6-9 3.5 6-9 9-12 3.5 9-12

12-24 2.8 12-24 24-36 0 24-36

-- *Distance from head of line.

R.P. HUMBERT, A S . AYRBS 529

These results are in harmony with the findings of Jenny, Ayers and Hosking (2) who, in laboratory studies with acid clay loams, observed a comparable retention of N from ammonia in the surface few inches of soil.

The ability of the soil to remove ammonia from ammoniated water must account in part for the decrease in concentration of nitrogen as the irrigation water flows down the furrow. Thirty-five tests were run to establish the relationship between concentration of nitrogen and distance from the head of the furrow. The data were analyzed in three groups, depending upon the initial concentration of ammonia in the water. Regressions for the three groups of data were all significant beyond the .0l level and show average decreases in nitrogen concentration of 21 percent from the head to the tail of the lines.

In big cane, conditions in the furrow are very different from those in young cane. A study was made of the effects of lodged cane with its accompanying blanket of trash on nitrogen distribution. Nitrogen was applied at two rates, 60 and 100 pounds N/acre, in year old cane. The results are shown in' Table IV.

TABLE IV

N CONTENT AMMONIATED IRRIGATION WATER APPLIED TO 12-MONTH OLD CANE AT WAIALUA AGRICULTURAL COhlPANY

~urrow* NO. Application of N Concentration Of Decrease in N Initial Final

1bs.-acre PPm PPm PPm percent 60 49 ' 26 2 3 47 60 43 3 0 13 3 0 60 50 26 24 48 60 47 27 20 41

100 8 8 72 16 18 100 91 73 18 20 100 92 80 12 13 100 90 75 15 17

These preliminary data indicate that a better nitrogen distribution can be tained by applying larger quantities of nitrogen at one time than by splitting o two or more applications. These conclusions are not supported by the data tained in trials with younger cane.

xcept that one had received 50 pounds nitrogen from sulphate of ammonia and

-- - - - - - - - - - -- - --

i"

530 SOIL S E C T I O ~

irrigation water, The results are presented in Table V. It is apparent that previous applications of nitrogen had little influence upon the concentration of ammonia in the irrigation water.

TABLE V

EFFECT OF PREVIOUS FERTILIZATION ON N CONTENT OF AMMONI'ATED IRRIGATION WATER

Distance from head of furrow Unfertilized Fertilized

Ft. ( N in p .p .m . )

0 30 3 6 10 29 3 6 3 0 28 36 5 0 31 3 3

l ? O 25 32 150 23 ' 29 200 22 27

Decrease 8 (27%) 9 (25%)

Comparisons with other nitrogen carriers. Decreases in concentration of ammonia down the irrigation furrows prompted similar studies with other nitrogen carriers. Tests were installed comparing aqua ammonia with sulphate of ammonia, urea and nitrate of soda. Nitrogen from the various sources was applied at the rate of 40 lbs. N/acre. The averages of three tests are presented in Table VI.

TABLE VI

NITROGEN CONTENT OF IRRIGATION WATER IN RELATION TO FORM OF N CARRIER

Distance from Distance from Carrier head of line Carrier head of line N&

Ft. PPm Ft.

Aqua ammonia 0 29 Urea 0 .50 26 , 9 , 50

9 9 9 9 100 25 9 9 100 150 25 9 3 150 . 200 22 200

Decrease 7 Decrease I Ammonium sulphate 0 43 Sodium nitrate 0

50 41 1 , 3, 50 $ 3 100 41 3 , 9 , 100 9 9 9, 150 40 9 3 1 150

, , 200 - 9 9 3 , 200

Decrease 3(150') Decrease .

"Average of three experimental results.

R. P. HUMBERT, A. S. tAYRES 53 1

It is apparent from Table VI that a substantially greater decrease in nitrogen in the irrigation water occurred where aqua ammonia was used than when other carriers of nitrogen were applied. The magnitude of the decrease declined in the following order : aqua ammonia, sulphate of ammonia, urea, and nitrate of soda.

Causes of decreased ammonia concentration. Presumably nitrogen is removed from the irrigation water at the interface between the moving water and the surface of the furrow. The rate of removal depends upon a number of factors, including the pH and the percentage ammonia saturation of the surface soil layers, the permeability of the surface soil, and the degree of turbulence of the irrigation water. The finely divided soil particles and organic material that are suspended in the irrigation stream as well as the larger particles that drift along the furrow surface are considered important factors. They are often highly saturated with ammonia and must play an important role in the distribution patterns of nitrogen down the furrows. To determine the influence of suspended material on the concentration of nitrogen, irrigation water was intentionally muddied by stirring the surface of the furrow with hoes at several stations along the furrow while water samples were being collected in the usual manner. In one test, the water was muddied as it emerged from the mixing flume and water samples were taken at intervals of a few feet down the furrow for a comparatively short distance. With both tests, corresponding measurements were also made where there was no effort to increase the amount of soil material suspended in the water. The results are shown in Table VII.

TABLE 'VII

EFFECT OF SUSPENDED PARTICLES ON N CONTENT OF AMMONIATED IRRIGATION WATER

Waialua Family- Waialua -

Molokai Family-Weipio

Distance from N in pgrn Distance from N in ppm

head of line Unmuddied Muddied head of line Unmuddied Muddied Ft. PPm PPm PPm PPm Ft. PPm PPm

0

10 30

50

100

150

a00

Decrease

0

2 5 8

11 14

17

Decrease

"Average of two replications.

SOII, SECTION

Increasiiig the quantity of soil particles in the irrigation waJer resulted in a marked decrease in ammonia concelitratioii of the water. This decrease does not constitute a loss of nitrogen to tlie furrow but does minimize the chances of obtaining a satisfactory distributioii of nitrogen.

Volatilization losses o f ammol~ia jrom irrigation water. Since ainmoliia is a gas, volatilizatioil losses were considered when the first application of aqua ammonia in irrigation water was made. I11 general, the losses were assumed to be small as long as one could not smell ammoiiia in the immediate vicinity of the area being treated.

To study losses under field conditions, a furrow with a siope of 1 .b percent was lined with a polyethyle~ie plastic material which prevented contact betweell the irrigation water and the soil. As ammoniated irrigation water flowed dowll this lined furrow, concentrations of nitrogen in the water at various points along the line were determined in tlie usual manner. The data resulting from the first test are show11 in Table VIII.

TABLE VIII

NITROGEN CONTENT OF AMMONIATED lRRlGAT1ON WATER IN A PLASTIC-LINED FURROW, NEW HSPA SUBSTATION, EWA

-- -. - - - -- -- --

Distance from N-ill ppni

head of furrow I 11 I11 Ft.

Decrease

In the first two runs, coiicelltrations of nitrogen at the elid of the furrow were found to be 5 and 6 ppm (6%) lower than at the head of the furrow. I11 the third run, which, owing to the failure of the water supply, was 110t completed, the corrcsponding decrease was somewhat higher, or 10 ppm (10%).

The movement of water in the plastic-lined furrow differed markedly in two respects from the sort of flow that would be expected in the absence of the lining. With the lining, tlie water moved much more rapidly than would otherwise be the case (lOOf/min.), and tlie flow was more turbulent. To effect a condition correspo~idilig more closely with that ~iormally e~icouiltered in the field, while yet retaining the lining, a futrow in a field at Waipio was carefully graded to zero slope and lined with the same plastic material. Tbe results of five runs in this furrow are shown in Table 1X.

R. P. HUMBERT, A. S. AYRES 533

TABLE IX

NITROGEN CONTENT OF AMMONTATED IRRIGATION WATER IN A PLASTIC-LINED FURROW : WATPIO SUBSTATION

Distance from N-in ppm head of furrow I I1 111 IV V

D t

The data reveal differences in nitrogen content between head and tail of the line ranging from 1 to 7 ppm. The mean of 4 ppm (4O/,) is a little lower than that observed in the previous test with a lined furrow. The smaller decrease in nitrogen concentration is attributed to the reduced turbulence of the water and to the shorter distance traversed.

The results of tests with plastic-lined furrows suggest that a portion of the observed decrease in The nitrogen content of ammoniated irrigation water, as employed in normal field fertilization, is the result of volatilization.

Controlled laboratory studieir of volatilization losses. Volatilization losses from surface-applied aqua ammonia have been studied on a variety of sugarcane soils ill closed systems using large desiccalors. Air is forced continuously over

lo r Makikl - - - - - - - _ - - - *

F- --- /-- A

Olaa - Hydrol hurnic lotowl - Grove Farm - Hurnlc terruginous latosol Hamakua - Hurnlc lotosol

Time-In hours

Fig. 4. Losses of ammoniafrom surface applicsticns of aqua to moist soils.

534 SOIL SECTION

the soil's surface and the ammonia in the air is trapped and titrated as it leaves the system. Losses of ammonia from surface applications to a variety of moist soils are shown in Fig. 4.

The curves of Figure 4 show losses ranging from about seven to ten percent from the wide variety of soils tested. When soils are air dry the initial losses from surface applications are shown to be larger than when these same soils are near field capacity (Figure 5). In the case of the slightly acid (pH 6.3)

Fig. 5. Losses of ammonia from surface applications of aqua to soils in air dry condition and at field capacity.

Waialua soil, the effect of moisture is greater than with the slightly alkaline (pH 7.5) Kahuku soil.

A blanket of cane trash on the surface results in a larger volatilization loss. Controlled laboratory tests with Olaa soils show losses o'f ammonia from aqua applied to moist soil to be eight percent, while the loss jumped to 19 percent when th'ere was a thin blanket of trash on the soil,

APPLICATION BY INJECTION EQUIPMENT

Only a small fraction of the total nitrogen purchased to date has been applied by injection equipment. Small scale application equipment was purchased

R. P. HUMBERT, A. S. AYRES 535

for.the initial trials on the unirrigated plantations. Problems of aqua placement, quantities required, corrosion, pump requirements, etc., were covered in some detail prior to the construction of the larger machines now in operation. . Placement studies. Surface applications of aqua ammonia were rejected on the basis of the first field trials. Chemical tests using "blotter" techniques with indicators showed that the losses of ammonia from surface applications on the cane line were excessive. The lower leaves of the young cane were severely burned from the volatilization losses. Applications on wet soils showed marked reduction in the loss of ammonia (Fig. 5) but were still high enough to warrant placement in the soil.

Volatilization losses from sub-surface placements have been very low. Detailed studies have shown a high percentage of ammonia adsorption by the soil even with placements as close as one inch to the surface. Placements two to three inches in depth are recommended for maximum efficiency of aqua ammonia applied. The ammonia spreads in all directions from the point of contact. The volume of affected soil varies with soil type and particularly with its porosity. In the heavier clay soils studied to date, the maximum zone of influence lies in a sphere five inches in diameter. The pH changes in the zone of application are appreciable. '

With applications up to 200 lbs. N/acre in bands, the pH has risen from 5.0 to as high as 9.2. Three months after application, the centres of the treated zone still have a pH of 7.5 to 8.0. In the zone of applicatioh, root systems of cane plants appear to be temporarily affected. Since sugarcane normally has a vigorous, widespread root system, the small percentage of roots affected by band placements of aqua does not appear to limit growth materially. Early in 1954, applications of aqua ammonia were made with the seed cane on the planting machine at Kahuku Plantation. The losses of ammonia were negligible when it was applied just ahead of the covering device on the planter. This operation has now been adopted as plantation practice a t Kohala Sugar Company, and othersare contemplating its use.

The bulk of the aqua ammonia applied by injection equipment has been used in connection with ratooning operations. Figure 6 shows the injection equipment used on Kohala Sugar Company's unirrigated fields. The aqua ammonia is applied through ground-driven positive displacement pumps mounted on a D-6 tractor. A clutch-operated transfer pump, driven by the rear power take-off, is used to fill the two 75-gallon tanks.

Figure 7 shows the two-row subsoiling and fertilizing machine usedin ratooning operations of irrigated fields at Wailua Agricultural Company. The fertilizer is placed on both sides of two 54 foot rows, 39 inches apart. Aqua ammonia and solid potash and phosphate fertilizers are applied immediately after harvest. The tractor is equipped with positive displacement piston-type pumps driven from a starr wheel which takes its power from the caterpillar tracks. The solid fertilizer is metered by a scroll arrangement driven by a gear train through the starr wheel. The tractor has two fertilizer hoppers that hold 700 pounds each and two aqua

SOIL SECTION

Fig. 6. Application of aqua ammcnia by injecticn equipment on un-irrigated fields at Kohala Sugar Company. The aqua is applied through ground-driven ,

positive displacement pumps mounted on a D-6 tractor. Aclutch-operated transfer pump, driven by the rear- power take-off, is used to fill the two 75-gallon truck tanks. Courtesy Kohala Sugar Company.

Fig. 7. Application of aqua ammonia and solid fertilizers at ratooning in irrigated fields at Waialua Agricultural Company. The liquid and solid fertilizers are applied on both sides of two cane rows and the rate of application isgeared to the speed of the tractor. This machine normally covers 5 to 6 acres per 8-hour day. Courtesy Waialua Agricultural Company.

R . P. HUMBERT, A. S. AYRES 537

allillloilia tanks with 55 gallolls each. This machine covers five to six acres per eight-hour day.

Onoii~ea Sugar Company's four-row, two-way n iach i~~e with full hydraulic co~ltrol applying aqua a ~ n ~ n o n i a on both sides of each cane row at approximately olie i~lcli depth is show11 in ~ i g u r e 8.

Fig. 8. Onomea Sugar Company's new fertilizer machinc : a four-row two way machine with full hydraulic control applying aqua ammonia on both sides of each cane row fro111 two 200-gallon tanks. Four stainless steel hoppers each holding 500 ~ O L I I I ~ S

~nur ia te of potash deliver the potash applied t o the surface of each cane line. Courtesy Onomza Sugar Company.

The need for potash fertilizers along with nitrogen at different periods in the growth of the crop postpolled the acceptance of aqua alnmonia on many of the u~iirrigated plantations. Muriate of potash, the forin in which potash is used in tlie sugar industry, has a low solubility in water. This low solubility resulted in a shift from foliar sprays of urea in 1951 and 1952 to air applicatioii of granular solid fertilizers of urea and granular rnuriate of potash for second-season fertilization. The unirrigated plantations accepted the challenge to engineer. cquipine~it that would apply both liquid iiitrogen fertilizer aiid solid potasli fertili,zer Four stainless steel hoppers, each holding 500 pounds of niuriate of potash, make it possible to apply 200 poundslacre to ten acres without reloading. The lnuriate of potash is applied to tlie surface of each cane line. ~ l i k position and depth of placelnent of aqua a~il~nollia are adjustable, the ain~iio~iia being applied back of tlie swept-back shaiilts designed by Brea Chemical Company. Two 200-gallon aqua ainlnoliia ta~llts hold enough liquid nitrogel1 to apply 75 pou~ids N/acre to eight acres vvitllsut reloading. The rate of aqua and potash applicatiolls can be

538 SOIL SECTION

varied by simple adjustments of the phmps and slides on the hoppers. A rate of six acres per hour has been attained without time out for refilling. The machines are supplied with fertilizer from a truck-trailer supply unit which holds 1200 gallons of aqua ammoilia in the flat tank and 30 bags of muriate of potash on top. .

SUMMARY I The Hawaiian Sugar Industry has made a rapid conversion to the use of

aqua ammonia because of substantial savings in cost of material, methods of handling, and application.

The bulk of aqua ammonia purchased in 1954 and 1955 was applied in irrigation water on the irrigated plantations. The problems involved in achieving a satisfactory distribution and utilization of aqua ammonia are discussed in as much detail as accumulated scientific facts permit. Results of current studies may modify the methods of application, but every effort will be made to use the cheaper liquid nitrogen.

Application of aqua ammonia by injection equipment on both unirrigated and- irrigated plantations is progressing satisfactorily. Examples of equipment now in use on Hawaiian plantations are discussed.

The authors wish to acltnowledge the assistance of R. B. Campbell, H. H. Hagihara, island representatives of ESPA and staffs of the various plantations who participated in this study. I

REFERENCES

1. Humbert, Roger P. 1954. Water Distribution Studies in the Hawaiian Sugar Indust~y. Hawaiian Planters' Record. Vol. LIV : 211-125.

2. Jenny, H., Ayers, A.D. and Hosking, J.S. 1945. Comparative Behaviour of Ammonia and Ammonium Salts in Soils. Hilgardia 16 : 429-457. I

DISCUSSION

Dr. Arakeri wanted to know how distribution of aqua ammonia wasregularized from furrow to furrow. In reply, Dr. Mangelsdorf stated that this could be regularized with the irrigation water ; but variations in the concentration of ammonia were observed from furrow to