Trials with Nauru Rock Phosphate as Pasture Topdressing

New Zealand Journal of Agriculture, Volume 84, Issue 3, 15 March 1952, Page 183

Trials with Nauru Rock Phosphate as Pasture Topdressing

Conclusions Drawn EXPERIMENTS summarised in this article lead to the following conclusions:— In most parts of Nev/ Zealand superphosphate gives better results than Nauru rock phosphate as a pasture topdressing. However, in some haying and mowing trials Nauru rock phosphate gave appreciable responses over unfertilised plots, and in most of the observational trials it gave some responses. . two early haying trials gave no evidence that fine grinding of Nauru rock phosphate would improve its effectiveness . as a pasture topdressing, but this requires further testing. In most trials Nauru rock phosphate was considerably slower than superphosphate in causing pasture responses. In only a few trials did Nauru rock ■phosphate show greater residual effect than did superphosphate, ; but observations for this purpose ..were not continued on a large number of trials when topdressing had ceased; ' Trials with,',', superphosphate - Nauru • ; phosphate. , mixtures have not, on the whole, given encouraging ' results ; so far.

THE first accurate trials, begun in 1921, were haying trials in which the growth on plots which had been topdressed was weighed at the hay stage to compare responses in pasture growth' from various fertilisers. Plots were closed for hay production after they had been topdressed and the hay yields measured by weighing the material green immediately after it had been cut. This technique has since been r ' superseded by other methods, but the results of a series of trials extending from 1921 to 1930 are of value, especially as many of the trials lasted for several years and were accompanied by observations on the appearance and composition of the pasture at all seasons.

GREEN WEIGHTS OF HAY MATERIAL (tons per acre) . January January IQ9?1 January January Tnt _i e Treatment 1922 1923 1924 1925 1926 Totals Control '.. 1.2 1.1 ’ . 1.3 0.7 4.3 Basic slag .. 1.5 1.6 No hay 2.2 1.0 6.3 Superphosphate 2.1 2.1 —area 2.6 1.2 8.0 Nauru phosphate 1.5 1.5 grazed 2.4 1.0 6.4 Superphosphate with and lime .. ■ 2.1 2.0 dairy 2.4 1.1 7.6 Nauru phosphate cows and lime .. 1.4 1.3 1.9 0.9 5.5

Haying Trials at Te Kumi One of the earliest haying trials was at Te Kumi, about 2 miles from Te Kuiti. This was begun in 1921 to compare the effect of ground Nauru rock phosphate with those of superphosphate and basic slag. The area selected had not been topdressed for 5 years. The land was a light loam with good drainage and carried a reasonably good sward of cocksfoot, perennial ryegrass, and dogstail, with some white clover. ....... The phosphates were applied annually at the rate of 3cwt. per. acre .from 1921 to 1924 inclusive. Half of the superphosphate and Nauru rock phosphate plots also received an initial topdressing in 1921 of 1 ton of carbonate of lime per acre. Thus a comparison was obtained between these two .forms of phosphate both with and without lime. Green hay yields were obtained in •each summer after topdressing except in the 1923-24 season, when the : area was grazed with . dairy cows’ and no hay crop was taken.' In addition the ■trial was continued for a season, without topdressing and hay yields were also secured for that year. Results were:-

The figures show that phosphate responses were considerable, with superphosphate giving the best yields. Ground Nauru rock phosphate, though giving definite responses in hay yields, produced lower yields than did superphosphate, though. with the progress of the trial it improved its position somewhat. Though there was no lime response in the trial, it appeared that Nauru phosphate was rather less effective on the limed plots than on the unlimed. This effect was consistent in all the hay crops. • Just before the hay crop of 1926 the superphosphate plots were the best in appearance, with a good dense sward and bottom growth. Nauru plots were comparatively poor, with many weeds. Haying Trials at Marion At Marton Experimental Area several long-term haying trials were conducted at this period to compare hay-growth responses to Nauru rock phosphate and other phosphates. The soil is Wanganui silt loam and is representative of large areas of farmland in the lower parts of the North Island. Moss’s Area In .this trial ground Nauru rock phosphate was 'compared with superphosphate, superphosphate and ; lime, lime, and basic slag. Each phosphate was applied at 3cwt. per acre yearly from 1925 to 1939 inclusive, except in 1927, when , there was no topdressing. Results were: —

GREEN WEIGHTS OF HAY MATERIAL (tons per acre) *1925Treatment (per acre) 26 and 1927-28 1928-29 1929-30 1930-31 Totals 1926-27 fLime (1 ton) .. .. 1.7 1.6 2.3 2.2 3.2 11.0 ILime (i ton) and \ „ superphosphate (3cwt.) 6.1 4.0 5.5 6.3 4.4 26.3 Superphosphate (3cwt.) 4.9 4.6 5.5 6.7 4.8 26.0 Nauru phosphate (3cwt.) 5.0 4.8 5.6 4.4 5.4 25.2 Basic slag (3cwt.) .. 5.8 4.8 6.8 4.6 4.7 26.7

There was a distinct hay response to superphosphate, as indicated by the comparison between superphosphate with lime and lime alone. The other phosphates, including Nauru, gave yields on the whole about equal to those of superphosphate. Nauru phosphate gave a low yield in comparison with that of superphosphate in 1929-30, but in the other years slightly outyielded superphosphate, especially in the last year in which yields were measured. Follett’s Area Superphosphate and ground Nauru rock phosphate were compared in this trial, but a third treatment was added consisting of fine Nauru rock phosphate dust collected at the grinding works. All three forms of phosphate were applied at the rate of 3cwt. per acre each year from 1927 to 1929 inclusive with these results:

GREEN WEIGHTS OF HAY MATERIAL (tons per acre) Treatment 927-28 1928-29 1929-30 1930-31 Totals Superphosphate .. .. 5.8 8.2 10.7 12.3 37.0 Nauru phosphate .. • • 4.1 8.4 10.3 11.6 34.4 Nauru phosphate dust .. 3.7 7.1 10.4 12.2 33.4

The plots treated with Nauru phosphate showed a distinct improvement after the first year and yielded almost as well as the superphosphate plots. Superphosphate yielded the greatest total over the 4 years, but its superiority was marked only in the first year. The Nauru rock phosphate dust gave yields similar to ordinary ground Nauru rock phosphate. Fineness of Grinding In 1924 two trials were begun in which two grades of fineness of grinding of Nauru rock phosphate were compared. The first grade was of normal fineness and the second was somewhat more finely ground. In the first trial the phosphates were applied only once, in June 1924 at the rate of 3cwt. per acre. Hay weights were obtained in 1924-25 and in 1925-26. In the first year the . plot treated with ordinary phosphate yielded 4.7 tons of green hay material per acre, the plot treated with finely ground phosphate 4.3 tons, and the untreated control plot 3.8 tons. Weights of material are not available for 1925-26, but both forms of Nauru phosphate had a more marked effect than in the first year. Over the 2 years ordinary phosphate gave greater yields than the more finely ground fertiliser. The trial was not continued beyond this stage. In the second trial phosphates were applied in June 1924 at 3cwt. per acre. In May 1926 the dressings were reapplied. In the 3 years of the trial five hay cuts were secured. The plot treated with ordinary Nauru phosphate yielded a total of 38.1 tons of green material per acre, the plot treated with finely ground material 38.2 tons, and the untreated control plot 33.6 tons. In each of these two trials the yields reflected a response to phosphate, but the special fineness of grinding had no apparent advantage. Brice’s Area

A long-term haying trial was conducted comparing various forms of phosphate. The treatments were not all strictly comparable because of differing dates of application before 1924, but from that date onward treatments were all applied at the same time. The materials compared were superphosphate, ground Nauru rock phosphate, basic slag, and North African phosphate, which were applied in 1924, 1926, and 1929. In addition the superphosphate plots received 1 ton of carbonate of lime per acre in August 1921. Results were: —

GREEN WEIGHTS OF HAY MATERIAL (tons per acre) Treatment 1924.25 1925-26 1926-27 927-26 928-29 1929-30 1930-31 Totals (per acre) SuperphosP 2cwt.)' 5.8 5.5 8.5 5.3 5.2 ' 7.4 6.3 44.0 Nauru ' U h cwt ) j ate 4.1 4.1 5.9 6.5 8.6 7.3 7.9 44.4 Ba (4cwtJ g 4.3 2.2 6.2 5.1 4.5 5.5 6.4 34.2 North • African phosphate 3.8 2.1 4.5 ' 7.9 7.2 5.8 7.0 38.3 (4cwt.) 3.8 2.1 4.5 7.9 7.2 5.8 7.0 38.3

The figures show that 2cwt. per acre of superphosphate had a quicker though shorter-lived effect than 4cwt. per acre of Nauru phosphate. The yield responses to superphosphate are well marked in the hay crops in the summers following the topdressings, with correspondingly welldefined depressions in the years of no topdressing. There are no such trends in the plots treated with Nauru phosphate, where successive yields show a steady, almost regular increase. The North African phosphate also showed this trend, though to a less extent. The total hay weights over the seven crops weighed are practically equal from the superphosphate and Nauru phosphate plots. On a basis of phosphate content superphosphate was applied at less than half the rate of ground Nauru rock phosphate. Haying Trials at Alfredton A haying trial was begun at Alfredton, in the Wairarapa district, in 1921. It was conducted on browntop pasture in an attempt to encourage the better grasses and clovers by topdressing. The soil was described as a white papa clay, rather impervious to drainage. Soil tests indicated that the lime requirement of the area was about 2| tons of carbonate of lime per acre. Superphosphate,. Nauru rock phosphate, and North African phosphate were each applied at 2cwt. per acre. In addition half of each plot was topdressed with carbonate of lime at 1 ton per acre. Though no subsequent topdressing was applied, hay weights were obtained for 2 years, with the following results: —

GREEN WEIGHTS OF HAY MATERIAL (tons per acre) Treatment 1921-22 1922-23 Totals Control .. .. . . • • 2.2 5.8 8.0 Superphosphate .. .. .. ; 7.0 10.0 17.0 Nauru phosphate .. .. ■ ■ 5.5 8.8 14.3 North African phosphate .. .. 3.0 7.9 10.9 .Superphosphate and lime .. .. 8.0 13.0 21.0 Nauru phosphate and lime .. .. 6.0 6.7 • 12.7 North African phosphate and lime 4.0 5.7 9.7

Yields showed a marked response to phosphate in the first crop -after topdressing, with superphosphate outstanding but Nauru phosphate also giving a large increase. The addition of lime was beneficial. In the second year, though no further topdressings were applied, responses continued to show in hay weights, with superphosphate giving best results. The addition of lime was of decided benefit with superphosphate, but had a depressing, effect with Nauru and North African phosphates. Mowing Trials Since 1930 newer techniques for measuring pasture production by mowing trials - have been used, enabling measurement at all seasons in conditions resembling those of grazing pasture. Two such trials involving the use of Nauru rock phosphate have been conducted at Marton Experimental Area. A mowing trial was begun in 1939 to compare the pasture production from plots topdressed with different forms of phosphates, including superphosphate and ground Nauru rock phosphate. The phosphates were applied annually at the rate of 4cwt. per acre from 1939 to 1944 inclusive. The Nauru phosphate was a well-ground product of which 95 per cent, passed through a 100-mesh sieve. No lime was applied. The annual pasture production figures were: —

GREEN HERBAGE PRODUCTION (lb. per acre) Year Control Superphosphate phosphate ■ 1939- .. .. 31,587 -4-5,070 -1-2,920 1940- .. .. 45,575 --7,616 --4,356 1941- .. .. 68,857 --7,103 --6,634 1942- .. .. 39,446 --6,141 --5,578 1943- .. .. 33,523 -f-6,516 -f-5,445 1944- .. .. 58,927 -4-12,451 4-10,866 Totals .. .. 277,915 + 44,897 +35,799 Relative production of ] dry matter for total period . . .. 100 116 113

Both fertilisers gave greater pasture production than the control, but superphosphate gave a greater increase than Nauru phosphate, though in some years its superiority was not marked. From the statistical analysis of the trial this superiority of superphosphate is statistically significant in 1940-41 and also in the total over the 6 years , of the trial. It may be concluded from the result of this trial that ground Nauru rock phosphate gave almost as high production as did superphosphate when both were applied annually for 6 years at the rate of 4cwt. per acre. At Marton Experimental Area a mowing trial was begun in 1940 to compare pasture production from treatments of superphosphate, serpentine superphosphate, and a hot mix of 3 parts of superphosphate and 1 part of ground Nauru rock phosphate. The phosphates were applied at the rate of 4cwt. per acre annually from 1940 to 1945 inclusive. Pasture production yields were:—

GREEN HERBAGE PRODUCTION (lb. per acre) Sprnpntinp Superphosphate Year Superphosphate su — t . te and superphosphate Nal|ru phosphate 1940- .. .. 58,212 —852 —6,492 1941- .. .. 86,664 —156 —4,428 1942- .. .. 45,060 —432 —1,932 1943- . . .. 47,268 ' —1,296 —1,968 1944- .. .. 64,596 —l2O —5,436 Totals .. . . 301,800 —2,856 —20,256 Relative production of dry matter for - total period .. 100 98 92

Observational Trials In 1940 a series of observational topdressing trials was begun to compare superphosphate with ground Nauru rock phosphate and 3 : 1 hot mix of superphosphate and ground Nauru rock phosphate. The plots received annual topdressings of phosphate at the rate of 3cwt. per acre. In addition carbonate of lime was applied to half of each plot at the rate of 1 ton per acre initially and scwt. per acre annually thereafter, so that the phosphates were compared in both the presence and the absence of lime. The Nauru rock phosphate was a well-ground material of which 95 per cent, passed through a 100-mesh sieve. The effects of the fertilisers were judged by allotting marks according to visual responses in comparison with unfertilised control plots, the following scale of points being used: 0, no difference from no manure; 1, slight difference; 2, fair difference; 3, good difference; 4, very good difference; and 5, excellent difference. The trials were continued throughout New Zealand for several years and most of the plots received at least three annual topdressings of fertiliser. On visual evidence superphosphate was generally judged superior to both Nauru phosphate and the superphosphateNauru phosphate mix." The mix tended to be intermediate between superphosphate and Nauru phosphate.

PERCENTAGE OF TRIALS IN WHICH SUPERPHOSPHATE WAS SUPERIOR BY AT LEAST 1 POINT On unlimed On limed ground ground Compared with ground Nauru rock phosphate .. .. .. 69 76 Compared with superphosphateNauru phosphate mix .. .. 25 36

RELATIVE MAGNITUDES OF RESPONSES (per cent.) Fertiliser Nil Slight Fair ' On Superphosphate 20 42 38 ' unlimed Nauru phosphate 6 80 13 1 ground Mix 2 31 55 12 On Superphosphate . 3 33 64 limed Nauru phosphate 5 57 26 12 ground Mix 13 47 40

Cumulative Effects In plots which received regular annual topdressings over the duration of the observational trials only a small percentage showed that ground Nauru rock phosphate gained relatively on superphosphate as time passed, and the superphosphate-Nauru phosphate hot mix tended to become progressively less effective than superphosphate on the limed plots.

RELATIVE POSITIONS EARLY AND AT FINAL STAGES OF TRIALS PERCENTAGES OF TOTAL TRIALS rATrrnpv Ground Nauru rock SuperphosphateuAitfaUKY phosphate Nauru phosphate mix Unlimed Limed Unlimed Limed Definitely improved in relation to superphosphate .. .. .. 16 18 7 '8 No change .... 80 76 90 75 Definitely deteriorated in relation to superphosphate .. .. .. 4 .6 3 'l6

In the “definitely improved” category in only one instance was Nauru phosphate better than superphosphate; that was on unlimed ground. The superphosphate-Nauru phosphate mix was better than superphosphate on only six occasionsfour times on unlimed ground and twice on limed ground. Residual Effects In some of the trials observations were continued for several years after topdressing had ceased. Surprisingly good responses were maintained in the two trials on which observations were continued for 4 years. In one (at Paemako, Waitomo County) both superphosphate and superphosphate-Nauru phosphate mix were showing good responses and the Nauru phosphate response was inferior on both limed and unlimed plots. In a trial at Ahuroa, on gumland soil, the phosphates were showing equal responses, slight in the absence of lime and fair on the limed plots. Four trials were continued for 3 years after topdressing had ceased. In a trial at Mairoa at the final inspection Nauru phosphate was still showing a slight to fair response, not affected by presence or absence of lime; this was the only fertiliser effect showing. In a trial in the Matapiro (Hawkes Bay) district, though no difference was apparent between the phosphates on unlimed plots, in the presence of lime both superphosphate and superphosphate-Nauru phosphate mix gave better responses than Nauru phosphate. In the trials at Warkworth and New Plymouth all the phosphates gave fair to good responses, especially on the limed plots, and there were no definite differences. Five trials were continued for 2 years after the final topdressing. At Waihi on medium to light volcanic loam superphosphate, though showing fair response, was inferior

to both Nauru phosphate and superphosphate-Nauru phosphate mix, rather more markedly in the absence of lime. On a semi-podzolised light pumice in the Waihi district all the phosphates were giving fair responses on both limed and unlimed plots, with no definite differences. At Tuakau there were only slight responses to the phosphates without lime, but on limed plots Nauru phosphate, though showing a fair to good response, was inferior- to the other phosphates, which showed good to very good responses. At Waitawheta (Ohinemuri County) superphosphate was still giving a good response much superior to that of either Nauru phosphate or superphosphate-Nauru phosphate mix, this result being unaffected by presence or absence of lime. At Hawera superphosphate and Nauru phosphate gave equal, slight responses, both with and without lime; super-phosphate-Nauru phosphate mix was not assessed.

RESIDUAL EFFECTS OF FERTILISERS No lime Lime Length of Superb Supertimp after . .. phos- phoSlast ton Locality Super- phate- Nauru Super- phate- Nauru Hrpcsinn phos- Nauru phos- pnos- Nauru phosJ phate phosphate phate phos phate phate phate mix mix 4 years J Paemako 21 21 J 31 . 3 11 | Ahuroa H | 1 1 2 | 21 . 2 I Mairoa 0 0 11 0 0 11 | Warkworth 11 2 H 2 21 2 3 years I New Plymouth 22 11 3 3 21 Matapiro i 11 2 11 j Waihi (medium to light volcanic loam) 11 3 3 2 3 31 Waihi (semi2 years podzolised ( ■ •light pumice) 11 2 11 21 22 Waitawheta 3 113 11 Tuakau 1 1 1 4 31 21 Hawera 1 1 1 1

In these trials ground Nauru rock phosphate showed no general superiority in residual effect over superphosphate or superphosphate-Nauru phosphate hot mix. Further Investigations The trial evidence summarised on page 183 is by no means complete, and extensive work is now being undertaken to investigate the effect of such aspects as greater fineness of grinding of Nauru rock phosphate, heavy initial dressings of Nauru phosphate, incorporating Nauru phosphate in the soil compared with applying it to the surface, and mixtures of superphosphate and Nauru rock phosphate in varying proportions. A more comprehensive survey will be made of the effects of Nauru rock phosphate on various soil types.

* The weights given are the sum of 2 years’ crops, t Applied only in 1925 and 1929. t Lime applied only in 1925.