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New Zealand Journal of Agriculture, Volume 84, Issue 1, 15 January 1952, Page 5

Experiments have shown that lime is generally . slow in moving down through peat. , Three years after a pasture had been topdressed with 4 tons of lime per acre very little lime below the surface 2in. could be detected by analysis. Thus heavy or repeated dressings of lime may not be any more beneficial than an initial application of, say, 1 or 2 tons per acre. In an experiment on acid peat the application, to the pasture of 2 tons of lime per acre gave results practically no better than those obtained from 1 ton of lime. The application of 1 ton of lime per acre was sufficient to raise the pH of the top inch of peat, and the heavier application was no better because the lime did not get down to the deeper layers where it was particularly required. Because lime is so slow in moving down, it is considered desirable to work it into the peat before the pasture is sown; the roots of the pasture plants may then go down as far as possible instead of being confined to the surface inch or so, which frequently happens with pastures on raw peat. A deep rooting system is perhaps even more desirable on peat than on normal mineral soils, because the weight of dry material in peat is very much less . than that in a similar volume of mineral soil. Therefore to enable them to have access to adequate quantities of available nutrients and water plants on peat require a greater volume in which to root. Effect of Peat on ant Roofs The effect of peat on the rooting systems of plants was strikingly demonstrated by an examination last February of lucerne roots in peat the surface layers of which were well decomposed. The area had been limed and topdressed and the analyses given in Table 1 show that the peat near the surface had a satisfactory pH and was well supplied with nutrients. Below 6in. the peat was very acid and deficient, in the major plant foods. It is not surprising that under these conditions the lucerne plant had changed its normal rooting habit and that the taproot went down about sin. only and

then grew horizontally, as shown on the right of the illustration on page 9. Although water could be squeezed out of the raw peat 9in. below the surface, the top 6in. were extremely dry, because all the available water had been removed by the lucerne roots and by evaporation. The unfavourable conditions in the deeper layers prevented the roots going down to the moist peat, and the crop had practically stopped growing ' through lack of water. However, the farmer kept it growing vigorously by spray irrigation and obtained two more cuts before winter, whereas in the previous year, without irrigation, there was very little growth after December.

Although lime is slow in working down through peat, recent experiments have shown that there is a slight loss in the water draining through 18in. of peat in lysimeters. Pasture ,was sown in the lysimeters after lime, at the rate of 3 tons per acre, had been worked into the top sin. of peat. Results so far available show that for the first 7 months calcium salts equivalent to 301 b. per acre of limestone have been recovered in the drainage. Even if the downward movement of lime were continued at this rate for several years, it would be negligible relative to the 1 or 2 tons per acre required to ameliorate raw peat to a depth of 3 or 4in. The successful establishment of a good ryegrass-white clover pasture on relatively undrained, acid peat 30ft. deep on the experimental area in the Rukuhia swamp is partly attributed to the incorporation of lime into the peat before sowing. This pasture, on an area which was previously practically waste land, is shown in the coloured reproduction of a photograph on the cover of the August

1951 issue of the “Journal”. Portions of the area before and after pasture establishment are shown in the illustrations below. After the manuka had been cut and burnt the peat was topdressed with 2 tons of lime per acre and then ploughed about 9in. deep. A further 2 tons of lime per acre were applied to the ploughed surface and disced in. Two hundredweight of serpentine superphosphate and lcwt. of muriate of potash were topdressed on the surface and the area was sown in April 1950 with a mixture containing perennial ryegrass, short-rotation ryegrass, cocksfoot, Yorkshire fog, paspalum, white clover, red clover, and Lotus major. Copper sulphate was also applied. The effect of the total application of 4 tons of lime per acre on this very acid peat is shown by the following figures: —

The application of 4 tons is not a general recommendation for use in peat development, because in practice the peat cultivated by the average farmer is less acid than that on the experimental area. Inquiries regarding the lime required on any particular - area should be referred to the local Instructor in Agriculture. Bare Patches in New Pasture Bare patches frequently develop in new pasture sown on peat. In time these patches become covered with sorrel, moss, or weeds, and may remain practically worthless for pasture production until the paddock is resown. The nature of the bare patches which developed were studied in the pasture sown on acid peat in the experimental area in the Rukuhia swamp in April 1950. When the new grass was up there appeared to be bare patches in the paddock, but this deceptive appearance was due to the smaller

size of seedlings on the drier hummocks where germination • was slower. Six weeks after sowing there was little difference between the hummocks and the hollows, and counts of 250 clovers and 500 grasses per square yard were obtained. Subsequent counts showed a decrease in the numbers, particularly in the clovers. At the last count (August 1950) there were about 100 clovers and 350 grasses per square yard. As the pasture was not sown until 24 April, some loss of clovers through frost lift was to be expected. By July bare patches started to develop in the paddock and became progressively more noticeable during August and September with the spring growth. Analyses showed that these bare areas were more acid and more deficient in lime than adjacent areas carrying good pasture. The bare areas were generally in strips across the paddock and were attributed to portions being missed when the lime was applied after ploughing. The surface at this stage was too soft to hold the narrow wheels of the topdresser, so the lime was put on by a rotary distributor attached to a trailer on aeroplane wheels. Apparently some runs with the distributor were too far apart, leaving strips with little or no lime and where the peat was too acid for the survival of the seedlings which had germinated. Strips of Good Clover Growth As the pasture improved in November and December the paddock became marked by another series of more frequent strips across the paddock. These were strips of good clover growth several feet wide and about 20ft. apart that were attributed to the heavy application of lime which fell immediately behind the rotary distributor. The lanes in between, corresponding to the edges of adjacent runs with the distributor, had sufficient lime for the establishment of Yorkshire fog, ryegrass, and some clover, but not enough for good clover growth. The lime thrown to the sides of each run would include the coarser particles . which according to the figures in Table 2 are much slower than fine material in reacting with acid peat. Similar weights of the various. fractions of lime were mixed with peat and the pH was determined on the same day, after 5 weeks, and again after 10 weeks. After being

mixed with the lime the peat was moistened with water and kept in stoppered flasks to prevent its drying out.

The results set out in Table 2 show that coarse lime has very little effect

on the peat, even after 10 weeks, whereas the fine material reacts immediately. This suggests that coarse lime, even if applied in sufficient quantity, may be so slow in reacting , that clover seedlings may germinate and then die before the pH is raised sufficiently for their survival. The minimum pH figure for good pasture establishment has not yet been determined. Peat at pH 4 is too acid, and pH 5 is satisfactory, but higner figures would be better. The minimum figure is probably about pH 4.7. If a distributor which throws the coarse particles to the outside is used, the runs should be close enough to give sufficient overlap to ensure that the . whole area has a dressing of at least some of the finer material. Importance of Even Distribution As most unimproved peat is deficient in plant nutrients, evenness of distribution of fertilisers is equally important. In one portion of the new pasture there was a poor strip which according to appearance and analyses was obviously suffering from phosphate deficiency. Apparently this strip had been missed when the serpentine superphosphate was put on by hand before the pasture was sown. ■ To enable the topdresser to be used, on the cultivated peat so that the lime and fertilisers could be distributed more evenly in subsequent experiments wooden cleats were attached by U bolts to the rims of the wheels of the topdresser. Ten cleats each 14in. long of 4in. x lin. hardwood were used on each wheel. The topdresser, fitted with these attachments, as shown in the illustration on page 9, was able to travel over soft peat in winter without difficulty. With only 10 cleats on each wheel the topdresser bumped somewhat when in motion,

thus giving an uneven flow of fertiliser. It would be better to have either extensions to the wheels or more cleats closer together. . By using similar extensions, bolted on to the plates of the tracks of tracklaying tractors, farmers and contractors have been able to work on soft peat, on which the machines would otherwise become bogged. A 5-g-ton tractor was able to work on very soft peat when it was fitted with extensions 31in. long. Tractors fitted with these extensions cannot be manoeuvred quite as easily and more care has to be taken in turning, particularly on hard ground or in timbered peat. When pasture is sown on acid peat both lime and fertilisers must be distributed evenly. The distribution of the lime should be even in both quantity and particle size. Topdressing of Established Pasture Information on the quantities of phosphate and potash required to obtain best results on good established pasture is being obtained from trials conducted by Instructors in Agriculture in various parts of New Zealand in addition to the experiments at the Soil Research Station. Different results are obtained according to the nature and fertility of the peat. It is simply a question of maintaining in the peat a balanced supply of the nutrients necessary for plant growth. Heavy applications of one fertiliser are of little value if the deficiency of another fertiliser is the main factor limiting plant growth. Generally peat is deficient in available potash, but if the available phosphate is also low, as in areas recently brought in from the raw state, or in a decomposed peat with high phosphate fixation, little benefit is obtained from heavy applications of muriate of potash unless heavy rates (more than 4cwt. per acre) of phosphate are also

applied. The results from the experimental area sown in April 1950 illustrate this point. When this area was topdressed in September 1950 it was found that 2cwt. per acre of potash ■ was little better than lcwt. when each was applied with 2cwt. of serpentine superphosphate. However, when various quantities of phosphate each mixed with 2cwt. of potash were applied 4cwt. of phosphate gave .excellent results, 2cwt. of phosphate was intermediate, and the plots with no phosphate were poor. These results con-

sidered in conjunction with analyses of the peat indicate that the low available phosphate limited the response to the potash. Two hundredweight per acre of serpentine superphosphate did not raise the phosphate status sufficiently to enable the heavy potash topdressing ,to be of much benefit. Results of Potash Topdressing In other areas where the soil phosphate had been built up by consistent topdressing and had not been rendered unavailable by fixation good results were obtained from 2cwt. or more per acre of potash when applied with moderate quantities of phosphate. The results obtained by the Instructor in Agriculture, Matamata, from trials on Hungahunga peaty loam near Te Aroha, are an example. An application of lcwt. per acre of muriate of potash gave 100 per cent, increase in yield of pasture, compared with no potash, and 2|cwt: of potash gave 170 per cent, increase. This was on an area which had received 12cwt. per acre of phosphate fertiliser during the previous 3 years and where the available phosphate in the peat was high. Thus big responses were obtained from heavy rates of potash when applied with only 11 cwt. of superphosphate, and heavier applications of phosphate did not increase the yields appreciably. However, this is not typical and most of the other peat experiments have shown that increasing the phosphate to 6cwt. per acre, and in some instances to 9cwt., is beneficial. Peat is not always low in available potash and ■ responsive to topdressing with muriate of potash. In an experiment in Southland in which no response to potash was obtained analyses showed that the peat was high in available potash. The response to any given mixture of phosphate and potash and the proportions of these which will give the best results are governed by the relative quantities of the available nutrients in the peat. This may appear an obvious general statement. However, it -applies more to peat than to mineral soils, because the latter have a big

reserve of minerals which may become slowly available to plants, whereas peat has much less mineral matter. The difference in content of mineral matter or ash is clearly shown in Table 3. Thus the supply of available nutrients in peat depends more on the topdressing than that in mineral soils. Consequently pasture on peat is liable to deteriorate more rapidly than that on mineral soils if topdressing is discontinued or if the correct fertilisers are not applied.

Recommended Topdressing Mixtures It is difficult to say what is the best fertiliser mixture for any peat area without a knowledge of the quantities of available nutrients already in the peat, and analyses of the peat are therefore of great assistance. Requests for sampling for analysis should be referred to the local Instructor in Agriculture. Owing to present staff limitations only a limited number of peat farmers may be able to receive advice before the next topdressing, and for the guidance of the others some recommendations are desirable, although it is very difficult to make general statements covering all types of peat and all districts. It is suggested that a mixture of 3cwt. of phosphatic fertiliser and lcwt. of muriate of potash per acre be regarded as a standard topdressing mixture for peat. This should be modified according to the particular conditions as follows: — If the peat has had less than 6cwt. of phosphatic fertiliser in the 2 previous years, more phosphate than the 3cwt. in the standard mixture should be applied. If the peat has had more than 6cwt. of phosphatic fertiliser in the 2 previous years, the potash in the standard mixture could be increased. The potash in the standard mixture could be omitted if potash is known to be of no benefit in the district concerned or if the clovers in the pasture are growing vigorously without potash topdressing. The position may arise where clover growth has been good in the past without potash being used, but deterioration of the pasture, though so gradual that it is not obvious, is suspected. Naturally it is not desirable to wait until deterioration of the pasture has reached an advanced state, and if the onset of potash deficiency is suspected, the advice of the Instructor should be sought or the farmer could conduct some trials himself. One

pound of muriate of potash (or. any other fertiliser) put on a strip 1 chain long and Iyd. wide is approximately equal to an application of 2cwt. per acre. - These recommendations are tentative only and may have to be revised as more information is available regarding the topdressing of peat, and they may require modification to suit particular circumstances. In the various experiments there has been little difference in the results obtained from superphosphate and serpentine superphosphate, and the term phosphatic fertiliser has been used in this article to include both these fertilisers. Results are not yet available from the recent “super, compound” on peat, but in the meantime it may be assumed that the quantities given for phosphatic fertilisers apply also to “super, compound”. Generally it is considered better to topdress peat in spring than in autumn. When the peat dries out severely in autumn so much rain is required to re-wet it adequately that by the time it is sufficiently wet for good pasture growth the weather is so cold that temperature is a limiting factor. Under these conditions autumn topdressing may not have much effect on pasture growth and there is a danger that the phosphate may become fixed and the potash leached down below the root zone before the temperature and moisture conditions in the spring are suitable to enable the pasture to utilise the added fertiliser. Other Experiments In addition to the trials with lime, phosphate, and potash, experiments have been conducted at the Soil Research Station with nitrogenous fertilisers. Early-spring applications of sulphate of ammonia gave outstanding responses on new pasture on peat, but there was a subsequent depression

of clover growth except on a portion of the nitrogen-treated area which was spray irrigated. On peat land where nitrogen deficiency is so acute nitrogenous fertilisers may have an important role in stimulating the growth of grasses during the establishment stages before the clovers are able to supply sufficient nitrogen. Further experiments along these lines will be carried out on new grass next winter. Nearly every year on most soils of New Zealand pasture growth during a portion of summer and autumn is limited by lack of water, and this effect is usually more prolonged on peat land because of the difficulty in re-wetting the dry peat. . In an experiment on decomposed peat in which pasture growth was measured it was found over two seasons that there was very little growth after the peat dried out in January until the following spring. Therefore considerable attention has been devoted to moisture relationships in peat and methods of maintaining adequate available moisture in the zone in which the pasture plants root. On the pasture sown on the deep peat on the Rukuhia swamp in April 1950 an endeavour was made to maintain a high water-table during summer and autumn. The side drain was • blocked at intervals and kept full of water from an adjacent bore and the water was reticulated through the. peat by mole drains. Owing to blockages in the moles caused by timber and the fine sludge and because of the unevenness of the surface the high watertable could not be maintained over the whole area. However, where the peat was kept moist and topdressed with sufficient phosphate and potash production was at a remarkably high level and equalled that of spray-irrigated pasture on clay loam. This work will be described in more detail when further results are available. Although there is still much to be learnt regarding the development of peat land and some of the projects are necessarily long term, the results so far obtained have already assisted many farmers on peat land in improving their pastures and using the money available for fertilisers to the best advantage. . ,

Depth of sample pH Calcium Phosphate Potash in. 0 to 3 6.3 High Very high High 3 to 6 5.4 Medium Medium Very low 6 to 9 4.4 Very low Very low Very low 9 to 12 4.1 Very low Very low Very low

TABLE 1—ANALYSIS OF PEAT FROM LUCERNE PADDOCK

Depth of pH of peat sample pH of peat Unlimed Limed in. 0 to 2 . . . . 4.3 ' 5.4 2 to 4 . . .. 3.9 4.7 4 to 6 . . .. 3.8 4.4

pH of peat Fineness of 1 5 10 grinding of lime day weeks weeks No lime .. 3.7 3.7 3.7 Retained on 8 mesh 4.0 3.7 4.3 Passed 8 mesh, retained on f6 mesh .. .. 4.0 4.1 4.5 Passed 16 mesh, retained on 30 mesh .. .. 3.9 4.2 4.8 Passed 30 mesh, retained on 60 mesh 4.0 4.7 5.3 Passed 60 mesh, retained on 120 mesh .. 4.0 5.1 5.2 Passed' 120 mesh .. 5.5 5.3 5.0

TABLE 2- EFFECT OF FINENESS OF GRINDING OF LIME ON pH OF PEAT

Weight Weight of Weight of mineral matter dry peat or Mineral (ash) soil per acre matter per acre Description 0 to 3ln. (ash) 0 to 3in. lb. per cent. lb. Very raw peat 50,000 5 , 2,500 Partly decom posed peat . 200,000 30 60,000 Peaty loam . . 350,000 60 210,000 Clay loam . 500,000 90 450,000

TABLE 3-MINERAL MATTER IN PEAT AND LOAM SOIL