Topdressing in Eastern Bay of Plenty

New Zealand Journal of Agriculture, Volume 93, Issue 6, 15 December 1956, Page 589

Topdressing in Eastern Bay of Plenty

TOPDRESSING is an important pasture management practice in eastern Bay of Plenty. Several soils; require potash as well as phosphates, and on some soils the improvement effected by superphosphate applications has been due in part to the sulphur supplied in superphosphate as calcium sulphate. This article by S. R. Hewitt, Instructor in Agriculture, Department of Agriculture, Whakatane, describes the soils and topdressing practices in Opotiki and Whakatane Counties and discusses the results of topdressing trials in relation to information supplied by the Department's advisory soil testing service.

THE eastern Bay of Plenty comprises the whole of Opotiki County and Whakatane County with the exception of Galatea and Murupara districts. The main agricultural area is the Rangitaiki Plains, which are approximately 8 to 12 miles deep and run some 12 miles along the coast west of Whakatane, and the rolling and hilly country which bounds the plains to the west and separates them in the east from the small area of alluvial flats at Opotiki. From Opotiki to Cape Runaway is a narrow strip of rolling to hilly country, which is backed by the steep Raukumara Range. : Farming .is confined mainly to the flat plains, valleys, and adjacent rolling country. Climate On the Rangitaiki Plains the annual rainfall is. about ..50in. The fall increases on the western hilly areas and on the southern/ high country the annual fall is about 60in. to 80in.; on the very steep country in from the

coast and leading up toward Cape Runaway it exceeds 80in. On the farmed country, therefore, the rainfall ranges from 50in. to about 70in. per annum. The monthly distribution, of rainfall is normally satisfactory. The greatest falls are recorded during winter and early spring. Frosts can be severe on the Rangitaiki . Plains in from the coast and along the valleys leading to Opotiki, but they are confined to winter. Land Use Farming naturally follows topography in the district, and the flat lands of the Rangitaiki Plains, with the fertile valleys of Opouriao and Waimana through Waiotahi to the Opotiki flats are almost entirely devoted to

dairying. Dairy farming is also carried out on the rolling country and low hills which fringe the valleys and plains between the coast and the higher hill country. Some of this potential dairying country is used for fat lamb raising and a small proportion of the steeper and poorer country developed from forest and scrub is used for the grazing of sheep and cattle. On the higher country in from Matata and including Manawahe mixed dairying and sheep farming is carried out. A few years ago in the Opotiki and Whakatane districts a large acreage was planted in maize for grain, but today small areas are grown and only as an adjunct to dairy farming. A considerable portion of the moderately hilly Tarawera ash country south of Te Teko has been planted in exotic pine forests. Pastures Paspalum is the dominant pasture plant throughout the eastern Bay of Plenty on the swamps and flats ■. and on the rolling to moderately hilly country. Where topdressing is regular white clover is the most common clover present, arid on lightly topdressed or untopdressed areas Lotus uliginosus {major), .suckling clover,, and. other annual- clovers are the dominant legumes. ' ■ '

Grasses associated with paspalum are varied, ranging from browntop, danthonia, and sweet vernal at the lower end of the fertility scale to ryegrass at the other end. With the exception of the pastures on the rich alluvial soils, ryegrass cannot compete with these other lower-producing grasses. The main factors contributing to the poor establishment of ryegrass in swards are, first, low fertility and secondly, insufficient moisture in summer. Occasionally on a moist, fertile soil paspalum has been allowed to grow rank in -summer and thus overshade and eliminate the ryegrass and white clover. As the area of moist, fertile soils is limited to the alluvial soils alongside the rivers and banks of old riverbeds, there are large areas of pastures on the Rangitaiki Plains which are dominantly paspalum and which produce very little growth from June to October and a very large amount from November until May, when paspalum is at its best. The introduction of short-rotation ryegrass, resowing, oversowing, the use of potash, and an appreciation of soil types in relation to the demands of the individual pasture species are factors all helping to level out this uneven growth curve.

Topdressing Opotiki County contains 112,000 acres of sown grass and Whakatane County 176,000 acres. Of this sown grassland 31 per cent, in Opotiki County was topdressed in 1952 and 68 per cent, in Whakatane County (see Table 1). A fair proportion of the sown grassland in both counties is on very steep country and will be topdressed only as aerial topdressing develops more in the area.

TABLE f—AREAS TOPDRESSED AS PERCENTAGES OF TOTAL SOWN GRASS ACREAGES Year Opotikl Whakatane per cent. per cent. 1931 12 50 1941 . 25 63 1948 28 59 1950 . . .. 31 67 1952 31 68 During the period covered in Table 1 the areas topdressed rose from 17,000 acres to 35,000 acres in Opotiki County and from 58,000 to 120,000 acres in Whakatane County. . For many years regular topdressing of pastures with phosphate fertilisers has been customary in the established dairy farming and fat lamb raising districts. Superphosphate or serpentine superphosphate is the phospha tic fertiliser mostly used today, and to a small extent basic slag is also applied, but the tendency is to use less of this type of manure. Rate of application is about 2cwt. to 3cwt. per acre and this amount is generally applied each

year. Today time of application is largely influenced by the rather irregular delivery of superphosphate, though the aim is to apply the fertiliser in autumn and early spring. There is a growing practice on the more established dairy farms to split the annual application and to apply two light dressings during the year. This is probably partly because more and more potash is being used each year throughout the districts and this fertiliser is generally applied in spring.

Rates of application of muriate of potash tend to be rather conservative, about |cwt. to lcwt. per acre. This is regarded as a maintenance dressing, and where soil potash levels are low heavier dressings are needed for the initial applications. Some farmers are applying potash on rolling to hilly country from the air, irrespective of whether the soil is known to be deficient. With the exception of sulphur, which is a normal constituent of superphosphate, it is not the rule to apply any of the usual trace elements for pasture growth. Both cobalt and copper are applied for animal health and there is an increasing demand for copperised superphosphate. Liming is not a regular practice on the average farm and it is uncommon for rates to exceed lOcwt. per acre when the lime is applied in bulk form, which is the usual method of application today. The demand for lime is spasmodic throughout the districts and there are many farms that have never been dressed with it, though some have had it applied occasionally. Aerial topdressing is well supported by hill country farmers as well as those on the easier country. It has almost completely replaced other methods of topdressing on such areas, though its full development is limited by the difficulty of establishing airstrips for access to much of the steeper country.

Soils Whakatane and Opotiki Counties have been covered by a number of volcanic ash showers (Whakatane, Kaharoa, and Tarawera showers) which have given weakly weathered soils. The Tarawera shower resulted from the eruption of Mt. Tarawera in 1886 and the ash was deposited over the country to the north-east of the mountain. This ash, which covers a large part of the Rangitaiki Plains, fades out toward Whakatane, covers the hills of Rotoma and Manawahe, and extends south toward Galatea. The bulk of this ash consists of small particles of black, scoria-like material the size of fine gravel which has not yet weathered. It is basalt, and is therefore likely to form a fertile soil in years to come. At present it is droughty and of moderate or rather low fertility. The Kaharoa shower is a pumice soil. It extends east to the Whakatane

River, appearing in the neighbourhood of Galatea and Te Whaiti, and covers the country in a north-wes* direction toward Tauranga. It is darl grey and rather coarse and sandy. The oldest of this group of ash showers is the Whakatane shower. From Whakatane to Opotiki and east as far as Te Kaha along the coast all but the steep slopes are covered in this ash. It is brownish, tending to become much darker as the organic matter content increases, is of medium texture, and forms a soil of high potential fertility. The subsoil is a yellow-brown loam which is friable and has a fairly high clay content. This volcanic shower is a mixture of andesitic and rhyolitic parent material. On some of the steep and very steep slopes of the whole region rain has tended to wash away the deposited ash and thus has exposed the underlying original hill soils. These are generally derived from greywacke and are coarse sandy silts known broadly as skeletal soils. They are of low to moderate natural fertility. This Whakatane ash also occurs on the flats and in the valleys as alluvium and the soils thus formed generally have a low clay content and are free draining and easily worked. Soil Types For convenience the soils of the eastern Bay of Plenty have been grouped into four main classes: — 1. Flat country soils: — (a) Rangitaiki Plains: Silt loams from river alluvium; coastal sands;

coarse wind- and water-sorted ash soils; coarse dark-grey Kaharoa ash soils; gravelly Tarawera black ash soils; peaty loams. (b) Opotiki Flats: Deep and shallow silt loams. 2. Rolling to hilly country soils: Whakatane dark brown ash soils; Tarawera black ash soils. 3. Hill soils: Whakatane ash on the eastern hills; Tarawera ash on the mid-eastern hills; Kaharoa ash on the mid-eastern hills.

4. Steep and very steep hill soils: Skeletal soils. Fertiliser Trials From 1951 to 1954 a number of observational , fertiliser trials were laid down on various soil types in the eastern Bay of Plenty. The aim of these experiments was to secure information on pasture responses on different soils to topdressing materials either alone or in combination. Superphosphate or serpentine superphosphate, muriate of potash, and . lime were used in almost all the trials, and a number included basic slag, North African phosphate, Nauru rock phosphate, and common salt. Also 14 molybdenum trials using sodium molybdate were laid down on the, main soil types, and six trials with sulphur in the form of calcium sulphate (gypsum) were put down, mainly on Tarawera gravel soils. The phosphates were applied at 3cwt. per acre and sometimes at 6cwt., and the potash was sown at either lewt. or IJcwt., with repeat applications of each manure every year during the life of the trial. Lime was used at from 3cwt. to 1 ton per acre, depending on the soil type and thereafter annually at 3cwt. in most trials. Sodium. molybdate was generally applied either at 2oz. or 2Joz. per acre and calcium sulphate was used at 1001 b. per acre on most trials with some at 1501 b. or 2001 b. Soil Tests Soil samples were taken before the trials were laid down and the samples were tested for phosphate, potash, pH, and calcium. Potash was the most deficient element and generally the levels were low, but there were some medium and some high tests. Phosphate was less deficient and results varied from a few low tests to equal numbers of medium, satisfactory, and high levels. The samples were only moderately acid, fluctuating about a pH of 6.0 and ranging from a pH of 5.5 to 6.4 The test levels for available molybdenum varied somewhat in magnitude, but they were not considered to be low. In the pH scale the higher the figure is the less acid it is until a pH of 7.0 is reached, when the reaction is neutral; above this the figure indicates alkalinity. Trial Results The trials are now advanced enough to summarise the results which were determined by observing improvements in the pasture. Each trial is carried on for at least 2 years and many for 3 years or more. Observations were made at intervals and responses are indicated by a system of points ranging from 0 to 5, 0 indicating no visible difference from “no manure” and 5 indicating an excellent difference.

Response in these observational topdressing trials was seen in several ways:— 1. Increase in clover content of sward. 2. Increase in proportion of better grasses to poor grasses and suppression of weeds. 3. Improvements in density, colour, and vigour of sward. , 4. Evidence of grazing preference by stock.

The results of the topdressing trials are summarised in Tables 2, 3, 4, and 5; these results and those of the soil tests have been grouped according to soil type.

Table 2 deals with the soils derived from Kaharoa and Tarawera ash. In nearly all trials pastures did not respond very well to phosphates on plots which had not received potassic fertilisers. Unfortunately too few of the experiments had a potash-alone treatment; for this reason it is impossible to estimate how well the soil test for phosphate agrees with trial results. It is obvious, however, that the soil test for potash has reliably indicated deficiencies of this element.

No pasture responses occurred to molybdenum; none was expected. Lime responses are uncommon on mineral soils derived from pumice ash, but could occur on peaty soils. In fact a clear pasture response to lime in Experiment No. 1694 at pH 5.6 suggests that the peaty loams intermixed with Tarawera ash should be farmed at slightly less acid conditions, say pH 6.0.

Since in a field experiment on Tarawera ash soil good responses were obtained from superphosphate (which contains sulphur) and no responses were obtained from basic slag (which contains no sulphur), it was suspected that pastures on this soil may respond to sulphur.

Accordingly a trial to study sulphur was laid down. Gypsum was used as the source of sulphur and double superphosphate (which contains no sulphur) as the source of phosphorus. The belief that sulphur is important for pasture vigour was confirmed.

Double superphosphate alone resuited in weak, pale clover growth, and double superphosphate and gypsum resulted in vigorous clover growth. A further four trials were put down on this soil type and also one on an alluvial silt deposit soil, Two of the trials were on lucerne, but the gypsum did not give obvious results and this is probably because superphosphate, which is about half gypsum by weight, had been regularly applied previously by the. farmers on whose farms the trials were laid own ■ ’ „ J . , zrT , ~ \ , On the three trials (Table 3) where a good response to gypsum was obtained superphosphate was applied over the past few years at a rather light rate. Superphosphate is only economical for correcting sulphur deficiency when at the same time it is meeting a deficiency of phosphorus. Such a deficiency will exist in the early stages of topdressing such soils as Tarawera ash and for a longer period on pumice soils. The use of gypsum is likely to become important in future because

of the ready build-up of phosphorus in many soils compared to the high leaching rate of sulphur, TT , „ , , ~ . , . Herbage samples from the mammal treatments were analysed for sulphur and, with the exception of the samples ! rom an alluvial silt loam soil, those Hom the gypsum plots have increased ln . s " lpl ? ur , co „ nte ? t Tbe sulphur level of t e h . e^ ba from the control plots in , tw ,° tria^ s 1? low and tbls ls con “ " lste " t W 1 \ the + gyP®™ responses, Further sulphur trials are required on other soil types m the Bay of Plenty before the extent of sulphur deficient areas can be defined Table 4 gives the results of topdressing responses on soils of the Rangitaiki Plains. There is a wide variation ™ Phosphate and potash test. Results sh ? w , Quite good agreement with the p ° tash + test and also with the phosP. hate , test provided a lack of potasslum is not limiting growth. The slight lime responses on soils derived from recent alluvia and on peaty loam soils suggest that these soils should be farmed at about pH 6.0.

Table 5 gives the results from topdressing trials on rolling and hilly country. Soils generally show a response to potash and superphosphate or serpentine superphosphate. Soil Test and Topdressing Results With a few exceptions the relation between soil test and trial results seems a fairly consistent one within the main soil groups. The phosphate test needs further evaluation by experiments because frequently in past work neither, potash nor sulphur was eliminated in the experimental design as a possible complicating factor. In practice, however, soil test results are a valuable aid in advisory work because they supplement other information such as the past topdressing history of a field, its appearance, and its management. Topdressing Recommendations The results of the topdressing trials have been summarised according to soil type and it is now possible to recommend the quantities and types of topdressing materials for these soils. Since superphosphate or serpentine superphosphate, irrespective of soil type, has proved superior to other forms of phosphate, the picture is not a complex one. Though there is no material difference in the responses from these two manures, it is recommended that superphosphate because of its higher phosphate and sulphur content (which cannot be ignored) .should be used. In the pasture sward vigour of clover growth is a reliable criterion of the level of plant nutrients in the soil. Compared to the grasses clovers are shallow rooting and are thus the first species to suffer from a deficiency and conversely are the most rapid in responding. In this respect potash has been spectacular and the greatest responses have been obtained from applications of superphosphate plus potash. In observing responses in trials the trained eye can probably note a 15 per cent, or less response, and even when a slight response is obtained it is regarded as a payable one. On recent alluvial silt loams and certain terrace alluvia which have a higher natural fertility rates can be lower than elsewhere. A maintenance dressing at l|cwt. to 2cwt. of superphosphate is generally adequate. Some farms have not received any manure, yet do not appear to have suffered any deleterious effects. Potash where required should be applied at lewt. to l|cwt. per acre

for the first application, followed by an annual rate of lewt. for a few years, After this generally a maintenance dressing of |cwt. is sufficient. It appears that potash deficiency has been induced in these soils by regularly cutting the same areas each year

for silage and hay, by cropping, and by the practice of using day paddocks f or the milking herd. ‘ ~ „ „ , £1 _ P the swamp soils ox the Rangitaiki Plains and other farmed areas generally superphosphate rates should

be heavier, 2cwt. to 3cwt. per acre, though if the past history has been one of heavy rates, these can be reduced to 2cwt. for a period. When soils are being grassed down for the first time after scrub, as on the rolling and hilly country, at least 6cwt. per acre is needed within the first year, but following rates need then to be only 2cwt. to 3cwt. Soils on this type of country in their unfarmed state are naturally fairly high in available potash but low or very low in available phosphate. An example is Whakatane gravelly sandy loam (derived from Whakatane ash) and also Ohinepanea sand (Kaharoa ash). After some years of farming on the easier rolling country potash deficiency seems to spread; this is similar to what happens on the silt loams. Today, on the bulk of the soils of the plains, such as the Awakeri and Otakiri soils, Tarawera ash, peaty loams, and coastal sands, potash deficiency is widespread and in many cases whole farms need muriate of potash applications. Rates of IJcwt. an acre or more are needed to begin with and after this a regular rate of lcwt. per acre each year is generally needed. How long this should be maintained is determined by the results obtained. On these soils common salt, which can be bought fairly cheaply in New Zealand, can replace some of the potash used, but potash should not be omitted from the topdressing programme. A satisfactory mixture would be lewt. of each material. Salt in some soils appears to release potash from the soil complex and make it available to plants. On the heavier soils and on peaty soils some lime is needed. Because most lime is now applied in bulk form, it is best to apply it at lOcwt. per acre every 4 to 5 years. Overliming can do harm by making certain trace elements unavailable. On the lighter soils derived from volcanic ash it is doubtful whether lime is ever of any benefit. Time of application of quick-acting manures such as superphosphate and potash is generally related to the urgency of need for fresh growth. Superphosphate can be applied in autumn on those pastures to be closed for winter-saved feed, and some can be applied in spring either on the same areas or else on pastures that are to be closed for silage and hay and including those not treated earlier. Initially potash gives the best results when applied in the early spring, though repeat dressings can go on some areas in early autumn. Late autumn and winter applications should be avoided, as there is little growth then and much of the potash will either be lost or made unavailable by the following spring.

* ono response ?—doubtful; —slight; —fair; 3—good; 4 —very good; s—excellent, f Lucerne.

* o—-no response; doubtful; I—slight; 2—fair; 3—good; 4—very good; s—excellent.

* 0-no response; ?—doubtful; I—slight; 2—fair; 3—good; 4—very good; s—excellent.

Treatments Responses* Kaharoa ash soils Tarawera ash soils On peaty loam Sandy silt on Experi- peat ment ExperiNo. ment 1998 No. ty loam Experiment No. 2145 Sandy silt on peat Experiment No. 1765 Well drained Black sand Experi- Experiment ment No. No. 2162 2150 drained Experi- Experiment ment No. No. 2011 On peaty loam Experiment No. 2164 On gravelly Experiment No. 1998 Experiment No. 2145 Experiment No. 2162 2171 Black sand Experi- Experiment ment No. No. 2171 2 i 50 Experi- Experiment ment No. No. 2011 1694 On pea Experi- Experiment ment No. No. 1694 2163 ty loam Experiment Experiment No. No. 2163 Experiment No. 2164 On gr san Experiment No. 1791 ivelly d Experiment No. 1802 Superphosphate 1 2 o 2 1 2 Serpentine superphosphate 3 0 1 2 2 Basic slag .. .. 3 North African phosphate . . 3 1 0 Fine Nauru ... .. . Basic slag + potash .. .. .. 3 21 4 4 i i Serpentine superphosphate + potash . , U 91 3 31 Superphosphate + potash 2J 21 3 3 3| 3 4 4 3 34 Phosphate + salt .. .. > 21 24 3 3 34 — 2 3 4 4 3 34 1J Phosphate -f- salt + potash .. Potash alone .. o 3 o 3 11 1 4 Lime .. .. .. Lime -4- phosphate + potash . . 4 1 44 0 *2 2J 0 4 2.1 3 1 0 2 3 3 0 1 0 3 21 ? ? 0 2J 4 ? 0 4 3 0 0 3 34 0 31 Lime -f- phosphate 4- potash 4- molybdenum .. 3 31 4 Lime -4- phosphate -f- molybdenum Lime -f- phosphate . . Soil analysis Phosphate ..' Low Low Very High High Medium Medium Medium Medium Medium High Medium Potash .. low Medium Low low Medium Low Low Low f Low Low Low Low Medium Low pH . . 6.1 6.4 6.1 6.3 6.1 6.5 5.9 5.6 6.0 6.0 6.2 6.2 Molybdenum .. .. .. . .. . High Low to medium High

TABLE TOPDRESSING RESPONSES ON KAHAROA AND TARAWERA ASH SOILS

Experiment No. Soil Phosphate test Responses* Double superphosphate and potash Double superphosphate, potash, and gypsum 2167 Tarawera ash . . High 1 3 2331 Tarawera ash . . Medium 1 3J 2320 Tarawera ash . . Very high . . 1 1 . 12329 Tarawera ash .. High .. z 2 2321 Alluvial silt loam Medium li 4

TABLE 3—RESPONSES TO PASTURE TOPDRESSING WITH CALCIUM SULPHATE ON TWO SOILS ON RANGITAIKI PLAINS

Treatments Responses* Recent silt loams from alluvium Peaty Deep loams Gravelly Coastal sands Black sands Deep Shallow Sandy Experiment No. . Experiment No. Experiment No. 1794 Experiment No. 1710 Experiment No. 1800 Experiment No. 2177 1821 2176 1822 2149 2147 Superphosphate 1 0 11 31 0 . 1 1 0 1 Serpentine superphosphate . 0 ■ 1 Basic slag .. 0 North African phosphate 0 0 Fine Nauru 0 0 Basic slag + potash Serpentine superphosphate 0 4- potash .. 0 1 Superphosphate + potash Phosphate + salt .. 4 0 21 1 3 2 Phosphate + salt + potash Potash alone 0 0 i Lime .. .. .. Lime + phosphate i+ 1 ' 0 4 0 0 4 0 0 potash 4 0 3 1 3 Lime + phosphate 4potash 4- molybdenum 3 Lime 4~ phosphate + molybdenum 14 2 Lime 4- phosphate 14 2 11 Soil analysis Phosphate Very Med. Very Low Low High Low Med. High Low high Potash Med. Phosphate Med. Low Low High Low Med. High Low high Potash . .. Med.Med.- Med. High | High High Very Low Low Low high low pH 5.9 6.1 5.5 5.8 5.8 5.9 5.9 5.4 5.4' 5 9 5.9 6.4 6.4 6.2 6.2 Molybdenum .. .. High High | Low Lowmed.

TABLE 4—TOPDRESSING RESPONSES ON SOILS OF RANGITAIKI PLAINS

Treatments Responses* Soils of easy rolling to hilly country Soils of the hills Loamy Whakatane ash Sandy loam on yellow loam Experiment No. Kaharoa ash on Whakatane ash Gravelly sand on sandy loam Experiment Kaharoa ash On white pumice sand Tarawera ash On coarse Kaharoa ash Experiment Experiment No. No. Tarawera ash On coarse Kaharoa ash Experiment Experiment No. No. 1790 g 1789 1711 1790 g 1789 2012 N 2012 2155 N 0. 2155 2148 0. 1792 2178 1711 2179 1793 2148 1792 2178 2179 1793 Superphosphate 1 2 u 1 1 2 Serpentine superphos1 2 2 u 1 a 2 phate U phate . . .. 1 1 u 0 1 2 1 Basic slag 0 0 I North African phos0 0 a phate .. .. 1 0 Superphosphate + potash 9 Q potash 2 2 2 2 1 1 2 2 Serpentine superphos•7 2i 3 9X 21 ■“2 24 11 phate + potasli . 11 phate + potash - 3 Potash alone . . I Lime 0 0 ? ? ? 0 0 0 0 Lime + phosphate 40 0 ? ? ? 0 0 0 0 potash 3 potash .. 2 9 2 2 3 2 2 21 2 21 Lime + phosphate + potash -j- molybdenum 21 2 21 denum .. 2 2 2i 2 21 Lime + phosphate + molybdenum Lime + phosphate . . U Lime + phosphate .. la 0 2 2 0 2 2 2 2 2 Soil analysis High High Phosphate High High Med. Med. Low Med. High Low Potash High High Med. Med.Med. Low Low High Med. Low Iiigh Med. Low Low High Med. Low pH 6 1 5.9 5.9 5.5 high 5.5 6.1 6.1 6.1 6.1 5.9 5.9 5.9 5.9 6.0 6.0 6.3 6.3 5 7 5.7 Molybdenum High High Med.high Med.high

TABLE S—RESPONSES TO TOPDRESSING ON ROLLING AND HILLY COUNTRY