Interim Report on Soils of Wairarapa Valley, New Zealand
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INTERIM REPORT ON SOILS OF WAIRARAPA VALLEY, NEW ZEALAND Compiled by J.C. HEINE From data by H.S. GIBBS &J.D. COWIE lit. B. MILLER N,Z, SOIL BUREAU RECORD 40 DIAECTOO, Department of Scientific and Industrial Research, New Zealand 1975 '(.· New Zealand Soil Bureau Records were previously New Zealand Soil Bureau Information Reports The information, map and extended legend in this record are interim only, and may not be quoted or cited without the permission of the Director, Soil Bureau, Lower Hutt A.R. SHEARER, GOVERNMENT PRINTER, WELLINGTON, NEW ZEALAND - 1975 3 CONTENTS Introduction 5 Physiography 5 Climate 6 Rainfall 6 Wind 6 Temperature 6 Vegetation 7 Soils 8 Soils of the Western Ranges 8 Soils of the Central Plain 8 Soils of the Eastern Hills 9 Soil Legend 10 Extended Legend 12 Explanatory Notes 12 References 16 Appendix 1 List of Published Reports 17 Appendix 2 List of Published Soil Bureau Maps 18 Appendix 3 List of Unpublished Reports 19 Appendix 4 List of Unpublished Soil Maps 20 Extended Legend 22 5 INTRODUCTION The Wairarapa is dominantly a region of pastoral farming based on sheep but with dairying important in parts of the central plains. Inter mittently over the last 30 years much soil work has been done.in the Wairarapa but little of it has been published for the information of the public. Between 1950 and 1968, H. S. ·Gibbs, J. D. Cowie and A. S. Wickens prepared a provisional soil map of the Wairarapa 'Valley'. This map has had limited circulation since. As an extended legend to accompany this soil map has been prepared by J. D. Cowie and H. S. Gibbs, it has been decided to make black and white prints of this updated interim soil map,and the extended legend available through the N.Z. Soil Bureau Record series. Most of the information in this text has been derived from Gibbs (1959) and Department of Industries and Commerce (1968), and the assistance of Professor Gibbs and Mr J.D. Cowie _is acknowledged. PHYSIOGRAPHY Wairarapa occupies an area of about 834 600 hectares, in the south-east part of Wellington Peninsula. In the south and east it is bounded by Cook Strait and the Pacific Ocean, in the west by the Tararua and Rimutaka Ranges. The northern boundary is geographically arbitrary but this record and accompanying soil map deals basically with the catchment of the Ruamahanga River and its main tributaries, the Waingawa, Waiohine, and Tauherenikau Rivers. Thus its northern boundary is the watershed between the Ruamahanga River (draining south) and the Mangatainoka River (draining north) . Its western boundary is again the main divide of the Tararua and Rimutaka Ranges but its eastern boundary is the watershed between the Ruamahanga and the eastward-draining catchments of the eastern hills. This region is called the Wairarapa Valley or Basin. Main centres of population are Masterton, Carterton, Greytown, Featherston, and Martinborough, which are generally geared to farm servicing, with manufacturing and other activities unrelated to farming now being developed. The Wairarapa Valley can be divided in three physiographic regions: 1. Western ranges, 2. Central plain, 3. Eastern hills. 6 The valley is up to 30 km wide and some 80 km long. Its southern end, that adjacent to the Cook Strait coastline, is flat and low-lying. The central plain is terraced and these terraces have been correlated with erosion cycles in the later Pleistocene. The eastern hills, between the central plain and the eastern coast, are composed of marine sediments of Tertiary age that increase in age and hardness eastward, and have been uplifted, folded and tilted. The predominant landform is of ridges and valleys that have been finely dissected by streams and rivers that have only small flood plains. This eastern area is prone to accelerated erosion. The western ranges comprise the Tararua and Rimutaka Ranges composed of Mesozoic greywacke rocks. CLIMATE (from Department of Industries & Commerce 1968) Rainfall Parts of the Wairarapa valley are sheltered by the Tararua and Rimutaka Ranges from rain-bearing north-westerlies and rain is fairly general from south-westerly and southerly winds. Winter is the wet season, and summer is dry when high evaporation levels cause serious moisture deficiency problems in shallow and stony soils. In the western ranges, annual rainfalls increase from 1520 mm adjacent to the central plains to 5000 mm on the ranges (1220 m above sea level). Annual rainfalls decrease across the central plain from 1520 to 890 mm to a zone receiving only 890 to 760 nnn around Martinborough. The distribution of this rainfall becomes more and more uneven as it decreases in total. The eastern hills receive about 890 to 1520 nnn. River flooding is a recurrent problem on the central plains, espec ially with heavy rain from southerlies. As well, north-westerlies bring heavy rain to the Tararuas causing rivers draining this range to rise rapidly and cause flooding. Wind The prevailing wind at Masterton is south-westerly, with frequent westerlies and north-westerlies. Three-quarters of the stronger winds are from these directions. Temperature Summers are rather warm, with a mean daily maximum temperature in February at 24oc at Masterton. Frosts are prevalent in the colder months e.g. Masterton averages 102 days of ground frost a year. June and July are critical months when low soil temperatures, frequent frosts and high soil moisture content cause slow pasture growth. Droughty conditions with high temperatures, low rainfall and high evaporation cause problems for stock and pasture growth during summer. Annual sunshine (2060 hours in Masterton) is about average for North Island. 7 VEGETATION (after Gibbs 1959) Most of the Wairarapa Valley has been extensively modified by man. For example, the central plain and eastern hills have been" cleared of their original forest and shrub vegetation and they now carry mainly pasture. 1. :r:he western ranges, especially the Tararua Ranges and Haurangi Mountains, carry their original forest vegetation although parts have been modified by fire and sawmilling. The vegetation of the ranges is tussock grassland above 1220 m, silver beech (Nothofagus menziesii) forest below that level grading down through red beech (N. fusca) to hard beech (N. truncata) in the southern part and down to podocarp forest in the northern part. Owing to low fertility and liability to scree and sheet erosion, pastoral farming has not been successful on the ranges. Some timber has been and may still be obtained from the lower slopes near the plains. Elsewhere the western ranges are best kept in permanent pro tective forest, especially as considerable erosion in the tussock grass land and upper forest has occurred, attributable to accidental fires and to concentrated grazing and browsing by deer and opossum. 2. The original vegetation of the central plain was probably podocarp or beech forest near the western ranges, open totara forest, fern, and grassland on the drier stony plains, podocarp and dicotylous forest on the low terraces and flood plains, with patches of podocarp forest, fern and grassland on the higher terraces. 3. The eastern hills carried a vegetation cover of mainly dicotylous and podocarp forest near the plains and some beech forest in areas of higher rainfall. 8 SOILS The soil pattern may be described in terms of the three physiographic regions and the rainfall pattern. 1. Soils of the Western Ranges These are steepland soils, and those that occur above 550 m in the higher rainfall zone (1520-5000 mm) are weakly podzolised and slightly to moderately gleyed. Small areas of soils of rolling and terrace land occur within valleys of the ranges but are not mapped separately. They are yellow-brown earths derived from greywacke or erosion products of greywacke. 2. Soils of the Central Plain From east to west, the pattern consists of: Soils of the rolling and hilly land, with remnants of an old (probably early Pleistocene) alluvial plain strongly leached yellow-brown earths Soils of the fans, built by the rivers draining the western ranges, are free draining, stony, and only 15-60 cm thick stony soils associated with intergrades between yellow-brown loams and yellow-brown earths Soils of the swamps, occurring on toes of stony fans and in interfan depressions where water tables are high - gley and organic soils Soils of the flood plains border the rivers or Lake Wairarapa where accumulation of alluvium is occurring recent and gley recent soils Soils of river terraces and undulating land, on the eastern side of the plain, that represent remnants of cycles of erosion, probably of late Pleistocene age, and are usually 1 to 2 m thick yellow-grey earths. The position and age of the physiographic unit on which the soils occur, as well as the rainfall received, is reflected in the classifica tion of the soils of the central plain. For example, on the older rolling and hilly land, near the western ranges where rainfall is 1520 to 1000 mm a year, the soils are classified as yellow-brown earths. However, in the 1140 to 760 mm rainfall zone, on river terraces and undulating land, especially on the eastern side of the plain, soils are classified as yellow-grey earths. This soil group is characterised by the presence of compact claypans in the subsoils. In the Wairarapa, yellow grey earths can be subdivided into soils with a less distinct claypan in areas receiving 1140-890 mm rain, and soils with a distinct dense claypan in the 890-760 mm rainfall zone. 9 Soils of the flood plain show only weakly developed profiles because of the short time they have been forming and show little relation ship to rainfall.