Grassed Orchards in New Zealand: A Review of Developments

New Zealand Journal of Agriculture, Volume 98, Issue 4, 15 April 1959, Page 323

Grassed Orchards in New Zealand: A Review of Developments

By

C. E. WOODHEAD,

Pip Fruit Specialist, Department of Agriculture, Palmerston North

CINCE the first orchards were grassed in New Zealand about 1948 the practice has ** developed until today grassed orchards are to be found in all fruitgrowing districts. There are now an estimated 2,000 acres of orchard in permanent grass, consisting mostly of pip fruit, but including some stone fruit and citrus. Of this total Hawke's Bay has 750 acres, Auckland 490, and Motueka 230. There has recently been a considerable expansion of grassing at Mapua and Alexandra. A representative selection of 35 grassed pip fruit orchards and a number of stone fruit and citrus orchards is under observation, so that the system is on trial on a great variety of soils and under such extremes of climate as are represented by the irrigation areas of Central Otago and the mild, high-rainfall districts of the North Island. Advantages already observed are a favourable effect on the condition of pip fruit trees, a better orchard surface for working on, the elimination or reduction of soil erosion, and in some instances improvement of drainage.

IN England the - practice of sowing down orchards to permanent grass has become widespread over the last 20 years, following the realisation that orchard soils were deteriorating after years of cultivation. In New Zealand frequent cultivation in spring and summer, followed by a winter cover crop, has been the accepted system of orchard soil management. • In recent years, however, injury to the soil caused by “clean cultivation” over periods of up to 40 or more years

has become increasingly evident in the loss of “crumb structure”, impeded drainage, and continuing erosion. Many fruitgrowers in New Zealand have therefore turned to permanent grassing as a means of restoring the fertility and physical condition of the soil. The earliest developments in this direction took place in the Auckland district between 1948 and 1950 when a few orchards were grassed. These were soon followed by others in the same district and also in Nelson and Hawke’s Bay, until today grassed orchards are to be found in all fruitgrowing districts. Advantages of Grassing Practical experience of the system in England, supplemented by comprehensive trials at research stations, has shown that with correct management the following benefits may be gained from grassing: 1. Pleasanter working conditions and a better working surface for orchard operations. 2. Prevention of soil erosion. 3. Increase of organic matter in the soil, resulting in better physical structure, aeration, and drainage. 4. Release of potash from the soil. 5. Correction of some trace element deficiencies; for example, iron. 6. Reduction of pre-harvest fruit drop. 7. Improved fruit colour. 8. Reduced storage loss from lowtemperature breakdown and lenticel rot. . 9. Grassing is an effective means of checking excessive growth and inducing earlier cropping of young trees on vigorous rootstocks; for example, M.XII. Observations in New Zealand Because of climatic and other differences it cannot be assumed that all the benefits noted in England will necessarily follow the grassing of orchards in this country or that the grass mixtures and management practices employed overseas will be the most suitable for conditions in New Zealand. Inevitably it will be some years before the long-term effects of grassing can be assessed. Information on the results of grassing since the system was introduced some 10 years ago will, however, assist fruitgrowers who are considering sowing down their orchards and this is being collected by the Horticulture Division, Department of Agriculture. Starting about five years ago with general observations in Auckland, Hawke’s Bay, and Nelson, investigations were extended in 1957 to include all districts with the selection of 35 grassed pip fruit orchards and a number of stone fruit and citrus orchards for more systematic observa-

tion over a term of years. The selected pip fruit orchards include both apples and pears, ranging in age from young trees to trees 52 years old. They are representative of orchards on flat, gently sloping, and moderately steep country, and the soil types include sandy loams, silts, clay loams, and shallow clays. The following account of grass ■swards, management practices, and effects of grassing on pip fruit orchards has been prepared both from the earlier general observations and those made more recently on the selected orchards. Grass Swards If the orchard is to benefit to the fullest extent from grassing, the sward should provide the. following requirements: 1. An abundance of grass roots to build up organic matter in the soil. Grass roots is used here in the wider sense to include clovers. 2. A high proportion of clover to supply nitrogen. 3. An even and dense ground cover in the shortest possible time. Grass roots are important for three reasons. In penetrating and breaking up the soil growing roots increase aeration and improve drainage. Dead roots provide the humus which is so necessary for the fertility and good physical condition of the soil. Finally, dead roots play an essential part in maintaining -a high population of earthworms. Research by Grasslands Division, Department of Scientific and Industrial Research, has revealed that the soil of a productive pasture contains an average of one ton of earthworms per acre, a greater weight than that of the stock grazed on the pasture (1). It was also shown that dead grass roots supply the chief food of the worms, decayed herbage above ground being of minor importance in this respect (2). In view of the major part played by earthworms in the decomposition and mixing of plant residues with the soil and in the improvement of soil structure, aeration, and drainage, this function of grass roots is particularly important. It is well known that clovers are able to obtain their nitrogen requirements from the free nitrogen present in the soil atmosphere and are thus independent of soil nitrogen. Research in New Zealand has shown that pedigree white clover in a pasture may contribute nitrogen equivalent to as much as a ton of sulphate of ammonia per acre annually, depending on the quantity of clover in the pasture (3). It should not be assumed, however, that a new sward containing a high proportion of clover will thus provide fruit trees with an abundance of nitrogen, as considerable demands on the nitrogen supply are made by

grasses in the sward and also by the numerous soil organisms concerned in the decomposition of organic matter. In practice it has been found that the trees are likely to suffer from nitrogen deficiency in the early years of grassing, unless supplied with greater amounts of nitrogenous fertiliser. The deficiency will be greater, however, in a predominantly grass sward and for this reason and also to provide for a gradual build up of soil nitrogen over the years, every sward should contain a good proportion of clover. The third requirement, speedy establishment of a close turf, is necessary to prevent invasion by weeds of little value compared with the selected grasses and clovers sown and also loss of soil moisture where the surface cover is patchy. Tumbledown Swards In a number of orchards, chiefly in the vicinity of Auckland, a sward has been established by mowing volunteer grasses and weeds. Of two such orchards where this method was followed three or four years ago, couch grass, Yorkshire fog, and white clover are now prevalent in one and couch grass and white clover in the other. In one of the two orchards fruit size was reduced, but in the first two seasons only. In the second orchard, consisting of mature pear trees which were growing too vigorously before grassing, growth of the trees has been checked and production is increasing. Both orchards have had greatly increased quantities of nitrogenous fertiliser since grassing. There is little general evidence that tumbledown swards have adversely affected growth or production, but this may be due to their being mainly confined to the Auckland district, which has a relatively high rainfall. For reasons discussed in the preceding section this method of establishing a sward is not recommended. Sown Swards In the majority of orchards sown down to grass a mixture of perennial ryegrass and white clover has been used, other grasses and clovers such as short-rotation ryegrass and Montgomery red clover being sometimes included. Perennial ryegrass and white clover mixtures have given good permanent swards, though in some Auckland orchards a considerable invasion by prairie grass has occurred. The ryegrass-clover sward is not favoured by some growers because of the very frequent mowing required to control the ryegrass in spring and early summer. However, in many orchards sown with this mixture it has been observed that after two or three seasons of frequent cutting, a sward consisting mainly of clover has

been produced. This suggests that the initial problem is unlikely to persist if the growth of clover is encouraged by correct management of the sward. White clover sown alone or with other clovers has given swards containing a proportion of undesirable grasses and weeds. As white clover is relatively slow in establishing itself, it is essential to include some grass seed to provide an initial close sward to suppress weeds. Results from pure sowings of red clover (cowgrass) have been still less satisfactory, weed invasion being encouraged by the short life of this clover species. Of other grasses and clovers included in mixtures, subterranean clover has not persisted under mowing. Browntop and Chewings fescue have also quickly disappeared from swards. At this relatively early stage of orchard grassing in this country recommendations of seed mixtures can be only tentative. Observations to date suggest that the perennial ryegrass and white clover mixture is the most generally suitable, experience having shown that the final composition of the sward may be influenced by management to produce either a clover-dominant sward or one in which both species persist to a similar degree. A mixed sward is probably desirable on rolling, country, as pure clover swards when wet are reported overseas to cause skidding of tractors and other heavy implements. This has also been noted in Nelson orchards. The following seeds mixture is recommended (lb per acre): lb Perennial ryegrass . . .. 16 Short-rotation (Hl) ryegrass 8 Certified white clover .. 2 Short-rotation ryegrass has a life of two to three years and is included to give quick ground cover until the other species are fully established. A similar mixture, but with 2 lb of the deep-rooting Montgomery red clover added to give greater bulk of herbage for a few years, is proving very suitable for Auckland orchards. Where short-rotation ryegrass is included in a seeds mixture the new sward should be mown or grazed a few weeks after it becomes established to prevent the young clover seedlings being smothered. Growers who may wish to establish a pure white clover sward are recommended to use the following mixture: lb Italian ryegrass .. .. .. 20 Certified white clover .. .. 2 Italian ryegrass has a life of about two years and will give ground cover and suppress weeds until the clover is established. As this ryegrass makes vigorous growth, early mowing or grazing of the new sward, as recommended for short-rotation ryegrass, is essential.

Grasses that have not yet been investigated for orchard swards but are worthy of trial on a small area by growers include prairie grass and Poa trivialis (rough stalked meadow grass). Prairie grass is a deep-rooting grass which produces a large bulk of herbage in winter and would therefore not compete seriously with the trees for moisture at other seasons.

To maintain a good sward of prairie grass mowing or grazing is necessary during winter. Sowing at 20 lb per acre, with white clover at 2 lb, is suggested. Poa trivialis is mainly a spring and early summer grass. It is not a vigorous grower, but forms a close turf which is easily mown. Though it has a wide climatic range, it succeeds best on moister soils of above-average fertility. A mixture of Poa trivialis 10 lb and white clover 2 lb per acre is recommended for trial.

A strain of timothy known as 5.50 is very popular for orchard grassing in England, where it forms a low, dense sward which grows chiefly from autumn to early spring, stands up to traffic particularly well, and requires less mowing than other grasses. However, 5.50 timothy is not available in New Zealand, as for general farming purposes it is regarded as inferior to the type of timothy grown here, which is a vigorous, tall-growing grass producing an abundance of feed. SWARD ESTABLISHMENT AND MANAGEMENT Preparation for Sowing A good sward will not be obtained if the ground is not adequately prepared for sowing. Preparation should consist of frequent cultivation in the summer preceding grassing to destroy weeds and secure a good tilth. As grasses require a well consolidated seedbed, cultivation should be shallow. Autumn sowing is preferable, as the sward is then well established by the time heavier traffic has to be carried. Weed growth is also less prolific in autumn. A further reason for autumn sowing is that a sward sown in spring may be adversely affected if the following summer is hot and dry. An application of superphosphate broadcast at 2 cwt per acre is recommended just before sowing. Mixing the fertiliser with the seed is not advisable, as unless the seed is sown immediately after mixing its germination may be impaired. Mowing On New Zealand grassed orchards the rotary type of mower is used almost exclusively. Mowing is usually carried out from September to February, though some growers continue until early winter. On about twothirds of the orchards under observation the grass was cut before it exceeded a height of 6 in. The average number of cuts last year in Auckland,

Hawke’s Bay, and Nelson orchards was 14, compared with an average of eight in irrigated orchards of Central Otago. The interval between mowings may be as little as 10 days in spring, increasing later in the season to one month. Frequent cutting in spring and early summer is essential to reduce competition with the trees for moisture and also for the preservation of clover in both new and established swards. At this season of the year clovers require ample light and air, and they will be weakened or killed outright if shaded and smothered by grasses. Therefore, to establish and maintain a clover-dominant sward mow frequently in spring and summer, cutting whenever the grass attains a height of 5 or 6 in. During the hot summer months cutting too close to the ground should be avoided. The mower height should be adjusted to leave about 2 in. of sward after cutting. This will provide a cover of vegetation to keep the ground cool and will also further encourage the spread of clover by allowing it to produce foliage. On the other hand, except during seasons of drought, cutting should be reduced to a minimum in autumn, when a cover crop would normally be growing in cultivated orchards. For trees in active growth some competition from the sward for nitrogen and moisture is beneficial at this season, as it assists in maturing the wood and improving the keeping quality and colour of the crop. Growth of the sward in autumn and winter is also necessary to build up the quantity and increase the depth of grass roots in the soil, as this is limited by the amount of top growth. Fertilisers for Trees That fruit trees in grassed orchards require heavier applications of nitrogenous fertiliser than those under cultivation has been known in England for many years and has also been demonstrated in recent trials in New Zealand (4). Being therefore forewarned by experience overseas, most growers here have paid particular attention to this requirement. Though it should be emphasised that the effect of grassing on fruit tree growth and cropping can be accurately determined only by precise measurement in field trials, observations made on the selected orchards indicate that where the nitrogen application has been increased to about double that given before grassing, growth and production are being well maintained and in several instances increased. On the other hand, though failure to increase nitrogenous manuring had an adverse effect on a few orchards, comparison has been complicated by the fairly

general practice of grazing sheep on grassed orchards. This is discussed in the next section. Increasing use is being made of non-acid nitrogenous manures of the ammonium nitrate plus calcium carbonate type in preference to sulphate of ammonia to avoid checking the growth of clovers. Grazing Grazing with sheep during, winter is a common practice in most districts, Auckland excepted. Of the 35 orchards under observation no fewer than 17 are winter grazed. Orchards with swards of high clover content but which have not had increased quantities of nitrogenous fertiliser since grassing have suffered no apparent check to growth and production where sheep grazing is practised.

In four of the 17 orchards there Is clear, evidence of over-stimulation of trees by nitrogen, resulting in excessive growth and, in one instance, serious deterioration, in the quality of the crop. Growers s who graze . their orchards -.are therefore advised to watch for signs of excess nitrogen, especially if the orchard is on fertile soil and the sward contains a high proportion of white clover. Mulches In Hawke’s Bay orchards mulching under trees with threshed hay or other material is often associated with grassing, . and reports . indicate that this practice prevents any check to growth of trees newly grassed. The difficulty experienced in establishing “replants” in grassed orchards has also , been effectively overcome in Hawke’s Bay by the maintenance of a heavy mulch round the young trees, a procedure that could profitably be followed in other districts.

When to Grass A definite answer cannot be given to the question of the age at which a young orchard should be grassed, as reliable information can be obtained only from field trials in which the growth of grassed and cultivated trees is compared. Such trials have not yet been carried out in this country. In England the grassing of trees under 5 years of age is not recommended and in view of the importance of ensuring rapid growth and the building of a strong framework in newly planted trees this is possibly the best advice that can be given here in the meantime. Certainly it may be said that grassing at an earlier age should not be considered unless mulching material is available at reasonable cost and the grower is prepared to mulch the young trees for a few years. Effects of Grassing In general grassing has had a favourable effect on the condition of pip fruit trees. In very few instances has there been a decline in vigour and on some orchards there has been a marked - improvement. On the few orchards where an adverse effect on growth or crop was noted failure to increase nitrogen applications was the most commonly associated feature. On others a poor sward had been established. . The improvement effected by grassing in providing a better surface for orchard operations and thus more congenial conditions for the orchardist was obvious on all orchards. Soil erosion has been eliminated or greatly reduced and in some instances drainage was reported to have improved. Fears that grassed pip fruit orchards would suffer in dry weather have not been realised, as they have come through summer droughts equally as well as cultivated orchards. In irrigation districts water penetration and the water-holding capacity of the soil appeared to have increased after grassing. In Central Otago there have been no obvious indications that frost injury is more severe than on cultivated orchards. The influence of grassing on disease and pest incidence and on fruit quality has not yet been sufficiently observed. So far as the effects of any cultural system can be assessed by observation only, grassing of pip fruit orchards has proved satisfactory where attention has been given to the known essentials of management. References (1) Waters, R. A. S., “Proceedings of the New Zealand Grassland Association”, pp. 168175, 1951. (2) Waters, R. A. S., “New Zealand Journal of Science and Technology”, A 36, No. 5, pp. 516-525, 1955. (3) Sears, P. D., "New Zealand Institute for Turf Culture: Report of Proceedings Greenkeepers Conference”, pp. 13-17, 1951. (4) Bollard, E. G., “New Zealand Journal of Science and Technology”, A3B, No. 5, pp 527-532, 1957.