The Home Garden in April: Soil Improvement

New Zealand Journal of Agriculture, Volume 84, Issue 3, 15 March 1952, Page 230

The Home Garden in April: Soil Improvement

By

C. L. NAPIER,

Orchard Instructor, Department of Agriculture, Hastings

AS many plots will be cleared of crops during April, gardeners would be wise io give attention to the replenishment of humus in their soil by adding organic matter in the form of green crops, compost, and other materials. Humus is the basis of soil fertility and plant health, and gardeners cannot hope to expect consistently good crops from their soil unless it contains adequate amounts of humus. MANY home gardeners are finding difficulty in growing crops which, in their opinion, should be grown easily in their particular soils. Without giving due thought to the problem some gardeners attribute lack of success to attacks - of pests and diseases or lack of trace elements. Though these may have been responsible, the trouble often can be traced to a soil poor in structure and generally lacking in humus. A good soil structure, is essential to efficient soil management and profitable crop production, and continuous “mining” of the soil without replenishment can only lead to worn-out soil. During April some growers will be clearing plots of crops and sowing them down to a green crop; others may be turning in a crop sown earlier or incorporating some organic material obtained outside their gardens. Any of these forms of soil improvement is essential sooner or later, and if the gardener • understands the manner in which humus assists in supplying plant foods, he is better able to ■ ensure heavy crops. Composition of Soil Soil can be termed a mixture of weathered fragments of rock and. organic matter of animal and plant origin. Its purpose is to provide a rooting medium for plant life and to act as a reservoir for plant foods and water. In all soils the rock fragments are in various stages of weathering and vary in size from boulders to particles of clay. Generally, a purely mineral or “rock” soil is inactive except for the clay particles in it. All stones, sand, and silt are inactive or infertile until by the process of weathering they are reduced still further in size.

Clay particles are the result of such reduction and are in a very fine state. Particles of such minute size ■ are termed colloids. Once the particles have reached this size they assume characteristics quite distinct from all the other types. They are capable of absorbing moisture and of taking up and. giving out certain important plant foods.

This- characteristic of clay colloids constitutes one of the most important aspects of soil fertility. The same characteristic is present in humus, the ultimate form of organic matter after it has been broken down by soil organisms.

Importance of Organic Matter In natural conditions organic matter is returned to the soil in the form of dead animal and plant tissue and animal by-products. Plant tissue probably constitutes the largest proportion returned. When the organic matter is broken . down and in combination with the mineral portion the material commonly known as soil results. Average fertile soils contain approximately 5 per cent, of organic matter. When deposited on the soil organic matter is immediately attacked by a varied population of soil organisms, including worms, fungi, and bacteria, which break it down to a dark brown or black product known as humus. When present in the soil humus has several important functions and properties, the chief of which are:— 1. It increases the water-holding capacity of the soil, thus providing a useful reservoir of moisture during the dry months. It also increases the base-exchange capacity, that is, the power of the soil to hold plant foods against leaching and later to give them up when they are required by plants. 2. It increases the biological activity of the soil. If adequate supplies of organic matter are applied, microorganisms will increase rapidly and the consequent breakdown to humus will supply important plant foods in an available form.

3. It increases the pore space of the soil, thus giving freer movement of air. This factor is important, as lack of air or restricted air about the roots of plants does not encourage healthy plant growth and in some instances may cause death. The increasing of pore space is also a safeguard against excess moisture in the soil. 4. It tends to make a soil darker, thus increasing its rate of warming in spring and its ability to retain heat during summer. Humus disappears to varying degrees in different types of soils and under different methods of cultivation. In light soils, in soils under continuous cultivation, and in alkaline soils humus will tend to disappear much more rapidly than in heavier soils and acid soils such as peats or under circumstances where cultivation is restricted. Cultivation increases aeration and this in turn tends to reduce quickly, by oxidation, the supplies of humus. The capacity of humic colloids for holding plant foods is many times greater than that of clay colloids, and for this reason the former are an important factor in soil fertility. Maintaining Organic-matter Content The importance of maintaining adequate supplies of organic matter cannot be over-emphasised. There are many sources of suitable material. Green CroppingGreen cropping is perhaps the most common method of retaining the level

of organic matter in the soil. It is nrobably the most convenient method, as the material is produced on the

area where it will be turned in later. Green crops can be grown at almost any time and any plot in the garden not required for vegetables for a considerable time should be sown down to a cover crop. Green cropping has several advantages over other methods of humus replenishment:— The root systems of the plants tend to open up the soil and make it more friable when the green crop is growing and the crop when dug in adds valuable fibre to the soil. The growing plants draw on foods that might otherwise be lost by leaching. These foods are later released when the material rots down. The speed of decomposition in the soil can be governed to some extent by turning in the crop at varying stages of growth. Young or immature crops tend to decompose much more readily than mature crops, because of the water content and lack of fibre. A. growing crop draws on large quantities of moisture from the soil. In a wet season this may be an advantage, as it tends to reduce the water content of the soil; in dry districts, however, gardeners should not lose sight of the fact that serious reduction of soil water could result. The longer a green crop is left the greater will be its fibre content. This is important and should be considered in relation to soil type. Light or heavy clay soils, for instance, benefit from a considerable amount of fibre; therefore it would be an advantage with such a soil to leave the crop until it r was fairly well matured. In good loams however, a green crop can be turned in when much younger. There are several kinds of crops which produce good . supplies of > ganic matter The legumes, such as

lupins and peas, are valuable, because in addition to fibre they supply considerable quantities of nitrogen. There are several types of peas, including ordinary garden green peas, which are suitable for turning in. If green peas suitable lor Turning m. ±i green p are available in quantity at reasonable cost, they can be sown broadcast and the pods picked as a vegetable before the vines are turned in. All green crops grow well in the warmer periods of the year if there is adequate soil moisture. This applies particularly to mustard and lupins, which often give a poor stand if sown too late into the autumn. Cereals such as barley and oats give good bulk of organic matter and will grow well ev<=>n during the cooler periods.

Sowing and digging in: To ensure good germination of seed the soil should be reasonably firm and moist at time of sowing. Seed can be broadcast over the soil .and then worked in with a rake or wheeled cultivator. . . g an a^van^a g e apply a dressing of supe r phosphate (about . 2oz. per square yard) when sowing legumes, and an additional application of l|oz. o f sulphate of ammonia to the square yard when sowing crops other than legumes. This treatment will encourage greater production of organic matter. The manures applied are not lost, as they later become available to vegetable crops when the cover crops rot down The various crops can be sown at the following rates. Lupins, loz. per 3 sq. yds.; peas, Ijoz. per

3 sq. yds.; oats, barley, rye, etc., loz. per square yard; mustard, |oz. per square yard. These quantities should ensure a good bulk of growth and yet should not be heavy enough to give soft, drawn plants. Turning in can begin at the stage of growth required by the gardener. At least 1 month and preferably 6 weeks should be allowed for the crop to break down before further planting takes place. For best results the soil should be moist and the green material should be incorporated with the soil as thoroughly as possible. Packing a thick layer of vegetation in the bottom of a trench does not provide the best conditions for rapid decomposition by micro-organisms, as air tends to be excluded. To assist non-leguminous crops in breaking down an additional light dressing of sulphate of ammonia is often an advantage. It can be applied just before the crop is dug in. Materials for Digging in or Mulches Animal manures, straw, sawdust, lawn clippings, wheat husks, grass seed cleanings, spent hops, and compost are some other materials that can be utilised profitably in the home garden. In all cases they can be dug in as are green crops, or they can be used on the surface of the soil as mulches. Mulches, which have several virtues, are valuable for soil improvement and in some instances are much easier to deal with. Mulches can be applied to the soil at any time of the year, but their value as soil improvers takes longer to be appreciated, as they are incorporated in the soil slowly. If a mulch is applied in spring to reduce loss of moisture from the soil, it can be dug in in a similar manner to green crops when vegetable crops have been removed. Animal manures and straw, separately or mixed, make good mulches. Animal manures are valuable, because of their greater plantfood content, which is gradually leached down to plant roots as the manures break down. Mixtures of animal manures and straw are ideal for turning in, as the plant food content is more balanced than when the constituents are used separately and the nitrogen released by the manure encourages more rapid breakdown of the straw than takes place with straw alone.

Straw, hay, sawdust, and other very fibrous and dry materials usually contain little nitrogen and when utilised as soil improvers should be supplemented with animal manure or a nitrogenous fertiliser such as blood and bone, dried blood, or sulphate of ammonia. Failure to do this often leads to temporary nitrogen deficiency through the microorganisms drawing on available soil nitrogen in the process of breaking down the organic matter. Poor growth in crops can be the result. The nitrogenous fertiliser is best applied as a light dressing to the soil before the mulch is applied. Alternatively, straw, hay, etc., can be dug in, but extra nitrogen should be added. Sawdust should be used judiciously, as its nitrogen content is very low. Too -much should not be used at one time. The addition of the fibrous materials such as straw, hay, and sawdust is valuable for opening up stiff clay soils, as pore space is thereby increased, which improves both air and water movement within the soil. The same materials are also valuable on sandy soils, and if applied in adeouate amounts, will, increase the

water-holding and base - exchange capacity of such soils, thus improving their fertility. Composting The generally accepted meaning of composting is reducing raw organic matter to humus before applying it to the soil. This definition is not strictly correct, as mulching with organic materials is often termed sheet composting. The value of compost, compared with other types of organic matter, lies in its more quickly available plant-food content. As there is no danger of nitrogen deficiency developing if compost is well matured, it can be applied safely at any stage of plant growth. If applied as a mulch, compost will gradually improve the mechanical condition of the soil, but to have any appreciable effect it must be applied in considerable quantity. A 5 to 6 weeks’ lapse between digging in and planting is not necessary with well-made compost as with green crops or other forms of crude organic matter dug in. Gardeners should realise that an occasional application of organic matter does not have any appreciable effect in improving the soil either in structure or fertility. To bring about the desired improvement gardeners must incorporate organic matter in the soil regularly. Nature provides a striking lesson in the bush, where a cycle of plant growth, death, return to the soil, and decay goes on continuously. There, nothing is removed and nutrients are provided for the next generation. Home gardeners should strive for a somewhat similar balance between what is grown and removed from the soil and what is returned. Garden Work for April In April there will be a considerable reduction in seed sowing, except in districts having a fairly mild autumn climate. As air and soil temperatures fall conditions for seed germination become less favourable and consequently results are not always heartening. Where seed sowing is to be attempted, it is wise to

construct raised beds, if there is any danger of a high water-table during winter. Asparagus: Once the top growth of asparagus has begun to change colour and turn brown it can be removed and composted or burnt. Removal of growth before the seed falls will prevent the establishment of many seedlings the following spring. After the fern growth has been removed opportunity should be taken to remove any weeds established during the season and to mulch the bed with stable manure. A mixture of poultry manure and straw or sawdust is a good alternative to stable manure. Broad beans: In favourable localities an early sowing of broad beans can be made, but gardeners should remember that very early crops do not always set as well as later crops. Broad ' beans do well in soils with a good supply of organic matter, and drainage should be good so that rotting of the seedlings does not occur during winter and spring rains. Two main types of broad beans are grown in New Zealand, the broad-podded or Windsor type and the long-podded type. Although the Windsor type is considered to have a superior flavour, the long-podded type usually bears ■earlier. Giant Windsor and Broad Windsor are popular broad-podded types and Early Long Pod and Mammoth Long Pod examples of the long-podded type. Tomatoes: In districts where frosts are expected in April, late-planted tomato plants should be covered at night to allow all available fruit to develop. Small quantities of foliage can be removed from about trusses to allow the extra light to aid ripening. However, this should be done with discretion, as the removal of foliage may even check development and expose the fruit to damage by sun or frost. If it is thought advisable to harvest all fruits, the whole plants can be pulled and hung up by the roots in a dry, warm, sunny position to allow as many fruits as . possible to ripen. Pumpkins, squashes, and marrows: If grown for winter storage, these crops should be selected carefully and harvested as they mature; details were given in the February issue of the ■“Journal”. In districts with mild autumns some vines may still be

developing and applications of liquid manure may be necessary to hasten development of the fruit. Rhubarb: As soon as summer rhubarb ceases active leaf production opportunity should be taken to overhaul the beds. If the clumps are old, they can be lifted, trimmed, and planted elsewhere. Rhubarb is a gross feeder, and if left 'in the one position too long, will tend to become weak. Old clumps are often hollow, but can be rejuvenated by splitting them before replanting. It is best to lay the lifted clumps under a hedge or other suitable position for the winter and cover them with straw or dry soil till sprouting occurs. The new bed can be prepared during winter. It should receive liberal quantities of compost, rotted stable manure, or other similar organic matter. As soon as good, plump buds develop on the clumps they can be split. A sharp spade is the handiest tool for this purpose. Only the youngest portions of roots, each with a crown attached, should be kept and all old portions discarded. . When replanted, crowns should be covered with about 2in. of soil. New plants of rhubarb can be produced easily from seed from established plants. Seed, which should be well ripened, should be sown thinly in early spring in a similar manner to other vegetables. Plants should be transplanted at greater distances the following spring and final selections made from these. Some good strains of rhubarb can be produced in this manner. Cabbages and cauliflowers: Plantings of spring cabbages can now be made in well-drained plots enriched with organic matter. Plants should be selected carefully from seedlings

raised earlier and the plants lifted so that roots are damaged as little as possible. Cauliflowers sown earlier can be planted out in districts with a fairly mild climate. As plants should not receive a check, growing conditions will not be suitable in all districts. In the least favourable districts it is best to make plantings about July and August. All seedlings should be firmly heeled in after planting to ensure quick root production. Reminders Onion seed should be sown if not sown in March. Pukekohe Long Keeper, Brown Spanish, and Straw Spanish, are good varieties. In some favourable coastal districts carrots may still be sown. Tubers and root crops should be harvested as described in the February issue of the “Journal”. In favourable localities a sowing of spinach should produce greens before the winter. Lettuce plants can still be set out, but to obtain all possible warmth, raised beds should be made. The dead tops should be removed from Jerusalem artichokes and the tubers left in the ground or lifted, according to local soil conditions. Celery not already blanched and leeks should be earthed up. The garden should be kept free of weeds and all available vegetable refuse and rubbish should be composted or dug in. All diseased vegetable refuse is best burnt; the ash can be stored in a dry place for use later as a fertiliser. Surplus peas and beans should be harvested as outlined in the January issue of the “Journal”. Remaining crops of onions and shallots should be harvested as described in the February issue of the “Journal”. Bulbs probably will have to be dried under shelter at this time of year. A watch must be kept for late attacks of pests and diseases on autumn and winter crops and preventive measures should be taken before appreciable damage is done.

Valuable Book For Home Gardeners DTHE most comprehensive work on ■*" home vegetable gardening under New Zealand conditions yet published is now available f om main offices of the Department of Agriculture or from Whitcombe and Tombs Ltd. It is Bulletin No. 342, “The Home Vegetable Garden”, by A. G. Kennedy, Vegetable Instructor, Department of Agriculture, Dunedin. The bulletin, which contains 214 pages, including a detailed index, is well illustrated with diagrams and photographs. Apart from sections on such topics as preparation of the soil, fertilisers, and composting, the bulletin includes a chapter which deals with all the vegetables likely to be grown in New Zealand in their alphabetical order. There is, too, a very comprehensive section on pests and diseases which should enable gardeners to identify these and take effective preventive or protective measures. “The Home Vegetable Garden” is 2s. 6d. per copy, post free.