Treatments Of Poor Soil
( Originally Published 1920 )
OUR conception of a healthy soil as has been indicated is one which is ideally suited to plant growth, through proper physical and chemical makeup, and by the presence of groups of beneficial micro-organisms. A sick soil is one in which plants would grow very languidly or not at all. Soil sickness may be caused through the improper use of fertilizers, or through the introduction of parasitic disease-producing organisms.
Soils which contain an excess of acid, in which crops refuse to grow, may be termed acid-sick. Acids in soils have a directly poisonous effect on plants. Soil acidity may be brought about by the loss of lime and of other bases; and by the decomposition of organic and of inorganic matter.
Crops are known to draw heavily on the lime of the soil, and thus to increase the proportion of acidity. This, then, is one direct way of depleting the soil lime. Lime and other bases are further lost from the soil by leaching. The soluble carbonates are but slowly soluble in pure water. However, carbon dioxide, nearly always present in soils, changes the calcium carbonate into calcium bicarbonate, which is very soluble, and readily leaches out with the drainage water.
Soils which are heavily manured are apt to be-come more acid. The decomposition of the organic matter yields large quantities of carbon dioxide which act on the carbonate in the manner above indicated. In addition to these causes, poor drain-age has a tendency to increase the soil acidity. The application of ammonium sulphate as a fertilizer leads to a development of acidity by the production of sulphuric acid. The same is true when other acid fertilizers are used. In the process of nitrification, in which nitrogen is made more available for plants, acids are produced. Acidity in a soil is usually characterized by a languid condition of the growing crop. This may be due directly to the effect of the acid on the plants, or to the inhibiting effect of the acid on the soil flora. In the latter case the plant food in the soil, although very plentiful, may not be in a form available for plants.
Not all crops are equally sensitive to soil acidity. Hartwell and Damon have determined the degree in which truck crops are benefited by the application of lime to an acid soil. Those which are very sensitive to soil acidity are followed by the number (3), while a lesser degree of sensitiveness is indicated by the numbers (2) and (1). Crops which tolerate a moderate amount of acidity are followed by the figure (o), and those which thrive best in acid soils (—I) ; beans (o), beets (3), carrots (1), cauliflower (2), celery (3), cucumber (I), egg-plant (2), lettuce (3), muskmelon (o), parsley (o), pea, garden (1), pepper (3), radish (1), rhubarb (3), sorrel (—i ), spinach (3).
TREATMENT OF ACID SOILS
The best known remedy for soil acidity is lime. Its effect is to neutralize the acidity, and to restore the normal equilibrium for the activity of the soil flora, thus overcoming the antagonism to normal growth. The amount of lime to be used depends on the kind of soil, its degree of acidity, and the crops grown. It is very unlikely that injury would result to greenhouse crops from the use of moderate amounts of lime. Lime is sold as ground limestone or as burned lime. A ton of burned limestone will yield 1,120 pounds. If enough water is added, it will weigh 1,48o pounds. If 1,120 pounds of burned lime or the 1,48o pounds of hydrated lime are allowed to air slack, the weight of both will be 2,000 pounds. Air slacked lime has the same composition as ground limestone. In buying hydrated lime we do not get any better quality, but merely pay an excess in freight for the amount of water it contains. The cost of delivery should determine the kind of lime to buy.
Wood ashes may often be used instead of lime to correct soil acidity. Hardwood ashes contain about 3o per cent. lime and 60 per cent. potash.
Two and a half tons of good wood ashes are equivalent to one ton of burned lime for overcoming soil acidity. Leached ashes have lost their potash and its lime is in the form of a hydrate or carbonate.
Magnesium lime, which contains a high percentage of magnesia, is not objectionable for use. In fact, a ton of limestone, which contains magnesium carbonate is more effective on acid soil than a ton of limestone without magnesium carbonate. Lime should be applied only when the acidity of the soil requires it.
Alkali soils are termed sick, since plants thrive there poorly or not at all. The alkali problem generally concerns only those greenhouse men located in the irrigated districts of the arid or semi-arid regions of the United States.
For convenience, alkali soils are here divided into black and white. The black alkali lands are known to contain sodium carbonate or washing soda as the essential salt. The latter does not act so much on the soil as on the organic matter, turning it black. This dark material is always found on the surface with the salts. The blackening of the soil, however, is not always an indication of black alkali. Many dark spots are found to contain the white alkali. Moreover, soils which contain little or no organic matter may contain large quantities of sodium carbonate and never turn black. The white alkali in reality is not a true alkali. The salts found in it are sodium chloride or table salt, calcium sulphate or gypsum, sodium sulphate, magnesium sulphate or epsom salt. In addition to these may be found salts of potassium.
Methods of Control. Generally speaking the alkali problem is not serious in greenhouse culture. The alkali soil when mixed at the compost heap generally loses much of its salts due to the action of the manure used. However, in alkali regions alkali soils should be avoided as much as possible. When this is not possible the soil to be used with the compost should be spread out and exposed to the action of winter weather conditions and to the washing by rain. This treatment will result in a loss of the injurious salts through leaching.
Damping off, whether induced by Pythium, Rhizoctonia or any other parasitic organism, is usually confined to seedlings in the seed bed under cover or in the open. The loss of seedling not only means a waste of seeds, but it also results in poor stands. The disease-producing-organisms are usually brought in with the manure and the compost. Most growers are in the habit of using the same soil in the seed bed or in the greenhouse year in and year out. A number make it a practice to empty their beds and use fresh soil every year. This, however, is too expensive and, moreover, is not always a safe method, for the new soil, too, may be contaminated, or may become infected as soon as it is placed in the bed previously contaminated. Fortunately, sick soils in the greenhouse, unlike the soil outdoors, may be readily treated so as to destroy all forms of parasitic micro-organisms or injurious animal life which are present in it. The various methods to be mentioned make it possible to use the soil over and again. Rid the soil of parasites, then all chances will be in favor of good crops whether vegetables or flowers.
SOIL TREATMENT WITH FORMALDEHYDE
When steam sterilization is not feasible, because of the absence of suitable steam pressure, the formaldehyde treatment is the next best. With this method we may control Fusarium, Rhizoctonia, and Pythium in infected beds. It is doubtful, however, if it will entirely eradicate eel worms from infested soils. The method is as follows : the beds are thoroughly prepared in the usual way with all fertilizers worked in and then the soil is drenched with a solution of formaldehyde composed of one pint of the chemical (40 per cent. pure) to 30 gallons of water applied at the rate of one gallon per square foot. The solution should be put on with a watering can and distributed as evenly as possible over the bed, so as to wet the soil thoroughly to a depth of one foot. It will, in most cases, be necessary to apply the solution in two or three intervals, as the soil may not absorb the full quantity of the liquid at one time. 'After treatment the beds should be covered with heavy burlap to retain the formaldehyde fumes for a day or two, and then aired for a week before planting. Stirring the soil at frequent intervals after uncovering hastens the more rapid escape of the formaldehyde fumes.
STERILIZING SOILS WITH STEAM
Steam sterilization of soils is by far the best method. There are four ways of steaming soils : (I) Inverted pan method, (2) the perforated pipe system, (3) the steam rake device, (4.) the drain tile method. The choice of any one of these methods is a matter of expediency. All four methods have been successfully used on a commercial scale.
The Inverted Pan Method. This was first devised by A. D. Shamel of the U. S. Department of Agriculture. To carry it out, the boiler must maintain a pressure of not less than 8o pounds, for at least one and a half hours. In setting a pan, the rim is sunk into the soil of the seed bed or bench, to a depth of two to three inches, to make the inclosed chamber steam tight. In heavy soil, trenching may be necessary. It is also advisable to put a heavy weight on the pan when the steam operates. For one pan, a traction engine or a portable boiler of ten to twelve H. P. will suffice. While the standard of the pan is six by eight feet, the dimensions may be modified to suit the seed beds or greenhouse benches.
Selby and Humbert* describe the method of constructing an inverted pan as follows :
"Material used for construction of a pan is galvanized sheet iron; the most useful weight is No. 20 gauge, which weighs 26.5 ounces per square foot. The heavier material requires little in the way of frame supports. The galvanized iron sheets come in sizes varying from two to three feet in width by eight to ten feet in length. The standard is a pan 6 x ro feet in area, six inches deep, constructed from 5 such strips 2 1/2 x 8 feet in size. These sheets are joined by double fold seam and riveted at intervals of 6 to I o inches to make the pan steam tight. This pan is further strengthened by a band of strap iron 2 x 1 inch riveted to the bottom edge, and stiffened by a brace of 1 1/4-inch angle iron across the top and extending down the sides. This is bolted at the sides to the supporting strap iron stiffener.
"The entrance pipe for the steam may be placed at the side or end of the pan or may enter from the top. The latter form has the advantage in that it will not interfere with the box boards when used on frames. The pipe, after entrance, should be a T form, so that steam in being forced into the pan when in place does not blow holes in the soil."
The pans, together with the sand bags used for weight, are mounted on a frame which rests upon wheels. The wheels run on the edges of the concrete walks on either side of the house. By using a pulley, the pan may be conveniently placed wherever desired.
Perforated Pipe Method. The apparatus consists of a set of perforated pipes buried in the soil and connected with a steam boiler. The main and cross-head pipes are 2 inches and those which are buried 1 1/2 inches. The length of the beds, and especially the capacity of the boiler, will determine the number of pipes to use. However, 7 to 8 pipes are as many as could be used to advantage. These should not be over 40 feet long. The perforations should be one-eighth to three-sixteenths of an inch in size, 12 to 15 inches apart and on the upper side of the pipes. The latter are buried about six inches deep and when the steam is turned on the beds are covered with a heavy canvas to retain the heat and to prevent the escape of steam (fig. 6, a and b.). When-ever convenient, it is well to have two sets of pipes sous to save time and fuel.
Steam Rake Method. This consists of a two-inch main pipe which may be run between two sets of houses. The pipe is connected with the boiler at one end and with a heavy hose at the other. The rake is attached to the hose through which the steam is introduced. There are either two rakes used in a single house, or four rakes operated in pairs, end to end in two adjoining houses. The rake is generally composed of three main pipes 13 feet long, which run crossways of the house, and of several cross pieces one inch in diameter that are gradually reduced to three-fourths inch, then to one-half inch, then to three-eighths inch. The pegs are six inches long, and are placed eight inches apart, and consist of one-fourth inch pipe pounded together at the lower end. The steam escapes through a three-sixteenths inch hole at the lower wedge-like end of the pipe. The advantage of this apparatus is that it can be made to fit any bed. At 90 to 100 pounds pressure, more steam will naturally pass through the pipes than at thirty to forty pounds pressure. During the operation, a canvas cover laid on the beds will prevent the rapid escape of steam.
The Tile Method. This system is at its best when the steam pressure is low, at 25 to 30 pounds. With higher pressures the steam will blow out between the tiles. With this method, therefore, the soil should be sterilized for a longer period of time, from two to four hours, depending on the depth of tile and on soil conditions. Usually the tiles are not laid over one foot deep and from two to three feet apart. The joints of the pipes should be well matched.
Hot Water Sterilization. Numerous greenhouse men seem to prefer the use of hot water as a soil sterilizer to any other method here mentioned. Mr. Wm. L. Doran of the Massachusetts Experiment Station, who has made considerable study of this method, writes as follows:
"The soil should be thoroughly dry in the beginning so that it will take up the maximum amount of water. Before treatment, it is spaded over to a depth of one foot to insure an open, porous condition. The water is heated in an ordinary boiler such as is used for heating the greenhouse, no extra equipment being needed. It is moved by a small pump operated by a motor and gasoline engine of a small horse power. The water comes out under forty pounds pressure, which insures considerable penetration into the soil. It is piped from the boiler through the center of the greenhouse in 1 1/2-inch iron pipes. Most growers take the water from the bottom of the boiler rather than from the top, the object being to keep the temperature high but to avoid the steam which is objectionable. A thermometer is screwed into the main outlet pipe and is read frequently; the temperature should be above 201 degrees F., but if it goes much above 215 degrees F. the outlet pipe spits steam and is difficult and dangerous to use. To this iron pipe in the center of the house is attached a one-inch rubber hose fifty feet in length. This hose is replaced annually to decrease the danger of blow-outs and burns. Most growers sterilize once a year, some twice. The rubber hose is attached at the other end to a Y joint which is in the middle of a five-foot iron pipe one inch in diameter. The upper half of this pipe is plugged at both ends, serving simply as a handle, and from the lower half the water is delivered to the soil. A few feet back of this exhaust pipe the rubber hose is wrapped with burlap so that it may be carried over the shoulder of the workman. Some growers shove the iron pipe down into the soil six inches; others hold it above the surface of the soil. The water penetrates equally well either way, because the soil is in a loose condition and the water goes out under pressure. There are no figures as to the exact amount of water per cubic foot of bed surface, but hot water is applied until it stands on the surface of the soil in pools and will no longer penetrate. The exact amount will, of course, vary with the physical condition of the soil and its relative dryness. The greenhouse men do not practice covering the soil with anything to hold in the heat. Out of doors, however, a cover would be desirable because of wind currents. Three or four days after treatment, the soil is cool enough and dry enough to plant."
It will require about two days for five men to treat a house 275 feet by 34 feet.
Roasting or Pan Firing. By this method, the soil to be sterilized is removed from the bed and placed in a pan, over a hot fire. After roasting, the soil is returned to the bed and more of it sterilized. This method is too slow and has the disadvantage, besides, of destroying the humus in the soil. The advantage of steam sterilization and of the "fire" methods lies in the destruction of all weed seed, together with the fungi which cause damping-off (fig. 7, a and b.) .
A NEW METHOD OF STEAM STERILIZATION FOR CONTROLLING NEMATODES
It has been our common experience, when at-tempting to control nematodes by steam sterilization of the soil, that very frequently one is unable to secure sufficient steam pressure satisfactorily to use the common harrow-type of sterilizer, the inverted pan or any modification of these types. When the steam pressure is only 5o to 6o pounds or less at the boiler, and where it becomes necessary to carry this a considerable distance in the green-house, condensation takes place, and as a result these sterilizers cause puddling of the soil and otherwise inefficient work. In our experiments, all modified types of steam sterilizers which originated from those already mentioned were equally unsatisfactory; therefore, a method which could utilize a low steam pressure and still do good work without in-jury to the soil, seemed urgent.
The method to be described herewith was used in a span of fifteen greenhouses, which had the soil badly infected with nematodes. For two successive seasons previous to the treatment of the soil, the entire crops of tomatoes and cucumbers were a total loss. After unsuccessfully trying out all styles of steam sterilizers, the device herein described was devised and proved successful.
It should be remembered where 80 pounds or more pressure is obtainable, the aforementioned kinds of apparatus may give very good results, but where the pressure is less, as in many cases in steam heated plants, they are not satisfactory.
The necessary equipment for this new device consists of two 2 x 4'S cut at suitable lengths, a few boards either the entire length or half the length of the width of the greenhouse, canvas, burlap, sacking or tarpaulin. This method has been devised purposely for greenhouses growing vegetables on the ground, although modifications of this method could be made to suit other conditions.
The first operation in carrying out the work consists of digging a pit at one extremity of the house to the depth that one wishes the soil sterilized. The width and length depend somewhat upon the width of the greenhouse. In our work the pits were dug 12 inches deep, 6 to 8 feet wide and 10 to 15 feet long. Two 2 X 4'S are laid on edge in the bottom of the pit. These pieces should be the length of the pit and placed about 6 to 12 inches from the sides of the pit. One or two leads of steam pipes with T out-lets in the center and at the ends of the pipes should be laid in between these two stringers (2 x 4's). The pipes can best be run in from the ends of the pits. It has been found better to let the steam out in large quantities and not through perforated pipes. Pieces of 2 x 4'S are then laid across these two stringers and should be long enough to reach across the width of the pit. Quite a large number are necessary to form a kind of platform. About a quarter of an inch should be left between the 2 X 4 cross pieces to allow for the ascent of the steam (fig. 8, a, b, c.).
When the bottom has been laid, the soil which was removed can be thrown onto the platform. Boards should be staked around the sides of the platform to retain the soil. This forms a kind of wagon box. The steam can then be turned on, thermometers placed in the soil and the entire pit covered with any suitable covering to retain the heat.
Since steam rises, this method is much more satisfactory than where it becomes necessary to force the steam downward. There is no puddling of soil, even at the lower pressures, and 212 degrees F. and higher temperature can be obtained when sterilizing 12 inches of soil. It should be remembered that a few inches of soil below the wooden platform is likewise sterilized in this process. The skeleton platform is easily removed by means of an iron bar with a hook at the end for catching hold of the 2 x 4's and jerking them from underneath the soil. When the framework has again been set and the steam pipes adjusted in place, the platform is ready for the second batch of soil, which is dug immediately adjoining the soil which was just sterilized. In order to avoid extra labor, it becomes necessary to have one pit already dug just ahead of the bed being sterilized, so when the 2 x 4'S are removed they can be laid immediately in the pit which is ready for them. This is accomplished by erecting the second bed on top of the first one, i.e., on top of the soil just sterilized,
When the second bed is ready for sterilization (it is directly on top of the one first sterilized), one has a pit already dug to set the framework in for the third batch, and from hence on, a pit will always be in readiness for the framework. It will be seen by this process and by such procedure that it becomes necessary to return one batch of sterilized soil to the opposite end of the greenhouse, after the whole house has been sterilized. This is the second batch, which was sterilized and sets on top of the first. This cannot be avoided, but the soil can easily be carted back by means of wheelbarrows.
Many greenhouses are irregularly constructed, with uprights and other obstructions more or less promiscuously scattered; therefore, the pan method is often difficult to use and it is less easy with the other unadjustable apparatus, but with the method just described these obstructions are much less serious, since they can be allowed to come in any part of the bed without hindrance to sterilization.
There is a little more expense connected with this method, on account of extra labor which is necessary, but this method is not being advocated as a superior way of steaming the soil, but rather to do the work where situations arise that cannot be handled otherwise.
Effect of Soil Sterilization on Seed Germination. The main object in sterilizing soils is to destroy the harmful fungus flora. Of all the methods here recommended, steaming is the most effective. Not all soils, however, are alike benefited by this treatment. With lettuce seed, for instance, there is a higher per cent. of germination usually obtained in the sterilized soil. With tomatoes, however, germination is retarded under similar soil treatment. On the average, germination is favored by soil sterilization.
Effect of Soil Sterilization on Plants. That soil sterilization is practicable cannot be doubted. With some crops, the beneficial effect is especially marked. The Massachusetts Experiment Station f found a considerable increase in the production of violet blossoms as a result of soil sterilization.
Not only was production of flowers increased in the sterilized soil, but there was also a decided decrease in leaf spots.
Changes in the Soil due to Sterilization. Various investigators have found that by steam heating, the physical, chemical, and physiological properties of a soil are more or less changed. Through chemical action there is an increase of soluble matter in some of the inorganic substances such as potash and phosphoric acid as well as in the organic matter. Ammonia is also formed by the reduction of nitrates to nitrites and by the decomposition of organic compounds, large amounts of which are also made available for plant growth. This, then, would explain the reason of the stimulation of growth in sterilized soils. However, steamed soils may also contain injurious substances, which upon becoming soluble are harmful to plant growth and to the germination of certain seed. This seems especially the case in steamed soils deficient in lime. The investigations of Schreiner and Lathrop have shown that as a result of heating, dehydroxystearic acid is produced, and that this is harmful to plant growth. Heating soil produces both beneficial and harmful substances. The fertility is raised or lowered, depending on which of these predominates. The result, however, is influenced by the crop, the fertilizer used, and the amount of lime applied. Cole-man t has found that intermittent sterilization by means of dry heat at 82 degrees C. for five successive days in moist soil produced but very slight chemical changes. But this slow method is not very popular with the grower. Since, however, sterilized soils lose their harmful substances by standing, the treatment of the soil during the summer months, when there is no crop in the greenhouse, will obviate the main difficulty.
Other Methods of Controlling Damping Off. Damping off may be largely controlled by careful cultural conditions. Unless the soil of the seed bed has been sterilized, it is unwise to use the same soil in the beds where damping off has occurred previously. Thick sowing, too, should be avoided. In Table 4, Johnson presents some interesting data, showing the -effect of thick sowing on damping off.
Certain soils are especially favorable to damping off. Soils which contain a higher percentage of unrotted vegetable matter, and those which are hard to drain need special attention. Great care should be taken to keep the seed bed at the right temperature. The latter cannot be guessed at by personal sensation. It should be accurately determined by thermometers placed in the bed at suitable distances. It should also be remembered that any covering cloth or sash will exclude light and air. Every precaution should, therefore, be taken to prevent the seedlings from becoming "drawn," for in that condition they are most susceptible to damping off. The safest plan is to keep the temperature a trifle lower than is generally required, and to allow as much ventilation as possible. Very often damping off starts only in one corner of the bed. To check the rapid spread of the disease, the infected area may be removed. Spraying the seedlings with various fungicides in a bed where damping off has become well established will be of little help.
Control of Insect-Infested Soil. Spraying the soil will be of little value in the control of under-ground insect pests. Fortunately, however, there are other means of dealing with them. All insect pests may, of course, be controlled by steaming the soil in the benches.
Gut worms may be controlled by the use of a poisoned bran made as follows : To three ounces of molasses add one gallon of water and sufficient bran to make a fairly stiffened mixture. To this add a teaspoonful of Paris green or arsenic and stir well into a paste. A heaping teaspoonful of the mixture is scattered here and there over the infested bed. The cut worms will he attracted to the sweetened bran and after eating it will die from the poison.
SUMMER TREATMENT OF GREENHOUSE SOIL
The greenhouse is rarely used the whole year round. During the summer the house is usually idle one or two months. This is especially true regarding truck crops, for at that time outdoor products put the greenhouse out of competition.
It is a common belief that if the soil is allowed to remain dry in the intense heat under glass during July or August all injurious insects, fungi and bacteria will be destroyed. To determine this point Green and Green* have carried out some interesting experiments. They used beds which had been treated as follows : New soil, straw mulch, manure mulch, and a summer soil, sun-dried soil, in the greenhouse. The results of these experiments with tomatoes are shown in Table 5.
Plot 1908 1909 1910 1911 1912 1913 Average
New soil 5.2 4.5 3.5 ... 3.3 4.1
Straw mulch 4.9 3.2 3.1 ... ... 2.5 3.4
Manure mulch 5.1 4.2 3.0 ... 2.6 3.7
Dry 2.6 3.1 2.1 ... ... .9 2.1
It is seen from Table 5 that as far as tomatoes are concerned the new soil gave the best results. The manure mulch is second in productiveness. The effect of the dry mulch shows a rapid decline, and the dried soil showed the poorest yield. It must be added that in this soil the greatest amount of disease was present.
The result obtained with the soil treatment of tomatoes was found to be different from that with winter lettuce.
This table shows that the drying of the soil does not affect the lettuce crop to the same extent as it does tomatoes. Unlike most crops in the green-house, lettuce thrives best in old soil. On the other hand, cucumbers are as sensitive as the tomato to old, well manured soil in the greenhouse. This does not imply, therefore, that it is necessary to renew the soil every year for cucumbers or tomatoes. Soil sterilization, good drainage, and liming will tend to overcome the ill effect of old soils on these crops.