DETERMINING SUITABILITY OF SOILS FOR PECANS

Pecan Research
-------------------- L. D. Romberg, Soil Specialist, State Dept. of Agriculture, Austin, Texas Mr. Burkett has just told you that he desires to have the suitability of our various Texas soils to pecan orcharding determined and that he has assigned me to this work and is holding me responsible for results. This is a great problem---that of determining beforehand by examination of the soil and subsoil and other information what results may be expected from the soil if proper care is given the trees. I do not know to what extent I will succeed in securing data on the effects of various factors necessary for these determinations, but I am sure here is a big field for very beneficial investigations. As yet I have not been able to analyze many of the types of soil taken in field work on account of other work and lack of equipment. So at this time I can only make a few statements drawn from observation. The chief need for pecan growing on most Texas soils is moisture. This we may secure from three sources. We may secure moisture in time of drought by capillary movement from a permanent water table underneath. Just how deep this may be on various subsoil types and still be effective probably no one knows. I am of the opinion that it must be much nearer the surface than generally thought, but as yet have no conclusive data on this point. According to my observations the great bulk of the pecan root system is near the surface, and the physical composition of the soil and drainage affect this considerably. I would estimate that on heavy clay 90 per cent of all roots are generally within three feet of the surface, on loam four feet, and on sand five feet. Where drainage is poor the depth is still less. I know many pecan men will disagree with me, and I may be wrong, as my observations have not been very extensive, but if they will measure all lateral roots of some natural pecan tree to the depth of ten feet or more and then the tap root, which will be comparatively small, tapering, and nearly free from lateral roots at this depth, apparently serving as an anchor, they will, I believe, find that the cross sectional areas of the lateral roots and tap root below combined will be approximately equal to the cross sectional area of the tree at the crown and the percentage of cross sectional area distributed as above stated. I have found that the lateral roots extend a surprising distance from the tree. A root two inches in diameter will sometimes go 50 feet, but approximately parallel to the surface of the ground. So I do not think the pecan secures very much moisture from below three to five feet except through subsoil capillarity. We may supply moisture by irrigation, provided the supply is dependable, the cost reasonable, and that the water is free from injurious salts. The latter point is important and applies to soil too. The worst rosette I ever saw was on a soil where it was only 10 feet to water. A chemical analysis of the water solution of a composite sample of this soil to the depth of eight feet showed the presence of.029 to.039 per cent of black alkali (NA2 CO3). On nearly all upland soils and to some extent on bottom soils we must depend 62 FOURTH ANNUAL SESSION on the rainfall stored in the soil for moisture. Except where rainfall is abundant the best upland pecan soils are necessarily those that are adapted to moisture retention and conservation, and that are favorable to the proper activity of the root system. A heavy clay soil is not adapted to pecan growing. In the summer droughts it cracks---often to a depth of several feet-and really dries out more than a lighter soil, though it may hold more moisture to begin with. The feeding roots being shallow and capillarity slow, are unable to secure the moisture needed. When summer plowing is practiced on such a soil it nearly always results in rosette. On the other extreme, we have the very deep, loose sandy soil. Such a soil is deficient in moisture holding capacity and generally deficient in plant food. Where such an upland soil was found the trees were generally rosette, often in spite of the best care and applications of fertilizer. However, on river bottom soils that overflow this was not found to be the case, possibly due to greater fertility. Between these two extremes are a great many types, both of top-soil and subsoil. A heavy top soil of a foot or eighteen inches over deep, loose sandy subsoil is very undesirable. A seven-year planting observed on such soil contained a great deal of rosette, many trees had died back to the ground, and the largest were about three inches in diameter. Such subsoil is unable to hold much moisture to lift it any appreciable distance by capillarity, and the heavy top soil will not conserve the little moisture there is below. This is just the reverse of what is desired. On postoak upland, with a sandy, loam top soil and clay subsoil, splendid wild pecan trees are generally found. Some of this is even better than some river bottom land where pecans are native. We have taken a considerable number of soil samples to the depth of eight feet, both by thrifty and by unhealthy trees, on uplands and bottom lands in various parts of the State ,part of which we have begun to analyze. The information secured should certainly be of value in determining the suitability of other soils. A great many things must be considered in this problem. No doubt the source and individuality of the seed often accounts for a puzzling behavior of trees that is attributed altogether to the soil. There is a great deal of difference in the constitutional vigor and adaptation of different trees. This may be seen in any orchard of uniform age. More attention should be given to the selection of seed adapted to the section of the State in which the trees are to be planted and all weaklings should be culled out---possibly 50 per cent or more. Seed is too cheap to use weaklings as foundations for trees to bear fine pecans for the many years to come. As I have said, our investigations have not been carried far enough to draw definite conclusions as to the relation of the mechanical composition and other qualities of soil to pecan growth. So I will just make a general outline of some of the things that should be considered in the selection of land for pecan growing. 1. The mechanical composition to a depth of eight feet or more, its. TEXAS PECAN GROWERS'ASSOCIATION 63 relation to moisture supply, root development and activity, drainage, soil fertility, etc. 2. The moisture supply as affected by the amount, regularity, seasonal distribution, and dependability of rainfall; the depth and permanency of the water table; the cost, dependability and suitability of water for irrigation; the mechanical composition of the soil to a considerable depth and its relation to water retention and conservation, and the movement of capillary water; cultural methods that may be used, etc. 3. The soil fertility as shown by a chemical analysis of this soil or a similar soil and by crops grown; whether the fertility has been maintained or depleted-if depleted, can it be built up and maintained profitably; is the soil level, rolling, or sloping; what is the physical nature of the top-soil and subsoil; how much rainfall is there; how much organic matter and commercial fertilizer will be necessary; is the soil adapted to the necessary operations, etc. 4. Is the soil drained; does water seep from above; does the land over- flow, how often and when; is the subsoil porous; does the water drain away; does vegetation indicate soil aeration; does the soil make good crops; does excessive moisture interfere with the operations of tillage, etc.; is drainage sufficient to allow deep pecan root development; how does the water table fluctuate; does the soil ever get very dry, etc. 5. Does the land overflow, how often and at what times of the year; may the soil be cultivated or will it wash; are the overflows beneficial; what is the danger of flood damage to the pecan crop and trees, to intertilled crops, to buildings, stock, etc. 6. What is the state of cultivation-is the land free from stumps, Johnson grass and Bermuda grass; what will be the cost of tilling properly. 7. Does the soil contain injurious salts, is it sour, or is it free from these. 8. Is pecan culture practical from the viewpoint of economics and farm management; does the soil require fertilizer; is the area adapted to the profitable use of modern machinery; who is going to take care of the trees; what is the first cost and final cost of the land and orchard, etc. --------------------------------- REFERENCES ON PECANS Farmers Bulletins: No. 700 Pecan Culture, With Special Reference to Propagation and Varieties. No. 843 Important Pecan Insects and Their Control. No. 995 Preventing Wood Rot in Pecan Trees. No. 1129 Diseases of Southern Pecans. The above may be obtained free by writing your Congressman 64 FOURTH ANNUAL SESSION or the Chief of the Division of Publications, U. S. Department of Agriculture, Washington, D. C. Department Bulletins: No.571 The Pecan Leaf Case Bearer. No.756 Pecan Rosette in Relation to Soil Deficiencies. No.1038 Pecan Rosette. No.1102 Kernel Spot of Pecan and Its Cause. No.2509 Notes on the Early History of the Pecan in America. May be obtained free as stated for Farmers Bulletins. Georgia Experiment Station, Experiment, Ga.: Bulletin No. 116 Pecans. Bulletin No.124 Two Groups of Varieties of Hicora Pecan and Their Relation to Self-Sterility. Press Bulletin No.132 Varieties of Pecans at the Georgia Experiment Station. Circular No.76 Report on Pecan Varieties for 1914, 15, 16. Texas Agricultural Experiment Station, College Station, Texas: A bulletin (perhaps two), dealing with the Pecan Nut Cast Bearer will be ready early in 1925. Circular No.20 Patch Budding in Large Limbs and Trunks of Pecan Trees. Bulletin No.187 Sprays and Spraying. Bulletin No.293 Cultivation and Care of Trees on Texas Farms. Texas Agricultural Extension Service, College Station, Texas: The supply of older publications has been exhausted, but a new Pecan Bulletin is now on the press. and is expected to be ready by Fall of 1924. Texas State Dept. of Agriculture, Austin, Texas: The supply of older publications has been exhausted. The Pecan in Texas (now on the press. Be ready early fall of 1924). Florida Agr. Experiment Station, Gainesville, Fla.: Bulletin No.147 Diseases and Insect Pests of the Pecan. Bulletin No.170 Top-Working Pecan Trees. Press Bul.No.351 A Spray Schedule for Pecans (1924). State College of Agriculture, Athens, Ga.: No.132 Pecan Growing in Georgia. No.258 Pecan Rosette. Louisiana Experiment Station, Baton Rouge, La.: Crop Pest Notice No.2 Phyloxera Gall Affecting Pecan Trees. Pecan Publications: The Pioneer Pecan Press, published at San Saba, Texas. The American Nut Journal, published at Rochester, N.Y. (Both the above are monthly.)