The Bittersweet differed from sour orange in fewer laterals and very few fine fibrous roots. However, the tap roots penetrated slightly deeper than sour orange. With the sweet oranges, Pineapple and Parson Brown, the root systems were very similar. Both showed well developed central roots, usually two, penetrating about the same depth as sour orange, about 90-125 cm deep, with numerous small laterals the full length of the tap roots. The laterals in the upper 30 cm of soil were not as long as sour orange. There were abundant fibrous roots in the first 30 cm. Their data did not agree with what Mills observed in California’s cooler and loamier soils, but rather with Hume’s observations in Florida, that roots of sweet orange and sour orange are about equal in development, which Oppenheimer also reports in the sandy soils of Israel. Rough lemon had the most vigorous root system of all 15 stocks. It had exceptionally large lateral roots with a spread of 150 cm or more from the trunk. The central tap extended as deeply as sour orange, but the fibrous roots were not as abundant around the crown as sweet orange or sour orange. For Duncan and Bowen grapefruit they found an abundance of fibrous roots and many large vigorous laterals and two or more large penetrating tap roots extending 92 cm with a mass of fibrous roots the full extension. The abundance of fibrous roots agrees with observations by Mills and Oppenheimer . The trifoliate orange had deeply penetrating central roots and numerous laterals with abundant fibrous roots in the upper 31-46 cm of soil. The root system was similar to sour orange except for the smaller spread of the laterals. Cleopatra mandarin had a cone-shaped root system with well developed central roots penetrating 125 cm or more. There were long fine-textured lateral roots in the upper 61 cm of soil well supplied with fibrous roots. Its root system didn’t differ much from sour orange except the tap root was straight, slightly longer, and less divided. The root system of Suen Kat was similar to Cleopatra. The root system of Morton Citrange had the tap root dividing into several which penetrated vertically and then fanned out,vertical farming equipments descending obliquely to about 91 cm. The laterals were similar to sour orange, with a good fibrous system.
The Rusk citrange was similar in root structure to Morton except there were fewer fibrous roots.There were no tap roots. The root system resembled grapefruit in fibrous roots, but grapefruit had a pronounced tap root. The Cuban Shaddock had a root system almost identical to Rough lemon except it had more fibrous roots. The calamondin had a group of vigorous central roots which penetrated deeply, in fact, more deeply than any of the other stocks observed. Yuzu displayed the smallest root system of all 15 stocks observed. It penetrated deeply, and there was a scarcity of laterals. Sweet orange cuttings had a shallow root system with many vigorous laterals which did not penetrate more than 61-91 cm. Savage, Cooper, and Piper thus concluded that Rough lemon and Cuban Shaddock had the most extensive root system, the calamondin the deepest, and sweet lime and grapefruit had the greatest amount of fibrous roots. In [date lacking] [“Check” appear here in typescript in the margin of the manuscript], Ross reported that trifoliate orange produces a well-branched root system with an abundance of fibrous roots which are very sensitive to drying. Robinson grew ten scion varieties on Cleopatra mandarin and sour orange in Norfolk sand in Florida, and at nine years of age reported that Cleopatra produced a deep tap root with numerous fibrous roots superior to sour orange. In India, Burns and Kulkarni exposed roots of Santara and Mosambi on Jamburi from fiveyear-old trees growing poorly. With the Santara trees 320 cm high, the lateral roots extended 42 M and average 2.5 M. The root spread was greatest parallel to the tree rows. With the Mosambi trees having a height of 2.1 M the diameter spread of the roots was 1.8 M. A 14-year-old tree of Santara had roots with a radius of 3 M with secondary roots of 4.9 M. The laterals were about 23 cm deep. He concluded Jamburi was surface rooting with a fair spread of laterals, but few deep penetrating roots under the tropical conditions of India. In Ceylon , Gandhi examined the root systems of Mosambi trees planted 5.5 x 5.5 M. The spread of the crown roots was 3.7 M, or less than 1.8 M between trees. Roots had spread 2.7-4.9 M from the crown and at four years the roots were intermingled. Grapefruit trees on Rough lemon at five years had a lateral spread of 4.9 M. Fifteen year-old Santara trees planted 4.6 x 4.6 M had roots which completely intermingled and extended trunk to trunk. The Santara trees on Rough lemon at 14 years had roots extending a radius of 3 M, some 4.9 M, and a similar situation occurred with Mosambi. He only studied the lateral spread of surface roots. He did not feel it necessary to ascertain the distribution of fibrous roots since he felt only the exposure of laterals to a depth of 10-20 cm was enough to give a general idea of the nature of the fibrous roots.
Gandhi also stated that the depth of rooting, lateral spread of main and subsidiary roots and their branching, and quantity of fibrous roots are specific characters. These specific characters may vary with different species, but the location of the fibrous roots on the root system did not seem to be a specific character. He felt it appeared to be more a result of environment and cultural treatment. Montenegro in Brazil found that sour orange seedlings had more superficial and less horizontal extensive root systems than Caipira sweet orange, and poorer feeder root systems as compared to the well-developed system of the Cravo tangerine. The root system of Caipira sweet orange was deep and had a vigorous feeder root system. The most vigorous root systems were Florida Rough lemon, sweet orange and Cravo tangerine. The least vigorous root systems were Rangpur lime, sweet lime, and trifoliate orange. Hamlin sweet orange scions strongly stimulated feeder root development in root stocks. This effect was moderate with Pera and slight in Baianinha sweet orange. Root development was more vigorous in well-drained and aerated soil than in imperfectly drained,vertical farm tower shallow layered soil. Exocortis and tristeza checked root development. Extensive root development was not necessarily associated with large tree crowns or high fruit yields. As root stocks for the sweet orange varieties Hamlin, Pera, and Baianinha, Rangpur lime stock showed poorer feeder root development than Caipira, Pera, Cravo tangerine, or Florida Rough lemon. Vigor was medium on Sampson tangelo which is deep rooted like Florida Rough lemon. Trifoliate orange on clay soils produced fewer roots than Florida Rough lemon, Cravo tangerine, or Caipira orange. With Baianinha scions Caipira was more abundantly rooted than Rangpur lime, Brazilian Rough lemon, or sweet lime. Nucellar clones of Baianinha on Caipira had excellent root development superior to that of an old clone on Pera orange or Cleopatra mandarin. Seedlings of Caipira orange rooted more deeply than those of sour orange and Cravo tangerine, and in these instances the roots tended to be massed around the trunk base. Ten-year-old Hamlin oranges on either trifoliate orange or sweet lime had 90 per cent of the root system within 90 cm of the surface, but for all of the remaining ten-year-old combinations of scion and stocks the top 60 cm of soil contained 90 per cent of the roots. On light soils the roots of grafted and seedling trees of Baianinha extended down to 90 cm.
In Japan, Okuchi et al. excavated a single tree of Satsuma mandarin on trifoliate orange which was 22 years of age. Roots extended down to 120 cm so the distribution was similar to that observed by others. Most roots were within 1 M of the trunk. The horizontal and vertical distribution of the roots showed 93 per cent within 2 M of the trunk and 94 per cent within 60 cm. Most feeder roots were within 20 cm of the surface with only a few at deeper depths. In Egypt, El Azzouni and Wali excavated the whole root system of 15- year-old Washington navels on Rough lemon, lime and sour orange. Roots were graded according to diameter and dry weights taken. There was some variability among trees on the same species. Roots of all stocks extended laterally outside the 5 M zone allocated. Sour orange extended laterally the most, with lime the lowest, and Rough lemon intermediate. The roots outside the 5 M radius were considered minor compared to the total root distribution. There was a high percentage of fibrous roots on all stocks. Woody roots .75 cm in diameter and greater extended 2.4 M from the trunk and beyond the 5 M radius, so greater extension was needed. Sour orange roots extended vertically 1.5 M, although Rough lemon and lime extended to 1.2 M with Rough lemon deeper than lime. Much of the root system of all three stocks was located in the 15-30 cm depth. There were considerable roots at .6 M, with lime having more roots in this zone than either Rough lemon or sour orange. Lime had the shallowest roots, Rough lemon intermediate, and sour orange the deepest. There were no direct orientation effects. Sour orange had the highest weight of total fibrous roots, with Rough lemon intermediate and lime the lowest. In contrast, the net weights of lime showed the highest percent of fibrous roots followed by Rough lemon and sour orange. All these stocks had fibrous roots located in the first .3 M and second .6 M, and with lime most were in the first .3 M, especially at 15 cm, even though the orchard was cultivated. Sour orange had the greatest root weight, followed by Rough lemon and lime, in that order. There were no tap roots on any of the stocks. Ford found Rough lemon roots penetrated to a depth of 4.3-5.2 M at 15 years of age in the warm deep well-drained Lakeland fine sand of Florida’s central ridge. At 25 years, the total amount of feeder roots was greater at the 76-152 cm zone than the 0-25 cm zone. Fifty per cent of the feeder roots were below 76 cm, and 15 per cent below 2.7 M. At 18 years sour orange feeder roots only penetrated occasionally to a depth of 5.2 M in sandy soils. Trees on Rough lemon had more feeder roots below 76 cm than trees on sour orange. The feeder roots of grapefruit were confined to 2.1-2.4 M zones. Temple oranges on Cleopatra had feeder roots to 5.2 M at nine years of age. Sweet orange at 15 years had root penetration to 3.4 M and had the greatest total weight of feeder roots per unit volume of soil than any other root stock observed. He reports Rough lemon feeder roots 7.6 M from the trunk. However, Ford reported Rough lemon roots had extended laterally a distance of 16.8 M. At Riverside, the author also observed the greatest lateral extension of roots on Rough lemon. One root extended parallel to the irrigation furrow a distance of over 9.1 M and was over 2.5 cm in diameter at the point at which it was severed during its removal. Ford reports that citrus trees in central Florida are very deep rooted. The root system of Rough lemon may penetrate to depths of 3 M at 6-8 years of age. Although 40 per cent of the feeder root system of a young five-year-old tree may be in the upper 25 cm of soil, by the time the trees are 20-30 years of age more than 50 per cent of the feeder root system may be below 76 cm in the soil, and of this amount 19 percent may be found below 2.7 M with roots extending down to 4.3-5 M.