Fertilization, Soils and Cultural Practices EFFECTS OF GROUND-WATER TABLE AND SOIL COMPACTION ON NUTRIENT ELEMENT UPTAKE AND GROWTH OF SUGARCANE T. C. Juang and G. Uehara Taiwan Sugar Experiment Station Taiwan and Hawaii Agricultural Experiment Station Honolulu, Hawaii \ ABSTRACT Water-table depths were maintained at 80, 50 and 30 cm in ceramic pots filled with a sandy loam or clay loam soil. Sugarcane performed best in the treatment with water table held 80 cm below the surface. Radioactive P and Rb were placed in soil cores compacted to bulk densities of 1.2, 1.4, 1.6 and 1.8 g/cm3. Uptake of P and Rb decreased with increasing bulk density. This coincided with the decreasing root proliferation that accompanied increasing bulk density. A sharp reduction in nutrient uptake was noted between bulk density of 1.4 and 1.6 g/cm3. Sugarcane grown in pots containing soil compacted to bulk densities of 1.2, 1.4, 1.6 and 1.8 g/cm3 performed best in the 1.6 bulk density treatment. For comparable bulk densities, sugarcane performed better at the higher fertilizer level. INTRODUCTION Optimizing the physics of the rooting environment is one responsibility of a sugarcane agronomist. Good tilth is one aspect of soil physics. Soil physics, however, is more than tilth-it involves transport of water, air and energy and understanding the mechanics of porous bodies. The desired physical features of a soil, such as high water holding capacity, good aeration, resistance to compaction, and optimum thermal conditions, can be altered in some ways but not to the same extent as its fertility. It is also true that physical limitations, e.g. a shallow or compacted soil, can be overcome to some degree by more frequent irrigation and fertilization. The reverse is also true; a soil in good physical condition permits more efficient use of fertilizer and water by plants. Improved cane varieties, better fertilizer practice and in general streamlined management procedure have helped to raise sugar yield in Taiwan over the last 20 years. In the earlier years soil physical limitations were masked by the greater need to manipulate soil fertility factors. There is now a need to assess the role of soil physics in sugar production in Taiwan. Two soil conditions appear to merit attention. They are the level of the water table and soil compaction. Both factors affect soil aeration, rooting volume and the general health and proliferation of sugarcane root. MATERIALS AND METHODS In order to study the effect of water-table depth on growth and nutrient +id 1:;~ 679. J,trlil, ' P, 9<.!
680 FERTILIZATION, ETC. element uptake, ceramic pots 120 cm high with inside diameters of 30 cm were filled with soil and packed to a bulk density of approximately 1.3 g/cm3. A gravel layer 2 cm thick was placed at the bottom of each pot, which was in turn covered with filter paper before addition of soil. An inlet tube located at the gravel layer and connected to a constant head device permitted control of the water table. The water level was maintained at depths of 30, 50 and 80 cm from the surface. Each treatment was replicated 4 times. The test plant was var F 146. The soils used were a clay loam and a sandy loam collected from the Taiwan Sugar Experiment Station Farm. These soils were fertilized with N, P and K at the equivalent of 250, 150 and 300 kg/ha of N, P,O, and I<,O, respectively. A I-month-old, single-eye seedling was transplanted to each pot and grown for a duration of 2 months, with water applied to the soil surface. After 2 months the water table was adjusted to 30-, 50- or 80-cm depth, and maintained at theje depths for 6 more months. Plant height, number of stalks, and stalk length were measured at 5, 6 and 8 months. At harvest, green and dry weight of leaves, weight of dead leaves, total dry weight of above ground portion and roots were measured. The plants obtained all water from the water table during the last 6 months. The number 3 leaf was analyzed for N, P and K at 6 months and at harvest time. The stalk was analyzed for N, P and K at harvest time. In another experiment designed to examine the effects of bulk density on growth and nutrient element uptake by sugarcane, test soils were compacted into cylindrical cores to bulk densities of 1.2, 1.4, 1.6 and 1.8 g/cm3. The cores were 9 cm high and 5 cm in diameter. The core contained 0.32, 0.38, 0.43 and 0.48 millicuries (mc) of 86Rb for densities 1.2, 1.4, 1.6 and 1.8 g/cm3, respectively. For P, cores were treated with 0.32, 0.37, 0.42, and 0.47 mc of 3,P for the densities 1.2, 1.4, 1.6 and 1.8 g/cm3, respectively. The cores were prepared in a manner described by Trouse and Humbert (1961). The P test was run separately from the Rb test. Each density treatment was replicated 3 times. Cores were centrally placed in a pot filled with loose soil. The top of the core was placed 5 cm below the soil surface (Fig. 4). Two week-old single-eye seedlings were planted in these pots and harvested 3 and 3+ months later for the P and Rb tests, respectively. At harvest, top dry weight of primary stalk and tillers, including leaves, was determined. Radioactivity of 32P and s6rb was determined on tiller and primary stalk samples. All experiments were conducted in the greenhouse. The relation of dry matter production to bulk density was investigated by having concrete pots 60 cm high with 36-cm inside diameter packed with sandy loam or clay loam soils to bulk densities of 1.2, 1.4, 1.6 and 1.8 g/cm3. The top layer of each pot consisted of loose, nonfertilized soil. This layer formed a seed bed for a single, month-old, single-eye seedling which was planted in December 1967. A high and low fertilizer treatment was superimposed on the density treatment. The high fertilizer treatment contained the equivalent of 300 kg/ha N, 150 kg/ha P20, and 200 kg/ha K,O. These values were reduced to half for the low fertility treatments. Each treatment was replicated 3 times. Irrigation was scheduled by tensiometers placed at 50 cm depth. The crop was harvested in August 1968.
T. C. JUANG, G. UEHARA Effect of Water-Table Depth RESULTS AND DISCUSSION Fig. 1 and 2 illustrate the effect of water-table depth on cane growth at harvest time. The data are presented in Table 1. While the data in Table 1 Fig. 1. Effect of water-table depth on sugarcane gown in a clay loam soil. From left to right the water-table depths were 80, 50, and 30 cm. Fig. 2. Effect of water-table depth on sugarcane grown in a sandy loam soil. From left to right the depths were 80, 50, and 30 cm. Table 1. Plant growth index as a function of time and water-table depth for 2 soils. Time of Sampling 6 5 Months 6 Months 8 Months (Harvest) Total 1 Depth of water Stalk Stalk Stalk Number Dry stalk above ground Dry root Soil table length length length of wt. dry wt w t type ( 4 (cm) (cm) (cm) stalks (g) (9) (9) 30 54 133 178 4.3 564 992 61.5 Clay loam 50 48 123 165 4.8 579 1043 67.5 80 41 120 164 4.8 614 1144 76.8 Sandy loam 30 18 63 141 2.8 209 403 47.5 50 17 6 1 141 3.0 273 529 49.0 80 19 78 160 3.5 47 1 844 63.5
682 FERTILIZATION, ETC. suggest certain trends between growth index and water-table depth, many of them are not statistically significant. The most important index is the dry stalk weight at harvest time. For this, the 80-cm water-table depth resulted in a significantly higher yield than the 50- and 30-cm depths in the sandy loam soil. In the clay loam the 80-cm depth missed significance at the 5y0 level by a small margin. Fig: 3 and 4 show the development of sugarcane roots under conditions Fig. 3. Effect of water-table depth on root Fig. 4. Effect of water-table depth on root dedevelopment in a clay loam soil. From left to velopment in a sandy loam soil. From left to right the water-table depths were 30, 50, and riqht the water-table depths were 30, 50, and 80 cm. 80 cm. 'I of the 3 water-table depths. Interestingly, the increasing depth of root proliferation with increasing water-table depth is not associated with increasing root weight. This means that approximately the same quantity of roots was distributed over a shallower depth of soil in the higher water-table treatments. Since fertilizer was thoroughly mixed throughout the pots, one can anticipate better utilization of fertilizer in the 80-cm water table treatment, which allowed roots to extend deeper into the soil. This is borne out by the data in Table 2. However, the high levels of N, P and K in the tissue from all pots indicate that even the smallest root volume, provided by the shallowest water table, was sufficiently well fertilized to maintain adequate levels of these elements in the tissue. One can speculate that response to drainage and deeper water table would be highest on sugarcane growing on a low fertility soil during wet seasons.
T. C. JUANG, G. UEHARA 683 Table 2. N, P, K, and moisture levels of no. 3 leaf blade at 6 months for 2 soils. c 6 < Soil water table 30 2.00 0.22" 1.25" 79.5 80 2.22 0.24 1.32 78.4 30 2.09 0.2 1 * 1.20" 76.4 "Values in columns with asterisk are significantly (5% level or better) correlated with water-table depth. Fig. 5 shows how water became distributed above the water table in the 2 soils when the bottom end of a soil column 100 cm long was allowed to come in - 0 0 lllltttiii lll'i1lllp-ll 0 0.5 1.0 1.5 2.0 Moisture Content, gmlgm Fig. 5. Adsorption moisture distribution curves in vertical soil columns packed with a clay loam (a) and sandy loam (b) soil. contact with free water and allowed to remain in this condition for 2 weeks. Free evaporation was allowed to occur from the upper end. The results essentially describe the adsorption-moisture-characteristic curve for the 2 soils. There is a i j, \
684 FERTILIZATION, ETC. capillary fringe of about 10 cm and 20 cm, respectively, for the clay loam and sandy loam. One can readily see from Fig. 5 why sugarcane performed somewhat better when the water table was maintained 80 cm from the surface. The aerated zone in all cases is the difference between depth to the water table and the height of the capillary fringe. In the sandy loam soil the aerated zone is only 10 cm for the 30-cm water-table treatment. In the 80-cm water-table treatment the moisture profile is such that 60-70 cm of aerated and well watered zone is available for root growth. Ideally, one would want a water table which drops with sugarcane age so that the increasing rooting depth of the crop can be accommodated. When no supplementary irrigation is applied, as in this case, an optimum water-table depth is one 'which provides a sufficiently large aerated volume as well as adequate wateg supply from the water table. This study suggests that 80 cm is adequate dep,fh) I to a water table for the clay loam and sandy loam. Pao and ~un&('$'961) conducted a similar study in Taiwan using a sandy loam soil. They maintained water-table depths at 50, 100 and 150-cm from the soil surface, and observed the best growth in the 150-cm treatment. From their report it is not clear, however, whether the treatments received supplemental surface irrigation. One must presume, however, that the test crop received water from rainfall since the study was conducted in the open. Effect of Soil ~orn~actioni Data on P and Rb uptake from cores compacted to bulk densities of 1.2, 1.4, 1.6 and 1.8 g/cm3 are presented in Tables 3 and 4. The critical bulk density for nutrient element uptake and root proliferation falls between 1.4 and 1.6 g/cm3. As expected there is a significant correlation between nutrient element uptake (cpm/g dry-matter) and root proliferation (root dry weight). There is some indication that nutrient element uptake drops off more rapidly than root proliferation, suggesting that roots which manage to enter compacted clods are not as effective absorbers of nutrient elements as their counterparts growing in loose soil. Table 3. Effect of bulk density on P uptake and root proliferation. Root dry wt Bulk density P in core Soil (glans) (c~m/g DM) (g) 1.2 385a* 0.4Ga Clay loam Sandy loam \ 1.8 22b 0.20b * Means not followed by the same letter are significantly different at the 5y0 level. I
T. C. JUANG, G. UEHARA 685 Table 4. Effect of bulk density on Rb uptake and root proliferation. Rb Root dry wt in Bulk density (cpm/g DM) y"'e (g) 1.2 10a' 0.42a 1.4 12a 0.36~1 1.6 4.5b 0.30a 1.8 5.5b 0.05b 1.2 28a 0.39a 1.4 18a 0.61a 1.6 8b 0.28a 1.8 8b 0.27a *Means not followed by the same letter are significantly different at the 5% level. In general, bulk density of coarse textured soils tends to be higher than fine textured soil. For this reason coarse textured soils tend to have higher critical bulk densities for root proiiferation than fine textured soil. Table 5 shows that, while soils differ in their critical bulk densities, the difference between their critical bulk densities and their normal field densities is similar. ee of compaction which soils can Table 5. Difference between critical and normal bulk densities for Hawaiian and Taiwan sugarcane soils. Normall Critical2 Soil name density density Difference (A) (B) (A - B) Hydro Humic Latosol 0.6 0.8' 0.2 Humic Latosol 1.06 1.21% 0.15 1.3' 0.1 1.3 1.5 0.2 Alluvial soil, sandy loam 1.3 1.5 0.2 * Trouse and Humbert (6). 1 Normal density is defined here as the maximum density at which healthy root development can be sustained. 2 Critical density is that density wherein root deformation is readily apparent. i).i. 4
686 FERTILIZATION, ETC: undergo is relatively constant before root growth is affected, they indicate nothing about the compactability of each soil. Sugarcane soils of Hawaii, particularly the latosols, have excellent structure (Cagauan and Uehara, 1965; Uehara, Flach and Sherman, 1962) and resist compaction. This is because the soils consist mainly of kaolinite and free oxide of Fe and Al. In Taiwan on the other hand, the soils which suffer from poor drainage and compaction contain large quantities of fine-grained micas and expanding clay (Juang and Hsieh, 1968). The soils of Taiwan undergo structural deterioration much,more readily than soils of Hawaii. Soil compaction in Hawaii is mainly the consequence of using heavy mechanical equipment for cultivation and harvesting of sugarcane. In Taiwan the inherently poorer physical conditions result in soil compaction even without the use of heavy equipment. Relation of Dry Matter Production to Bulk Density While the core experiment showed that lower amounts of mineral elements were extracted from compacted material and fewer roots penetrated the denser cores, this trend was not found to be true when the entire soil in the pot was compacted. This is shown by the data in Table 6. The best top and root Table 6. Effect of bulk density and fertilizer level on green weight of sugarcane. Bulk density Fertilizer Soil (g/cm3) level -- - - Clay loam 1.2 High 1.4 High 1.6 High, Av. stalk no. Av. stalk length (cm) Green wt/ Pot (kg) Dry root wt/pot (g) 200 175 245 265 495 430 1.8 High 7.9 59, 2.10 320 7.0 59 1.75 265 Sandy loam 1.4 High High High High growth occurred in soil compacted to bulk density of 1.6 g/crn3. In the clay soil the top and root weights were higher for plants grown in soil of 1.8 bulk density than plants grown in 1.2 bulk density. These statements are based on the existence of a significant curvilinear regression of green weight and dry root weight on bulk density with maxima occurring near bulk density 1.6.
I T. C. JUANG, G. UEHARA For comparable densities, higher top and root weights were generally obtained in pots which received the higher fertilizer treatment. The average increase in top weight was approximately 0.11 kg for each additional 100 kg of nitrogen, 0.21 kg for each additional 100 kg of P,O, or 0.16 kg for each additional 100 kg of K,O, when all bulk densities were averaged. Part if the increased growth with increasing bulk-density can, therefore, be attributed to the higher fertilizer content per pot in the higher density treatments. This higher fertilizer content arises from the fact that fertilizer added to each soil was constant on a weight basis for all pots, and thus not constant and higher in the high density pots on a volume basis. One can speculate that if fertilizer was still a limiting factor, plants might respond to the higher fertilizer content in the high density pots. The response to the higher bulk density was obviously the result of more than merely increasing fertilizer concentration. Root weight was in all cases maximum or near maximum in the pots with soil compacted to a bulk density of 1.6 g/cm3. Shiue (1967) conducted a similar experiment using corn as the test plant and measured decreasing growth with increasing bulk density. His densities ranged from 1.2 to 1.9 g/cm3. For comparable densities he obtained significant responses to irrigation, but could show no response to fertilizer. Kong (1968), using the same soils as Shiue, grew sugarcane as the test crop and recommended bulk densities be kept below 1.6 g/cm3. It appears that for sugarcane, bulk density in itself is not a particularly useful index for predicting crop performance. A well fertilized and aerated soil supplied with adequate water appears to be able to grow healthy sugarcane even at relatively high bulk densities. REFERENCES 1. Cagauan, B., and G. Uehara. 1965. Soil anisotropy and its relation to aggregate stability. Soil Sci. Soc. Amer. Proc., 29:198-200. 2. Juang, T. C., and T. S. Hsieh. 1968. Clay mineralogical studies of Taiwan sugarcane soils. Proc. ISSCT, 13:769-778. 3 ICong, L. 1968. Effect of soil compaction on the growth of young cane plants. Journ. Chinese Agri. Chem. Soc., 6:91-94. 4. Pao, T. P., and S. L. Hung. 1961. Effect of depth of underground water table on growth, yields and root system of sugarcane (NCo 310). Taiwan Sugar Expt. Station Report, 24: 19-54. 5. Shiue, J. J. 1967.- Effect of soil bulk density on the growth of sugarcane. Taiwan Sugar Expt. Station Report, 44:195-201. 6 Trouse, A. C., and R. P. Humbert. 1961. Some effects of soil compaction on the development of sugarcane roots. Soil Sci., 91:208-217. 7. Uehara, G., K. Flach, and G. D. Sherman. 1962. Genesis and micromorphology of certain soil structural types in Hawaiian latosols and their significance to agricultural practices. Int'l. Soc. Soil Sci. Trans. 1962:264-269.