| Teak (Tectona grandis Linn f.) is one of the most well known timber species in the world. The species has been widely introduced into counties or regions in the tropics due to its high timber qualities, highly economic value and market demand. It was introduced into China over 170 years. In recent decade, teak plantations have been attracted investment interests from and have been rapidly and largely established by private companies or individuals mostly using superior clones in the southern part of China. The climate conditions in south China are suitable for the growth and development of teak, in terms of light intensity, temperature, rainfall and moisture in the region, but site conditions are highly variable. Soils in south China are mostly and highly acidic. Soil acidification usually causes loss of available nutrients, particular calcium element, limiting the growth and development of teak. The present study aims to identify and overcome Ca limiting nutritional factor. The detailed aims are (1) to establish teak foliar diagnosis index and norms; (2) to assess if teak growth is limited by Ca, and to establish foliar Ca critical value; (3) to make out suitable Ca-fertilizer and the relationship between Nitrogen, Phosphorus, Potassium, Boron and Calcium nutrients and their optimal rates and ranges on acidic soils.Firstly, this study focused on the evaluation and diagnosis of tree nutritional status in teak plantations planted on acidic soils of Guangdong province. Secondly, two pot culture experiments and four field trials were conducted by employing Randomized Block Design, Split Plot Design, Optimal Hybird Regression Design (311-A) and Orthogonal Experimental Design respectively. Optimum Ca concentration range and critical value in leave of teak clone seedling and young plantations were singly established. The results contribute to the establishement of suitable Ca fertilizer application both in lateritic red soil and in purplish soil, optimal rates f Ca, B and N for seedlings, and the optimum range of Ca, B and N rates as well as N, P, K and Ca rates for teak plantations. One laboratory experiment was undertaken to test the growth and nutrient-uptake responses of teak seedlings in vitro to Ca concentrations and pH treatments of subculture medium.The results of nutrient diagnosis for 19 representative teak plantations of 5-8 years old and totaling 7 experiments or trials were summarized as follows.1)Stepwise multiple regression analysis indicated that N, Ca, Zn, B and Fe in leave, available P, base saturation percentage, Zn and Al in soil properties were the main factors affecting tree nutrition and growth. The mean annual volume increment of teak can be estimated by N and Ca concentration in leave, or by soil available P concentration and base saturation percentage based on established regression functions. To increase soil total P content and base saturation percentage can not only suppress exchangeable Al activities, but also can enhance soil pH value and concentration of N and Ca in leave. Only Ca and Mg contents in soil were enhanced, can the increase of soil base saturation percentage benefit to teak growth.2) Diagnosis and Recommendation Integrated System (DRIS) on teak plantations indicated that the nutrient balance of Ca with Mg, Fe and Al is the key to promote the growth of teak plantations. The optimum value of three diagnosis indices, Ca/Mg, Ca/Fe and Ca/Al, is 3.52,46.78 and 67.52,with balance range from 3.23 to 3.80,26.54 to 67.01 and 1.41 to 93.63 respectively.3) The optimum Ca concentration in leaves of clone 7559 seedlings (six month old) ranges from 10.05 to 10.35 g·kg-1,and critical value ranges from 8.36 to 8.54 g·kg-1. The optimum concentration of five nutrients in leaves of clone 7544 plantation (seven month old) on acidic lateritic red soil respectively range were 0.354-0.659 g·kg-1 for water-extractable Ca, 3.44-5.21 g·kg-1 for total Ca, 2.4-3.44g·kg-1 for P, 2.147-3.215g·kg-1 for Mg, 49.60-73.59 mg·kg-1 for Mn, and 19.40-23.046 mg·kg-1 for Zn, and the critical value is 0.35g·kg-1 for water-extractable Ca, 3.44g·kg-1 for Ca, 2.4 g·kg-1 for P, 2.15 g·kg-1 for Mg, 49.6 mg·kg-1 for Mn, and 19.4mg·kg-1 for Zn respectively. The critical value of Ca in leaves of 5-8 years old plantations is 7.267 g·kg-1,and optimum Ca concentration ranges from 7.267 to 13.55 g·kg-1.4) An experiment to test the growth and nutrient-uptake responses of teak seedlings in vitro to 0,3 , 6 , 9 and 12 mmol·L-1 of calcium concentrations and pH treatments of subculture medium. Results indicated that the height increments and dry weights of leaf and stem were positively related to the Ca2+ concentration. The height increments and dry weights of leaf and stem at optimum Ca2+concentration at 9 mmol·L-1 increased by 50.0% and 65.2%, compared with the control. The height growth was significantly affected by pH treatments, and the optimal pH value was 6.0; The interaction between Ca2+concentrations and pH values was not significant.5)Ca-spray (CaCl2 and Ca (NO3)2 ) on the leave of teak seedlings can significantly promote seedling growth, such as height and root collar diameter, enlarge leaf area and absorbing and active absorbing area of root system, increase the number of lateral roots and root volume, and creat biomass accumulation of leave, stem, and total dry biomass. In Comparison with the control (Water-spray), the growth increment in terms of height, root collar diameter and total dry biomass at the six month after discharging sprays of CaCl2 of 3 and 30 mmol (Ca2+)·L-1 increased by 69.7% and 72.1%, 32.8% and 40.0%, as well as 53.3% and 61.3% respectively. The effectiveness of discharging sprays of CaCl2 is better than that of Ca (NO3)2, and 30 mmol(Ca2+)·L-1 concentration is more effective than 3 mmol(Ca2+)·L-1 .6) The growth of trees at six months with three Ca-fertilizers treatments on both sites showed significant difference. On the acidic lateritic red soil, the height (H) and root collar diameter (RCD) growth was increased with increasing amount of CaO (lime), and CaO was the best Ca-source fertilizer. The height increment of CaO treatment was increased by 11.9% and 12.2% compared with that of Ca (NO3)2, and CaSO4, and the growth of root collar diameter was increased by 6.2% and 20.4% respectively. However, on the acidic purplish soil, the H and RCD growth was increased with increasing amount of Ca (NO3)2. Ca (NO3)2 was the best Ca-source fertilizer. The height increment at this treatment was increased by 8.7% and 22.5% compared with that of CaO and CaSO4, and the growth of root collar diameter was increased by 5.1% and 10.7% respectively.7) A pot culture experiment of was carried out to study the growth response of teak clone seedlings in acidic lateritic red soil to Ca (0-1.2g·kg-1), B (0-0.8mg·kg-1) and N (0-1.2g·kg-1). The results indicted that the growth of seedling height, root collar diameter, and dry mass of leave,shoot (without leaf) and root weights were greatly significant difference among 11 treatments. Ca (CaO), was identified to be the major nutrient element, and a limiting factor for seedling growth in acidic soil. The seedling growth was evidently supressed with the increasing addition of N ((NH2)2CO) while no or little lime was applied. The optimal nutrient rates were Ca 1.2 g·kg-1, B 0.4 mg·kg-1 and N 0.3 g·kg-1, equivalent to CaO of 1.68 g·kg-1 , H3BO3 of 2.3mg·kg-1 , and (NH2)2CO of 0.65g·kg-1. Moreover, the same field test trial on acidic lateritic red soil revealed that the growth of tree height and root collar diameter at six months was significantly affected by Ca, B and N. Calcium was also identified to be the major nutrient element and limiting factor.Response Surface Methodology (RSM) was fitted for modeling optimization of height and root collar diameter growth as a function of three variables. The optimal application rates ranged: Ca 615-647.4 g·plant-1,B 0-0.101g·plant-1 and N 18.27-21.93 g·plant-1, equals to optimal CaO 869.7-915.5 g·plant-1, Borax 0-0.96 g·plant-1 and (NH2)2CO 39.7-47.7 g·plant-1.8) A field fertilizztion trail of rates of N, P, K and Ca on acidic lateritic red soil showed that both Ca and P significantly promoted the growth of tree height and diameter at breast height, while N and K had no significant effects. The optimum range of N, P, K and Ca was N 0-75g·plant-1,P 150-225g·plant-1,K 0-75g·plant-1 and Ca 867g·plant-1,and corresponding ranges of fertilizers were (NH2)2CO 0-163g·plant-1, calcium-magnesium phosphate compound 1071-1607 g·plant-1, KCl 0-125 g·plant-1,lime 1000 g·plant-1. On this soil,the optimum rates of Ca, N, P and K can promote teak to effectively uptake necessary nutrient. Teak grew worst when without or inadequate lime and phosphate application. Ca concentration in leaves of 7 months old of teak plantation in this trial was closely related to the growth potential of its spouting plantation of 6 months old after cut. It can be used as an index or predictor to diagnose and predict the growing status of its sprouting plantation. |
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