Eng Hai Lok?Bernard Dell

Phosphorus requirements for containerized Pterocarpus indicus seedlings

Eng Hai Lok1?Bernard Dell2

Pterocarpus indicus Willd is a tropical woody legume that holds promise for plantation forestry.Two glasshouse experiments were undertaken on two soiltypes to determine the phosphorus(P)concentration ranges in the foliage of P-stressed and healthy plants,and to define critical P concentrations for the diagnosis of deficiency and toxicity.There was a narrow range in rates of P fertilizer, supplied as Ca(H2PO4)2·H20,between deficiency and toxicity compared to other tree species.The relationship between shoot yield and P concentration in the youngest fully expanded leafenabled criticalP concentrations for the diagnosis of deficiency(0.17%)and toxicity(0.41%)to be determined at 90%maximum yield from linear regressions fitted to the data.The foliar P concentration ranges for deficiency and toxicity were similar to other nitrogen-fixing trees.The defined P concentration ranges and the critical P concentrations for the diagnosis of P deficiency and P toxicity should be useful for monitoring the P status of nursery stock and the health of young seedlings after out-planting.

Deficiency·Diagnosis·Nutrition· Symptoms·Toxicity

Introduction

Pterocarpus indicus is a large deciduous tree native to SE Asia.Its brightyellowish red to golden brown heartwood is highly valued for furniture.Due to excessive harvesting the species is now classified as vulnerable by IUCN and trade in the species is restricted by listing in Appendix 2 of CITES.Nursery planting stock is in demand for urban planting,forreforestation programs and fora smallnumber of experimental plantations in the region.Nursery managementpractices for the production of P.indicus planting stock are in their infancy and the lack of a nursery grading system compromised the success of reforestation in the Philippines(Gazaletal.2004).Several attempts have been made to optimise the production of nursery stock(Zhou et al.2006;Yang et al.2012)but fertilizer regimes are yet to be defined foroptimalgrowth ofcontainerized seedlings and their survival after out-planting.Whilst screening for effective nitrogen-fixing symbionts(Lok et al.2006),we noticed that nursery seedlings often displayed stress symptoms indicative of deficiency or excess of phosphorus (P)fertilization.

Therefore,glasshouse trials were undertaken with P. indicus seedlings with the following objectives:(a)to define symptoms of P stress,(b)to determine the P concentration ranges in foliage ofstressed and healthy plants,and (c)to define the criticalP concentration forthe diagnosis of P deficiency.The results should be useful for nursery managers and can also serve as a guide for identifying P constraints in seedlings following out-planting in the field. Although the relationship between foliar nutrients andgrowth has been broadly studied and successfully applied to a range of plantations species(Dell et al.2001;Salifu and Jacobs 2006),it has not been widely applied to many tropical hardwood species.

Materials and methods

Experimentaldesign

Separate P rates trials were carried out under glasshouse conditions on two soil types:Yalanbee sandy loam(YB) and a yellow sand(YS).A randomized complete block design was used for each trial,consisting of ten treatments and four replicate pots.The P treatments for the YB trial were 0,5,10,20,40,80,160,320,640 and 1280 mg P kg-1soil,hereafterdesignated as P0,P5,and P1280,and for YS were 0,2,4,8,16,32,64,128,256,and 512 mg P kg-1sand,hereafter designated as P0,P2,and P512.Lower rates were used for YS because ithas a lower P adsorption capacity than YB and,in previous experiments,rates exceeding 512 mg P kg-1sand caused death of all seedlings.Phosphorus was supplied as aerophos[Ca(H2PO4)2·H2O,and Wilson Australia Ltd].Pure monocalcium phosphate was used as itis widely applied as single superphosphate in forestry applications in Australia and its reaction with soils is welldescribed(Barrow 2002). The trials were undertaken with natural light in an evaporatively cooled glasshouse in Perth,Western Australia from October to January(YB trial)and July to October(YS trial).The glasshouse conditions were:YB trial–mean min temperature 19.9°C,mean max temperature 32.2°C,totalnumber of cloudy days 13,mean daily solar exposure 15 MJ m2;YS trial—mean min temperature 17.5°C,mean max temperature 29.9°C,total number of cloudy days 36,mean daily solar exposure 8 MJ m2; relative humidity was notrecorded.

Soil description

YB soil is a typical lateritic soil of the Darling Range in Western Australia.These soils are infertile and strongly adsorb phosphate.Crops require inputs of P and N fertilizers and secondary deficiencies of micronutrients such as Zn and Cu occur.Soilwhich had never been fertilized was collected at 0-20 cm depth from the Allandale Research Farm in Wundowie,63 km east of Perth(31°47′S, 116°22′E).It was sieved through a 4×4 mm stainless steel mesh and mixed.The soil properties were:Colwell P 20 mg kg-1,nitrate–N 1 mg kg-1,ammonium-N 5 mg kg-1,Colwell K 60 mg kg-1,organic carbon 2.26%,pH(H2O)5.7,and pH(CaCl2)6.3.YS,partof the Karrakatta Sand system,was obtained from under virgin banksia woodland on the Swan Coastal Plain near Gnangara north of Perth(31°46′S,115°51′E),and sieved and mixed as above.The soil properties were:Colwell P 4 mg kg-1,nitrate–N＜1 mg kg-1,ammonium-N 5 mg kg-1,Colwell K 20 mg kg-1,organic carbon 0.06%,pH(H2O)5.6 and pH(CaCl2)6.2.The soils were steam pasteurized at90°C for1 h to killany pathogenic or symbiotic organisms,allowed to cool for 24 h,and resteamed.The pasteurized soil was air-dried for 5 days. Three kilograms ofdry soilwere transferred into each nondraining plastic pot(150 mm diameter×175 mm height) lined with a clear plastic bag.

Plant material

Seeds were obtained from large trees in the campus ground of the Forest Research Institute of Malaysia,Kuala Lumpur,Malaysia.Seeds were surface sterilized in 70%(v/v) ethanolfor 60 s,followed by 45 s in freshly prepared 4% (v/v)sodium hypochlorite,and then rinsed in sterile distilled water before sowing.The seeds were germinated in trays of yellow sand thathad been sterilized by autoclaving for 20 min at121°C.Seedlings atthe two-leaf stage were transferred into each treatmentpotafter 10 days.

Fertilizer

Adequate rates of basal nutrients,containing all essential nutrients exceptfor P,were applied to the surface of soilin solution as described previously(Dell et al.1987;Shedley etal.1995;Chen etal.2000).When dry,the basalnutrients and P treatments were mixed throughout by shaking the soilin a plastic container for 2 min by hand.Nitrogen was supplied fortnightly as NH4NO3in an aqueous solution over11 weeks to give a totalof99 mg N/pot.As the plants were supplied with adequate inorganic N they were not inoculated with N-fixing bacteria.The pots were watered and left to incubate for 2 days before planting.After planting,pots were watered daily to field capacity.

Harvesting and plant analysis

At10 weeks after transplanting,when the plants had 8–15 nodes,shoots were separated from roots at one cm above the soil level and then partitioned into the youngest fully expanded leaf(YFEL)and the restofthe shoot.The YFEL was chosen because this leaf cohort is suitable for determining the nutrient status of many broad-leaf plants(Bell 1997;Reuter and Robinson 1997;Dell et al.2001).The plantparts were oven-dried at70°C to constantweightand shoot dry weight was determined.The dried YFELs were ground by hand using a porcelain mortar and pestle.The plant material was digested in concentrated nitric acid(70%w/w)and H2O2(30%w/w)using an open-vessel microwave oven(CEM Mars 5)as described by Huang et al.(2004).All chemicals used were of analytical grade. A standard reference material,Eucalypt 2000,was included in each digestbatch for quality control.Total P was measured by induction coupled plasma spectroscopy.For ColwellP(Colwell1963),soilsamples taken from each pot at harvest were shaken for 16 h in a bicarbonate solution before the soluble extract was analyzed for P.

Data analysis

Data were analyzed using SPSS version 11.5.The effects of P treatments on shoot dry weigh were subjected to analysis of variance(ANOVA).Means were compared using Duncan’s New Multiple Range Test(DMRT)where ANOVA showed that there was a significant difference between treatment means(p≤0.05).All data were checked for normality before being analyzed and square root transformation was carried out where appropriate to satisfy the homogeneity test by using Bartlett test at F≤0.01.Linear fit estimates(JMP.SAS Version 5)were used to explore the relationship between shoot dry weight and total P concentration in the YFEL.

Results

Shoot growth

There was a significantshootgrowth response of P.indicus to P fertilizer(p≤0.05).In both soils there was a steep increase in growth atlow P rates,a narrow optimum range and shootgrowth athigh P rates was depressed.Maximum seedling growth occurred atlower rates of P in YS(P128) than in YB(P320).However,growth was maximum at similar soil Colwell P concentrations(Fig.1),namely 118 mg P kg-1soil.Withholding P reduced plantyield by up to 3.9 and 3.3 fold in YS and YB,respectively(data not shown).Growth was greater in YB than in YS and this was attributed to fewer cloudy days,higher daily solar exposure and higher glasshouse temperatures experience by YB plants in October to January as compared to July to October.

Foliar nutrient concentrations and plant symptoms

The P concentration(y)increased linearly with fertilizer P rate(x)from 0.05 to 1.92%in YS plants(y=0.0375x, R2=0.94)and 0.05 to 0.55%in YB plants(y=0.0043x, R2=0.88).Symptoms of P deficiency and toxicity(Fig.2) are described in Table 1 along with P concentration ranges in the corresponding YFELs.

Critical P concentrations

Critical P concentrations in the YFEL of P.indicus seedlings corresponding to 90%of maximum shootdry weight were derived from linear relationships fitted to the shoot dry weight and the YFEL P data(Fig.3).The fitted lines were divided into three zones,namely:(1)zone of deficiency,(2)zone of adequacy and(3)zone of toxicity.The estimated P concentration in the YFEL for the diagnosis of P deficiency at90%maximum shootyield was 0.17%and for diagnosis of P toxicity was 0.41%.

Discussion

Fig.1 Response in shoot dry weight of Pterocarpus indicus seedlings to soil available P (Colwell P)in two soils, Yalanbee sandy loam(a)and yellow sand(b),fertilized with 10 rates of Ca(H2PO4)2·H2O. Data are means of 4 replicates with standard error bars

Fig.2 Symptoms in Pterocarpus indicus seedlings of P deficiency (left)and P toxicity(right).Leaffrom a plantwith adequate P is in the centre

There was a strong growth response of Pterocarpus indicus to fertilizer P in the two soils.The soils were selected because they had low concentrations of available P and differed in P adsorption capacity.In the Western Australia region,acute P deficiency historically occurs when land is first cleared for agriculture or plantation forestry.Usually, when P fertilizers are applied the water-soluble P componentreacts rapidly with the surfaces of soilconstituents by adsorption to iron or aluminum oxides and with cations in soil solution(Barrow 1980).We recorded increases in Colwell P and plant growth with increasing application of fertilizer P to experimental seedlings.This sodium bicarbonate soil test is widely used in Australia and has been applied to prescribe fertilizer P requirements,but because soil tests only provide crude estimates for predicting crop yield(Bolland et al.1989),plant analysis is preferred for diagnosis of P deficiency.

Compared to the growth response of other woody plants and field crops in these soils,there was a narrow response range between P deficiency and P toxicity for P.indicus. Although P toxicity was anticipated at the high fertilizer rate in yellow sand due to its low buffering capacity,itwas not expected in the Yalanbee soil where the P adsorption capacity is much higher(Barrow 1977).This raises the possibility that P.indicus may be sensitive to levels of fertilizer P supply thatwould normally notadversely affect the growth of other legume tree species with fast growth potential.

Fig.3 Relationship between P concentration(%)in the YFEL and totalshootdry weight(%)for Pterocarpus indicus seedlings using the combined data from the two experiments.The fitted line was obtained using JMP.SAS linear fit estimates

The adequate P foliar concentration range in P.indicus (0.24–0.35%)was higherthan in Acacia auriculiformis A. Cunn.ex Benth.(0.12–0.25%)(Zech 1990)but was similar to other nitrogen-fixing trees such as Acacia mangium Willd(0.35–0.5%)(Amir and Wan Rashidah 1993) and Casuarina equisetifolia L.(＞0.25%)(Walker et al. 1993).Overall,the adequate P concentration range in most legume tree species is higher than in non nitrogen-fixing tree species such as Corymbia maculata(Hook.)K.D.Hill and L.A.S.Johnson(0.1–0.26%)(Dell and Robinson 1993),Eucalyptus urophylla S.T.Blake(0.1–0.3%)(Dell et al.2001),Hevea brasiliensis Mull.Arg.(0.14–0.17%) (Yew and Pushparajah 1984)and Swietenia macrophylla King.(＞0.07–0.09%)(Yao 1981).

The foliar P concentration range in the most deficient plants was 0.05–0.09%which was similar to young mature leaves in P-deficient Acacia auriculiformis(Zech 1990); Cedrela odorata L.(＜0.10%),Dalbergia sissoo Roxb.(＜0.08%)and Gmelina arborea Roxb.(0.05%)(Drechsel and Zech 1991).Differences in the spread of the deficiency and adequate concentration ranges measured may arise due to differences in soil P buffering capacity,the plant part sampled,the age of the plantwhen samples were taken,the developmental stage of growth(e.g.vegetative,reproductive),and differences between species and provenances (Reuter and Robinson 1997).

Table 1 Symptoms of P deficiency and toxicity and leaf P concentrations in Pterocarpus indicus seedlings

The P toxicity range for P.indicus was 0.47–1.68%and this range has been reported in six year-old A.mangium (＞0.5%)(Amir and Wan Rashidah 1993).The toxicity range for other tree species falls within a similar range,for example,Pinus radiata D.Don(＞0.8%,Humphreys and Truman 1964),and Prunus persica(L.)Stokes(＞0.4%, Leece 1976).

Whilst foliar concentration ranges are widely used to guide fertilizer management in plantations,such ranges need to be calibrated in the field.Although the lowerend of the deficiency range and the upper end of the adequate range can be expected to vary between sites differing in soil fertility,critical concentrations for the diagnosis of deficiency should be independent of site and fertilizer type fora particularplantpartand plantage.Furthermore,plant tissue tests are independent of fertilizer placement.

Some symptoms of nutrient disorders have been described previously for P.indicus.Srivastava(1979)grew P.indicus using river sand and reported an increase in the numberofbranches displaying P deficiency thatresulted in rosette-like plants.This symptom was only observed for high P treatments in the current study.However,no foliar analyses were carried out and no detail was provided for the trial duration.Where symptoms are severe,this provides an early indication ofthe P status ofa crop.However, symptoms in the mild deficiency/toxicity ranges are often difficult to detect and can easily be confused with some other limiting nutrients or stress factors.

Linear fits were used to determine critical P concentrations for the diagnosis of deficiency and toxicity using the relationships between foliar P concentration and maximum shoot dry weight.The linear regression lines were based and determined on the highest correlated regression coefficients(R2).Examination of Fig.3 shows thatthe fitofthe lines is imperfect in the regions where growth is just affected by deficiency or toxicity,and this might underestimate true criticalconcentrations.

In conclusion,care needs to be taken in the use of phosphatic fertilizers in forest nurseries producing P. indicus seedling stock in conjunction with other tree species thatare more resilient to P fertilization.The defined P concentration ranges and the critical P concentrations for the diagnosis of P deficiency and P toxicity should be usefulfor monitoring the P status of nursery stock and the health of young seedlings after out-planting.

AcknowledgmentsThe first author thanks the Malaysian Government for a PhD scholarship offered through the Ministry of Science, Technology and Innovation and Public Service Department.

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15 April 2014/Accepted:17 July 2014/Published online:1 May 2015

?Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2015

The online version is available athttp://www.springerlink.com

Corresponding editor:Zhu Hong

?Bernard Dell b.dell@murdoch.edu.au Eng Hai Lok lokeh@frim.gov.my

1Forest Plantation Programme,Forest Research Institute Malaysia,52109 Kepong,Selangor Darul Ehsan,Malaysia

2Schoolof Veterinary and Life Sciences,Murdoch University, Perth 6150,Australia