Effects of Fertilization on Growth and Soil of Middle-aged Slash Pine Forest

Xingcui XIAO,Rongxiu XIE,Zhihui LI*,Weijing KANG,Jiyou WU

1.Sichuan Academy of Forestry,Chengdu 610081,China;2.Central South University of Forestry and Technology,Changsha 410004,China;3.Tiger Forest&Paper Group Co.,Ltd.,Yueyang 414002,China;4.Hunan Academy of Forestry,Changsha 410004,China

Fertilization is one the important measures for adjusting soil nutrients,promoting tree growth and improving yield and quality[1].Rational fertilization can increase soil fertility[2],improve contents of soil organic matter,total N and rapid available N,and promote growth of symbiotic bacteria for forest trees[3].Fertilization on young plantations can improve increment in crown breadth,promote crown closure of stands in advance,control growth of weeds and shrubs under trees and shorten years needing weeding[5]as well as promoting growth of young plantations;and fertilization on grown plantation can obviously im prove growth increment[9-11]and yield per unit area.Improper fertilizer types and fertilizing amounts can act on wood growth negatively[12-13],and fertilization to soil with high fertility can cause poor fertilizer efficiency,ineffectiveness and even negative effect[14-15].

Pinus elliottiigrows in America natively,and it is a kind of tree species for both of resin and timber and has become one of the most important forestation tree species for southern hilly area of China.There were a lot of researches on fertilization toPinus elliottiiabroad,Pritchett[16]and Jokelaet al.[17]found that rational fertilization could notably promote the growth ofPinus elliottii;Fisheret al.[18]applied N fertilizer to plantations at various age stages,and found after 6-10 years,all fertilizedPinuselliottiigrew well;Cropperet al.[19]and Zhaoet al.[20]con-ducted fertilization onPinus elliottiistands repeatedly and improved growth incrementand productivity thereof;and Williamset al.[21]and Gilmoreet al.[22]improved timber yield by fertilizing 8-9 year-oldPinus elliottii.In China,Ruet al.[23],Huet al.[24]and Wanget al.[25]carried out experiments on youngPinus elliottiiplantations with base fertilizer and different types of fertilizers which were found to have certain promoting effect on growth of young plantation;and Chenet al.[26]performed experiment on mid-agedPinus elliottiiplantation at low hilly area in subtropical zone and reckoned that applying P and K fertilizers had remarkable promoting effect onPinus elliottiigrowing on quaternary red clay and granite skeletal red-yellow soil.So far there has been no research on systematic fertilization onPinus elliottiigrowing on low hilly area in Hunan.Therefore,in this study,the effects of different fertilizing amounts of formula fertilizer were studied on the growth,the soil and cost-benefit of 9 year-oldPinus elliottiiplantations in the northern part of Hunan,aiming at providing basis for fertilizing mid-agedPinus elliottiiplantations in low hilly area of Hunan and promoting growth of midagedPinus elliottiiplantations.

Materials and Methods

Time and location

The experiment was carried out on 9 year-oldPinus elliottiistand in April of 2010 at Paotang village,Miluo,Yueyang,Hunan at 113°9′6″-113°9′43″E and 28°49′6″-28°49′38″N,belonging to the mid-subtropical transitional area with an annual average temperature of 17℃and an amount of precipitation of about 1 345 mm;the frost-free period is of 263 d;the altitude is of 61-69 m with a slope below 10°,and the soil is quaternary red clay with an effective soil layer above 60 cm with a pH value of 4.9.

Materials

The fertilizer for fertilization was the compound fertilizer special for pine produced by Hunan Miaoyuan Forestry Co.Ltd.according to soil testing and fertilizer recommendation,with a total nutrient content of 28.7%at N∶P∶K of 1.7∶3.3∶1.

Pinus elliottiiplantation for manurial experiment was constructed in March of 2002 with a plantation density of 2 000 trees/hm2(2 m×2.5 m),the site preparation of big pit was carried out before forestation,and superphosphate was applied in an amount of 500 g/tree as a base fertilizer;at the end of the year conducting forestation,a few dead seedlings were replaced with the seedlings at the same age;manual weeding was conducted in May of the year for forestation,and cutting of weeds and shrubs was conducted once every year within the first three years in October-November;and this experiment did not conducted intermediated cutting.The shrubs under the experimental plantation mainly wereCamellia sinensis,Cleredendrum cwtophyllum,Rhus chinensis,Phyllostachys nidularia,Tetradium glabrifolium,etc,which were distributed unevenly;and at the age of 9 years,the weeds mainly were Pteridium aquilinum var.latiusculum andSmilaxchinaL.in regional distribution,and at the age of 11 years,a lot ofPhytolaccae Americanagrew locally.

Method

Experiment designThere were 10 fertilization treatments (fertilizing amounts),which were 100,200,300,400,500,600,700,800,900 and 100 g/tree,respectively,with the treatment without fertilization (CK)as control;each treatment had 30 trees per plot in random distribution,with 3 repetitions;and dressing furrows(50 cm×15 cm×15 cm)were digged on upslopes in the shadows of crowns,and the fertilizer was put into the dressing furrows and covered.In order to facilitate fertilization and prevent weeds from contending for nutrients and water,weeds and shrubs were cut completely before fertilization,and 1 month after fertilization,Nonda (41%glyphosate)was adopted to clear away weeds and shrubs.

Before fertilization in March of 2010,30 trees was fixed in each plot of various treatments,and they were determined for diameter at breast height(DBH),tree height and clear bole height;DBH,tree height and clear bole height were determined in the Decembers 1,2 and 3 years after fertilization for 3 times sequentially;before fertilization,soil sampling was conducted by “S”type method,and mixed samples for 0-20 cm and 20-40 layers were obtained,respectively,to analyze the background values of soil;2 years after fertilization,soil sampling was conducted in the 3 repetitions of the treatments of 200,400,600,800 g/tree and the control,the sampling locations were next to the dressing furrows,for each treatment 3 trees were chosen,each of which was set with 8 points uniformly around corresponding dressing furrow,24 points in total,the sampling depths were 0-20 and 20-40 cm,the soil at the 24 points of the 2 layers were respectively mixed,obtaining 2 samples as the soil samples for each fertilization treatment;and the soil samples obtained before and after fertilization were determined for analysis of pH value,organic matter,rapid available nitrogen, rapid available phosphorus and rapid available potassium.Soil analysis adopted corresponding nationalstandards, in which,pH value adopted potentiometric analysis method-pH meter determination(LY/T 1239-1999),organic matter adopted calcium bichromate volumetricmethod (LY/T 1237-1999),rapid available K adopted 0.05 mol/L ammonium acetate leaching-flame photometry(LY-T 1236-1999),rapid available N adopted alkaline hydrolysis diffusion method (LY-T 1229-1999),and rapid available P adopted doubleacid leaching method with 0.05 mol/L hydrochloric acid-0.025 mol/L and 1/2 sulfuric acid (LY-T 1233-1999).The November of 1-3 years after fertilization,the number of symbiotic fungus-Pisolithus tinctoriusfruiting body in the soil of each treatment was observed.

Statistic analysisData was processed with Microsoft excel 2003,and variance analysis andLSDmultiple test were performed with SPSS 19.0.Individual tree volume ofPinus elliottiiwas calculated with Hunan foreign pine variable parameter volume equation[27],shown as equation(1):

Results and Analysis

Effect of fertilization on growth of Pinus elliottii

The growth data ofPinus elliottiiby different fertilization treatments at different stages before and after fertilization was shown in Table 1.

As shown in Table 1,the DBH,tree heights and clear bole heights of different treatments and those of the control were not significantly different before fertilization,the differences between the maximum values and the minimum values were of 0.71 cm,0.46 m and 0.35 m,respectively,and variance analysis showed that there was no significant difference between different fertilization treatments and the control(P＜0.05).

Effect of fertilization on DBH increment ofPinus elliottiiIt was shown in Fig.1 that,1-3 years after fertilization,the DBH increments by different fertilizing amounts were of 0.56-0.65 cm,1.14-1.26 cm and 1.67-1.81 cm,respectively,which were higher than those of the control by 22.36%-42.17%,14.62%-25.83%and 5.96%-15.14%,respectively,indicating that the fertilization effect was decreasing,with a greatest effect appearing 1 year after fertilization;however,the DBH increments of different fertilizing amounts differed notably,and variance analysis showed that different fertilizing amounts had no significant effect on DBH increment(P＜0.05)1 year after fertilization,but there were significant effects 2 and 3 years after fertilization;2 years after fertilization,the DBH increments were the largest at the fertilizing amounts of 200 and 400 g/tree,having significant differences with the control and no significant difference with other fertilizing amounts;3 years after fertilization,the greatest DBH increment appeared at the fertilizing amount of 700 g/tree,having a significant difference with the control and no significant difference with other fertilizing amounts,indicating that 3 years after fertilization,700 g/tree had greater continued promoting effect on DBH growth.

Effect of fertilization on increment in tree heightFrom Fig.2,it could be seen that 1-3 years after fertilization,the increments in tree height by different fertilizing mounts were of 0.64-0.69,1.21-1.32 and 1.67-1.80 m,respectively,which were higher than those of the control by 2.51%-10.18%,1.03%-10.18%and 0.14%-7.56%,respectively,while the proportion of increase slightly decreased over time,indicating that 1 year after fertilization,the promoting effect of fertilization on increment in tree height was the great-est;the increments in tree height were the greatest at 500,500 and 700 g/tree,respectively,indicating that 3 years after fertilization,700 g/tree had a greater continued promoting effect on growth of tree height,but there was no significant effect on the increment in tree height within 3 years after fertilization(P＜0.05).

Table 1 Statistics of growth data of Pinus elliottii at different stages before and after fertilization

Effect of fertilization on increment in individual tree volumeAs shown in Fig.3,1-3 years after fertilization,the increments in individual tree volume by differentfertilizing amounts were of 0.007 3-0.008 3,0.015 2-0.016 8 and 0.022 3-0.026 3 m3,respectively,which were higher than those of the control by 22.22%-38.89%,16.03%-28.50%and 9.84%-29.51%,respectively;the increments in individual tree volume were the greatest at 400 g/tree,1 000 g/tree and 700 g/tree,respectively;and the proportion ofincrease slightly decreased over time,indicating that 1 year after fertilization,the promoting effect of fertilization on increment in individual tree volume was the greatest,while the differences between different fertilizing amounts increased notably,resulting in a significant effect appearing 3 years after fertilization on the increment in individual tree volume ofPinus elliottii(P＜0.05),and in specific,the fertilization treatment with the fertilizing amount of 700 g/tree had a significant difference with the control,without significant difference with other treatments.

Effect of fertilization on stock volume increment of standAs shown in Fig.4,1-3 years after fertilization,the stock volume increments under different fertilizing amounts were of 14.53-16.74,30.38-33.70 m3/hm2and 44.54-52.10 m3/hm2,respectively,which were higher than those of the control by 21.54%-38.09%,16.01%-28.67%and 8.08%-26.42%,respectively,and the stock volume increments were the greatest at the fertilizing amounts of 1 000 g/tree,1 000 g/tree and 700 g/tree,respectively;the proportion of increase in stock volume increment of stand slight decreased over time,while the differences between different fertilizing amounts increased notably,resulting in a significant effect appearing 3 years after fertilization on the stock volume increment of stand (P＜0.05),and in specific,the stock volume increment of the fertilization treatment with the fertilizing amount of 700 g/tree was significantly different with that of the control,without significantdifference with other treatments.

Cost-benefit analysis of fertilization

Fertilization cost included fertilizer expense,fertilization expense and ex-pense for cutting weeds and shrubs.From Table 2,it could be seen that the fertilization expense increased with increasing fertilizing amount,while after 3 years since fertilization,there was no obvious linear relation between stock volume increment and fertilizing amount and between earnings and fertilization amount;the profits of all fertilization treatments were greater than the control,among the fertilization treatments,100 g/tree exhibited the greatest profit,which was higher than that of the control by 58.1%,and the treatments of 300 and 700 g/tree were the second,which were higher than that of the control by 55.1% and 52.7%,respectively;and the fertilization treatment of 900 g/tree had the lest profit,which was higher than that of control by 21.7%.

Table 2 Cost-benefit analysis after 3 years since fertilization

Table 3 Soil nutrients 2 years after fertilization compared with before fertilization

Table 4 Pisolithus fruiting body 7 months after fertilization

Effect of fertilization on soil

Effect of fertilization on soil nutrientsAs show in Table 3,after 2 years since fertilization,all pH values of different soil layers under different fertilization treatments decreased,there was no significant difference between the 4 fertilizing amounts and the control(P＜0.05)and their decrease degrees were slightly lower than that of the control.Except the organic matter content in the 20-40 cm layer of the control,the organic matter contents in various layers of the different fertilization treatments increased compared with those before fertilization.The increases in the 0-20 cm layer were remarkably higher than those in the 20-40 layer,the organic matter contents in the two layers of the different treatments were higher than those of the control by 303.6%-460.7%and 177.3%-307.7%,but there was no significant difference between the different fertilizing amounts and between them and the control(P＜0.05),with the greatest organic matter increases appearing in the treatment of 400 g/tree.

The rapid available N contents in different soil layers of various treatmentsincreased greatlycompared with those before fertilization.The increases in the 0-20 cm layer were higher than those in the 20-40 cm layers,the increases in the two layers of various treatments were higher than those in the control by 111.0%-126.6%and 104.7%-114.8%,with the greatest rapid available Nincreases appearing in the treatment of 200 g/tree,among which the increase in the 0-20 cm layer was significant different with that of the control(P＜0.05),and differed with those of other treatments at a non-significant level,and the increase in the 20-40 cm layer was not significantly different with that of the control and those of other treatments.

The rapid available P contents in different soil layers of various treatments decreased compared with those before fertilization to varying degrees,mainly due to the fact thatPinus elliottiiwas in great demand for P.The overall decrease in 0-20 cm layer was greater than that in the 20-40 cm layer,the decreases in the 0-20 cm layer of the treatments of 600 and 800 g/tree were obviously lower than that of the control and accounted for 58.3%and 13.1%of the control,respectively,while all the decreases in the 20-40 cm layer were lower than that of the control to varying degrees and accounted for 32.6%-70.7%of the control;the decrease in the 0-20 cm layer decreased with increasing fertilizing amount,and there was no obvious linear relation exhibited between the decreases in the 20-40 cm layer and the fertilizing amounts;the decreases ofrapid available P were the greatest in different layers at the fertilizing amount of 800 g/tree,which were significantly different with the those of the control(P＜0.05),for the 0-20 cm layer,the decrease in the treatment of 800 g/tree was significantly different with those of other treatments except the treatment of 600 g/tree,and for the 20-40 cm layer,the decrease at 800 g/tree was not significantly different with other treatments.

The rapid available K contents in different layers of various treatments increased compared with those before fertilization and were higher than those of the control to vary degrees,with the greatest rapid available K increases appearing at the fertilizing amount of 800 g/tree,among which the increase in the 0-20 cm layer was significantly different with that of the control(P＜0.05),and the increase in the 20-40 cm layer was not significantly different with those of other treatment and that of the control.

Effect of fertilization on soil symbiotic fungusShort roots of pine often grow symbiotically with some fungi,forming ectotrophic mycorrhizas,which absorb nutrients from pine roots and synthesize enzymes and growth hormone which promotes growth of pine roots;mycelia covering short roots can function instead of root hairs to absorb water and inorganic salt,to thereby enlarging the absorption area of root system,improve drought resistance in trees and accelerate tree growth.Pisolithus tinctoriusis a kind of common mycorrhiza fungus,whose mycelia can form with pine ecto-endotrophic mycorrhizas which absorb nutrients and water for pine roots,thus promoting growth of pine seedlings[28].

Seven months after fertilization,it was found by observation that the symbiotic fungus-the numbers ofPisolithusfruiting body at the dressing furrows of different fertilizing amounts and nearby places thereof increased obviously (Table 4),and were 2.0-24.0 times of that of the control,with the greatest number of Pisolithus fruiting body appearing at the fertilizing amount of 800 g/tree,which was significantly different with that of the control(P＜0.05),and the next one appearing at the fertilizing amount of 700 g/tree;in the fertilizing amount range of 100-800 g/tree,the numbers of Pisolithus fruiting body generally increased with increasing fertilizing amount,but the numbers of Pisolithus fruiting body at 900 and 1 000 g/tree were less than those at other fertilizing amounts,which might be due to the fact that excessive fertilizing amount inhibited the growth ofPisolithus tinctorius.ThePisolithusfruiting body was very few 2 and 3 years after fertilization,which might be caused by the droughty occurring in the second year after fertilization.

Conclusions

(1)Three years after topdressing conducted on 9 year-oldPinus elliottiiwith N,P,K formula fertilizer,different fertilizing amounts increased the DBH,tree height,individual tree volume,and stock volume increment of stand by 5.96%-15.14%,0.14%-7.56%,9.84%-29.51%and 8.08%-26.42%compared with the control;1-3 years after fertilization,the proportion of increase in each growth index ofPinus elliottiislightly decreased over time since fertilization,while the differences between different fertilizing amounts increased over time to varying degrees,and they had significant effects on DBH increment ofPinus elliottii2-3 years after fertilization(P＜0.05)and as well as on individual tree volume and stock volume increment of stand 3 years after fertilization,with the greatest continued promoting effectappearing at the fertilizing amount of 700 g/tree on increment in each index ofPinus elliottii,thereby increasing individual tree volume ofPinus elliottiiby 29.51%.

(2)Cost-effectiveness of fertilization:By performing topdressing to midagedPinus elliottiiplantation once,it could be seen that the fertilization cost increased with increasing fertilizing amount,all the fertilizing amounts had profits higher than the treatment without fertilization by 21.7%-58.1%,among them,the fertilizing amount of 100 g/tree had the highest profit,and the next ones were 300 g/tree and 700 g/tree.Only from the point of economic benefit,the fertilizing amount of 100 g/tree is the best,but in practical production,the purpose of fertilization is to obtain more timber.Therefore,from the point of improving yield per unit area while taking benefit into consideration,performing topdressing with N,P,K formula fertilizer 700 g/tree can achieve the best effect.

(3)In the aspect of effect of fertilization on soil,2 years after fertilization in the 0-20 cm layer with different fertilizing amounts,compared with the nutrients before fertilization,pH values decreased to varying degree,rapid available P content decreased to varying degrees,while all the decreases were lower than those of the treatment without fertilization and the decreases in the upper layer were lower than those in the lower layer;organic matter and rapid available K content both increased;rapid available N content increased greatly,and the increases in the upper layer were higher than those in the lower layer.After seven months since fertilization,the number ofPisolithusfruiting body increased with increasing fertilizing amount in the fertilizing range of 100-800 g/tree,and was 2.0-24.0 times of that of the control.

Discussion

Effect of fertilization on the growth of mid-aged plantation

The quaternary red clay at hilly area in Hunan mainly lacks P,supplementing P fertilizer can effectively promote the growth ofPinus elliottii,and applying compound fertilizer on midaged plantations can achieve better effect[9].This study conducted topdressing on 9 year-old plantation growing on quaternary red clay in the northern part of Hunan with N,P,K formula fertilizer once,and found that after 3 years,there were significant effects on DBH,individual tree volume and stock volume,which accorded with the results ofPinus elliottiiat home and abroad[18,26];fertilization had no significant effect on increment in tree height,indicating that fertilization had a greater promoting effect on DBH ofPinus elliottiithan that on tree height,which accorded with the research results ofPinus massoniana[10]andPinus elliottii[21,23].Furthermore,the promoting effect on tree growth is in relation to time since fertilization and so on.This study found that,1,2 and 3 years after fertilization,the stock volume ofstand was increased by 21.54%-38.09%,16.01%-28.67%and 8.08%-26.42%compared with the control,respectively,and the effect of fertilization decreased over time,which accorded with the results ofEucalyptusandEucalyptus urophylla[29]as well asEucalyptus globulus[30].

Effect of fertilization on soil

Two years after fertilization,pH values decreased to varying degrees compared with before fertilization,which accorded with the result of decreased rhizosphere pH value ofPinus massoniana[31];and rapid available P content also decreased to varying degrees after fertilization,mainly due to the fact that the experiment field was short of P while the demand of midagedPinus elliottiiplantation for P was huge[32],but the overall P content was higher than that of the treatment without fertilization mainly because of the P,N,K formula fertilizer applied in the 0-20 cm layer.Therefore,it is necessary to supplement rapid available P content in soil of mid-agedPinus elliottiiplantation by fertilization to satisfying the requirement from the growth ofPinus elliottii,to thereby promote the growth ofPinus elliottii.The contents of organic matter and rapid available K in soil both increased compared with before fertilization;and the increases were higher than those of the control,and the increases in the upper layer were higher than those in the lower layer to varying degrees,which was also due to fertilization in the upper soil layer.Seven months after fertilization,the number ofPisolithusfruiting body increased obviously,which accorded with the result thatPisolithusfruiting body increased with increasing P fertilizer amount in mid-agedPinus massonianaplantation 3 months after fertilization[3].This study promoted the growth ofPisolithus tinctoriusby improving the growth condition ofPisolithus tinctoriusthrough rational fertilization,and thus demonstrated that rational fertilization could promote the growth ofPinus elliottiifrom another perspective while excessive fertilizer could inhibit the growth ofPisolithustinctoriusas well as harming growth of pine.

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