Effects of Fertilization on Ramie (Boehmeria Nivea L.) Growth, Yield and Fiber Quality

sustainability

Article Effects of Fertilization on Ramie (Boehmeria nivea L.) Growth, Yield and Fiber Quality

Sana Ullah, Lijun Liu, Sumera Anwar, Xu Tuo, Shahbaz Khan, Bo Wang and Dingxiang Peng *

MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China; [email protected] (S.U.); [email protected] (L.L.); [email protected] (S.A.); [email protected] (X.T.); [email protected] (S.K.); [email protected] (B.W.) * Correspondence: [email protected]; Tel.: +86-27-8728-7136

Academic Editor: Iain Gordon Received: 5 June 2016; Accepted: 29 August 2016; Published: 2 September 2016

Abstract: Ramie (Boehmeria nivea L.) is one of the most important sources of natural fiber. The yield and fiber quality of ramie are affected by mineral nutrients, particularly nitrogen (N), phosphorus (P), and potassium (K). In the present study, we aimed to quantify the influence of N, P, and K fertilizers on growth, yield, and fiber quality of ramie. To this end, ramie plants grown under different fertilizer treatments (no fertilizer, N, P, K, NP, NK, PK, and NPK) were evaluated for differences in plant height, stem diameter, stem fresh and dry weights, number of stems, fiber fresh and dry weights, fiber quality (breaking strength, elongation, and diameter), and total N and P content. Across all fertilizer treatments, NPK, followed by NK, had the greatest significant effect for increasing plant growth, yield, and fiber quality as compared with control plants, whereas P application had the least effect. Plants fertilized with NPK showed strong positive correlations among fiber yield and quality traits with morphological parameters such as plant height, biomass, stem diameter, and numbers of stem. The p correlation of fiber breaking strength with stem diameter (r2 = 0.79), stem biomass (r2 = 0.88), N contents (r2 = 0.91) and P contents (r2 = 0.83) indicated that the combined application of NPK (150, 75,150 kg·ha−1) significantly enhances yield and fiber quality in ramie. Thus, it is suggested that optimum fertilization is important for sustainable ramie production.

Keywords: ﬁber; yield and quality; morphology; nutrients; ramie

1. Introduction Natural cellulosic plant fibers have gained attention due to their high production, biodegradability, low cost, and high thermo stability [1,2]. Ramie (Boehmeria nivea L.), a herbaceous perennial plant that belongs to the family Urticaceae, is the second most important fiber crop after cotton in China. China is the world’s leading producer of ramie, accounting for more than 90% of the global production [3] and supporting approximately five million people [4] Ramie fiber is harvested three times a year and is used for textile and rope production [2]. The numerous advantages of ramie include its high length (longer than any other commercial plant fiber), tensile strength (eight times greater than cotton and seven times greater than silk), luster, stain resistance, moisture absorbency, antibacterial properties, drying speed, low shrinkage, and ease of dying. Conversely, ramie does have certain disadvantages, namely brittleness, stiffness, low elasticity, and easy wrinkling [5,6]. In addition to its use in fiber production, ramie is also used as a feedstock and mulch, and in the manufacture of bio-ethanol, and medicines. It is also grown on the slopes of hilly areas to reduce soil erosion and water loss [7]. However, ramie rapidly depletes soil nutrients due to its rapid growth and high productivity and therefore, fertilization, particularly with nitrogen (N), phosphorus (P), and potassium (K), is important for normal

Sustainability 2016, 8, 887; doi:10.3390/su8090887 www.mdpi.com/journal/sustainability Sustainability 2016, 8, 887 2 of 9 Sustainability 2016, 8, 887 2 of 8 and high productivity and therefore, fertilization, particularly with nitrogen (N), phosphorus (P), and potassium (K), is important for normal growth and sustainable yield [8,9]. Information concerning growth and sustainable yield [8,9]. Information concerning the effects of nutrient management on the the effects of nutrient management on the morpho-physiological traits, yield, and fiber quality of morpho-physiologicalramie is nevertheless traits, limited. yield, In the and present fiber study, quality we of accordingly ramie is nevertheless aimed to assess limited. the effects In theof the present study,single we accordingly or combined aimed use of to N, assess P, and the K effectsfertilizers of theon the single growth, or combined yield, and use fiber of N,quality P, and of Kramie. fertilizers on theFertilizers growth, were yield, applied and fiber in qualitylow concentrations of ramie. Fertilizersto reduce werefertilization applied intensity in low concentrationsand achieve to reduceeconomically fertilization viable intensity fiber production. and achieve economically viable fiber production.

2. Materials2. Materials and and Methods Methods

2.1. Experimental2.1. Experimental Design Design and and Fertilizer Fertilizer Treatments Treatments The studyThe study was was conducted conducted in in a greenhousea greenhouse (25–30(25–30 °C◦C)) at at the the experimental experimental station station of Huazhong of Huazhong Agricultural University (114.20′E, 30.28′N; 50 m above sea level) from March to October 2014. Agricultural University (114.200E, 30.280N; 50 m above sea level) from March to October 2014. Root segments (15 cm) of the high yielding ramie cultivar Huazhu 5 were individually planted in Root60-cm-tall segments × (1540-cm-wide cm) of thepots high on 6 yieldingMarch 2014 ramie and cultivararranged Huazhuin a completely 5 were randomized individually design planted in 60-cm-tall(Figure 1).× 40-cm-wide pots on 6 March 2014 and arranged in a completely randomized design (Figure1).

Figure 1. Ramie (Boehmeria nivea L.) plants grown under different fertilizer treatments (no fertilizer, K, Figure 1. Ramie (Boehmeria nivea L.) plants grown under different fertilizer treatments (no fertilizer, NK, P, NP, N, PK, and NPK) at 7 days post-planting. (N: nitrogen; P: phosphorus; and K: potassium). K, NK, P, NP, N, PK, and NPK) at 7 days post-planting. (N: nitrogen; P: phosphorus; and K: potassium).

EachEach treatment treatment (no (no fertilizer fertilizer [CK], [CK], N,N, P,P, K,K, NP, NK, PK, PK, and and NPK) NPK) was was replicated replicated three three times times and includedand included 9 pots, 9 pots, from from which which 3 pots3 pots were were harvested harvested at each stage. stage. N N (150 (150 kg·ha kg·−ha1) was−1) applied was applied in in the form of urea (46% N), P (75 kg·ha−1−1) in the form of calcium super-phosphate (14% P2O5), and K the form of urea (46% N), P (75 kg·ha ) in the form of calcium super-phosphate (14% P2O5), and K (150 kg·ha−1 −1) in the form of potassium chloride (54% K2O). P was applied in a single dose at planting, (150 kg·ha ) in the form of potassium chloride (54% K2O). P was applied in a single dose at planting, whereas N and K were applied in three doses: the first at planting (40%), with subsequent whereas N and K were applied in three doses: the ﬁrst at planting (40%), with subsequent applications applications in June (30%) and August (30%). Soil samples were collected for physicochemical in Juneanalysis (30%) before and Augustplanting (30%).and after Soil harvesting samples (Table were 1). collected for physicochemical analysis before planting and after harvesting (Table1). Table 1. Soil analysis before planting and after harvesting of ramie (Boehmeria nivea L.) plants grown Tableunder 1. Soil different analysis fertilizer before treatments planting and(no fertilizer, after harvesting CK; N, P, K, of NP, ramie NK, ( BoehmeriaPK, and NPK). nivea N:L.) nitrogen; plants P: grown underphosphorus; different fertilizer and K: potassium. treatments (no fertilizer, CK; N, P, K, NP, NK, PK, and NPK). N: nitrogen; P: phosphorus;Treatment and K: potassium.EC (dS/cm) pH Organic Matter (g/kg) N (g/kg) P (%) K (g/kg) Pre-Sowing 2.1 5.1 11 40 0.18 61.94 Post-HarvestingCKTreatment (Control) EC (dS/cm)2 pH5.3 Organic 11.1 Matter (g/kg) N 41 (g/kg) 0.18 P (%) 49.44 K (g/kg) Pre-SowingK 2.12.1 5.15.4 11.2 11 45 40 0.19 0.18 67.84 61.94 Post-HarvestingCKPK (Control) 22.2 5.35.5 11.5 11.1 46 41 0.18 0.18 72.84 49.44 KNK 2.12.7 5.45.7 12 11.2 49 45 0.18 0.19 69.44 67.84 PKN 2.22.2 5.55.6 12.1 11.5 45 46 0.19 0.18 61.04 72.84 NKP 2.72.4 5.75.2 11.4 12 43 49 0.18 0.18 65.24 69.44 NNP 2.22.7 5.65.7 11.6 12.1 47 45 0.19 0.19 48.24 61.04 PNPK 2.42.7 5.25.8 12.2 11.4 48 43 0.18 0.18 52.74 65.24 NP 2.7 5.7 11.6 47 0.19 48.24 NPK 2.7 5.8 12.2 48 0.18 52.74

2.2. Plant Growth and Fiber Evaluation Plants were harvested in June, August, and October. Stem diameter (mm) was measured using a digital vernier caliper (ST22302, SG tools, Hangzhou, China), and stem fresh and dry weights using a digital scale. The cortex layer of the stem was separated (decorticated) and weighed to calculate Sustainability 2016, 8, 887 3 of 9

2.2. Plant Growth and Fiber Evaluation Sustainability 2016, 8, 887 3 of 8 Plants were harvested in June, August, and October. Stem diameter (mm) was measured using a digital vernier caliper (ST22302, SG tools, Hangzhou, China), and stem fresh and dry weights using a digital scale. The cortex layer of the stem was separated (decorticated) and weighed to calculate fiber yield. Then, 20 g of decorticated ramie fiber was boiled for 1 h in an Erlenmeyer flask containing fiber yield. Then, 20 g of decorticated ramie fiber was boiled for 1 h in an Erlenmeyer flask containing 100 mL100 of mL degumming of degumming solution solution (1 (1 g NaOHg NaOH and and 0.050.05 g g EDTA) EDTA) (Figure (Figure 2a,b).2a,b). Degummed Degummed fiber fiberthen then ◦ bleachedbleached with 2%with H 2%2O H2 2andO2 and 0.1% 0.1% Tween-80 Tween-80 for for 11 h at a a 94 94 °CC inin water water bath. bath. Then, Then, fibers fibers were washed were washed with distilledwith distilled water, water, dried dried and and combed. combed. Fiber Fiber diameterdiameter (µm) (µm) was was measured measured using using a computerized a computerized fiber finenessfiber fineness tester tester (Model (Model No.YG002C, No.YG002C, Changzhou, Changzhou, China) China) connected connected with with an optical an optical microscope microscope (Figure(Figure2c). An 2c). electronic An electronic single fibersingle strength fiber streng testerth (YG004, tester (YG004, Nantong Nant Hongdaong Hongda Experiment Experiment Instruments, Qidong,Instruments, China) was Qidong, used toChina) determine was used fiber to breakingdetermine strengthfiber breaking measured strength in centimeasured Newton in centi (cN) and Newton (cN) and elongation rate (%) (Figure 2d), following the Chinese National Standards (GB elongation rate (%) (Figure2d), following the Chinese National Standards (GB 5882-86). 5882-86).

(a) (b)

Figure 2. Fiber treatment prior to analysis and measurement of fiber diameter, breaking strength, and Figure 2. Fiber treatment prior to analysis and measurement of fiber diameter, breaking strength, elongation rate. (a) Fiber degumming; (b) Degummed fiber; (c) Fiber under a microscope; (d) and elongationMeasurement rate. of fiber (a) streng Fiberth degumming; and elongation (rate.b) Degummed fiber; (c) Fiber under a microscope; (d) Measurement of fiber strength and elongation rate. 2.3. Plant and Soil Chemical Analysis 2.3. Plant andFor Soilthe Chemicaldetermination Analysis of plant total N and P, whole-plant samples were dried in an oven at For70 the°C. determinationOven-dried samples of plant were total weighed, N and ground P, whole-plant (granule samplessize, 0.5 weremm), driedand digested in an oven using at 70 ◦C. concentrated H2SO4–H2O2 acid solution [10]. The resulting digest was analyzed for P concentration Oven-dried samples were weighed, ground (granule size, 0.5 mm), and digested using concentrated using a spectrophotometer (Biochrom, Cambridge, UK) at 880 nm. The total N concentration of the H2SO4plant–H2O digest2 acid and solution soil was determined [10]. The using resulting the Kjeldahl digest method was analyzed [11,12]. for P concentration using a spectrophotometer (Biochrom, Cambridge, UK) at 880 nm. The total N concentration of the plant digest and soil was determined using the Kjeldahl method [11,12].

2.4. Statistical Analysis LSD analyses were used to identify the significant differences among the treatments at a p < 0.05 level. Data were analyzed using SAS software (SAS Institute, Cary, NC, USA), and charts were constructed using Excel 2010 (Microsoft Corp., Redmond, WA, USA). Pearson correlation coefficient (r2) were calculated to examine the strength and direction of the linear relationship between fiber quality and yield variables and morphological traits. Sustainability 2016, 8, 887 4 of 9

2.4. Statistical Analysis LSD analyses were used to identify the significant differences among the treatments at a p < 0.05 level. Data were analyzed using SAS software (SAS Institute, Cary, NC, USA), and charts were Sustainability 2016, 8, 887 4 of 8 constructed using Excel 2010 (Microsoft Corp., Redmond, WA, USA). Pearson correlation coefficient (r2) were calculated to examine the strength and direction of the linear relationship between fiber 3. Resultsquality and yield variables and morphological traits.

3.1. Effect3. Results of Fertilizer on Plant Morphology 3.1.Plant Effect height of Fertilizer was significantly on Plant Morphology affected by N, P, and K fertilization (Figure3a). The lowest plant height wasPlant observed height was in control significantly plants affected (45.4 cm), by N, whereas P, and K the fertilization highest was (Figure observed 3a). The in lowest plants plant fertilized withheight NPK (90.6was observed cm), followed in control by plants those (45.4 fertilized cm), wh withereas NK the (87 highest cm) andwas observed N (71 cm). in plants Stem diameterfertilized also showedwith aNPK positive (90.6 cm), response followed to fertilizersby those fertilized (Figure wi3b);th NK the (87 largest cm) and diameter N (71 cm). was Stem recorded diameter in thealso NPK treatmentshowed (8.7 a positive mm), followed response byto fertilizers that in K (Figure (7.5 mm), 3b); the and largest NP (7.4 diameter mm). was Stem recorded fresh and in the dry NPK weights weretreatment significantly (8.7 mm), higher followed in fertilizer by that treatments in K (7.5 mm), compared and NP with(7.4 mm). CK (FigureStem fresh3c,d). and The dry lowestweights fresh and drywere weights significantly (0.11 higher kg and in 0.04 fertil kg,izer respectively) treatments compared were observed with CK in (Figure the control 3c,d). (CK),The lowest and the fresh highest in plantsand dry fertilized weights with (0.11 NPKkg and (0.27 0.04 kg, kg andrespectively) 0.13 kg, we respectively),re observed in although the control these (CK), latter and the values highest did not in plants fertilized with NPK (0.27 kg and 0.13 kg, respectively), although these latter values did not differ significantly from those obtained for plants fertilized with NK (0.25 kg and 0.12 kg, respectively) differ significantly from those obtained for plants fertilized with NK (0.25 kg and 0.12 kg, and NPrespectively) (0.21 kg and NP 0.1 (0.21 kg, respectively) kg and 0.1 kg, (Figure respectively)3e). The (Figure lowest 3e). number The lowest of stemsnumber (3.1) of stems was recorded(3.1) in controlwas recorded plants (CK)in control and theplants highest (CK) and in plants the highest fertilized in plants with fertilized NPK (7.1), with followed NPK (7.1), by followed that in NK by (6.3), PK (4.78),that in NP NK(4.67), (6.3), PK N (4.78), (4.33), NP K (4.22),(4.67), N and (4.33), P (4) K fertilized(4.22), and plants. P (4) fertilized plants.

100 a b a 10 c 80 e d b b c bc f d e e 8 60 g f 6 40 4

20 2 Plant height (cm)

0 0 Stem diameter (mm) CK K PK NK N P NP NPK CK K PK NK N P NP NPK

(a) (b) 0.3 ab a 0.15 d ab a 0.25 abc bc abc c c c bc 0.2 c c c 0.1 0.15 d d 0.1 0.05 0.05 0 0 Stem freshStem biomass (kg) Stem drybiomass (kg) CK K PK NK N P NP NPK CK K PK NK N P NP NPK

Sustainability 2016, 8, 887 5 of 9 (c) (d) 8 a e a 6 b bc bc bc bc 4 c

2 Numbers of stem Numbers 0 CK K PK NK N P NP NPK (e)

Figure 3. Morphological traits of ramie (Boehmeria nivea L.) plants grown under different fertilizer Figure 3. Morphological traits of ramie (Boehmeria nivea L.) plants grown under different fertilizer treatments (no fertilizer, K, PK, NK, N, P, NP, and NPK). (a) Plant height; (b) Stem diameter; (c) Stem fresh treatmentsbiomass; (no (d) fertilizer, Stem dry biomass; K, PK, NK,(e) Number N, P, NP, of stems. and NPK).N: nitrogen; (a) Plant P: phosphorus; height; (b and) Stem K: potassium. diameter; Error (c) Stem freshbars biomass; indicate ( oned) Stemstandard dry error. biomass; Different (e) letters Number indicate of significant stems. N: differences nitrogen; at P:p < phosphorus;0.05. and K: potassium. Error bars indicate one standard error. Different letters indicate signiﬁcant differences at3.2.p Effect< 0.05. of Fertilizer on Fiber Yield and Quality The measures of fiber yield and quality also showed positive responses to fertilizer treatment, including the fiber fresh and dry weights, breaking strength, elongation rate, and diameter (Figure 4). The fibers with the lowest fresh and dry weights (0.02 kg and 0.019 kg, respectively) were obtained from unfertilized plants (CK), although the values were not significantly different from those observed for fibers from K-, N-, and P-fertilized plants, and the heaviest fresh and dry fiber weights were obtained from NPK (0.058 kg and 0.049 kg, respectively) and NK-fertilized plants (0.053 kg and 0.042 kg, respectively) (Figure 4a,b). The lowest breaking strength (21.6 cN) was observed for fibers from unfertilized plants (CK), whereas the highest breaking strength (47 cN) was observed in fibers from NPK-fertilized plants, followed by those from NP- (42.9 cN) and NK-fertilized (40.4 cN) plants (Figure 4c). The lowest elongation rate was observed for fibers from unfertilized plants (2.3%), although this rate was not significantly different from that of fibers from K-fertilized plants. The highest elongation rate was recorded in fibers from NPK-fertilized plants (3.92%), although this rate was not significantly different from that of fibers from NK-fertilized plants (3.72%) (Figure 4d). Similarly, the thinnest fibers were obtained from unfertilized plants (14.8 µm), although these fibers were not significantly thinner than those from K- or P-fertilized plants. The thickest fibers were from obtained from NPK- and NK-fertilized plants (30 µm and 27.1 µm, respectively) (Figure 4e).

0.07 0.06 a a a 0.06 b 0.05 0.05 c b c 0.04 bc b bc c c c 0.04 bc 0.03 0.03 d c 0.02 0.02 0.01 0.01 Weight of dry yield (kg) Fiber fresh fresh Fiber weight (kg) 0 0 CK K PK NK N P NP NPK CK K PK NK N P NP NPK

(a) (b) Sustainability 2016, 8, 887 5 of 9

8 a e a 6 b bc bc bc bc 4 c

Sustainability 2016, 8, 887 of stem Numbers 5 of 8 0 CK K PK NK N P NP NPK 3.2. Effect of Fertilizer on Fiber Yield and Quality (e) Figure 3. Morphological traits of ramie (Boehmeria nivea L.) plants grown under different fertilizer The measurestreatments of fiber (no fertilizer, yield K, andPK, NK, quality N, P, NP, and also NPK). showed (a) Plant height; positive (b) Stem responses diameter; (c) Stem to fresh fertilizer treatment, including the fiberbiomass; fresh (d) Stem and dry dry biomass; weights, (e) Number breaking of stems. N: strength, nitrogen; P: phosphorus; elongation and K: rate, potassium. and Error diameter (Figure4). bars indicate one standard error. Different letters indicate significant differences at p < 0.05. The fibers with the lowest fresh and dry weights (0.02 kg and 0.019 kg, respectively) were obtained from unfertilized3.2. Effect plants of Fertilizer (CK), on althoughFiber Yield and the Quality values were not significantly different from those observed for fibers from K-,The measures N-, and of P-fertilizedfiber yield and quality plants, also and show theed positive heaviest responses fresh to andfertilizer dry treatment, fiber weights were obtained fromincluding NPK the (0.058 fiber kgfresh and and 0.049dry weights, kg, respectively) breaking strength, and elongation NK-fertilized rate, and plantsdiameter (0.053 kg and (Figure 4). The fibers with the lowest fresh and dry weights (0.02 kg and 0.019 kg, respectively) were 0.042 kg, respectively)obtained from (Figure unfertilized4a,b). plants The (CK), lowest although breaking the values strength were not significantly (21.6 cN) different was observed from for fibers from unfertilizedthose observed plants for (CK), fibers whereas from K-, N-, the and highest P-fertilized breaking plants, and strength the heaviest (47 fresh cN) and was dry observed fiber in fibers from NPK-fertilizedweights were plants, obtained followed from NPK (0.058 by those kg and from 0.049 kg, NP- respectively) (42.9 cN) and and NK-fertilized NK-fertilized plants (0.053 (40.4 cN) plants kg and 0.042 kg, respectively) (Figure 4a,b). The lowest breaking strength (21.6 cN) was observed for (Figure4c). Thefibers lowest from unfertilized elongation plants rate (CK), was whereas observed the highest for fibers breaking from strength unfertilized (47 cN) was plants observed (2.3%), in although this rate wasfibers not from significantly NPK-fertilized different plants, followed from by thatthose from of fibers NP- (42.9 from cN) and K-fertilized NK-fertilized plants.(40.4 cN) The highest elongation rateplants was (Figure recorded 4c). The lowest in fibers elongation from rate NPK-fertilizedwas observed for fibers plants from unfertilized (3.92%), plants although (2.3%), this rate was although this rate was not significantly different from that of fibers from K-fertilized plants. The not significantlyhighest different elongation from rate was that recorded of fibers in fibers from from NK-fertilized NPK-fertilized plants plants (3.92%), (3.72%) although (Figure this rate4 d). Similarly, the thinnestwas fibers not weresignificantly obtained different from from unfertilized that of fibers from plants NK-fertilized (14.8 µm), plants although (3.72%) (Figure these 4d). fibers were not Similarly, the thinnest fibers were obtained from unfertilized plants (14.8 µm), although these fibers significantlywere thinner not significantly than those thinner from than K- those or P-fertilizedfrom K- or P-fertilized plants. plants. The The thickest thickest fibers fibers were were from from obtained from NPK- andobtained NK-fertilized from NPK- and plants NK-fertilized (30 µ mplants and (30 27.1 µm andµm, 27.1 respectively) µm, respectively) (Figure (Figure 4e).4e).

60 a 4.5 a ab 4 50 bc b b dc de 3.5 c ef 40 d fg 3 de e g 2.5 30 f 2 20 1.5 10 1 0.5 0 elongation Fiber rate (%) Fiber breaking strength (cN) strength breaking Fiber 0 CK K PK NK N P NP NPK CK K PK NK N P NP NPK

(e)

Figure 4. Fiber quality and yield traits of ramie (Boehmeria nivea L.) plants grown under different Figure 4. Fiberfertilizer quality treatments and (no yield fertilizer, traits K, PK, of NK, ramie N, P, NP, (Boehmeria and NPK). nivea(a) FiberL.) fresh plants weight; grown(b) Fiber dry under different fertilizer treatmentsweight; (c) (noFiber fertilizer, breaking strength; K, PK, (d NK,) Fiber N, elongation P, NP, rate; and (e NPK).) Fiber diameter. (a) Fiber N: freshnitrogen; weight; P: (b) Fiber phosphorus; and K: potassium. Error bar indicate one standard error. Different letters indicate dry weight; (c) Fiber breaking strength; (d) Fiber elongation rate; (e) Fiber diameter. N: nitrogen; significant differences at p < 0.05. P: phosphorus; and K: potassium. Error bar indicate one standard error. Different letters indicate signiﬁcant3.3. differences Effect of Fertilizer at p on< N 0.05. and P Uptake and Partitioning The N and P contents of stems, leaves, petioles, and fiber bark also increased with fertilizer application (Figure 5). The lowest N and P contents were observed in unfertilized plants (CK), whereas higher N contents were observed in NPK- and NK-fertilized plants, and higher P contents were observed in NPK- and PK-fertilized plants. In addition, the highest N content was observed in the leaves of NPK-fertilized plants, and the highest P content was observed in the petioles in NPK- fertilized plants.

stem leaves petiole fiber bark stem leaves petiole fiber bark 3.5 0.9 0.8 3 0.7 2.5 0.6 2 0.5 1.5 0.4 1 0.3 0.2 0.5 0.1

Nitrogen contents (%) Nitrogen contents 0 0 Phosphorous contents (%) Phosphorous

(a) (b) Sustainability 2016, 8, 887 6 of 9

(e)

Figure 4. Fiber quality and yield traits of ramie (Boehmeria nivea L.) plants grown under different fertilizer treatments (no fertilizer, K, PK, NK, N, P, NP, and NPK). (a) Fiber fresh weight; (b) Fiber dry weight; (c) Fiber breaking strength; (d) Fiber elongation rate; (e) Fiber diameter. N: nitrogen; P: phosphorus; and K: potassium. Error bar indicate one standard error. Different letters indicate Sustainability 2016, 8, 887 6 of 8 significant differences at p < 0.05.

3.3. Effect Effect of Fertilizer on N and P Uptake and Partitioning The N and P contents of stems, leaves, petioles, and fiber ﬁber bark also increased with fertilizer application (Figure 55).). The lowest N andand PP contentscontents werewere observedobserved inin unfertilizedunfertilized plantsplants (CK),(CK), whereas higher N contents were observed in NPK- and NK-fertilized plants, and higher P contents were observed in in NPK- NPK- and and PK-fertilized PK-fertilized plants. plants. In In addition, addition, the the highest highest N Ncontent content was was observed observed in thein the leaves leaves of NPK-fertilized of NPK-fertilized plants, plants, and andthe highes the highestt P content P content was observed was observed in the inpetioles the petioles in NPK- in fertilizedNPK-fertilized plants. plants.

stem leaves petiole fiber bark stem leaves petiole fiber bark 3.5 0.9 0.8 3 0.7 2.5 0.6 2 0.5 1.5 0.4 1 0.3 0.2 0.5 0.1

Nitrogen contents (%) Nitrogen contents 0 0 Phosphorous contents (%) Phosphorous

(a) (b)

Figure 5. Total nitrogen and phosphorus in the stem, leaves, petiole, and ﬁber bark of ramie (Boehmeria nivea L.) plants grown under different fertilizer treatments (no fertilizer, K, PK, NK, N, P, NP, and NPK). (a) N and (b) P content.

4. Discussion Nutrients, particularly N, P, and K, play a vital role in plant growth and production, since they are involved in many biological processes [13]. Ramie is a plant with vigorous growth and thus has a high nutrient demand [7]. In the present study, the maximum increases in plant height, stem diameter, stem fresh and dry weights, and the number of stems were observed in plants treated with combined NPK fertilizer, followed by those receiving NK fertilization. It has been suggested that N in combination with K significantly improves crop yield and quality [14]. Aulah and Malhi [15,16] reported that the + absorption of N, in the form of NH4 , is not affected by K and that the interaction between N and K is the second most important factor after NPK for increasing crop yield, which is not further increased by the increasing concentrations of N and P without the addition of K. Deng et al. [13] suggested that several metabolic activities of ramie are affected by N, P, or K deficiency. For instance, the expression of profilin is down regulated under P-deficient conditions, and this affects fiber synthesis [13,17]. Fiber fresh and dry weights were also increased by fertilizer application, particularly NPK, which is consistent with the results reported by Liu et al. [18]. Apart from NPK, the effect of K on fiber fresh and dry weights was more evident than that of P. Tewolde and Fernandez [19] reported that P application does not improve fiber properties in cotton, and concluded that a moderate deficiency of P does not affect fiber quality. Thus, on the basis of our results and those reported by Liu et al. [18], we recommend that the current application doses of P fertilizers could be reduced without having any significant effect on fiber yield and quality. However, K application had a significant effect on fiber yield and quality, which is consistent with the results reported by Subandi in 2012 [8], and Liu et al. [20] also suggest that N in combination with K significantly increases fiber yield in ramie by increasing the weight and number of stems. Improvement of fiber quality is one of the major objectives in ramie breeding programs. It is known that fiber-breaking strength is directly related to fiber wall thickness and that this is an important Sustainability 2016, 8, 887 7 of 8 parameter for physically accessing fiber quality [19,20]. In the present study, fiber breaking strength was significantly increased by fertilizer application compared with the control treatment. Since stems are the main source of fiber, any increase in fiber yield would be attributed to an increase in stem weight. A positive correlation (Table2) has been reported between the K content of the stem and fiber yield [21]. Our results indicated that NPK increased the N content in different plant parts more than a single application of N, which is consistent with the findings of Aulakh and Malhi [15], who showed that the interactive effect of N and P increased the N use efficiency in rice, wheat, and grasses. Similarly, the application of NP increased the P content in different plant parts to a greater extent than the single application of P, because it enhanced the P use efficiency.

Table 2. Correlation coefﬁcient (r2) of ﬁber yield and quality parameters with morphological traits in ramie (Boehmeria nivea L.) plants.

Plant Biomass Stem Fresh Numbers Stem Total Total P Height Weight Biomass of Stem Diameter NUptake Uptake Fiber breaking strength 0.86 *** 0.89 *** 0.88 *** 0.84 *** 0.79 *** 0.91 *** 0.83 *** Fiber elongation rate 0.88 *** 0.93 *** 0.92 *** 0.88 *** 0.72 *** 0.94 *** 0.80 *** Fiber diameter 0.84 *** 0.87 *** 0.84 *** 0.86 *** 0.71 *** 0.89 *** 0.74 *** Fiber yield fresh biomass 0.92 *** 0.96 *** 0.95 *** 0.95 *** 0.79 *** 0.92 *** 0.73 *** Fiber yield dry biomass 0.92 *** 0.94 *** 0.93 *** 0.94 *** 0.83 *** 0.92 *** 0.79 *** *** Indicated signiﬁcant r2 values at p < 0.001.

In the present study, a positive correlation was observed between N content and fiber yield and quality parameters. Previous studies have indicated that N application significantly improves fiber quality in ramie and that the improved morphological parameters, including dry matter and leaf area index, lead to increased crop yield [22,23].

5. Conclusions In summary, the present study clearly indicates that NPK, and to a lesser degree NK, significantly improve ramie growth, yield, and fiber quality, whereas P had the least effect among the investigated fertilizer applications. Furthermore, the results revealed that fiber yield and quality were directly related to morphological traits. Thus, it is suggest that optimum fertilization is important for sustainable ramie production.

Acknowledgments: This research was supported by the National Natural Science Foundation of China (31571717) and China Agriculture Research System (CARS-19-E12) project (2662015PY059) supported by the Fundamental Research Funds for the Central Universities. Author Contributions: Lijun Liu and Dingxiang Peng supervised and designed the project. Sana Ullah and Xu Tuo performed the experiment and collected data. Shahbaz Khan helped in conducting experiment. Sumera Anwar analyzed data. Bo Wang gave technical support. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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