effects of potassium fertilizer on the ... cotton (gossypium hirsutum l.), the king of natural...
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Pak. J. Bot., 49(3): 935-943, 2017.
EFFECTS OF POTASSIUM FERTILIZER ON THE PHYSIOLOGICAL
MECHANISMS OF COTTON FIBER QUALITY
BOLANG CHEN, ZHONGPING CHAI, JIANDONG SHENG, WENTAI ZHANG AND PINGAN JIANG
College of Grassland and Environmental Sciences, Xinjiang Agricultural University,
Xinjiang Key Laboratory of Soil and Plant Ecological Processes, Urumqi 830052, China *Corresponding author, s e-mail: email@example.com; Tel: 86-991-88763882, Fax: +86-991-88763041
Endogenous hormones are a key factor in cotton fiber quality. Studying the relationship among endogenous hormone
contents and fiber quality can provide a theoretical basis for exploring physiological measurements to improve fiber quality.
The relationships among endogenous hormone contents and fiber quality for different boll positions and potassium (K)
conditions were investigated for the main cultivar ‘Xinluzao 24.’ We used eight application rates of K fertilizer (K2O 0,
37.5, 75, 112.5, 150, 37.5 and sprayed 1% K2SO4, 75 and sprayed 1% K2SO4, and 150 and sprayed 1% K2SO4 kg ha-1 under
field conditions). We then measured the contents of indoleacetic acid (IAA), gibberellin (GA3), zeatin (Z), and abscisic acid
(ABA) in relation to changes in fiber quality indices. Results showed that application of K fertilizer significantly increased
the contents of IAA, GA3, and Z in the upper and middle boll, and decreased the contents of ABA in the upper, middle, and
the lower boll. Compared with the control, applying K fertilizer between 37.5 kg K2O ha–1 and 112.5 kg K2O ha–1 can
significantly increase the length, uniformity, strength, micronaire, and maturity of fiber in three parts of the plant. However,
excessive application of K fertilizer can reduce fiber uniformity, strength, and micronaire in these locations. Through
comprehensive comparison, we determined that the optimal application of K fertilizer for regulating endogenous hormones
and improving fiber quality was a basal application of 75 kg K2O ha–1 and a spray application of 1% K2SO4. The
endogenous hormones IAA, GA3, and Z can improve cotton fiber quality, but ABA can inhibit cotton fiber quality. Results
indicate that reasonable applications of potassium fertilizer could regulate endogenous hormones and improve fiber quality.
Key words: Potassium nutrition, Cotton, Endogenous hormones, Fiber quality.
Cotton (Gossypium hirsutum L.), the king of natural
fibers, is of prime importance in the economy of many countries, providing renewable natural fiber resources for the global textile industry (Zhang et al., 2015). The yield and quality of cotton are influenced by genetics and environmental conditions (Ramey, 1986; Reddy et al., 1999; Lokhande & Reddy, 2015). Fertilizer management has a decisive effect on fiber quality, and potassium (K) is one of the major mineral nutrients impacting cotton plant growth, development, lint yield, and fiber quality (Kerby et al., 1985; Cassman et al., 1990; Reddy & Zhao, 2005; Derrick et al., 2013). K deficiency has negative effects on cotton plant photosynthesis (Bednarz et al., 1998; Reddy & Zhao, 2005; Hu et al., 2015), biomass production (Zhao et al., 2001; Reddy & Zhao, 2005; Gerardeaux et al., 2010), lint yield (Pettigrew, 2003; Li et al., 2012), and fiber quality (Pettigrew et al., 1996). The impact of K is not always visible and consistent in terms of improvement in fiber quality parameters (Bauer et al., 1998). However, researchers have reported that K can be conducive to fiber elongation, increased thickness of the secondary fiber wall, and enhancement of fiber strength (Cassman et al., 1990; Read et al., 2005; Pervez et al., 2005a; Yang et al., 2008; Temiz et al., 2009; Kaur et al., 2011; Waraich et al., 2011). K has the greatest impact on fiber maturity and micronaire, less on length and strength, and little effect on uniformity (Pettigrew, 2003; Zhao et al., 2013). It is often reported that K nutrition can also influence endogenous hormone content (Liu et al., 2006). Research shows that spraying K significantly increases IAA content in the boll shell within 30 days after blossom in the middle and upper bolls. Additionally, the differences in IAA content between the
middle and upper boll shells tend to narrow with the intensification of potassium applications. ZR content in the middle and upper boll fiber peaks thirty days after blossom, while ZR content at the tenth day after blossom in the middle boll is higher than that after 50 days.
Considerable evidence indicates that endogenous hormones play a decisive role in regulating cotton fiber growth and development (Beasley & Ting, 1973; Beasley & Ting, 1974; Naithani et al., 1982; Dasani & Thaker, 2006). In vitro culture of ovules indicated that IAA plays an important role in fiber development, and that ABA inhibits fiber development (Beasley & Ting, 1973). Addicott (1982) observed that ABA content was higher in mature cotton fruits than in young, healthy fruits. Related information shows that GA3 and IAA help the fiber elongation process, and that ABA is counterproductive. Increases in ZR are beneficial for differentiation of fiber and the extension of the fiber enrichment period. Brassinosteroids (BRs) affect cotton fiber initiation and elongation, ethylene promotes cotton fiber elongation, and GAs stimulate cotton fiber differentiation and elongation. Additionally, ZR content has a significant or very significant positive correlation with fiber length and maturity (Gokani & Thaker, 2002; Du et al., 2004; Seagull & Giavalis, 2004; Cheng et al., 2005; Pervez et al., 2005a; Chen, 2006; Dasani & Thaker, 2006; Fuller et al., 2009;Liao et al., 2009; Xiao et al., 2010).
Reports of the separate influence of K on seed yield, fiber quality, and endogenous hormones have been received over the past decade. Thus, there is insufficient information regarding K influence on fiber quality and endogenous hormones, and also the correlation between fiber quality and endogenous hormones. Therefore, the objectives of this research were to: (i) identify K fertilizer doses and management that may improve fiber yield and quality, (ii) discuss the correlation between fiber quality
BOLANG CHEN ET AL., 936
and endogenous hormones, and (iii) understand the regulated pathways and physiological mechanisms underlying the role of K in improving fiber quality.
Materials and Methods
Experimental material and design: The trial was located at the Experimental Farm of the Fertilizer Institute of Agriculture, Changji City (87°27′ E, 44°15′ N), in northern Xinjiang, China. The area has a semi-arid climate, and the average annual temperature was 7.2 °C in 2013. The hottest month is July (mean daily maxima and minima of 27.2°C and 22.6°C, respectively), whereas January is the coldest (mean daily maxima and minima of –12.2°C and –20.4°C, respectively). The area has a mean annual precipitation of 194.3 mm with a mean annual surface evaporation of 1988.5 mm, a frost-free period of 175 d, annual sunshine hours of 3110 h, and total annual solar radiation of 5560 MJ m–2. Surface soil (0–0.2 m) had 7.8 pH (H2O), 17.2 g kg–1 organic matter, 1.2 g kg–1
total nitrogen, 0.9 g kg–1 total phosphorus, 6.7 g kg–1 total K, 32.3 mg kg–1 available nitrogen, 8.0 mg kg–1 0.5 M NaHCO3-P, and 207 mg kg–1 NH4OAc-K.
Eight treatments of K fertilizer (K2O) at five different levels (0, 37.5, 75, 112.5, 150) were applied using three management methods (37.5 and spraying 1% K2SO4, 75 and spraying 1% K2SO4, and 150 and spraying 1% K2SO4 kg ha-1, referred to as K0, K1, K2, K3, K4, K5, K6, and K7 respectively, among which, K5, K6, and K7 were management designs of K fertilizer. Treatments were arranged in a randomized complete block design with four replicates. All treatments received 300 kg ha–1 of N as urea; the treatments were applied by drip irrigation in three different stages: 180 kg ha–1 before sowing, 60 kg ha–1 at the bud stage, and 60 kg ha–1at the flower boll stage. K fertilizer (potassium sulphate with 40% K2O) and 150 kg ha–1 of P2O5 as TSP (triple superphosphate with 46% P2O5) were added to the topsoil before sowing by broadcast application and then mixed by conventional tillage (0–0.3 m depth). The spray applications of K fertilizer were applied during blossing and boll-forming stages. The area of each experimental block was 64 m2 (6.4 m×10 m).
The cotton variety used was XinluZao 24, a standard
cotton variety for the region. The cotton was planted in
row spacings of 0.5 m, 0.3 m, 0.5 m, and 0.3 m and plant
spacing within the rows of 0.1 m. The density was
195,000–225,000 plants ha-1. Cotton seeds were sowed on
April 25, 2013. The frequency of drip irrigation was
seven days. The first irrigation was applied on June 15
(bud stage) and there were a total of 10 or 11 irrigations
throughout the period of crop production. Weeds were
controlled by manual removal. Control of pests and
diseases was provided as needed during the growing
season, according to local recommendations. All other
production practices followed recommended practices.
Harvest and sample analysis: After all harvestable bolls
had matured, boll and fiber data were obtained from 30 boll
samples, hand-harvested at 8-m lengths from the four center
rows in each block. The cotton bolls i