•Light intensity in densely planted maize canopies plays an important factor in lodging.•The leaves 10–12 played a very important role in the strength of the third basal internode.•Improving light ...intensity at leaves 10–12 at flowering can reduce lodging by increasing dry matter accumulation and stalk strength formation at the third basal internode.
Close planting often increases the lodging rate of maize, but the cause is unclear. Close planting reduces light intensity within the canopy; therefore, we hypothesized that light intensity may be the main factor affecting maize lodging. To test this hypothesis, three field experiments involving plant density, shading and defoliation were designed to explore how the light environment in a maize canopy affects stalk strength formation and lodging rate. The results showed that close planting and artificial shading treatments both reduced light intensity in the lower canopy. This reduced the dry weight per unit length (DWUL) and rind penetration strength (RPS) of the third basal internode and increased the lodging rate. Removal of leaves 10–12 reduced the DWUL and RPS of the third internode and increased lodging rate. This showed that leaves 10–12 play a crucial role both in the formation of RPS of the third basal internode and in lodging resistance. Removal of either all or part of leaf 16 and above not only increased ptotosynthetic active radiation (PAR) at leaves 10–12 but also increased the DWUL and RPS of the third basal internode. This resulted in a decline in lodging. Therefore, we conclude that light intensity is an important factor affecting maize lodging at high plant density. Increasing light intensity at leaves 10–12 can enhance stalk strength and reduce lodging.
Cotton has many leaves and even more bolls, which results in a complicated source–sink relationship. Under water stress, the single boll weight (SBW) of cotton remains relatively stable, while both ...the leaf area and leaf photosynthetic rate decrease greatly. It is therefore difficult to understand how the formation of SBW is regulated under water stress solely by considering single-leaf photosynthesis. Considering the cotton boll–leaf system (BLS: including the main-stem leaf, sympodial leaves, and non-leaf organs) as the basic unit of the cotton canopy, we speculated that the formation of SBW may depend on photosynthesis in the corresponding BLS under water stress. To verify this hypothesis, five water treatments were set up in the field. The results showed that with increasing water stress, the relative water content (RWC) of the main-stem and sympodial leaves decreased gradually, and the decrease in the sympodial leaves was more obvious. The SBW and the number of BLSs decreased slightly with increasing water stress, while the number of bolls per plant decreased significantly. The area of the BLS decreased gradually with increasing water stress, and the area of sympodial leaves decreased more than that of the main-stem leaves. Gas exchange showed that the photosynthetic rate of the BLS (Pn
(BLS)
) decreased gradually with increasing water stress. In addition, the single-leaf photosynthesis and carboxylation efficiency (CE) decreased progressively and rapidly with the increase of water stress. Compared with the main-stem leaf, the photosynthetic function of the sympodial leaf decreased more. Further analysis showed that compared with leaf photosynthetic rate, there was a better correlation between Pn
(BLS)
and SBW. Thus, the formation of SBW mainly depends on Pn
(BLS)
under water stress, and the increase of BLS to boll is also helpful to maintain SBW to some extent. In BLS, the photosynthesis of the main-stem leaf plays a very important role in maintaining the stability of SBW, while the photosynthetic performance in sympodial leaves may be regulated plastically to influence SBW.
Estimating the boll development and boll yield from single-leaf photosynthesis is difficult as the source-sink relationship of cotton (
Gossypium hirsutum
L.) is complicated. As the boll-leaf system ...(BLS), which includes the main-stem leaf, sympodial leaf, and non-leaf organs, is the basic unit of the cotton source-sink relationship and yield formation, the concept of "BLS photosynthesis" is introduced in this study. We speculate that the characteristics of BLS gas exchange can more accurately reflect the photosynthetic function of the system, thus revealing the law of photosynthesis in the process of boll development. The results showed that the photosynthetic rate of single leaves measured by a BLS chamber was consistent with that measured by a standard single-leaf chamber. BLSs exhibited typical light response curves, and the shape of the curves was similar to those of single leaves. The light compensation point and respiration rate of BLSs were higher than those of single leaves, while the apparent quantum efficiency of BLSs was lower. Compared with single leaves, the duration of the photosynthetic function of BLSs was longer. Increasing plant density decreased the gas exchange rate per unit BLS more significantly under field conditions. There was a better linear correlation between the net CO
2
assimilation rate, respiration rate of BLSs and boll biomass. Therefore, we think that the gas exchange of BLSs can better reveal the changes in photosynthetic function of BLSs and boll development. This provides a new basis for analyzing the mechanism and regulation of cotton yield formation.
It is of great importance to explore agronomic management measures for water conservation and cotton yield in arid areas.
A four-year field experiment was conducted to evaluate cotton yield and soil ...water consumption under four row spacing configurations (high/low density with 66+10 cm wide, narrow row spacing, RS
and RS
; high/low density with 76 cm equal row spacing, RS
H and RS
L) and two irrigation amounts (CI:conventional drip irrigation; LI:limited drip irrigation) during the growing seasons in Shihezi, Xinjiang.
A quadratic relationship was observed between the maximum LAI (LAI
) and seed yield. Canopy apparent transpiration rate(CAT), daily water consumption intensity (DWCI) and crop evapotranspiration (ET
) were positively and linearly correlated with LAI. The seed yields, lint yields, and ET
under CI were 6.6-18.3%,7.1-20.8% and 22.9-32.6%higher than those observed under LI, respectively. The RS
under CI had the highest seed and lint yields. RS
L had an optimum LAI
range, which ensured a higher canopy apparent photosynthesis and daily dry matter accumulation and reached the same yield level as RS
; however, soil water consumption in RS
L was reduced ET
by 51-60 mm at a depth of 20-60 cm at a radius of 19-38 cm from the cotton row,and water use efficiency increased by 5.6-8.3%compared to RS
under CI.
A 5.0<LAI
<5.5 is optimum for cotton production in northern Xinjiang, and RS
L under CI is recommended for high yield and can further reduce water consumption. Under LI, the seed and lint yield of RS
were 3.7-6.0% and 4.6-6.9% higher than those of RS
L, respectively. In addition, high-density planting can exploit the potential of soil water to increase cotton yields under water shortage conditions.
Manual removal of the main stem tips of cotton (Gossypium hirsutum L.) is a traditional topping approach in China. However, chemical topping has become an inevitable trend. Therefore, it is of great ...significance to study the effect and appropriate concentration of agents for advancement of cotton whole process mechanization management technology. A two-year field experiment was conducted to evaluate the effects of different methods of topping on cotton yield and plant architecture in Shihezi, Xinjiang, China. Plant topping included manual topping, non-topping as the control, and chemical topping (high, medium, and low concentrations of topping agent) to determine a suitable topping method and topping agent concentration for machine-picked cotton. Chemical topping was performed using fortified mepiquat chloride (DPC+). Chemical topping and manual topping increased seed cotton yield compared with non-topping. Compared with non-topping, high, medium, and low concentrations of topping agent significantly increased the yield by 19.5–27.9%, 24.1–29.4%, and 24.3–28.4%, respectively. Topping treatment mainly regulated yield and total boll number per unit area by affecting the boll number per plant and had a certain positive effect on fiber strength but no significant effect on boll weight. Chemical topping affected both vertical and horizontal plant architecture characteristics of cotton; the plant height of low-, medium-, and high-concentration treatments increased by 7.2–11.4 cm, 4.0–5.7 cm, and 2.3–4.4 cm, respectively, compared with manual topping and decreased by 5.1–7.8 cm, 8.3–13.5 cm, and 9.4–16.9 cm, respectively, compared with non-topping. The number of main stem internodes was significantly different between high- and low-concentration treatments, which showed that the higher the concentration, the lower the number of the main stem internodes. Chemical topping controlled the increase in the length of the upper branches, the higher the concentration, the lower the increase in the length of the upper fruit branch. Compared with non-topping, the medium concentration of topping agent controlled the number of fruit branches, similar to manual topping. The role of upper internode length of cotton cannot be ignored under chemical topping. The peak leaf area index (LAI) of medium- and high-concentration treatments was delayed for 1 week in the late growth period (after topping for 28 d) compared with manual topping. The LAI values were high, and the duration of high values was prolonged. The optimal chemical topping agent was the medium concentration.
The application of harvest aids is an important prerequisite for the mechanical harvesting of cotton that can effectively reduce the impurity content and improve the picking rate and operating ...efficiency of machine-picked cotton. However, determining the appropriate spraying time of harvest aids to achieve the synergistic improvement of cotton boll weight and fiber quality is still unclear. In this study, the damage of harvest aids to cotton boll weight and fiber quality as well as its quantitative relationship to cotton boll age were studied through testing different harvest aid compounds and spraying times. The spraying of harvest aids significantly shortened the boll growth period of cotton by 3.60–6.45 d, and concentrated boll opening was beneficial to cotton mechanical harvesting. The boll weight of immature cotton was significantly decreased by 0.63–1.12 g; the fiber strength was significantly decreased by 2.48–2.77 cN·tex−1, and the micronaire value deteriorated. The negative effect on the boll weight and fiber quality was aggravated by the decrease in the ratio of boll age to boll period (Rd/b) during the harvest aid spraying time. When the fiber strength damage was controlled at 1%, the spraying time Rd/b of the harvest aids was 0.77–0.82, and the boll weight loss was also controlled at 5%. Therefore, it is recommended that an Rd/b of 0.77–0.82 be used to balance the contradiction between cotton yield and fiber quality under harvest aid application.
Purpose
This study was conducted to understand the effects of water and nitrogen (N) on net root productivity, root longevity, root length, and canopy characteristics of cotton (
Gossypium hirsutum
...L.), and to quantify the associations between canopy characteristics and indicators of root dynamics.
Methods
A two-year field experiment was performed to evaluate the variation in canopy growth and root dynamics of cotton in response to three nitrogen levels (320 kg ha
−1
, high N; 272 kg ha
−1
, moderate N; 224 kg ha
−1
, low N) and two water levels (400 mm, high-water group; 267 mm, low-water group) during the growing seasons of 2019 and 2020 in Xinjiang, China.
Results
Plants exposed to low-water environments increased root longevity more than all other high-water treatments. Under high-water conditions, a moderate N rate obtained a higher root longevity compared to high-N and low-N treatments. Net root productivity (NRP) was strongly associated with leaf area expansion rate and leaf number. A moderate N rate under high-water conditions exhibited a significant 30.0% increase in NRP, resulting in a relatively high leaf area and the highest leaf relative water content, and had an equivalent canopy photosynthetic rate compared with high-N plots. Plants receiving moderate N in the high-water group had greater total root length by increasing root longevity and productivity.
Conclusions
Estimates of NRP may need to be included along with leaf growth estimates in future efforts to scale from root to canopy level developmental performance in cotton.
Graphical abstract
•Mulched drip irrigation had a larger SRL and more fine roots at early growth stages.•Fine roots and R/S decreased under mulched drip irrigation at late growth stages.•Biomass of reproductive organs ...and boll number increased with the decrease of R/S.•Productive capacity of fine root system was increased under mulched drip irrigation.•Mulched drip irrigation reduced the growth redundancy of root and shoot in cotton.
Mulched drip irrigation is a common water-saving irrigation technology that can improve water resource utilization efficiency in arid areas. The change of irrigation method affects the growth of crop root system and then regulates the growth of aboveground organs. However, there have been limited comparative studies on how mulched drip irrigation affects the cotton root growth and regulates the relationship between cotton root and shoot. The objective of this study was to determine whether mulched drip irrigation could achieve water-saving and high-yield cotton cultivation by regulating the growth redundancy of root and shoot. Under field conditions, mulched drip irrigation (conventional drip irrigation and excessive drip irrigation) and traditional flood irrigation (conventional flood irrigation and reduced flood irrigation) were used in this experiment. Traditional flood irrigation was used as the control group. The results showed that compared with the traditional flood irrigation, the higher soil water content under mulched drip irrigation increased the specific root length (SRL), which promoted the growth of fine root length and biomass at the full flowering stage and prophase full boll stage. The growth of fine roots increased the root-shoot ratio (R/S) of mulched drip irrigation, and then inhibited the excessive vegetative growth of the aboveground parts. When entering the late full boll stage and boll opening stage, the fine root biomass and fine root mass fraction decreased rapidly under the mulched drip irrigation, resulting in a lower R/S. The smaller R/S of mulched drip irrigation facilitated the distribution of photosynthetic products to reproductive organs, which increased the boll number per plant by 7.30 %–25.10 %, thus increasing the boll loading of fine root system and seed cotton yield. However, compared with conventional drip irrigation, over irrigation led to excessive vegetative growth of cotton under excessive drip irrigation, which resulted in the decrease of boll opening rate and seed cotton yield by 8.71 %–17.19 % and 14.14 %–24.27 %, respectively. Moreover, the smaller R/S at the late growth stage enabled conventional drip irrigation to achieve the maximum water use efficiency (WUE). Therefore, mulched drip irrigation promoted the root growth of cotton and inhibited the vigorous vegetative growth of shoot before the prophase full boll stage, and then reduced the growth redundancy of root and increased the productive capacity of the fine root system after the prophase full boll stage, which increased boll number per plant and yield. However, only under the appropriate irrigation amount (390 mm), mulched drip irrigation can increase both yield and WUE, thus achieving the goal of water-saving and high-yield cultivation.
The morphological characteristics of crop roots, especially the plasticity of fine roots, are directly related to the crop’s ability to obtain soil water. Mulched drip irrigation can effectively ...regulate soil water distribution to achieve high cotton yield with reduced water consumption. In the previous study, from the perspective of root-shoot coordination, we found that mulched drip irrigation reduced the growth redundancy of roots and improved the root productivity of cotton, thus achieving the goal of water-saving and increased yield. However, it is unclear if and how mulched drip irrigation enhances absorptive capacity of roots via regulating dry and wet soil areas and optimizing fine root morphology and distribution compared with traditional flood irrigation. To achieve this, the effects of fine root plasticity on the absorptive capacity of roots were studied in a two-year field experiment. Mulched drip irrigation (conventional drip irrigation and excessive drip irrigation) and traditional flood irrigation (reduced flood irrigation and conventional flood irrigation) were used, and soil water distribution and root distribution were determined. The results showed that compared with traditional flood irrigation, mulched drip irrigation significantly increased the soil water content (SWC) in the 0–60 cm soil layer and reduced the fluctuation amplitude of SWC at the flowering and boll stage of cotton. Mulched drip irrigation formed different dry and wet areas in the root zone, i.e., the SWC was higher in the shallow layer (0–40 cm) at 0–20 cm on both sides of the drip line, and most of the cotton roots were in the wet area. The higher SWC increased the distribution of fine roots in this area and shaped the shallow fine root system, which enhanced the cotton plant’s ability to absorb soil water. Statistical analysis showed that the higher fine root biomass in the 0–40 cm soil layer at the late full boll stage of cotton under mulched drip irrigation was beneficial to increase aboveground biomass, thus increasing total bolls and seed cotton yield. However, compared with the irrigation amount of field production (390 mm), an excessive amount of irrigation (600 mm) reduced the seed cotton yield of mulched drip irrigation, resulting in the decrease of irrigation water use efficiency (IWUE). Therefore, mulched drip irrigation optimizes the distribution of fine roots and enhances water uptake by effectively regulating the water–root relationship, and thus improves seed cotton yield and IWUE.
•Mulched drip irrigation formed different dry and wet areas in the shallow soil layer.•Most of the cotton fine roots developed and grew in the wet area under mulched drip irrigation.•Mulched drip irrigation enhanced the absorptive capacity of roots in the shallow soil layer.
