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Article

Negative and Positive Impacts of Rape Straw Returning on the Roots Growth of Hybrid Rice in the Sichuan Basin Area

by
Xuechun Wang
1,*,†,
Naseem Samo
1,
Changkun Zhao
1,†,
Hongni Wang
1,
Guotao Yang
1,
Yungao Hu
1,*,
Youlin Peng
1 and
Fahd Rasul
2
1
College of life science and engineering, Southwest University of science and technology, Mian Yang, Sichuan 621010, China
2
Agweathernet, Washington State University, Prosser, WA 99350, USA
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work and should be considered co-first authors.
Agronomy 2019, 9(11), 690; https://doi.org/10.3390/agronomy9110690
Submission received: 28 September 2019 / Revised: 22 October 2019 / Accepted: 24 October 2019 / Published: 28 October 2019
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Abstract

:
Incorporating oilseed-rape straw in soil is one of the effective methods for enhancing the use efficiency of agricultural resources in the rape-rice rotation system. However, the impacts of oilseed-rape straw incorporation on root growth and dynamic changes in soil are still unclear. In order to provide a deeper understanding of the oilseed rape straw return on rice growth and productivity, the experiment was conducted in the field and in a specially-designed pots system from 2016 to 2017 by means of two straw returning methods and four straw returning amounts. In the early stage of rice growth (0–36 days after rice transplanting) the straw returning treatments decreased 1.0–8.6 mg/plant in bleeding density and 0.10–6.11, 0.06–0.31, and 0.52–0.84 μmol/(g h) in the activity of glutamine synthetase (GS), glutamic-oxalacetic transaminase (GOT), and glutamic-pyruvic transaminase (GPT), respectively. Oilseed rape straw returned by mulching induced negative impacts on new germinating roots in 0–10 cm of soil, while the negative impacts were observed on roots in 10–30 cm of soil for straw returned by plowing. In the later stage of rice growth (56–75 days after rice transplanting), oilseed rape straw returning produced some positive impacts on rice roots, which enhanced the yield of rice. Conclusively, our findings suggested that dynamic root growth and the activity of root enzymes are two major factors behind the slow reviving of rice after transplanting in the straw returning field. Plowing is a more appropriate method of straw returning than mulching in the rape-rice rotation system in the Sichuan basin area, with a straw incorporation rate of 3.0 t/hm2.

1. Introduction

Incorporating oilseed-rape straw in soil is one of the effective methods for enhancing the use efficiency of agricultural resources in the rape-rice rotation system [1]. Mulching straw over the field and plowing straw into deep soil are two primary methods generally operated by farmers to return oilseed-rape straw back to the soil in rape-rice rotation areas [2]. Mulching treatment is appropriate for hilly areas due to lesser usage of machinery, while plowing treatment is suitable for plain areas where the mechanization is relatively higher [3,4]. Previous research has explored that continuous straw incorporation in soil built a better growth environment for rice when considering long periods, by means of increasing the nitrogen, phosphorus, potassium [5,6,7], and organic matter content of the soil [8,9,10]. Most of the earlier studies reported that straw incorporation enhanced rice yield in rape-rice rotation fields when considering long periods. Straw incorporation technology, either by mulching or plowing, has been widely implemented in the Sichuan Basin area of China [11] and other rape-rice rotation regions in the world over the last 10 years [9,12,13], which significantly increased the use efficiency of crop’s straw in rape-rice rotation fields. However, a delay of reviving after transplanting and a reduction of grain yield were found in some rape-rice rotation fields [2,14], where lots of straw were returned back to the soil. This instability of rice yield impeded the application of straw returning technology in the rape-rice rotation region. Therefore, it is crucial to comprehend the reasons that lead to the slow revival of rice and reduction in the grain yield after transplanting to straw incorporated fields.
Former studies reported several reasons for the late reviving of rice in straw incorporated fields, though most of them agreed that straw incorporation has a significant influence on rice growth and grain yield [8,9,11]. However, the impacts of oilseed-rape straw incorporation on root growth and dynamic changes in soil are still unclear. The earlier investigation unveiled that the rice roots grow slowly and appear blackish in color [15], which indicated that root growth and dynamic changes might be one of the important factors for the delay of rice revival and reduction of yield in oilseed-rape straw-incorporated fields.
The objectives of this paper are to clarify the impacts of straw incorporation on root growth, root bleeding, and root distribution to explain why rice revives slowly after transplanting to straw incorporated fields from the perspectives of root growth and dynamic changes in soil.

2. Materials and Methods

2.1. Study Area

The present study was carried out in Mianyang city, which is located in the northwest part of the Sichuan Basin area, in the middle and upper reaches of the Fujiang River. It has a typical subtropical monsoon climate with an annual rainfall of 826–1417 mm, an annual temperature of 14.7–17.3 ℃, and a frost-free period of 252 and 300 days. The soil of the corresponding region is typical clay-loam soil with a bulk density of 1.29 g/cm3 in which the organic matter content is 28.6 g/kg, total nitrogen content is 1.68 g/kg, total phosphorus is 0.37 g/kg, and total potassium is 1.86 g/kg. As the primary food crops, rice and oilseed rape constitute a Paddy-dryland rotation system in this area. Oilseed rape is cultivated from late September to early May, and rice is cultivated from April to September. Rice is generally sowed in seedbed during April and then transplanted to the field by machinary during early May.

2.2. Experimental Design

The experiment was carried out in the field and in a specially-designed pots system (China National Invention Patent, ZL201610221861.1) from 2016 to 2017. Two oilseed rape straw returning methods, mulching over the soil surface and plowing into the soil with 4 straw amounts, were used in this experiment (Table 1). All oilseed rape straw was crushed by a special machine (Jinyang 4LZ-1.2, Deyang Jinxing agricultural equipment Co. Ltd.) and stored for further use. The field experiment was performed by split block experimental design, 8 treatments with 3 replications were arranged in 24 plots. The area of each plot was 160 m2 (16 m × 40 m) with 4 subplots of 40 m2 (4 m × 10 m); four straw amounts were incorporated in four subplots of each plot. A 0.5 m wide and 0.3 m high ridge was made between plots, and a plastic film (0.5 m deep) was coated over the ridge to prevent flooding from one plot to another and to keep the experiment results out of the impacts of nutrition transferring from one plot to another by runoff and infiltration. For the root growth and root distribution analysis, a pot planted experiment was designed with 8 treatments and 3 replications, which were distributed in 144 pots. The experiment was conducted using the same quality rice and the same soil from the experiment field.
Deyou4727, a hybrid rice variety was chosen for this experiment, seeds were sowed in early April. In order to avoid the impacts of seedling quality on root growth, strong and healthy seedlings with similar quality and 2 tillers were selected and transplanted to the field plots and in the pots during the mid of May. The rice was supplied with 180 kg/hm2 of nitrogen (N), 225 kg/hm2 of potassium (KCl), and 120 kg/hm2 of phosphorus (P2O5) during growth season. Nitrogen was (urea) applied as a base, tiller, and panicle fertilizer in the ratio of 5:3:2; potassium fertilizer was (potassium chloride) applied as a base and panicle fertilizer in the ratio of 1:1; phosphorus fertilizer was (calcium superphosphate) applied as a base fertilizer along with soil tillage before transplanting rice. Shallow water irrigation was used at the tillering, booting, and full filling stage (1:1:1), and no irrigation was used at other growth periods of the rice. All management, including transplanting, fertilization, and irrigation, was the same for the field experiment and pots planted experiment.

2.3. Samples and Measurement

Ten plants were selected to record the total number of tillers each 10–12 days until 115 days after rice transplanting. Five plants were taken as the samples to calculate the dry weight of shoot each 0–12 days until 75 days after rice transplanting. After maturity, 10 plants of rice were collected from each plot to calculate the rice yield and the yield component.
Once rice transplanted, roots were sampled from 0–10 cm, 10–30 cm, and 30–50 cm soil layers each 10–12 days from the pots system until 75 days after rice transplanting. The length and weight of roots were measured, and the number of roots was counted in each soil layer. At the same time, 10 typical plants were chosen in the experimental field to determine the bleeding amount per plant. The SS content, as well as the activity of glutamic-oxalacetic transaminase (GOT), glutamic-oxalacetic transaminase (GPT), and glutamine synthetase (GS) were measured in roots bleeding at 36 days and 65 days after transplanting. Five typical plants were selected and harvested to measure the yield component of each treatment and 15 m2 of rice from each plot harvested by hand to measure the yield.
For the root sampling, three inner pots were taken out from large external pots and cut into 3 parts, the top layer (0–10 cm depth), the middle layer (10–30 cm), and the bottom layer (30–50 cm). All roots were washed and picked out from different parts, and root length and root weight (fresh) were measured, and the number of roots was counted for each part. Root length and root weight were measured by a standard ruler and 1/1000 balance; if 60% of the length of the root appeared blackish or brownish, it was calculated as a black root, and the rest were calculated as white roots; the roots shorter than 1 cm in length or decomposed were not calculated in root length and root weight. Root bleeding was collected by the cotton traps method [16], SS was performed according to Hu et al. [17], GOT activity was measured through the method of Sax et al. [18], and GPT and GS activity was tested via the methods of Zhong et al. [19] and Yu and Zhang [20], respectively.

2.4. Data Analysis

The average values were calculated based on 3 biological replications. When ANOVAs returned a significant result, the means were compared with Fisher’s LSD test (p < 0.05) in SPSS (version. 20, Chicago, IL, US). The correlations between root growth, enzyme activity, and rice yield were analyzed by the Pearson correlation method in SPSS (version. 20, Chicago, IL, USA).

3. Results

3.1. Impacts of Straw Incorporation on the Tillering Dynamics of Rice

During the early stages (0–36 days after transplanting), straw incorporation has a negative impact on tiller growth (Figure 1). In a comparison of MU0, the tiller number of MU1, MU2, and MU3 decreased 1.0–3.0 tillers (p < 0.05); meanwhile, the tiller number of PL1, PL2, and PL3 decreased 1.0–2.4 tillers than PL0 (p < 0.05). In either 2016 or in 2017, the tiller number of PL3 was near to 0; these results indicated that a plenteous amount of straw (4.5 t/hm2) caused a part of the rice tillers to die in the early stage of rice growth.
Either by mulching or plowing, straw incorporation has a positive impact on the tiller number during the tillering stage of rice growth. As compared to MU0, the tiller number of MU1, MU2, and MU3 decreased 1.2 and increased 1.1 and 0.4 tillers respectively; whereas, compared with PL0, the tiller number of PL1, PL2, and PL3 increased 2.0, 2.6, and 2.5 tillers, respectively (Figure 2). Though the maximum tillers of MU3 and PL3 were higher than that of MU2 and PL2; however, the effective tiller number was nearly the same. An ANOVA analysis (Supplementary Materials) showed that the number of tillers of MU2 was significantly higher than MU3, however, the effective tillers of MU2 were not significantly higher than MU3, and similar results were observed for PL2 and PL3. These results might have bee caused by the self-regulating of the population in a rice field.
In appropriate amounts, straw returning did not produce significant negative impacts on the total length and fresh weight of rice roots, while the total length and fresh weight of roots decreased significantly when excessive straw was incorporated into the soil (Figure 3), either by mulching or by plowing, during the early stage of rice growth (0–36 days after transplanting). In comparison of MU0, the length of rice roots in MU3 decreased 5 cm/d (p < 0.05), and its fresh weight reduced 0.05 g/d (p < 0.05); while there was no significant difference among MU0, MU1, and MU2 (Figure 4A,C), similar results were found for plowing treatments (Figure 4B,D). The root shoot ratios of PL3 and MU3 are lower than those of PL0 and PL3 at 12 days after rice transplanting (Table 2). Further analysis (Supplementary Materials) showed that straw incorporation by mulching produced a significant negative impact on root length in the 0–10 cm soil layer, while this negative impact reached the 10–30 cm soil layer for the excessive straw mulching treatment. Straw returning by plowing caused a significant reduction in root length in the 10–30 cm soil layer in comparison to PL0, while this negative impact reached the 30–50 cm soil layer for the excessive straw plowing treatment.
During the late stage of rice growth (56–75 days after transplanting), the impacts of straw-returning on the length and fresh weight of rice root was different between different straw returning methods (Figure 4). In comparison of MU0, the root length of MU1, MU2, and MU3 decreased 5, 15 (p < 0.05), and 20 cm/d (p < 0.05), respectively, with the reduction in fresh weight of 0.07, 0.22 (p < 0.05), and 0.14 g/d (p < 0.05); while the root length of PL1, PL2, and PL3 increased 56 (p < 0.05), 75 (p < 0.05), and 80 cm/d (p < 0.05), respectively, with the increase in fresh weight of 0.39 (p < 0.05), 1.00 (p < 0.05), and 0.90 g/d (p < 0.05), compared with PL0. The root shoot ratios of PL3 and MU3 are higher than those of PL0 and PL3 at 75 days after rice transplanting (Table 2). Further analysis (Supplementary Materials) showed that straw incorporation by mulching produced a significant negative impact on the root length in the 0–10 cm soil layer and a positive impact in the 10–30 cm soil layer. Straw returning by plowing caused a significant increase of root length in the 0–10 cm and 10–30 cm soil layers, in comparison to PL0.

3.2. Impacts of Straw Incorporation on the Dynamics of White Root

The straw incorporation, either by mulching or plowing, produced negative impacts on the number and fresh weight of white roots during the early stage (0–36 days after transplanting) of rice growth (Figure 5). Compared with MU0, the length of white root of MU1, MU2, and MU3 decreased 9 (p < 0.05), 3, and 13 cm/d (p < 0.05), with the reduction in fresh weight of 0.06 (p < 0.05), 0.03, and 0.12 g/d (p < 0.05), respectively; the length of white root of PL1, PL2, and PL3 reduced 1, 2, and 4 cm/d (p < 0.05), respectively, compared to PL0 and decreased in fresh weight of 0.01, 0.05, and 0.01 g/d, respectively, compared to PL0. These results indicate that straw-returning hindered the generation of new roots during the early stage of rice growth. Further analysis of root distribution (Supplementary Materials) showed that straw incorporation by mulching produced a significant negative impact on the length of white root in the 0–10 cm soil layer, while straw incorporation by plowing caused a negative impact on the white root in the 10–30 cm soil layer.
During the late stage of rice growth (56–75 days after transplanting), the impacts of straw-returning on the length and fresh weight of the white root were different between different straw-returning methods. In comparison of MU0, the length of white root of MU1, MU2, and MU3 increased 9 (p < 0.05), 13 (p < 0.05), and 8 cm/d (p < 0.05), with the increase in fresh weight of 0.34 (p < 0.05), 0.38 (p < 0.05), and 0.32 g/d (p < 0.05), respectively; while the root length of PL1, PL2, and PL3 increased 87 (p < 0.05), 105 (p < 0.05), and 112 cm/d (p < 0.05), respectively, compared with PL0, and increased in fresh weight of 0.25 (p < 0.05), 0.45 (p < 0.05), and 0.65 g/d (p < 0.05), respectively, compared with PL0. Further analysis of root distribution (Supplementary Materials) showed that straw incorporation by mulching produced a negative impact on the length of white root in 0–10 cm soil layer; while this negative impact existed in the 0–10 cm and 30–50 cm soil layer for straw incorporation by plowing treatments.

3.3. Impacts of Straw Incorporation on Root Bleeding

Straw returned through mulching or plowing induced a negative impact on the bleeding intensity of rice roots during the early stage (0–36 days after transplanting) of rice growth (Figure 6). Compared with MU0, bleeding intensity of MU1, MU2, and MU3 decreased 0.3 (p < 0.05), 0.9 (p < 0.05), and 2.1 (p < 0.05) mg/(plant·d) respectively; while the bleeding intensity of PL1, PL2, and PL3 reduced 0.1, 0.9, and 1.3 (p < 0.05) mg/(plant·d), respectively, compared with PL0. These results indicated that straw incorporation decreased the activity of rice roots during the early stage of rice growth.
At the later stage of rice growth (56–75 days after rice transplanting) the bleeding intensity of MU1, MU2, and MU3 decreased 4.9 (p < 0.05), 7.4 (p < 0.05), and 9.4 (p < 0.05) mg/(plant·d), respectively, compared with MU0; while it increased 0.9, 1.1, and 3.0 mg/(plant·d) of PL1, PL2, and PL3 (p < 0.05), respectively, compared with PL0. These results specified that straw returning by plowing is better for increasing root activity during 56–75 days after rice transplanting compared with straw returning by mulching.
Straw returned by mulching or plowing caused the reduction of SS, GPT, GOT, and GS, in comparison to no straw-returning treatments during 36 days after rice transplanting. Compared with MU0, the SS, GPT, GOT, and GS of MU3 reduced 17.4%, 14.7%, 8.7%, and 34.6%, and PL3 reduced 22.6%, 13.6%, 9.6%, and 25.5%, respectively, in comparison to PL0. These results provide some physiological reasons as to why straw-returning hindered root growth during the early stage. Also, these results explained why nitrogen fertilizer cannot relieve the slow revive and growth of roots in excessive straw-incorporating fields during the early stage of rice growth.
SS, GPT, GOT, and GS all appeared with an ascending trend at 56 days after rice transplanting compared with that at 36 days after rice transplanting (Table 3). Compared with MU0, the SS, GPT, GOT, and GS of straw returning treatments (MU1, MU2, and MU3) reduced significantly, and its reduction rate became higher and higher from MU1 to MU3. However, compared with PL0, the SS, GPT, GOT, and GS of straw returning treatments (PL1, PL2, and PL3) all increased significantly, and its increasing rate becomes higher and higher from PL1 to PL3. These results indicated that with the time going on, the impacts of straw-returning on the roots activity were relieved. Compared with straw mulching, straw returning by plowing was better for increasing the activity of nitrogen invertase in the roots during the tillering stage.

3.4. Impacts of Straw Returning on Rice Yield and Its Component

Straw returning, either by mulching or by plowing, increased grain yield by increasing panicles of each plant, spikelet per panicle, and 1000-grain weight, in comparison to no straw returning treatments (Table 4). The grain yield of MU2 and MU3 increased 1.11 (p < 0.05) and 0.79 (p < 0.05) t/hm2 in comparison to MU0; the grain yield of PL2 and PL3 increased 1.36 (p < 0.05) and 1.10 (p < 0.05) t/hm2 compared to PL0. Compared with MU0, MU2 and MU3 increased 0.77 and 0.91 in panicle per plant, 0.71 and 0.72 g in 1000-grain weight, and 29.02 and 28.93 spikelets per panicle; compared with PL0, PL2 and PL3 increased 3.63 and 3.88 in panicle per plant, 0.59 and 0.24 g in 1000 grain weight, and 32.40 and 31.01 spikelets per panicle.
Straw returning by plowing increased more yield than straw returning by mulching. Compared with MU2, the yield of PL2 increased 0.31 t/hm2, and the yield of PL3 increased by 0.37 t/hm2 compared to MU3. These results showed that oilseed rape straw returning by plowing is more suitable for the oilseed rape-rice rotation system.

3.5. Correlation Analysis

The length of total root, length of white root, activity of nitrogen invert enzyme, and amount of root bleeding all have some impacts on the rice yield and its components under straw incorporation conditions. However, their effective period was different (Table 5), and the total root length has a significant impact on yield, panicle per plant, and 1000-grain weight at the later stage of rice growth.
The length of white root, activity of nitrogen invert enzyme, and amount of root bleeding have a significant impact on spikelet per panicle. These outcomes suggested that root growth and its quality have a great impact on the rice yield in straw-returning fields.
Compared with 36 days of transplanting, there were more factors that had a significant relation to yield and the yield component at 65 days after transplanting (Table 5). These findings revealed that the effect of straw returning at the late stage contributed more to the rice yield in comparison to the early stage.

4. Discussion

4.1. Impacts of Straw Returning on Root Growth

After the returning of oilseed rape straw, the decomposition of straw under an anaerobic environment caused the oxygen content to reduce rapidly [21,22], and the reductive substance content increased dramatically in soil [23,24,25,26], which deteriorated the root growing environment in rice fields. Results of this research showed that root length, root weight, and root bleeding reduced significantly in straw-returning treatment compared with no straw-returning treatment, either by mulching or by plowing, during the early stage of rice growth. These results indicated that oilseed rape straw incorporation hindered the growth of roots during the early stage of rice growth. Furthermore, our investigation unveiled that straw returning by mulching induced a negative impact on new germinating roots in the 0–10 cm soil layer, and in the 10–30 cm soil layer for straw returning by a plowing method during the early stage of rice growth.
As time went by, due to the flooding ending and the slow process of straw decomposition, the oxygen content and the oxidation-reduction potential of the soil increased, which make a better environment for root growth [27,28,29,30]. The results of this research showed that after 56–75 days of rice transplanting, root length of straw mulching treatments (MU1, MU2 and MU3) were not increased significantly in comparison to no straw-returning treatment (MU0), while root lengths of the plowing treatments (PL1, PL2, and PL3) were significantly higher than no straw-returning treatment (PL0). Furthermore, this research found that root length and root weight of the straw mulching treatment was significantly lower than that of no straw-returning treatment in the 0–10 cm soil layer, while straw returning by plowing caused a significant increase of root length in the 0–30 cm soil layer, in comparison to PL0. These results demonstrated that straw incorporation by plowing produced more positive impacts on root growth than that by mulching during 56–75 days after rice transplanting.

4.2. Impacts of Straw Returning on Tiller Growth and Yield of Hybrid Rice

Straw incorporation caused deterioration of the soil environment, which leads to late revival and the reduction of tiller during the early stage of rice growth [11,31], while nutrients released from straw decomposition promoted tiller growth in the late stage of rice growth [5,32,33,34]. The reason for the negative impacts of straw incorporation on rice tiller is complex [35,36,37] and has been reported by many scientists [38,39,40,41,42]. The results of this research revealed that straw returning, either by mulching or by plowing, produced a negative impact on root length and weight during 0–36 days after rice transplanting. Furthermore, we have found that straw incorporation significantly reduced the activity of nitrogen invertase (GPT, GOT, and GS) in roots (Table 3); this may be due to the lower content of oxygen in the soil during 0-36 days after rice transplanting. Our findings suggested that the slow growth of roots and lower activity of nitrogen invertase are other reasons for late revival and slow growth of rice in straw-returning fields. This conclusion also explains why nitrogen fertilizer cannot speed up the rice growth during the early stage of rice growth in straw-returning fields.
Similar to Hu et al. [16] and Yang et al. [27], this research showed that the maximum tillers of all straw-returning treatments was higher than no straw-returning treatment. Moreover, this research confirmed that it was the recovery of roots and the increase of the activity of nitrogen invertase that promoted the tillers growth during 56–75 days of rice transplanting and the positive impacts of straw incorporation on tiller growth during 56–75 days of rice transplanting, and explained its reason from the perspective of root activity, root growth, and nitrogen invertase activity. These outcomes provided a more basic understanding of the impacts of straw incorporation on rice growth in the rice-rape rotation system.
Most previous reports have shown that straw incorporation increased grain yield [43,44,45], while other studies reported the negative impacts of straw returning on rice yield [30,46]. The results of this paper displayed that the variation of rice yield was affected by the amount and the method of oilseed rape straw returning. In comparison to no straw returning treatment (MU0 and PL0), spikelet fertility, panicle per plant, and grain yield of PL1 did not increase significantly (p > 0.05); while of MU1 decreased significantly (p < 0.05). In a comparison of no straw returning treatment (MU0 and PL0), the panicle per plant, spikelet per panicle, spikelet fertility, and grain yield of MU2, MU3, PL2, and PL3 increased significantly (p < 0.05). Compared with mulching, the grain yield of the plowing treatment was slightly higher. Considering the variation of rice yield, a reasonable amount of oilseed rape straw in the rice field is not more than 3.0 t/hm2, and straw returning by plowing is better than mulching in the Sichuan Basin area.

5. Conclusions

During the early stage (0–36 days after rice transplanting), oilseed rape straw returning either by mulching or by plowing produced a negative impact on tiller growth. This negative effect might cause lower root activity (white root amount, root bleeding amount) and lower activity of nitrogen invertase in roots in straw-returning fields. Oilseed rape straw returning by mulching performed a negative impact on new roots generating in the 0–10 cm soil layer; straw returning by plowing produced a negative impact on root growth in the 10–30 cm soil layer.
During the later stage (56–75 days after rice transplanting), oilseed rape straw returning produced some positive impacts on rice roots, which caused the yield of rice to increase in the straw-returning field. The variation of yield in the oilseed rape straw returning field is the balance of negative and positive factors that are produced by straw decomposing under an anaerobic environment. Considering the roots growth, rice yield, and dynamics of tillering, a reasonable amount of oilseed rape straw returned into rice filed is 3.0 t/hm2, and straw returning by plowing is a more appropriate method than mulching in the rice-rape rotation system in the Sichuan Basin area.

Supplementary Materials

The following are available online at https://www.mdpi.com/2073-4395/9/11/690/s1, Figure S1: Dynamic changes of root length in different soil layers under different straw incorporation treatments. MU0, MU1, MU2, MU3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2 and 4.5 t/hm2 of straw respectively, which were incorporated in soil by mulching method. Whereas PL0, PL1, PL2, PL3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2 and 4.5 t/hm2 of straw respectively, which were incorporated in soil by ploughing method, Table S1: Tiller dynamics of rice under different treatments during 2016 (data for Figure 2 in manuscript); Table S2: Tiller dynamics of rice under different treatments during 2017 (data for Figure 2 in manuscript); Table S3: Total weight of rice root under different straw returning treatments (data for Figure 4 in manuscript); Table S4: Total length of rice root under different straw returning treatments (data for Figure 4 in manuscript); Table S5: Total weight of white root under different straw returning treatments (data for Figure 5 in manuscript); Table S6: Total length of white root under different straw returning treatments (data for Figure 5 in manuscript); Table S7 Bleeding intensity of rice root under different straw incorporation treatments during 2016 (data for Figure 6 in manuscript); Table S8: Bleeding intensity of rice root under different straw incorporation treatments during 2016 (data for Figure 6 in manuscript); Table S9: The ANOVA analysis of the tillers and effective tillers.

Author Contributions

X.W. and Y.H. proposed the ideas, designed the experiments, and provided funding*, N.S. and C.Z. conducted the experiment and wrote the paper, H.W. and G.Y. analyzed the dada, Y.P., and F.R. reviewed paper.

Funding

This research received no external funding.

Acknowledgments

This work was supported by the National Science and Technology Innovation Project for Grain Enrichment and Efficiency (2017YFD0100206; 2016YFD0300210), the National Natural Science Foundation of China (31401347; 31601269), and the Sichuan Science and Technology Program (2018HH0039; 2018NZZJ001).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Dynamic changes of rice tillers without straw treatment (PL0) and under straw treatments (PL3).
Figure 1. Dynamic changes of rice tillers without straw treatment (PL0) and under straw treatments (PL3).
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Figure 2. Dynamic changes of rice tillers under different straw incorporation treatments during 2016 and 2017. MU0, MU1, MU2, and MU3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in soil by a mulching method. Whereas PL0, PL1, PL2, and PL3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in soil by a plowing method. Impacts of straw incorporation on the dynamics of root distribution.
Figure 2. Dynamic changes of rice tillers under different straw incorporation treatments during 2016 and 2017. MU0, MU1, MU2, and MU3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in soil by a mulching method. Whereas PL0, PL1, PL2, and PL3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in soil by a plowing method. Impacts of straw incorporation on the dynamics of root distribution.
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Figure 3. Comparison of root length of rice under different straw returning treatments, MU0, MU1, MU2, and MU3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated into the soil by a mulching method. Whereas PL0, PL1, PL2, and PL3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in soil by a plowing method.
Figure 3. Comparison of root length of rice under different straw returning treatments, MU0, MU1, MU2, and MU3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated into the soil by a mulching method. Whereas PL0, PL1, PL2, and PL3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in soil by a plowing method.
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Figure 4. Comparison of total length and weight of rice root under different straw returning treatments. A and B are the total root length of mulching and plowing treatment respectively; C and D are the fresh weight of rice root for mulching and plowing treatment respectively.
Figure 4. Comparison of total length and weight of rice root under different straw returning treatments. A and B are the total root length of mulching and plowing treatment respectively; C and D are the fresh weight of rice root for mulching and plowing treatment respectively.
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Figure 5. Comparison of total length and weight of white root in rice fields under different oilseed rape straw-returning treatments. MU0, MU1, MU2, and MU3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in the soil by a mulching method. Whereas PL0, PL1, PL2, and PL3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in the soil by a plowing method. A and B are the total length of white root under mulching and plowing treatment respectively; C and D are the fresh weight of white root for mulching and plowing treatment respectively.
Figure 5. Comparison of total length and weight of white root in rice fields under different oilseed rape straw-returning treatments. MU0, MU1, MU2, and MU3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in the soil by a mulching method. Whereas PL0, PL1, PL2, and PL3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in the soil by a plowing method. A and B are the total length of white root under mulching and plowing treatment respectively; C and D are the fresh weight of white root for mulching and plowing treatment respectively.
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Figure 6. Dynamic changing of the bleeding intensity of rice roots under different straw incorporation treatments. MU0, MU1, MU2, and MU3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in the soil by a mulching method. Whereas PL0, PL1, PL2, and PL3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in the soil by a plowing method.
Figure 6. Dynamic changing of the bleeding intensity of rice roots under different straw incorporation treatments. MU0, MU1, MU2, and MU3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in the soil by a mulching method. Whereas PL0, PL1, PL2, and PL3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in the soil by a plowing method.
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Table
Table 1. Detailed information on oilseed rape straw treatments.
Table 1. Detailed information on oilseed rape straw treatments.
MU0MU1MU2MU3PL0PL1PL2PL3
Straw returning amount0.0 t/hm21.5 t/hm23.0 t/hm24.5 t/hm20.0 t/hm21.5 t/hm23.0 t/hm24.5 t/hm2
MU; represents the straw mulching over the soil surface, and PL represents the straw plowing into soil.
Table
Table 2. Comparison of root shoot ratio under different straw incorporation treatments.
Table 2. Comparison of root shoot ratio under different straw incorporation treatments.
12 d56 d75 d
MU00.34 ± 0.04a0.44 ± 0.04b0.21 ± 0.01d
MU10.33 ± 0.02b0.43 ± 0.02c0.22 ± 0.02c
MU20.32 ± 0.02c0.44 ± 0.02b0.27 ± 0.02b
MU30.30 ± 0.01d0.45 ± 0.01a0.29 ± 0.02a
PL00.31 ± 0.02a0.51 ± 0.02a0.22 ± 0.03d
PL10.28 ± 0.03b0.48 ± 0.03c0.25 ± 0.01c
PL20.26 ± 0.03c0.48 ± 0.03c0.27 ± 0.01b
PL30.24 ± 0.05d0.49 ± 0.05b0.28 ± 0.02a
MU0, MU1, MU2, and MU3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in the soil by a mulching method. Whereas PL0, PL1, PL2, and PL3 represent 0.0 t/hm2, 1.5 t/hm2, 3.0 t/hm2, and 4.5 t/hm2 of straw, respectively, which were incorporated in soil by a plowing method.
Table
Table 3. The content of soluble saccharide and the activity of nitrogen invertase in rice roots under different straw incorporation treatments.
Table 3. The content of soluble saccharide and the activity of nitrogen invertase in rice roots under different straw incorporation treatments.
DFPTRTSS (%)GPT (μmol/(g·h))GOT (μmol/(g·h))GS (μmol/(g·h))
36MU01.84 ± 0.08a2.53 ± 0.07a5.71 ± 0.06a17.64 ± 0.09a
MU11.72 ± 0.11b2.48 ± 0.06ab5.64 ± 0.05b15.21 ± 0.08b
MU21.61 ± 0.09bc2.46 ± 0.06b5.02 ± 0.08c13.62 ± 0.07c
MU31.52 ± 0.09c2.31 ± 0.09c4.87 ± 0.07d11.54 ± 0.07d
PL01.86 ± 0.09a2.51 ± 0.07a5.73 ± 0.09a17.65 ± 0.09a
PL11.76 ± 0.08b2.45 ± 0.08a5.51 ± 0.07b16.28 ± 0.11b
PL21.51 ± 0.07c2.35 ± 0.07b5.26 ± 0.08c14.02 ± 0.09c
PL31.44 ± 0.08c2.27 ± 0.08c4.95 ± 0.07d13.15 ± 0.10d
56MU02.05 ± 0.08a3.04 ± 0.07a5.86 ± 0.08a18.18 ± 0.12a
MU11.99 ± 0.06ab2.98 ± 0.08ab5.72 ± 0.08b18.02 ± 0.09a
MU21.95 ± 0.08b2.95 ± 0.05b5.65 ± 0.07bc17.98 ± 0.12ab
MU31.86 ± 0.07c2.73 ± 0.06c5.59 ± 0.07c17.84 ± 0.09b
PL02.08 ± 0.06b3.01 ± 0.08d5.78 ± 0.08c18.24 ± 0.08b
PL12.10 ± 0.08b3.14 ± 0.06c5.86 ± 0.09bc18.58 ± 0.07b
PL22.16 ± 0.06ab3.27 ± 0.07b5.94 ± 0.08ab18.75 ± 0.11ab
PL32.23 ± 0.06a3.46 ± 0.08a5.98 ± 0.07a19.02 ± 0.12a
In each column, values followed by different letters are significantly different at p < 0.05 using Fisher’s LSD test. DFP means days after transplanting of rice, TRT was treatment; SS was the soluble saccharide; GOT was the activity of glutamic-oxalacetic transaminase; GPT was the activity of glutamic-pyruvic transaminase; GS was the activity of glutamine synthetase.
Table
Table 4. Comparison of the rice yield and its component for different straw incorporation treatments during 2016 and 2017.
Table 4. Comparison of the rice yield and its component for different straw incorporation treatments during 2016 and 2017.
YearTreatmentPanicle per Plant1000 Grain Weight (g)Spikelet FertilitySpikelet per PanicleYield (t/hm2)Yield per Plot
(kg)
2016MU09.74a29.26b0.92b255.54b7.54b29.94c
MU17.38b29.24b0.94a258.15b7.98ab31.18b
MU210.19a29.99a0.94a284.97a8.82a34.34a
MU310.38a29.54ab0.93ab283.62a8.49a33.21a
PL09.82b29.27b0.93ab254.91b7.67b31.38b
PL111.20b29.23b0.94a261.48b7.98ab31.18b
PL213.37a29.90a0.94a286.68a8.95a34.79a
PL313.65a29.56ab0.92b285.87a8.67a33.82a
2017MU09.65a29.24b0.91c254.55b7.40b29.46b
MU17.75b29.24b0.94a256.26b7.54ab29.94ab
MU210.74a29.92a0.93ab283.17a8.34a32.69a
MU310.84a29.42ab0.92bc284.34a8.02a31.59a
PL09.72b29.24b0.91b252.75b7.38b29.39b
PL111.25b29.24b0.94a257.07b7.88ab31.11b
PL213.43a29.80a0.93a285.78a8.82a34.34a
PL313.65a29.51ab0.92ab283.80a8.58a33.52a
In each column, values followed by different letters are significantly different at p < 0.05 using Fisher’s LSD test.
Table
Table 5. Correlation analysis between root growth and rice yield.
Table 5. Correlation analysis between root growth and rice yield.
YearItemTotal Root LengthLength of White RootNitrogen Invert-AseRoot Bleeding
36d65d36d65d36d65d36d65d
2016Yield−0.350.75 *−0.400.07−0.490.77 *0.62 *0.21
EPP−0.540.61 *−0.380.45−0.450.75 *−0.480.69 *
GW0.070.65 *0.01−0.23−0.390.08−0.070.63 *
SPP−0.320.32−0.66 *0.74 *−0.90 *0.88 *0.91 *0.01
SPF0.300.490.260.250.000.18−0.240.19
2017Yield0.260.81 *−0.350.13−0.380.65 *0.66 *0.32
EPP−0.410.63 *0.150.370.120.71 *−0.310.62 *
GW0.150.66 *−0.110.14−0.33−0.010.060.72 *
SPP−0.440.41−0.62 *0.71 *−0.87 *0.88 *0.86 *0.13
SPF0.290.380.280.22−0.020.190.190.20
The values shown are Pearson correlation coefficients, and significant correlations are indicated by * (p < 0.05). EPP, Panicle per plant; GW, 1000-grain weight; SPP, Spikelet per panicle; SPF, Spikelet fertility.

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Wang, X.; Samo, N.; Zhao, C.; Wang, H.; Yang, G.; Hu, Y.; Peng, Y.; Rasul, F. Negative and Positive Impacts of Rape Straw Returning on the Roots Growth of Hybrid Rice in the Sichuan Basin Area. Agronomy 2019, 9, 690. https://doi.org/10.3390/agronomy9110690

AMA Style

Wang X, Samo N, Zhao C, Wang H, Yang G, Hu Y, Peng Y, Rasul F. Negative and Positive Impacts of Rape Straw Returning on the Roots Growth of Hybrid Rice in the Sichuan Basin Area. Agronomy. 2019; 9(11):690. https://doi.org/10.3390/agronomy9110690

Chicago/Turabian Style

Wang, Xuechun, Naseem Samo, Changkun Zhao, Hongni Wang, Guotao Yang, Yungao Hu, Youlin Peng, and Fahd Rasul. 2019. "Negative and Positive Impacts of Rape Straw Returning on the Roots Growth of Hybrid Rice in the Sichuan Basin Area" Agronomy 9, no. 11: 690. https://doi.org/10.3390/agronomy9110690

APA Style

Wang, X., Samo, N., Zhao, C., Wang, H., Yang, G., Hu, Y., Peng, Y., & Rasul, F. (2019). Negative and Positive Impacts of Rape Straw Returning on the Roots Growth of Hybrid Rice in the Sichuan Basin Area. Agronomy, 9(11), 690. https://doi.org/10.3390/agronomy9110690

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