Introduction

Rice is one of the primary crops produced and consumed in China, with its yield having a direct impact on the country’s food security and social stability1. The Northeast region stands out as a significant rice-producing area, benefiting from unique geographical advantages that contribute to the exceptional quality and nutrient richness of Northeast rice. However, this region often suffers from low-temperature cold damage, which delays the rice regreening stage, affects the number of tillers and reduces the number of mature panicles2, restricting the growth of rice yield in Northeast China. Therefore, studying suitable cultivation measures for rice in Northeast China is of vital importance to ensuring a stable supply of rice in China.

Plastic film mulching can reduce water vapor transfer in the soil and increase soil temperature by reducing heat exchange between the atmosphere and the ground, alleviate the damage of low temperature and cold damage to crops, effectively increase the effective accumulated temperature during crop growth, and promote the growth of rice3. Zhang et al4. found that film mulching in paddy fields was beneficial for promoting the early tillering of rice, increased the SPAD value of rice, and ienhancing the net photosynthetic rate of rice leaves. With the increase in soil temperature and the maintenance of appropriate water content for rice growth, the rhizosphere soil conditions of rice are improved. This strengthens microbial metabolism in the soil, which in turn accelerates the mineralization of soil organic matter, further improving soil nutrient supply to rice and ultimately increasing rice yield. Gao et al5. conducted a meta-analysis quantifying the impact of mulching on maize, wheat, potato, and cotton yields in China and found that mulching significantly increased crop yields by 24.32%. However, due to the difficulty of degradation and recycling of traditional PE plastic mulching film and the serious problem of plastic pollution in farmland, biodegradable mulching film is now mostly used6,7.

Fertilizers supply essential nutrients to crops and constitute an indispensable factor for sustaining and promoting crop growth. Chemical fertilizers can rapidly supply plants with the required nutrients over a short period, thereby promoting plant growth, increasing crop yields, and alleviating the imbalance between arable land resources and food demand in China8. Organic fertilizers can continuously supply nutrients to plants, thereby promoting grain filling and improving rice quality. Meanwhile, they can increase the content of soil organic matter, enhance soil fertility, ameliorate soil physical and chemical properties, enrich soil microbial flora, and further create a favorable growth environment for plants9,10. Studies have found that chemical fertilizers are more effective in promoting plant growth and development and improving yield, while organic fertilizers have advantages in improving plant nutritional value, taste and other qualities11.

Mulching with plastic film and fertilization have positive effects on the growth and yield of rice. However, there are relatively few studies on how they affect the accumulation and transportation of substances in rice, and the specific mechanisms of the effects of plastic film mulching and different fertilizer types on the formation of rice yield are still unclear. Therefore, a field experiment was conducted to study the effects of four different cultivation modes in the local area on the growth of rice and the transport of photosynthetic substances. Formulate the hypotheses: (1) Mulching with plastic film can accelerate the process of rice regreening and tillering; (2) Applying organic fertilizer can slow down the decline of photosynthesis in rice from the grain filling stage to maturity; (3) Mulching with plastic film combined with the application of organic fertilizer can coordinate the growth of rice in the early and late stages, achieving an increase in yield.

Materials and methods

Test materials

The test was conducted with the japonica rice varieties ‘Jinongda 738’ (Provided by Jilin Agricultural University) and ‘Jijing 525’ (Provided by Jilin Academy of Agricultural Sciences) as the test materials, in compliance with the national and international guidelines and legislation. The fertility period of ‘Jinongda 738’ is about 141 days, and it needs ≥ 10 ℃ active cumulative temperature of about 2820 ℃, and the rice quality meets the requirements of the third-class edible japonica rice varieties quality regulations. The growth period of ‘Jijing 525’ is about 142 days, and the accumulated temperature of ≥ 10℃ is about 2850℃. The rice quality meets the quality requirements of first-class edible japonica rice varieties.

Test site

This experiment was conducted in 2020 and 2021 at Niejia Village, Jiujiao Township, Jiutai District, Jilin Province (125°83′E,44°14′N). The average annual temperature of the experimental site was 4.7 ℃, and the annual rainfall was 557 mm. The soil of the experimental site was black calcium soil with organic matter content of 21.56 g/kg, total nitrogen content of 1.15 g/kg, total phosphorus content of 0.82 g/kg, alkaline dissolved nitrogen of 61.25 mg/kg, and quick-acting phosphorus of 15.28 mg/kg.

Experimental design

Four treatments were set up under two varieties: 1) Bare land with organic fertilizer application (NMF0); 2) Plastic-mulched land with organic fertilizer application (MF0); 3) Bare land with chemical fertilizer application (NMF1); 4) Plastic-mulched land with chemical fertilizer application (MF1), with three replications and a total of 24 plots. The plots were 550 m2 in area, and the different treatments were separated by plastic film wrapped ridges to ensure that the plots were drained separately and to prevent stringing of fertilizers. Choose the fully biodegradable black agricultural plastic film produced by Baishan Xifeng Plastics Co., Ltd. for the plastic film, with a thickness of 0.01 mm.

The experimental plots were applied with 150 kg/ha of N, 100 kg/ha of P2O5, and 90 kg/ha of K2O amount, which the amount of N, P and K fertilizers were the conventional fertilizer used for local rice, and there should be a difference in different fertilizer application for mulching. The chemical fertilizer treatment used urea (N mass fraction of 46.4%), calcium superphosphate (P2O5 mass fraction of 12.0%), potassium sulphate (K2O amount of mass fraction of 50.0%); organic fertilizer treatment in organic fertilizer (11% high-nitrogen activated organic fertilizer—Qingda Yuanyong, Beijing Qingda Yuanyong Bio-technology Co., Ltd.) the nitrogen, phosphorus and potassium of the mass fraction of 5%, 3% and 3%, respectively. The amount of fertilizer applied was calculated as K fertilizer, and the shortfall was made up with urea and calcium superphosphate. The conventional treatment used normal fertilizer, organic fertilizer was applied in batches at the ratio of w (basal fertilizer): w (tiller fertilizer): w (spike fertilizer) = 4:3:3, nitrogen fertilizer was applied in batches at the ratio of w (basal fertilizer): w (tiller fertilizer): w (spike fertilizer) = 4:3:3, phosphorus fertilizer was applied as a base fertilizer, potash fertilizer was applied at the ratio of base fertilizer: spike fertilizer = 1:1, and the ground cover treatment was applied at one time without any fertilizer follow-up.

In 2020, seeds were sown on April 11, transplanted on May 23 and harvested on October 7; in 2021, seeds were sown on April 9, transplanted on May 23 and harvested on October 1. Row spacing is 30 cm, hole spacing is 16.5 cm, and 3 basic seedlings are transplanted in each hole. After transplanting, timely checking and replenishing, other management methods are consistent with field production.

Measurements and methods

Tiller number and plant height

After the occurrence of tillering in rice, 10 representative rice holes were selected at fixed points in each plot, and the number of stem tillers was investigated at 7-day intervals. The distance from the base of the rice to the highest point of the plant was determined as plant height using a straightedge.

Leaf ageing process

Five holes of uniformly growing rice were selected at fixed points in each plot, and the leaf age of the main stem of the rice was recorded at 7-day intervals after the occurrence of tillering in rice.

Dry matter weight

Based on the average number of tillers measured in each plot, five holes of rice with uniform growth were taken at the spike stage and maturity stage (physiological maturity), and the leaves, stem sheaths, and spikes were divided in the laboratory, and then weighed after being killed in an oven at 105 ℃ for 30 min and dried at 80 ℃ to a constant weight.

SPAD value of leaves

The SPAD value of leaves was measured by CCM-200Plus handheld chlorophyll meter. Six rice plants with uniform growth were selected in the plot, and the middle part of the flag leaf of rice was measured at tillering stage, jointing stage, filling stage, heading stage and mature stage (physiological mature stage) respectively. The time of each measurement is from 9: 00 to 10: 00 on a sunny day, and the average value of each measurement is taken as the SPAD value of this growth period.

Photosynthetic rate of flag leaf

Starting from the tillering stage of rice, the photosynthetic rate of flag leaves of rice was measured by LI-6400XT photosynthetic apparatus at 9: 00 a.m. to 11: 00 a.m. on a sunny day at the tillering stage, jointing stage, heading stage, filling stage and mature stage (physiological mature stage). The flag leaf of rice with uniform growth was selected in each treatment plot, and it was measured at one third below the tip of the flag leaf of rice.

Yield and Harvest Index

Take 5 m2 of rice from each plot at maturity to measure yield, and repeat for 3 times.

Calculation formula

Stem and leaf matter translocation amount (kg/hm2) = stem and leaf dry weight at heading stage—stem and leaf dry weight at maturity stage;

Stem and leaf matter translocation rate (%) = [(stem and leaf dry weight at heading stage—stem and leaf dry weight at maturity stage)/stem and leaf dry weight at heading stage] × 100%;

Post-heading matter assimilation amount (kg/hm2) = total dry weight at maturity stage—total dry weight at heading stage;

Stem and leaf matter contribution rate (%) = [(stem and leaf dry weight at heading stage—stem and leaf dry weight at maturity stage)/rice grain weight at maturity stage] × 100%;

Post-heading matter assimilation contribution rate (%) = [(total dry weight at maturity stage—total dry weight at heading stage)/rice grain weight at maturity stage] × 100%.

Data analysis

All data were collected and analyzed using Microsoft Excel 2019 software. The data were then analyzed using the SPSS statistical package version 22 (IBMCorp., Armonk, NYUSA). Descriptive statistics were used to test the mean and standard error of measurement parameters. The Duncan multiple comparison method was utilized to assess the statistical significance of the difference (p < 0.05). The results are presented as standard error (SE). Graphs were created using Origin 2021 software.

Results and analysis

Effects of different cultivation modes on leaf age, tiller number and plant height dynamics

Mulching with its unique thermal insulation can provide a good growing environment for rice, increase the leaf-out speed and accelerate the process of leaf age (Fig. 1). Under the same mulching conditions, the leaf age of rice F1 treatment was consistently higher than that of F0 treatment in both years. Under the same fertilizer conditions, the maximum difference in leaf age of rice in the mulched treatment compared to the non-mulched treatment was 0.64 leaves, respectively.

Fig. 1
figure 1

Effect of different cultivation modes on rice leaf age of Jinongda 738 (a, c) and Jijing 525 (b, d) in 2020(a, b) and 2021(c, d). The mean values of three repetitions ± SE (n = 3) were used. NMF0:no mulching, organic fertilizer; MF0: mulching, organic fertilizer; NMF1: no mulching, chemical fertilizer; MF1: mulching, chemical fertilizer.

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Figure 2 shows that under the same fertilizer conditions, mulching increased the number of tillers in rice between two years. The number of tillers in the mulching treatment at the tillering stage was always greater than that in the non-mulching treatment, and the difference gradually decreased with the death of ineffective tillers, so that the final number of effective tillers was higher than that in the non-mulching treatment, but the percentage of effective tillers showed the opposite trend (Table 1). During the rice reproductive period, under the same mulching conditions, the number of tillers in rice F1 treatment was consistently higher than that in F0 treatment during both years, but the percentage of effective tillers showed the opposite trend.

Fig. 2
figure 2

Effect of different cultivation modes on rice stems and tillers of Jinongda 738 (a, c) and Jijing 525 (b, d) in 2020 (a, b) and 2021 (c, d). The mean values of three repetitions ± SE (n = 3) were used. NMF0:no mulching, organic fertilizer; F0: mulching, organic fertilizer; NMF1: no mulching, chemical fertilizer; MF1: mulching, chemical fertilizer.

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Plant height is closely related to the biological yield of rice, and an appropriate increase in plant height is conducive to the accumulation of rice biomass, which in turn increases rice yield. Figure 3 shows that mulching increased the plant height of rice, and the plant height of rice F1 treatment was consistently higher than that of F0 treatment during the two years.

Table 1 Effective heading number and tiller heading rate of effective rice population under different cultivation modes.
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Fig. 3
figure 3

Effect of different cultivation modes on rice plant height of Jinongda 738 (a, c) and Jijing 525 (b, d) in 2020 (a, b) and 2021 (c, d). The mean values of three repetitions ± SE (n = 3) were used. NMF0:no mulching, organic fertilizer; MF0: mulching, organic fertilizer; NMF1: no mulching, chemical fertilizer; MF1: mulching, chemical fertilizer.

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Effects of different cultivation modes on SPAD values of rice leaves

As shown in Table 2, mulching increased the SPAD values of rice leaves. Compared with organic fertilizer application, application of chemical fertilizer at tillering to tasseling stage increased the SPAD values of rice leaves, but the opposite trend was shown at grouting and maturity stages. Under without/with mulch cover, rice leaf SPAD values were significantly higher in F0 treatment at the filling stage by 14.77% (NM), 22.42% (M) and 15.11% (NM), 31.16% (M), and at the maturity stage by 22.71% (NM), 37.45% (M), and 10.50% (NM), respectively, as compared to F1 treatment, 6.62% (M). It is evident that application of chemical fertilizers increased leaf SPAD values in the early stage of rice fertility, while application of organic fertilizers had some advantages in increasing the late stage of rice fertility.

Table 2 SPAD values of rice leaves under different cultivation modes.
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Effects of different cultivation modes on net photosynthetic rate of rice

The net photosynthetic rate of rice leaves showed an increasing and then decreasing trend as the reproductive period progressed, reaching a peak at the tasseling stage (Fig. 4). Under the same fertilizer conditions, mulching increased the net photosynthetic rate of rice. Compared with organic fertilizer application, chemical fertilizer application increased rice net photosynthetic rate from tillering to tasseling stage, but showed an opposite trend at filling and maturity stages. The net photosynthetic rate of rice was significantly increased by 29.27 per cent (NM), 16.88 per cent (M) and 15.04 per cent (NM), 25.47 per cent (M) for the two varieties of F0 treatment at the filling stage and 78.52 per cent (NM), 59.23 per cent (M) and 41.67 per cent (NM) at the maturity stage, respectively, compared with the F1 treatment in the absence/presence of mulch cover condition, 34.48% (M). This shows that application of chemical fertilizers increased the net photosynthetic rate of rice in the early stage of rice fertility, while application of organic fertilizers had some advantages in increasing the late stage of rice fertility.

Fig. 4
figure 4

Effect of different cultivation modes on rice net photosynthetic rates of Jinongda 738 (a, c) and Jijing 525 (b, d) in 2020 (a, b) and 2021 (c, d). The mean values of three repetitions ± SE (n = 3) were used. NMF0:no mulching, organic fertilizer; MF0: mulching, organic fertilizer; NMF1: no mulching, chemical fertilizer; MF1: mulching, chemical fertilizer.

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Effects of different cultivation modes on dry matter accumulation and translocation in rice

As can be seen from Table 3, mulching increased the dry matter accumulation of each upper organ at the tasseling and maturity stages of the two varieties of rice, and the differences were significant at the tasseling stage. The application of chemical fertilizers significantly increased the dry matter accumulation of each upper organ at the tasseling and maturity stages of the two varieties of rice.

Table 3 Dry matter accumulation in rice organs at heading stage and mature stage under different cultivation modes.
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As shown in Table 4, under the same fertilizer conditions, mulching improved the stem and leaf dry matter transfer, post-siphoning matter assimilation, stem and leaf matter transfer rate and stem and leaf matter assimilation contribution of the two varieties in the two years, and the differences were significant under the application of organic fertilizer. Under the same mulching conditions, the amount of stem and leaf matter transported, the amount of matter assimilated after tasseling and the contribution rate of matter assimilated after tasseling were higher in the F1 treatment than in the F0 treatment in the two years as a whole, but the rates of stem and leaf matter transported and the contribution rate of matter assimilated in the stem and leaf showed the opposite trend.

Table 4 Transfer of dry material after heading of rice under different cultivation modes.
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Effects of different cultivation modes on rice yield and harvest Index

Under the same fertilizer conditions, ground cover increased rice yield and its harvest index with differences in yield increase between the two years (Fig. 5). Yield increase of 7.40 per cent (F0), 3.30 per cent (F1) and 1.39 per cent (F0), 2.98 per cent (F1) was observed in ground cover rice, respectively. The application of organic manure significantly increased the harvest index of both varieties of rice by 26.44% (NM), 21.62% (M) and 23.19% (NM), 25.13% (M) in the F1 treatment compared to the F0 treatment under no/with mulch cover condition, respectively.

Fig. 5
figure 5

Effect of different cultivation modes on rice yield and harvest index of Jinongda 738 (a, c) and Jijing 525 (b, d) in 2020(a, b) and 2021(c, d). The mean values of three repetitions ± SE (n = 3) were used. NMF0:no mulching, organic fertilizer; MF0: mulching, organic fertilizer; NMF1: no mulching, chemical fertilizer; MF1: mulching, chemical fertilizer.

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Discussion

Effects of plastic film mulching and fertilizer types on agronomic characters of rice

Soil temperature is critical for the growth and development of crops. Plastic film coverage can improve the soil environment: on one hand, it reduces heat loss from the soil surface to regulate soil temperature; on the other hand, it decreases soil moisture evaporation to maintain humidity. Together, these effects achieve insulation and moisture retention, ultimately providing suitable soil growth conditions for crops12,13. The results of this study showed that plastic film mulching could accelerate the leaf aging process, with the maximum leaf age difference being 0.64 leaves. This may be due to the increased effective accumulated temperature from the plastic film coverage, which accelerates the leaf emergence speed of rice, shortens the entire growth cycle, and promotes early maturity of rice14,15. Stable soil moisture conditions help regulate the soil redox potential within a more suitable range, creating a rich mineral nutrient reserve for rice. Furthermore, it aids in the absorption of nitrogen by rice, thereby supporting rapid growth and the development of a large number of tillers16.

At present, the performance regarding the impact of organic fertilizers and chemical fertilizers on crops is inconsistent. Research has shown that compared to the application of organic fertilizers, the use of chemical fertilizers results in faster leaf emergence, a higher number of tillers, and more vigorous and taller growth in rice17,18. However, some studies have shown that crops treated with organic fertilizers perform better in agronomic traits compared to those treated with chemical fertilizers alone19. This study found that, compared to the application of organic fertilizers, the use of chemical fertilizers is beneficial for increasing the height of rice plants, accelerating the leaf age process, and promoting early tillering. However, the percentage of effective tillers is lower in rice treated with chemical fertilizers than in those treated with organic fertilizers. The possible reason for the analysis is that the growth and development of rice are significantly affected by fertilizers. Chemical fertilizers release nutrients quickly, providing rice with the necessary nutrients for growth and development, thereby accelerating the growth speed. However, this can lead to insufficient nutrient supply in the later growth stages, negatively affecting the percentage of effective tillers. In contrast, the application of organic fertilizers can continuously supply nutrients to rice over the long term, effectively reducing ineffective tillering caused by nutrient deficiency20,21. However, organic fertilizers have a certain decomposition period. In this phase, the rate of tillering is slow, leading to a low number of tillers and consequently an overall lower total number of tillers compared to chemical fertilizer treatments..

Effect of mulch cover and fertilizer type on production and translocation of photosynthetic substances in rice

The dry matter accumulation and material transport of rice are closely related to its growth and development22. Photosynthesis is the foundation of biomass production, directly influencing the accumulation of dry matter and the transportation of substances. It is closely related to the SPAD values of rice leaves and the net photosynthetic rate of flag leaves23. Therefore, enhancing the SPAD values and net photosynthetic rate of flag leaves in rice is beneficial for coordinating the transportation of substances in rice plants, promoting their growth and development, and ultimately achieving higher yields. The results of this study indicate that mulching significantly increases the SPAD values of rice leaves and the net photosynthetic rate of flag leaves during the tillering to maturity stage. The underlying reason for this enhancement may be attributed to the thermal insulation and moisture retention effects of mulching cultivation, which promote root growth during the nutritional growth phase of rice. This, in turn, lays a foundation for the growth of stems and plant density, leading to an increase in the number of rice leaves, a larger photosynthetic area, and enhanced photosynthesis. These factors are beneficial for the accumulation of photosynthetic materials and the transportation of substances during the nutritional growth phase15.

Different types of fertilizers have different effects on the photosynthesis, dry matter accumulation and transport of crops24,25. In this study, the accumulation of dry matter, the translocation of stem and leaf materials, the assimilation of substances after heading, and the contribution rate of post-heading assimilation were all higher in the chemical fertilizer treatment compared to the organic fertilizer treatment. This is related to the ability of chemical fertilizers to rapidly supply nutrients to rice in the short term, promoting plant growth and enhancing the accumulation of aboveground dry matter. Furthermore, it accelerated the translocation of materials from the stem and leaves to the panicle, thereby increasing the translocation of stem and leaf materials, the assimilation of substances post-heading, and the contribution rate of post-heading assimilation26. The application of organic fertilizers significantly increased the SPAD values, net photosynthetic rate, stem and leaf dry matter transport rate, and the contribution rate of stem and leaf material assimilation during the grain-filling and maturation stages of rice. At this time, the organic fertilizers are fully decomposed, providing continuous nutrients that delay leaf senescence and maintain chlorophyll content, allowing rice to sustain a higher net photosynthetic rate, which is beneficial for the transport of leaf materials.

Effect of mulch cover and fertilizer type on rice yield

The results indicate that mulching can enhance the tiller number, plant height, and leaf age of rice. It promotes the growth and development of rice, improving its agronomic traits and laying a solid foundation for increased rice yield27,28,29,30. This study found that mulching, while reducing the percentage of effective tillers, significantly accelerated the onset of tillering and the speed of tillering. This indicates that mulching effectively stimulates the vigor and speed of early tillering in rice, thereby creating favorable conditions for maximizing photosynthetic duration and resource utilization. Additionally, some studies have found that mulching is beneficial for the growth of rice root systems, promotes nutrient accumulation, improves plant dry matter accumulation, and increases the harvest index3,31,32. The greater the amount of photosynthetic products stored in various organs of rice, the larger the proportion of these products allocated to the panicle in the later stages, resulting in a higher rate of material transport, which is more beneficial for increasing rice yield33.

Long-term application of organic fertilizers can increase soil organic matter content, improve soil physicochemical properties, promote the growth of rice root systems, and ultimately enhance crop yields34. Moreover, the sustained nutrient release characteristics of organic fertilizers can adequately meet the nutrient requirements during the grain-filling period, facilitating balanced development of various parts of the rice plant35. In contrast, the use of chemical fertilizers provides essential quick-acting nutrients during the early tillering stage of rice, significantly promoting the tillering process and ensuring a sufficient number of effective panicles36. This study anticipates that the combination of plastic film covering with organic fertilizer can coordinate growth in the early and later stages, leading to an increase in yield. However, it was found that the treatment with plastic film covering and chemical fertilizer yielded the best results. This may be because the film cover optimizes soil thermal and moisture conditions, providing a favorable soil growth environment for crops; while chemical fertilizers enhance the accumulation of photosynthetic materials during the nutritional growth stage, resulting in increased rice yield. It should be noted that this study primarily focuses on the effects of a single type of fertilizer on rice growth under four cultivation models. Future research could further investigate the ratios of different types of fertilizers, optimizing the application ratio of organic and chemical fertilizers, and explore their impacts on soil properties and rice growth, thereby providing a more comprehensive basis for optimizing the soil environment for rice cultivation.

Conclusion

Compared with the bare soil, plastic film mulching could increase the number of tillers, plant height, leaf age, SPAD value and photosynthetic rate of rice, which was conducive to material accumulation and transport of rice and increased yield by 1.39–7.40%. The application of chemical fertilizer was beneficial to photosynthesis, dry matter accumulation and transport from the tillering stage to the heading stage. The application of organic fertilizer could slow down the decline of rice photosynthesis from the grain filling stage to the maturity stage. Compared with the application of organic fertilizer, plastic film mulching combined with chemical fertilizer (MF1) increased yield by 2.98–30.62%.