Silicon–calcium fertilizer increased rice yield and quality by improving soil health

It is important to ensure the nutritional quality and safe production of rice. Here, plot experiments were used to analyze the effects of three soil amendments—10 t ha−1 of biochar (BC), 1.5 t ha−1 of lime (LM), and 2.25 t ha−1 of silicon–calcium fertilizer (SC)—on the soil characteristics, rice yield and quality of double-cropping rice grown in mildly cadmium-polluted paddy fields. Compared with the control treatment (CK), the BC and SC treatments significantly improved rice processing, appearance and nutritional quality, but reduced cooking quality. All three soil amendments significantly reduced cadmium (Cd) content in brown rice. Soil amendments could significantly increase soil pH and reduce soil available Cd content. The application of the BC and SC treatments increased the content of each nutrient index in the soil (SOM, NN, AP, AK). Correlation analysis showed that the improvement in rice processing, appearance, and nutritional quality was mainly affected by the comprehensive effects of soil SOM, NN, AP and AK; the hygiene quality was mainly affected by soil pH and available Cd. In terms of benefit analysis combined with cost, the SC treatment had the highest benefit effect. Taken together, in mildly cadmium-polluted paddy fields, the application of silicon–calcium fertilizer improved the soil quality, thereby increased the yield and quality of rice, and had the best effect on increasing income.


Test site and materials
The experiment was performed in a mildly Cd-contaminated paddy field in Hengyang County (26.970°N, 111.370°E), Hunan Province, China in March to October 2021.A typical double-cropping rice-growing system is used in the study area, which is in the central continental part of China.The site has a subtropical monsoon climate with annual precipitation of 1452 mm and a mean annual temperature of 17.9 °C.The mean Cd content of the soil at the study site was 0.47 mg kg −1 , and the mean soil pH was 6.02.According to the Chinese National Soil Pollution Evaluation Technical Regulations, the soil was classed as mildly contaminated with Cd (Cd content 0.3-0.6 mg kg −1 ).The study site had red soil with a bioavailable Cd content of 0.12 mg kg −1 , a cation exchange capacity of 7.57 cmol kg −1 , an alkaline hydrolysable-N content of 119.88 mg kg −1 , an available phosphorus content of 8.54 mg kg −1 , an available potassium content of 57 mg kg −1 , an organic matter content of 29.49 g kg −1 , a total nitrogen content of 3.51 g kg −1 , a total phosphorus content of 0.91 g kg −1 , and a total potassium content of 10.13 g kg −1 .
The early rice cultivars tested in the experiment were hybrid rice Zhuliangyou 819 and Luliangyou 996; the late rice cultivars were conventional rice Xiangwanxian 13 and Yuzhenxiang.Three soil amendments were selected for this study.Lime (CaO content ≥ 35% and MgO content ≥ 5%) was obtained from Hengyang Fulong Fertilizer Company (Hengyang, China) and had a Cd content of 0.15 mg kg −1 .Biochar (produced by pyrolyzing rice husks at 550-600 °C for 2 h) was purchased from Wangcheng (Changsha, China) and had a Cd content of 0.18 mg kg −1 .Silicon-calcium fertilizer (CaO content ≥ 25% and SiO 2 content ≥ 20%) was obtained from Hunan Runbang Bioengineering Company (Changsha, China) and had a Cd content of 0.10 mg kg −1 .

Experimental design
A flat plot with uniform fertility was used for the experiment.Four treatments-blank control (CK treatment), biochar application at 10 t ha −1 (BC treatment), lime application at 1.5 t ha −1 (LM treatment), and SC application at 2.25 t ha −1 (SC treatment)-were set up (Table 1).All soil amendment was applied one week before the early rice seedlings were transplanted, and was not applied in the late rice.The soil amendment was spread evenly on the soil surface and the top soil was plowed to evenly mix the amendment and the soil.
This experiment used a two factor randomized block experiment with 4 treatments (three soil amendments and a control) and 2 varieties.Each treatment was repeated three times, and a 1.5 m-wide protective row was

Measurement items and methods
After the rice matured, 80 rice plants were randomly harvested in each plot, avoiding the three rows on the edge.After threshing, the straw and empty grains were removed and the grain was weighed.The moisture content was measured by the drying method, which was converted to the actual yield with a moisture content of 13.5%.The calculation formula was: actual yield = actual harvested yield × (1 − measured moisture content)/0.865.Then store the grain at room temperature for 3 months before conducting rice quality analysis.
Each sample was dehulled with a brown rice machine, and the brown rice rate of the sample was analyzed.A part of each brown rice sample was crushed with a stainless steel plant sample grinder, and the nitric acidperchloric acid high-temperature digestion method was used to detect the Cd content in the digestive juice with an atomic absorption spectrophotometer.Another part of each brown rice sample were selected using the NP-4350 air separator, and the brown rice rate, milled rice rate and head milled rice rate were measured according to GB/T 17891-1999 "High Quality Rice".Then, Another part of each milled rice sample were selected using the instrument JMWT12, and the length and width, chalkiness rate and chalkiness degree were tested according to GB/T 1354-2022 "Rice" japonica rice standard.Finally, the milled rice sample was ground into rice flour to determine the gel consistency, amylose content and protein content of the sample according to the "Rice Quality Determination Standard" 4 .The characteristic value analysis of the rice starch spectrum was measured with a fast viscometer produced by Australia Instrument Company and analyzed by TWC (Thermal Cycle for Win-dows) supporting software.
Samples of soil 0-20 cm deep were collected using a five-point sampling method before the soil amendment was added and when the early and late rice had matured.The soil samples were air dried, ground and passed through 20-and 100-mesh sieves.The soil pH was determined by extracting a sample with CO 2 -free distilled water at a water:soil ratio of 2.5:1 and then determining the pH using a PHSJ-3FX pH meter.For total Cd, 0.5 g of dry soil samples were weighed and digested with a mixed acid solution (HF-HClO 4 -HNO 3 ) in a graphite digestion box (DS-360; China National Analytical Center, Guangzhou, China).For the bioavailable Cd, 5 g of dry soil sample with 0.1 mol CaCl 2 solution (soil-to-liquid ratio 1:10) at 25 °C for 2 h at 250 rpm.Total Cd and CaCl 2 -extracted Cd concentrations were determined by graphite furnace atomic absorption spectrometry (AA800; Perkin Elmer, USA).The soil properties were determined according to Lin et al. 13 .The soil organic matter (SOM) was obtained by multiplying organic carbon with 1.724.Available N was determined by the alkaline hydrolysis diffusion method.Available phosphorus content was determined by colorimetric determination.Available potassium content was determined by flame photometer.Soil total nitrogen, total phosphorus and total potassium were determined by semi-micro KJELDAHL method.

Operation formula
The formula for calculating the economic benefit is as follows:

Statistical analysis
All statistical analyzes were completed using SPSS 22.0 software, and the LSD test was used to test for significant differences between treatments (p < 0.05).Origin 2021 draws graphics.

Declaration
The manuscript file confirming that the experimental research and field studies on plants complied with relevant institutional, national, and international guidelines and legislation.

Processing quality
Table 2 shows the effects of the soil amendments on the processing quality of different varieties of rice.Compared with the CK treatment, the BC and SC treatments significantly increased the rate of brown rice, milled rice and head milled rice (p < 0.05), while the LM treatment had no significant effect.For early rice, the rate of brown rice, milled rice and head milled rice increased by 9.60-12.71%,8. 16

Cooking quality
The RVA profile characteristics of rice treatment with different soil amendments are shown in Table 3. Except for the gelatinization temperature and peak time, the other indicators of the RVA profile were significantly different among different soil amendment treatments and cultivar types.Compared with the CK treatment, the BC and SC treatments significantly decreased the peak viscosity, hot pulp viscosity, final viscosity and setback of rice, and significantly increased the breakdown (p < 0.05), while the LM treatment made no significant difference.A high peak and trough viscosity, large breakdown value, and small setback value lead to high eating value.Therefore, the results of comparison among different cultivars showed that the characteristic of the RVA profile of late conventional rice was better than that of early hybrid rice, which was consistent with the results of amylose content and gel consistency.
The amylose content and gel consistency are important indicators for evaluating the taste of rice.As shown in Table 4, there was no significant difference in the amylose content of early and late rice cultivars under different treatments, but there were differences among cultivars.The amylose content of the late rice cultivars (YZX and XWX-13) was generally lower than that of the early rice cultivars (LLY-996 and ZLY-819).Compared with the CK treatment, there was no significant difference in the gel consistency of the LM treatment, but the BC and SC treatments significantly increased the gel consistency of rice (p < 0.05).For early rice, the gel consistency of the BC treatment increased by 17.09-31.43%compared with the CK treatment, and that of the SC treatment increased by 11.97-32.86%.For late rice, the gel consistency of the BC treatment increased by 13.14-17.91%compared with the CK treatment, and that of the SC treatment increased by 10.22-13.43%compared with the CK treatment.

Effects of different soil amendments on soil properties
The application of the soil amendments had different effects on soil physical and chemical indicators.As shown in Fig. 1, the application of soil amendments could significantly increase soil pH (A), and the effect was LM > SC > BC (p < 0.05).The soil pH of the LM treatment was significantly higher than that of the SC and BC treatments.On the basis of the results of the four cultivars, compared with CK, the soil pH of LM, SC, and BC increased by 1.31-1.39,0.93-1.01,and 0.81-0.92unit, respectively.
From the perspective of soil SOM (B) change, the LM treatment had no significant effect on soil organic matter, while the BC and SC treatments significantly increased soil organic matter.For early rice, compared with CK, the SC and BC treatments significantly increased soil organic matter by 11.57-14.77%and 16.41-18.91%,respectively.For late rice, compared with CK, the SC and BC treatments significantly increased soil organic matter by 12.16-13.91%and 19.48-19.94%,respectively (p < 0.05).
The soil NN (C), AP (D) and AK (E) under the SC and BC treatments all had an increasing trend compared with the CK treatment, and the effects of the two soil amendments were consistent (Fig. 1).For early rice, compared with CK, the NN, AP and AP in the SC treatment increased significantly by 21.17-23.22%,62. 34 The three soil amendments had a significant effect on reducing the soil A-Cd (F).Consistent with the pH results, the degree of reduction was LM > SC > BC, and the reductions with the LM and SC treatments were significantly higher than those with the BC treatment.Compared with CK, the Cd content in LM, SC, and BC soils decreased significantly by 37.79-48.24%,26.89-41.23%and 10.92-15.74%,respectively (p < 0.05).

Correlation analysis of soil properties and rice quality
The correlation analysis of rice processing, appearance, cooking, nutrition and hygiene quality and soil properties is shown in Fig. 2. The brown rice rate and milled rice rate in rice processing quality were significantly positively correlated with SOM, NN, AP and AK (brown rice rate: R = 0.87-0.97,p < 0.01; milled rice rate R = 0.70-0.80,p < 0.01).The head milled rice rate was significantly positively correlated with soil available nutrients (R = 0.52-0.67,p < 0.05).The chalkiness rate and chalkiness degree of rice appearance quality were significantly or extremely significantly negatively correlated with pH, SOM and available nutrients (chalkiness rate: R = − 0.54-0.78,p < 0.01; chalkiness degree: R = − 0.56-0.64,p < 0.05).A significant positive correlation existed between gel consistency and AK (R = 0.51, p < 0.05).The amylose content and RVA profile characteristics were not significantly correlated with soil properties indicators.Protein content had an extremely significant positive correlation with SOM and available nutrients (R = 0.79-0.84,p < 0.01).The rice Cd content in rice hygienic quality was significantly negatively correlated with pH (R = − 0.63, p < 0.01), and significantly positively correlated with A-Cd (R = 0.50, p < 0.05).

Effects of different soil amendments on rice yield and economic benefit
As shown in Fig. 3 and Table 5, the application of soil amendments could increase the rice yield.The yield of each cultivar was in the order of BC > SC > LM > CK, and the BC and SC treatments were significantly higher than the CK treatment (p < 0.05).The average early rice yields for the BC and SC treatments were 6.83 t ha −1 and 6.54 t ha −1 , which was an increase of 25.78% and 20.44% compared with the CK treatment.The average yields of late rice were 7.35 t ha −1 and 7.13 t ha −1 , which was an increase of 24.93% and 21.25%, respectively, compared with the CK treatment.It can be seen that the application of biochar and silicon-calcium fertilizer can significantly increase rice yield.
Table 5 shows a trend of BC > SC > LM in terms of the effect of soil amendments on increased rice yield.However, in terms of benefit analysis combined with cost, the BC treatment showed a negative benefit effect, while the LM treatment and the SC treatment showed a positive benefit effect.The SC treatment had the highest benefit effect.

Effects of soil amendments on soil properties
In the current study, the soil amendments significantly increased soil pH and reduced soil available Cd content, among which lime was more effective than biochar and silicon-calcium fertilizer.Beacuse the application of lime is mainly aimed at increasing the soil pH value, thereby increasing the soil redox potential and reducing the availability of heavy metals in the soil 18 .However, lime application had no significant effect on the soil's available nutrient content (SOM, NN, AP, AK).In contrast, the BC treatment with biochar application and SC  treatment with silicon-calcium fertilizer significantly increased the soil nutrient content.As an alkaline compound fertilizer, biochar can promote the growth of crops by improving the physical and chemical environment of the soil.Applying biochar to the soil can increase the pH value of the acidified soil, reduce the loss of soil nitrogen and effectively alleviate the release of fertilizers in the soil, thus meeting the needs of crops for nutrients in the later stages of growth 19 .According to reports, the application of silicon fertilizer can regulate the pH and alleviate soil acidification, and it also contains some nutrients, which have the effect of fertilizing the soil 20 .Wang et al. 21reported that the application of multi-element mineral soil amendments can increase the diversity of soil microorganisms, especially the richness of species, enhance the activity of soil urease, catalase and other enzymes, introduce organic carbon sources into the soil, and directly increase the content of soil organic matter.The increase effect of the BC treatment in late rice was significantly higher than that of the SC treatment, which may have been due to the more thorough decomposition of biochar by microorganisms over time, which was more conducive to the accumulation of nutrients in the soil 22 .

Effect of soil amendments on rice quality
The formation process of rice quality is essentially the carbon and nitrogen metabolism in rice and the process of grain filling 23 .In addition to the genetic characteristics of cultivars, environmental conditions and cultivation measures, especially artificial application of soil amendments, are important factors affecting rice quality 24 .
The application of organic carbon can reduce the soil bulk density and promote the nutrient absorption of rice roots, while the nutrients produced after its decomposition can increase the nitrogen content in the plant and the synthesis of related enzymes and improve the photosynthesis of leaves.This promotes the transfer of nutrients from all parts of the plant to the ear, which increases the hardness of the grain, enhances the ability of rice to resist milling damage and reduces the formation of rice chalkiness 25 .A previous study on the effect of lime on rice did not find that it had a significant effect on the rice quality indicators, although the application of CaO did significantly reduce the Cd content of brown rice 26 .However, in tomato research, it was found that the application of calcium fertilizer soil amendment could improve tomato quality, and the content of soluble solids increased by 20.2% 27 .Studies have reported that silicon-calcium fertilizer can enhance the activity of glutamic acid aminotransferase in rice leaves, increase the chlorophyll content and photosynthetic rate of leaves and, thus, increase the accumulation of photosynthetic substances after heading 21,28 .
In this study, the application of biochar and silicon-calcium fertilizer increased the brown rice rate, milled rice rate and head milled rice rate, and reduced the chalkiness rate and chalkiness degree of rice, and the two effects were relatively consistent.These findings indicated that the application of biochar and silicon-calcium fertilizer could increase the hardness of rice, reduce the occurrence of chalkiness, and improve the processing quality and appearance quality of rice.Studies have shown that the dominant factor affecting rice processing quality and appearance quality is grain filling.When the grain filling is fuller, the endosperm cells and tissues are more abundant and there are smaller internal gaps in the grain; when the arrangement is tighter, the hardness of the grain is higher and the probability of chalk formation is lower 29,30 .Both biochar and silicon-calcium fertilizer improve soil properties, increase the photosynthetic rate of rice leaves, prevent premature senescence of leaves, prolong the effective filling period of grains and enhance the transfer of filling materials to grains, thus increasing grain quality and fullness.
Rice with a low amylose content and long gel consistency has better cooking quality.Gel consistency is influenced by environment more than genotype, while amylose content shows the opposite influences 31 .In the results of the current study, the BC treatment and the SC treatment significantly improved rice gel consistency but had no significant effect on amylose content.It may be that both biochar and silicon-calcium fertilizer can promote the absorption of nutrients by rice by increasing the nutrient content of the soil, improve the photosynthesis of plant leaf, and promote the transport of nutrients into the grains, thereby increasing the gel consistency of rice 32,33 .
There was a significant correlation between RVA profile and cooking quality.Studies have shown that rice with high peak viscosity, large breakdown and small setback value was considered to have better cooking quality 34 .Protein content is not only the key factor affecting the cooking quality, but also the main index to measure the nutritional quality of rice.Studies have shown that the protein content is negatively correlated with the cooking quality of rice but positively correlated with the nutritional quality 35 .
The results of the current study showed that, for the RVA profile characteristics, the BC treatment and the SC treatment significantly reduced the peak viscosity, hot pulp viscosity, final viscosity and breakdown of rice, while significantly they increased the setback.The protein content of rice treated with BC and SC increased significantly by 21.01-52.49%and 14.78-43.96%,respectively, compared with the CK treatment (p < 0.05).Thus, the application of biochar and silicon-calcium fertilizer can improve the nutritional quality of rice to a certain extent, but at the same time can reduce its eating quality.In this study, both biochar and silicon-calcium fertilizer could significantly increase the soil nutrient content, especially alkaline hydrolysable-N.This promotes the absorption of carbon and nitrogen in the soil by rice, improves the carbon and nitrogen assimilation ability of the plant, promotes the transport of assimilated substances in various vegetative organs to the grain, stimulates the activities of enzymes related to starch synthesis and nitrogen assimilation enzymes in the grain and increases protein synthesis 36 .Studies have shown that the protein content has a significant negative correlation with breakdown and peak viscosity, and a very significant positive correlation with setback 37 .The results of the current study are basically consistent with the previous ones.Because of the higher protein content, the pores between starch grains are reduced, and the structure of rice grains is denser, which leads to slower water absorption and insufficient gelatinization of starch, which eventually leads to reduced palatability 38 .Therefore, further study is needed into how to regulate the structure of protein components and their correlation with the nutritional and eating qualities of rice.Soil amendments generally reduce Cd content in brown rice in several ways.The application of alkaline amendments increases the soil pH value, promotes the precipitation of Cd, and reduces the available Cd content in the soil, thereby reducing the absorption of Cd by rice 39 .In regulating soil acidification, lime and biochar are common amendments.Lime reduces the content of exchangeable Cd in the soil by increasing the cation exchange capacity in the soil.Biochar is a porous carbon structure, which can chelate Cd through abundant oxygen-containing functional groups (acidic functional groups such as carboxyl and phenolic hydroxyl groups) on the surface 40 .In the current study, the SC treatment had the best effect on reducing Cd content in brown rice.The composition of silicon-calcium fertilizer was: CaO ≥ 25%, SiO 2 ≥ 20%, K 2 O + P 2 O 5 ≥ 3%.The calcium element in its composition can increase the cation exchange capacity in the soil, and the silicon element can combine with the Cd in the soil to form a compound that cannot be absorbed by plants.At the same time, silicon can also improve the growth of rice, induce cells to produce small molecular chelating agents, enhance the chelation of Cd and reduce the content of free Cd in cells 41 .

Correlation between soil properties and rice quality
Rice quality is mainly determined by the interaction between genotype and environment.Environmental influences have largely been considered as single factors interacting with specific genotypes of specific plants.Because plants grow in changing environments, plants at different growth stages are affected by changes in environmental conditions even when grown in the same area 42 .Therefore, it is necessary to investigate the impact of environmental factors on specific crops.
In the current study, soil nutrient indexes (SOM, NN, AP, AK) were significantly positively correlated with rice processing quality and nutritional quality, and significantly negatively correlated with appearance quality.They were not significantly correlated with cooking and eating quality and hygienic quality.Soil pH was significantly negatively correlated with brown rice Cd content, and soil available Cd content was significantly positively correlated with brown rice Cd content.The analysis showed that the application of soil amendments increased the soil nutrient content (SOM, NN, AP, AK), and the increase in soil nutrient content significantly improved the growth and development of rice, which in turn promoted the improvement of rice processing, appearance and nutritional quality.The effect of soil amendment on the hygienic quality of rice is mainly through increasing the soil pH and reducing the available Cd content in the soil, thereby reducing the Cd content in brown rice.In summary, the improvement in rice processing, appearance and nutritional quality was mainly affected by the comprehensive effects of available nitrogen, phosphorus, potassium and organic matter content in the soil.Hygiene quality was mainly affected by soil pH and available Cd content.Cooking and eating quality had little correlation with soil properties.Among the environmental factors, nitrogen is an important factor affecting rice quality and nitrogen is the main element in the synthesis of major nutrients such as protein and starch in rice grains.Therefore, increasing the available nitrogen content in the soil can promote the absorption of nitrogen elements by rice, increase the nitrogen content in various organs of the plant, and promote the transport of nitrogen elements into the grains, thereby improving the rice quality 43 .Studies have shown that the impact of potassium on rice quality is second only to nitrogen and increasing the soil potassium content can effectively improve the nutritional and eating quality of rice 44 .It has also been reported that the application of appropriate amounts of phosphorus can improve the aroma, taste and cooking and eating quality of rice.It has also been reported that spraying foliar phosphorus and silicon fertilizers can improve the aroma, taste, texture and cooking and eating quality of rice 45 .

Effects of different soil amendments on rice yield and economic benefits
In this study, all three soil amendments could increase rice yield.However, the cost and potential risks of their application must be considered before these amendments can be applied to large-scale practical production fields.As shown in Table 5, among the soil amendments, only lime and silicon-calcium fertilizer could improve the economic benefits of rice planting.The SC treatment had the highest synergistic effect, reaching 561.26 US dollars ha −1 , followed by LM, which was 104.28 US dollars ha −1 .Although biochar can significantly improve rice yield and rice quality, the high cost has been an important reason hindering farmers from widely accepting it.In contrast, silicon-calcium fertilizers are low in cost and perform better in terms of high yield and high efficiency and they are worthy of large-scale promotion and application.
Additionally, limitations of this study include the fact that the experiment was conducted in one region for only 1 year.This experimental location was conducted on a lightly cadmium contaminated rice field and generalizability to other regions or soil types may be limited.Considering the effects of soil nutrient properties, temperature and light conditions on yield and quality of rice plants.This study may need to be strengthened through multiple years and multiple regions to verify the results of this study.At the same time, the physiological

Figure 3 .
Figure 3.Effect of soil amendment on rice yield.CK control, BC biochar, LM lime, SC silicon-calcium fertilizer, ZLY 819 Zhuliangyou 819, LLY 996 Luliangyou 996, YZX Yuzhenxiang, XWX 13 Xiangwanxian 13.The different letters indicate that significant differences were found between the treatments for each cultivar using least significant difference tests.The numeric values represent mean ± standard error.Values followed by different lowercase letters in the same group indicate significant difference among treatments n = 3, p < 0.05.

Table 1 .
Trial treatment and specific measures.
LimeLMLime was applied at an amount of 1.5 t ha −1 , equivalent to 3.15 kg of per plot.Other indicators are the same as CK Silicon-calcium fertilizer SC The silicon-calcium fertilizer was applied at an amount of 2.25 t ha −1 , equivalent to 4.73 kg of per plot.Other indicators are the same as CK Biochar BC Biochar was applied at an amount of 10 t ha −1 , equivalent to 21 kg of per plot.Other indicators are the same as CK -8.96% and 8.45-14.01%,respectively, in the BC Increased production (t ha −1 ) = Annual yeild (soil amendment treatment) − Annual yeild (CK treatment); Benefit(dollar ha −1 ) = Incremental production value − Cost.

Table 2 .
Effects of soil amendments on rice processing and appearance quality.The different letters indicate that significant differences were found between the treatments for each cultivar using least significant difference tests.CK control, BC biochar, LM, lime, SC silicon-calcium fertilizer, BR brown rice rate, MR milled rice rate, HMR head milled rice rate, L/W length/width ratio, CR chalkiness rate, CD chalkiness degree, ZLY 819 Zhuliangyou 819, LLY 996 Luliangyou 996, YZX Yuzhenxiang, XWX 13 Xiangwanxian 13.Values followed by different lowercase letters in the same group indicate significant difference among treatments n = 3, p < 0.05.
SeasonCultivar Treatment BR (%) MR (%) HMR (%) CR (%) CD (%) L/W (%)Vol.:(0123456789)ScientificReports|(2024)14:13088 | https://doi.org/10.1038/s41598-024-63737-xwww.nature.com/scientificreports/NutritionqualityTheprotein in milled rice is more easily digested and absorbed by the human body than the protein in any other grains, thus milled rice has been identified as an excellent vegetable protein.As shown in Table4, compared with the CK treatment, the BC and SC treatments significantly increased the rice protein content (p < 0.05), while the LM treatment showed no change.For early rice, the protein content of the BC treatment significantly increased by 24.68-52.49%compared with the CK treatment, and that of SC treatment significantly increased by 14.81-43.96%

Table 4 .
Effects of soil amendments on the cooking, nutrition and hygiene quality of rice.The different letters indicate that significant differences were found between the treatments for each cultivar using least significant difference tests.CK control, BC biochar, LM lime, SC silicon-calcium fertilizer, AC amylose content, GC gel consistency, PC protein content, BR-Cd brown rice Cd content, ZLY 819 Zhuliangyou 819, LLY 996 Luliangyou 996, YZX Yuzhenxiang, XWX 13 Xiangwanxian 13.Values followed by different lowercase letters in the same group indicate significant difference among treatments n = 3, p < 0.05.p < 0.05).For late rice, the protein content of the BC treatment significantly increased by 21.01-25.04%comparedwiththe CK treatment, and that of the SC treatment was significantly increased by 14.78-21.43%(p<0.05).qualityAsshown in Table4, all three soil amendments could significantly reduce the Cd content in rice (p < 0.05), and the Cd reduction effects among the soil amendments were consistent.Compared with the CK treatment, the soil amendments significantly reduced the rice Cd content of LLY-996 rice by 25.24-32.04%,significantly reduced the rice Cd content of ZLY-819 rice by 15.48-30.32%,significantly reduced the rice Cd content of YZX by 32.99-41.17%,and significantly reduced the rice Cd content of XWX-13 by 21.09-28.91%(p < 0.05).Comparatively speaking, the Cd reduction effect of SC was the greatest, followed by LM and then BC.

Table 5 .
Economic benefit analysis with different soil amendments.The price of rice is 400 US dollars t −1 (RMB to US dollar exchange rate 1:6.84).CK control, BC biochar, LM lime, SC silicon-calcium fertilizer.