Novel Semi-IPN Nanocomposites with Functions of both Nutrient Slow

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Cite This: J. Agric. Food Chem. 2019, 67, 7598−7608

Novel Semi-IPN Nanocomposites with Functions of both Nutrient Slow-Release and Water Retention. 2. Effects on Soil Fertility and Tomato Quality Haidong Zhao,†,‡ Jiang Song,†,‡ Guizhe Zhao,†,‡ Yang Xiang,*,†,‡ and Yaqing Liu*,†,‡

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†

Shanxi Province Key Laboratory of Functional Nanocomposites, School of Materials Science and Engineering, North University of China, Taiyuan 030051, China ‡ Research Center for Engineering Technology of Polymeric Composites of Shanxi Province, North University of China, Taiyuan 030051, China S Supporting Information *

ABSTRACT: So far, the effects of the semi-interpenetrating polymer network (semi-IPN) composites with functions of both nutrient slow-release and water retention on soil physicochemical properties, yield, and quality of crops have not been studied. In Part 1 of this paper (Song, J.; Zhao, H.; Zhao, G.; Xiang, Y.; Liu, Y. J. Agric. Food Chem.2019, DOI: 10.1021/ acs.jafc.9b00888), superabsorbent polymers SAPWS (grafting wheat straw (WS) to poly(acrylic-co-acrylamide), which is WS-gP(AA-co-AM)) and SAPHEC (HEC (hydroxyethyl cellulose)-g-P(AA-co-AM)), and their semi-IPN nanocomposites SI-PSRF/ SAPWS and SI-PSRF/SAPHEC (formed by chemical bonding of SAPWS or SAPHEC with PSRF (NPK-containing polymeric slowrelease fertilizer)) were prepared, and their microstructures and degradation performances were systematically studied. In this study, effects of these two nanocomposites on soil physicochemical properties, crop yield, and quality as well as soil fertility, especially the relationships between these effects and the degradation performances of the materials themselves, were investigated by a pot experiment of the tomato. Results show that SI-PSRF/SAP nanocomposites can regulate the pH values of weak alkaline soils close to 7.0. The changes of soil pH values, in our study, are basically synchronized with the degradation rates of SI-PSRF/SAP, the higher the degradation rate of SI-PSRF/SAP, the lower the pH value of the alkaline soil treated. Compared with PSRF+SAP (the simple physically mixed system of PSRF and SAP) and PSRF, during the whole growth period of the tomato, SI-PSRF/SAP treatments have the lowest nitrogen release amounts, 4.74 g for SI-PSRF/SAPWS and 4.88 g for SIPSRF/SAPHEC, the highest nitrogen contents of soils after day 40, and the highest nitrogen contents of plants on day 100, 1.16 and 1.68 g for SI-PSRF/SAPWS and 1.26 and 1.86 g for SI-PSRF/SAPHEC. While for PSRF+SAPWS, PSRF+SAPHEC, and PSRF, they are 5.16 g, 0.81 g, 0.63 g and 5.26 g, 0.87 g, 0.66 g and 5.17 g, 0.63 g, 0.52 g, respectively. There is a significant positive correlation between the material degradation rates and their nitrogen release amounts in this study, while SI-PSRF/SAP systems have the highest correlation coefficient, 0.950. In addition, compared to the control blank, the SI-PSRF/SAP system significantly increases tomato yield, 270.1% for SI-PSRF/SAPWS and 301.7% for SI-PSRF/SAPHEC. Compared with PSRF+SAP, the SI-PSRF/SAP system can make the soil treated become a high-quality soil by influencing the soil pH value, conductivity, cation exchange capacity, and the contents of nitrogen, phosphorus, organic carbon, and active organic carbon, which have significant impact on the soil quality. The chemical-bonded functional nanocomposites with a semi-IPN three-dimensional network structures formed by hydrogen-bonding interactions among functional groups of their components can more efficiently improve soil fertility, increase soil nutrient supply capacity, and promote plants growth and development as well as solve the environmental pollution caused by traditional fertilizers. The technology reported in this paper is simple and feasible for largescale production of fertilizer with both water retention and nutrient slow-release, even nanofertilizer, which has great application potential. KEYWORDS: nanocomposites with semi-IPN, nitrogen utilization, phosphorus utilization, tomato yield and quality, soil fertility

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INTRODUCTION Fertilizers, especially containing nutrients nitrogen and phosphorus, play irreplaceable roles in improving soil quality and crop yield.1,2 Researchers have shown that traditional instantly soluble fertilizers have high water solubility and low molecular weight, causing the loss of a large number of nutrients, which would lead to not only the low fertilizer utilization efficiency ( PSRF+SAP > PSRF. Nitrogen Flow from Material to Soil and Plant. Figure 2A,B shows the changes in nutrient nitrogen release behaviors of different treatment materials in tomato pot experiments. From day 0 to day 10, the nitrogen cumulative release rates of SI-PSRF/SAP, PSRF+SAP, and PSRF reveal a quick rise, but the nitrogen amounts released by SI-PSRF/SAP are much lower than those from PSRF+SAP and PSRF. After that, the cumulative release rates of nitrogen slow down. Before day 40, the release amounts of nitrogen from PSRF+SAP are greater than that from PSRF and SI-PSRF/SAP is the least. But after day 40, SI-PSRF/SAP is the most and PSRF+SAP is the least. Because of the dissolution and hydrolysis of nitrogencontaining small molecules and short-chain polymers contained in the macromolecule networks, the nitrogen cumulative release rates of SI-PSRF/SAP, PSRF+SAP, and PSRF reveal a quick rise in the initial stage. However, SI-PSRF/SAPHEC and SI-PSRF/SAPWS only release 1.85 and 1.38 g of nitrogen, accounting for 30.22% and 22.55%, respectively, of their own total nitrogen contents, far less than 3.73 g, 3.32 g, and 3.22 g of the nitrogen amounts released by PSRF+SAPHEC, PSRF +SAPWS, and PSRF. From day 10 to day 100, due to slow degradation of the remaining macromolecular chains by soil microorganisms, the cumulative release rates of nitrogen slow down. It can be clearly seen that the release amounts of nitrogen from PSRF+SAP are greater than that from PSRF, because the water-absorbed SAP could increase the rate at which PSRF is hydrolyzed or degraded by microorganisms. In general, the better the water absorption properties of SAP, the greater the degradation rate of PSRF(+SAP). However, SAP could adsorb some small molecule nutrients generated during PSRF degradation, which can also be clearly proved by Figure 2A; therefore, in some cases, the nitrogen release rate of PSRF(+SAP) is slower than that of PSRF. The maximum nitrogen release amounts from these two SI-PSRF/SAP treatments occur from 40 to 70 days, which is the time when tomatoes need most nutrients for growth, releasing 33.33% and 36.60% of the total nitrogen contents of their own, respectively. The reason why the nitrogen release of these two SI-PSRF/SAP materials reaches a maximum at the 70th day is that, as mentioned above, from the 10th day, the release of nutrient nitrogen from all materials mainly depends on the microbial degradation of their macromolecules, and the microorganisms need a period of time to accommodate to the material environment, so the biodegradation rate of the material at this stage is small, resulting in a decrease in the release amount of nutrient nitrogen. This could also be confirmed by the fact that there is no large amount of

Figure 3. SEM images of SI-PSRF/SAPWS (A) and SI-PSRF/SAPHEC (B) on days 40 and 70.

many microorganisms could be found attached on the surface of the material through SEM, as shown in Figure 3 A2,B2, and the rate of microbial biodegradation of material increases, thus increasing the amount of nitrogen released from the material. Our group has studied and reported the effects of PSRF on microbial numbers in soils, and the results are shown in Figure S8 in Part 1,29 which can provide direct data support for the numbers of soil microorganisms at different incubation periods. From 40 to 70 days, PSRF+SAPHEC, PSRF+SAPWS, and PSRF treatments only release 4.08%, 3.10%, and 8.49% of the total nitrogen contents of their own, respectively, thus causing lack of nutrient nitrogen for tomato growth in this stage. The maximum nitrogen release of these three treatments is 55.06%, 54.25%, and 60.95% of the total nitrogen of their own in the first 10 days. However, in this stage, crops require less nutrition, which would inevitably lead to the loss of fertilizer. Therefore, SI-PSRF/SAP shows the better nitrogen release performances and could provide nutrition nitrogen for plants steadily throughout the growth period. Of course, on day 100, there are still 20.26%, 22.55%, 15.69%, 14.05%, and 15.52% of the total nitrogen contents of these five materials remaining, indicating that further improvements still need to be optimized for their nutrient nitrogen releasing performances, especially for the SI-PSRF/SAP system, and more suitable for the needs of short-term crops. Through studies of the effects of structures on the release behaviors, it could be concluded that after applied into soils, the viscosity of SIPSRF/SAP increases and a high-viscosity hydration film or a three-dimensional semi-IPN structure are gradually formed, which limit the movements of water and nutrient molecules, reduce the rate of material dissolution, and form large aggregates, which contribute to the reduction of the material nutrient transport rate with water through exchangeable adsorption and interception.36 In addition, SI-PSRF/SAPHEC has a slightly faster release rate of nitrogen compared with SIPSRF/SAPWS, due to the same reason in Part 129 for a higher degradation rate of SI-PSRF/SAPHEC than SI-PSRF/SAPWS. All these results indicate that the chemical-bonded functional nanocomposites SI-PSRF/SAPWS and SI-PSRF/SAPHEC produced by the hydrogen-bond interactions among functional groups in each component are more effective in controlling 7602

DOI: 10.1021/acs.jafc.9b00889 J. Agric. Food Chem. 2019, 67, 7598−7608

Article

Journal of Agricultural and Food Chemistry

significant positive correlation between the material degradation rate and its nitrogen release amount of different treatments in this study. SI-PSRF/SAP systems have the highest correlation coefficient, followed by PSRF and PSRF +SAP systems. This indicates that the degradation rate of SIPSRF/SAP material systems can be more effectively controlled by further designing of components and microstructures of themselves, thereby more effectively controlling the nitrogen slow-release performances. The changes in soil total nitrogen (STN) contents of different material treatments are presented in Figure 2C. There are significant differences among the STN contents treated by different materials, due to the differences in soil nitrogen mineralization rate and release rate caused by the structural properties of different treatment materials. The rate at which STN content decreases the fastest in PSRF treatment, followed by PSRF+SAPWS, PSRF+SAPHEC, SI-PSRF/SAPWS, and SIPSRF/SAPHEC. For SI-PSRF/SAP systems, due to their threedimensional semi-IPN structures, the release amounts of nitrogen could be more effectively controlled, and then the changes in STN contents during the whole tomato growth period are relatively more stable than other treatments. Specifically, the STN contents of SI-PSRF/SAP treatment in the first days are lower than that of PSRF+SAP and PSRF treatment but higher than these in the late stage, which is also consistent with the previous analyses on the nitrogen release rates of these materials. Figure 2D show the changes of nitrogen content in plants throughout the growing period of tomatoes. The nitrogen content in plants is significantly increased by the application of these materials compared with the control treatment. Among

nitrogen release. Specific data of nitrogen release amounts of all materials are show in Tables S1−S5. Combining the above results with the weight loss test results (Table S2 in Part 129) and the analyses on the degradation processes of all materials (Figure S13 in Part 129), it can be concluded that the degradation of functional group −CONH− in the SI-PSRF/SAP system, the main source of nutrient nitrogen, mainly occurs from day 40 to day 70, whereas PSRF and PSRF+SAP systems used as the controls mainly occur between 10 and 40 days. An interesting conclusion may be drawn from this part and the results in Part 1:29 semi-IPN structures formed by the hydrogen-bonding interactions can slow down the degradation rate of the polymer with a fast selfdegradation rate and increase the degradation rate of the polymer with a slow self-degradation rate. Of course, the universality of this conclusion still needs to be further confirmed. In addition, in order to compare the contribution of the nitrogen release amount in different treatment materials to their weight loss during the degradation process, the correlation between the material release nitrogen amount and its weight loss rate was analyzed. Table 1 show that there is a Table 1. Correlation between Weight Loss Rate and Nitrogen Release Amount of Materials treatment

correlation

PSRF PSRF (+SAP) PSRF+SAP SI-PSRF/SAP

0.923* 0.922* 0.793* 0.950**

Figure 4. Effects of PSRF, PSRF+SAP, and SI-PSRF/SAP on phosphorus cumulative release rate (A) and release amount (B) of materials and phosphorus content of soil (C) and plant (D) at different tomato growth periods. Dotted lines are only a guide to the eyes. 7603

DOI: 10.1021/acs.jafc.9b00889 J. Agric. Food Chem. 2019, 67, 7598−7608

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Journal of Agricultural and Food Chemistry

backbone which is easily hydrolyzed and degraded by microorganisms, see Figure S13A in Part 1.29 Therefore, PSRF has the fast release rate of nutrient phosphorus. Compared with PSRF, PSRF+SAPWS and PSRF+SAPHEC show a relatively good slow-release properties of phosphorus, which could be attributed to the adsorption of SAP for the small molecules, see Figure 4A. In contrast, in our study, SIPSRF/SAPWS and SI-PSRF/SAPHEC show better slow-release properties to phosphorus. On the one hand, the reason could be the physical barrier of the superabsorbent network and the molecular chain of PSRF for H2PO4−. On the other hand, it is also possible that SAPWS and SAPHEC contain many reactive groups which could adsorb small molecules. As described in Part 1,29 SI-PSRF/SAPHEC has a greater water absorption capability than SI-PSRF/SAPWS, and after absorption water, its spatial structure becomes larger and then can adsorb more small molecules containing phosphorus. Therefore, SI-PSRF/ SAPHEC shows better phosphorus slow-release performance than SI-PSRF/SAPWS. Figure 4C show the changes in soil phosphorus contents. It is observed that the change rule of phosphorus contents in soils is the same in all treatments, increasing first and then decreasing. As mentioned earlier, the release rate of phosphorus from all materials is the fastest in the early stage, which is one of the reasons for the increase of soil phosphorus content in each treatment. For another, in this stage, although the release of nutrient phosphorus from material is greater than them absorbed by plants, phosphorus is easily fixed by soil through physical adsorption or chemical reaction, which would greatly reduce the amount of nutrient phosphorus loss,36−38 which also result in an upward trend of soil phosphorus content. After 40 days, tomatoes absorb a large amount of nutrient phosphorus from soils during their growth, resulting in a decrease in the soil phosphorus content. In the initial stage, soil phosphorus content of PSRF is the highest, followed by PSRF+SAP and SI-PSRF/SAP. While in the later stage, soil phosphorus content of SI-PSRF/SAP is the highest, followed by PSRF+SAP and PSRF. The changes in phosphorus content of plants are demonstrated in Figure 4D, which show an obvious increase during tomato growth periods, with SI-PSRF/ SAPHEC treated plants having the highest phosphorus content, followed by SI-PSRF/SAPWS, PSRF+SAPHEC, and PSRF +SAPWS processing, the lowest PSRF treatment. All of these could be explained by the above-mentioned phosphorus nutrient release characteristics of the materials. For PSRF, PSRF+SAPWS, PSRF+SAPHEC, SI-PSRF/SAPWS, and SI-PSRF/SAPHEC, the total masses of phosphorus released by them during the whole growth period are 113.43 mg, 112.82 mg, 113.33 mg, 113.47 mg, and 113.46 mg, respectively. On day 100, the phosphorus contents of soils treated with them in turn are 82.86 mg, 91.52 mg, 93.52 mg, 102.52 mg, and 105.52 mg, and the phosphorus contents in plants planted in turn are 35.57 mg, 35.85 mg, 36.40 mg, 39.52 mg, and 39.99 mg, respectively. In the case that the total masses of phosphorus released during the whole growth period is almost the same, the phosphorus content of soils treated by PSRF+SAP is significantly higher than that of PSRF treatment, while the phosphorus content of plants is slightly higher than that of PSRF treatment; and the phosphorus content of soils treated by SI-PSRF/SAP is significant higher than that of PSRF +SAP treatment, while the phosphorus content of plants is slightly higher than that of PSRF+SAP treatment, suggesting that the phosphorus utilization efficiency could be improved by

all treatments, the highest nitrogen content in plants occurs in SI-PSRF/SAPHEC treatment, followed by SI-PSRF/SAPWS, PSRF+SAPHEC, PSRF+SAPWS, and PSRF, basically coinciding with the nitrogen release performances of materials, indicating that SI-PSRF/SAPHEC-treated and SI-PSRF/SAPWS-treated plants are more effective at absorbing nutrient nitrogen, thereby increasing nitrogen utilization efficiency. For PSRF, PSRF+SAPWS, PSRF+SAPHEC, SI-PSRF/SAPWS, and SI-PSRF/SAPHEC, the total masses of nitrogen released during the whole growth period are 5.17 g, 5.16 g, 5.26 g, 4.74 g, and 4.88 g, respectively. On day 100, the STN contents of soils treated by the above materials in turn are 0.63 g, 0.81 g, 0.87 g, 1.16 g, and 1.26 g, and the nitrogen contents in plants planted in turn are 0.52 g, 0.63 g, 0.66 g, 1.68 g, and 1.86 g, respectively. In the case that the total masses of nitrogen released during the whole growth period is hardly any difference, the STN and plant nitrogen contents of PSRF +SAP treatments are obviously higher than these of PSRF treatment, suggesting that the nitrogen utilization efficiency could be improved by the introduction of the water-absorbing and water-retaining components. Furthermore, it can also be concluded that SI-PSRF/SAP treatments have the lowest nitrogen release amounts of materials and the highest STN contents after day 40, while the plants have the highest nitrogen uptake, about three times that of PSRF treatment, indicating that SI-PSRF/SAP could significantly improve the nitrogen utilization efficiency. From these data, it can also be concluded that nutrient nitrogen loss in PSRF treatment is the largest, followed by PSRF+SAP treatments, and the smallest loss of nutrient nitrogen belongs to the SI-PSRF/SAP systems. The semi-IPN three-dimensional network structures formed by hydrogen-bonding interactions among functional groups in their components can effectively improve the nitrogen utilization efficiency. Phosphorus Flow from Material to Soil and Plant. Changes in nutrient phosphorus release behaviors of different treatment materials are shown in Figures 4A,B. For all materials, the cumulative release rates of phosphorus increase sharply in the first 10 days. After 10 days, they increase slowly, with the slowest growth rate of PSRF, followed by PSRF+SAP, and the increase of SI-PSRF/SAP is the relatively largest. Figure 4B shows the phosphorus release amount curves (see Tables S1−S5 for the specific data), from day 0 to day 10, and the phosphorus release amounts of SI-PSRF/SAPHEC, SIPSRF/SAPWS, PSRF+SAPHEC, PSRF+SAPWS, and PSRF are 86.16 mg, 83.28 mg, 93.38 mg, 90.04 mg, and 98.29 mg, accounting for 72.40%, 69.98%, 78.47%, 75.66%, and 82.59% of their own total phosphorus contents. The key period of phosphorus requirement for general plants and crops is the seedling stage, and during this period the application of phosphorus can bring maximum efficiency. From day 10 to day 100, the amount of phosphorus released from PSRF is consistently reduced. During days 40−70, the most critical stage for tomatoes growth, the phosphorus release amount of SI-PSRF/SAPHEC is significantly higher than those of other materials, but by 100 days, 95.34% of its own total phosphorus content is released, which is more complete and higher than those of others. In general, the release rate of nutrient phosphorus is relatively faster than that of nutrient nitrogen, because phosphorus is partially present in the form of KH2PO4 in PSRF, as indicated by the white arrows in Figure S3, and the other part is in the segments of the PSRF macromolecular 7604

DOI: 10.1021/acs.jafc.9b00889 J. Agric. Food Chem. 2019, 67, 7598−7608

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Table 2. Yield and Sugar to Acid Ratio of Tomatoes Planted and the Utilization Efficiencies of N and P of Materialsa treatments CK PSRF PSRF+SAPWS SI-PSRF/SAPWS PSRF+SAPHEC SI-PSRF/SAPHEC

yield of tomatoes/kg 1.77 3.98 4.58 6.55 4.86 7.11

f e d b c a

sugar to acid ratio 10.89 14.33 15.52 16.45 15.62 16.67

e d c b c a

N utilization efficiency (%) 10.80 11.76 36.09 12.85 39.89

P utilization efficiency (%)

d cd b c a

31.00 31.77 34.82 32.11 35.24

b b a b a

a

Means followed by different lowercase letters in the same column were significantly different by Duncan’s test (P < 0.05).

Figure 5. Effects of PSRF, PSRF+SAP, and SI-PSRF/SAP on total organic carbon content (A) and active organic carbon content (B) of soil at different tomato growth periods. Dotted lines are only a guide to the eyes.

the introduction of the water-absorbing and water-retaining components and the semi-IPN three-dimensional network structures formed by hydrogen-bonding interactions among functional groups of their components can improve the phosphorus utilization efficiency Tomato Quality and Nutrient Utilizations. The quality and yield of tomatoes treated with different materials and the nutrient utilization efficiencies of materials are significantly different, as shown in Table 2. The yields of tomatoes treated with water-retention fertilizers PSRF+SAP and SI-PSRF/SAP are significantly higher than that of PSRF treatment. This is due to the addition of SAP, which could provide a relatively good water supply for plant growth and enhance the slowrelease performance of PSRF. These also fully demonstrate that water and fertilizer are essential for plant growth. The yields of SI-PSRF/SAP are higher compared with PSRF+SAP, indicating that SI-PSRF/SAP are more conducive to the growth of tomatoes. It should be noted that the ripe fruits before harvest had to be picked in advance. Thus, it is hard to compare the effects of different material treatments on plant growth by the images of tomato fruits at a point in time. The total weight and number of fruits picked at different times are recorded in Table S6, and Figure S4 is images of representative tomato plants on day 100 of different material treatments. As can be seen from the ratio of sugar to acid, the tomatoes taste of SI-PSRF/SAP treatment can be significantly improved.39 The nitrogen and phosphorus utilization efficiencies of PSRF +SAP are higher than that of PSRF, which may be due to the water-absorbing and water-retaining effect of SAP can slow down the probability of nutrients nitrogen and phosphorus leaching with water, thereby increasing the absorption and utilization efficiency of plants. Especially, the chemical-bonded functional nanocomposites significantly outperform simple physical mixed materials in nitrogen and phosphorus

utilization efficiencies, mainly due to their more effective control of nutrients and moisture, making them closer to the demand for nutrients during the whole tomato growth period. All these results show that the chemical-bonded functional nanocomposites with semi-IPN three-dimensional network structures formed by the hydrogen-bonding interactions among functional groups of their components can markedly improve crop yield and quality and material nutrients utilization efficiency compared with the simple physical mixed materials. Soil Fertility in Different Treatments. Figure 5A shows the changes in total organic carbon (TOC) contents of soil, which is an important index for soil fertility.40,41 The TOC contents of soils treated with these materials increase first and then decrease throughout the tomato growth period, and SIPSRF/SAP treatments are higher than that in PSRF+SAP treatments. The reason for the decrease is that the addition of exogenous nitrogen accelerates the decomposition of soil organic carbon and further leads to a decrease in soil TOC content after 40 days of incubation. TOC contents in SIPSRF/SAP treatments are higher than that in PSRF+SAP treatments, because of the better degradation performances and then the higher carbon release contents of SI-PSRF/SAP, demonstrating that SI-PSRF/SAP could more effectively increase the vitality of tomato roots, which promote the secretion of root organic matter. Figure 5B shows the changes in active organic carbon contents of soil. Soil activated organic carbon (SAOC) refers to the part of soil carbon that is more active to plants and microorganisms in its form and spatial position.42 In all material treatments, the contents of SAOC increase first and then decrease throughout the growth period, and SI-PSRF/ SAP treatment is highest in all treatments. The reason for the early increase is that the increase of carbon source and nitrogen 7605

DOI: 10.1021/acs.jafc.9b00889 J. Agric. Food Chem. 2019, 67, 7598−7608

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Figure 6. Principal component analysis (A) and cluster analysis (B) of soil fertility index of different material treatments.

source in soil enhance the activity of soil microorganisms, thereby increasing the conversion rate of microorganisms to soil organic carbon.43 In the later stage, the number and activity of microorganisms are all increasing, resulting in higher consumption than the conversion of SAOC. The SAOC contents in SI-PSRF/SAP treatment are higher than those in other treatments, indicating chemical-bonded functional nanocomposites can better improve soil carbon conversion rate and improve soil fertility. The CO2 and CH4 flux from soils treated by PSRF, PSRF+SAP, and SI-PSRF/SAP at different tomato growth periods are shown in Figure S5. From Figure 6A, it can be seen EC, CEC, and contents of nitrogen, phosphorus, organic carbon, and active organic carbon of soils in our study have higher loading values on PC1, indicating that these soil indicators have higher correlation with PC1 and significantly effect the soil quality. However, the pH value has a negative effect on PC1 and PC2, indicating that the reduction of pH in weakly alkaline soils is beneficial to improve the soil fertility. From the above results, it can be concluded that PC1 and PC2 can effectively reflect the seven quality indicators of soil, indicating that the two main components extracted can be used to characterize the level of soil quality. It can be seen from Figure 6B that the classification of each material treatment can be clearly seen from the clustering tree diagram. Soil quality can be divided into three grades: high-quality soil (SI-PSRF/SAPWS and SIPSRF/SAPHEC), medium-quality soil (PSRF, PSRF+SAPWS, PSRF+SAPHEC), and low-quality soil (CK). This indicates that polymeric slow-release fertilizer is beneficial to improve soil fertility, and the effect of chemical-bonded semi-IPN nanocomposite is the most significant. It can be concluded that chemical-bonded functional nanocomposites with semi-IPN three-dimensional network structures formed by hydrogenbonding interactions among functional groups of their components can more efficiently improve soil fertilizer fertility, increase soil nutrient supply capacity, and promote plants growth and development compared with the simple physical mixed materials.

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Preparation processes of all materials; Scheme S1, neutralization mechanism of potassium dihydrogen phosphate and alkali metal carbonate in soil; Table S1, specific data of nutrient release amounts during PSRF degradation; Tables S2−S5, specific data of nutrient release amounts during PSRF+SAPWS degradation, PSRF+SAPHEC degradation, SI-PSRF/SAPWS degradation, and SI-PSRF/SAPHEC degradation; Table S6, total weight and number of tomato fruits picked at different times; Figure S1, photograph of soil column leaching experimental device; Figure S2, weight loss rate, pH, and electric conductivity of soils treated in the soil column leaching experiment; Figure S3, SEM images of PSRF; Figure S4, photographs of representative tomato plants on day 100 of different material treatments; Figure S5, effects of PSRF, PSRF+SAP, and SI-PSRF/ SAP on CO2 flux and CH4 flux at different tomato growth periods (PDF)

AUTHOR INFORMATION

Corresponding Authors

*Phone/fax: +86-351-3559669. E-mail: [email protected]. *E-mail: [email protected]. ORCID

Yaqing Liu: 0000-0002-2643-5139 Funding

The authors gratefully acknowledge the financial support from Shanxi Province 1331 Project Key Innovation Team of Polymeric Functional New Materials and Shanxi Province Innovative Disciplinary Group of New Materials Industry. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Geng, J.; Sun, Y.; Zhang, M.; Li, C.; Yang, Y.; Liu, Z.; Li, S. Long-term effects of controlled release urea application on crop yields and soil fertility under rice-oilseed rape rotation system. Field Crops Research 2015, 184, 65−73. (2) Zhao, L.; Cao, X.; Zheng, W.; Scott, J. W.; Sharma, B. K.; Chen, X. Copyrolysis of biomass with phosphate fertilizers to improve biochar carbon retention, slow nutrient release, and stabilize heavy metals in soil. ACS Sustainable Chem. Eng. 2016, 4, 1630−1636.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jafc.9b00889. 7606

DOI: 10.1021/acs.jafc.9b00889 J. Agric. Food Chem. 2019, 67, 7598−7608

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DOI: 10.1021/acs.jafc.9b00889 J. Agric. Food Chem. 2019, 67, 7598−7608

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DOI: 10.1021/acs.jafc.9b00889 J. Agric. Food Chem. 2019, 67, 7598−7608