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Excessive application of nitrogen fertilizer during rice cultivation leads to progressive soil contamination in the long term and increases production costs. An alternative to reduce over fertilization is to partially replace the fertilizer with microbes that promote nutrition and growth, such as arbuscular mycorrhizal fungi (AMF). We investigated the combination of four different rates of AMF (M): (M0: 0 g polybag−1, M1: 15 g polybag−1, M2: 30 g polybag−1, and M3: 45 g polybag−1) and three rates of nitrogen (N) fertilizer: (N0: 0 kg N ha−1, N1: 90 kg N ha−1, N2: 180 kg N ha−1) on Trisakti rice cultivar cultivated in polybag. Our findings indicate that the combination of 45 g AMF polybag−1 and 180 kg N ha−1 decreased soil bulk density by 38.02% and 37.24%, increased soil pH by 14.81% and 14.95%, soil porosity by 60.68% and 61.09%, soil organic matter by 28.62% and 30.46%, total N by 92.59% and 89.66%, available phosphorus by 30.12% and 29.85%, available potassium by 3.75% and 4.01%, rice plant height by 19.19% and 19.79%, tiller number by 25.27% and 26.08%, SPAD by 20.71% and 20.62%, flag leaf area by 107.76% and 108.02%, panicle length by 49.72% and 52.31%, panicle number by 67.44% and 72.35%, 1000-grain weight by 30.70% and 32.44%, root dry matter by 54.34% and 53.69%, shoot dry matter by 26.08% and 28.26%, root length by 54.68% and 56.44%, root volume by 42.73% and 43.37%, and N uptake by 107.93% and 108.06% compared to control during the early and late seasons, respectively. Conclusively, the combined application of AMF and N fertilizer increased the physiochemical properties, rice growth, rice productivity, and N uptake compared to AMF alone, N fertilizer alone, and the control treatment.

The combined use of organic manure and chemical fertilizer (CF) is considered to be a good method for sustaining high crop yields and improving soil quality. We performed a field experiment in 2019 at the research station of Guanxi University, to investigate the effects of cattle manure (CM) and poultry manure (PM) combined with CF on soil physical and biochemical properties, rice dry matter (DM) and nitrogen (N) accumulation and grain yield. We also evaluated differences in pre-and post-anthesis DM and N accumulation and their contributions to grain yield. The experiment consisted of six treatments: no N fertilizer (T 1 ), 100% CF (T 2 ), 60% CM + 40% CF (T 3 ), 30% CM + 70% CF (T 4 ), 60% PM + 40% CF (T 5 ), and 30% PM + 70% CF (T 6 ). All CF and organic manure treatments provided a total N of 150 kg ha −1 . Results showed that the treatment T 6 increased leaf net photosynthetic rate ( Pn ) by 11% and 13%, chlorophyll content by 13% and 15%, total biomass by 9% and 11% and grain yield by 11% and 17% in the early and late season, respectively, compared with T 2 . Similarly, the integrated manure and CF treatments improved post-antheis DM accumulation and soil properties, such as bulk density, organic carbon, total N, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) relative to the CF-only treatments. Interestingly, increases in post-anthesis DM and N accumulation were further supported by enhanced leaf Pn and activity of N-metabolizing enzyme during the grain-filling period. Improvement in Pn and N-metabolizing enzyme activity were due to mainly improved soil quality in the combined manure and synthetic fertilizer treatments. Redundancy analysis (RDA) showed a strong relationship between grain yield and soil properties, and a stronger relationship was noted with soil MBC and MBN. Conclusively, a combination of 30% N from PM or CM with 70% N from CF is a promising option for improving soil quality and rice yield.

Improving soil quality is critical for increasing rice yield, and biochar could be a beneficial soil amendment for high yield. This study was conducted to determine the effects of continuous (repeated seasonal) applications of biochar on nitrogen (N) uptake and utilization in rice. A fixed field experiment was done in Yongan Town, Hunan Province, China, in six continuous seasons (the early and late rice-growing seasons from 2015 to 2017). Results showed that biochar application did not significantly affect soil N uptake in the first four seasons. The effect of biochar application on fertilizer N uptake was not significant in three of the first four seasons. In the fifth and sixth seasons, biochar application resulted in 14–26% increases in soil N uptake but 19–26% decreases in fertilizer N uptake. Soil N availability did not explain the increased soil N uptake with biochar application. The decreased fertilizer N uptake with biochar application was attributed to both decreased fertilizer N availability and increased N loss through ammonia volatilization. As a consequence of a compensation between the increased soil N uptake and the decreased fertilizer N uptake, the effect of biochar application on total N uptake was not significant in the fifth and sixth seasons. However, biochar application led to 7–11% increases in internal N use efficiency in the fifth and sixth seasons and 6% increase in grain yield in the sixth season. Our study suggests that the effects of repeated seasonal applications of biochar on N uptake and utilization in rice depend on the duration of biochar application. Longer continuous applications of biochar can increase internal N use efficiency and grain yield in rice with insignificant change in total N uptake.

Excessive reliance on chemical fertilizer (CF) in conventional farming is a serious concern owing to its negative effects on soil health, the environment, and crop productivity. Organic manure is an alternative source of fertilizer to reduce the amount of CF usage in agriculture, decrease environmental pollution, and ensure sustainable crop production. This study assessed the integrated effect of poultry manure (PM) and cattle manure (CM) with CF on soil properties, plant physiology, and rice grain yield. Additionally, the difference in pre-and post-anthesis dry matter (DM) and nitrogen (N) accumulation and their relationship with grain yield was also determined. Pot experiments were performed in the early and late growing season at the experimental station of Guangxi University, China, in 2018. A total of six treatments, i.e., T.sub.1 -CF.sub.0 ; T.sub.2 -100% CF; T.sub.3 -60% CM + 40% CF; T.sub.4 -30% CM + 70% CF; T.sub.5 -60% PM + 40% CF, and T.sub.6 -30% PM + 70% CF were used in this pot experiment. Results showed that T.sub.6 enhanced leaf photosynthetic efficiency by 11% and 16%, chlorophyll content by 8% and 11%, panicle number by 12% and 16%, and grain yield by 11% and 15% in the early and late seasons, respectively, compared to T.sub.2 . Similarly1, post-anthesis N and DM accumulation, N uptake, and soil properties (i.e., soil organic carbon, total N, and bulk density) were improved with integrated CF and manure treatments over the sole CF treatments. Interestingly, increases in post-anthesis N uptake and DM production were further supported by enhanced N-metabolizing enzyme activities (i.e., nitrate reductase, glutamine synthetase, and glutamate oxoglutarate aminotransferase during the grain-filling period in combined treatments. In-addition, the linear regression analysis showed that post-anthesis DM (R.sup.2 = 0.95) and N (R.sup.2 = 0.96) accumulation were highly associated with grain yield of rice. Thus, the combination of 30% N from PM or CM with 70% N from CF (i.e., urea) is a promising option for improvement of soil quality and rice grain yield. Furthermore, our study provides a sustainable nutrient management plan to increase rice yield with high N use efficiency.

Direct-seeded rice is exceptionally vulnerable to chilling stress, especially at the seed germination and seedling growth stages in the early season of the double cropping system. Therefore, we conducted two experiments to evaluate the role of various seed primings and their different concentrations of plant growth regulators [experiment 1-abscisic acid (ABA), gibberellin (GA ), salicylic acid (SA), brassinolide (BR), paclobutrazol, uniconazole (UN), melatonin (MT), and jasmonic acid (JA)] and osmopriming substances (chitosan, polyethylene glycol 6000 (PEG6000), and CaCl ) and experiment 2-GA, BR (two best), CaCl (worst), and control (CK)] on rice seedlings under low temperature condition. Results showed that the maximum germination rate of 98% was recorded in GA (10 mgL ) and BR (0.3 mgL ) among treatments. Compared to CK, root and shoot length were improved in ABA (0.5 mgL ) and GA (100 mgL ) by 64% and 68%, respectively. At the same time, root and shoot weights (fresh and dry) were enhanced in Paclobutrazol (300 mgL ) and GA3 among treatments. Furthermore, the average root volume, average root diameter, and total root surface area were increased by 27%, 38%, and 33% in Paclobutrazol (300 mgL ), Paclobutrazol (200 mgL ) and JA (1 mgL ) treatments, respectively compared to CK. In the second experiment, a respective increase of 26%, 19%, 38%, and 59% was noted in SOD, POD, CAT, and APX enzyme activities in GA treatment compared to CK. Similarly, proline, soluble sugar, soluble protein, and GA content were also improved by 42%, 25.74%, 27%, and 19%, respectively, in GA treatment compared to CK. However, a respective reduction of 21% and 18% was noted in MDA and ABA content in GA treatment compared to CK. Our finding highlighted that better germination of primed-rice seedlings was associated with fresh and dry weights of the roots and shoots and the average root volume of the seedlings. Our results suggested that GA (10 mg L ) and BR (0.3 mg L ) seed priming prevent rice seedlings from chilling-induced oxidative stress by regulating antioxidant enzyme activities and maintaining ABA, GA, MDA, soluble sugar, and protein content. However, further studies (transcriptome and proteome) are needed to explore the molecular mechanisms involved in seed priming-induced chilling tolerance under field conditions.

The current farming system is heavily reliant on chemical fertilizers, which negatively affect soil health, the environment, and crop productivity. Improving crop production on a sustainable basis is a challenging issue in the present agricultural system. To address this issue, we assumed that the combined use of organic manure and inorganic nitrogen (N) fertilizers can improve rice grain yield and soil properties without the expense of the environment. This study explores the combined effects of cattle manure (CM), poultry manure (PM), and chemical fertilizer (CF) on soil properties, rice growth, physiology, and grain yield and quality. Six treatments in the following combinations were included: T1—no N fertilizer; T2—100% CF; T3—60% CM + 40% CF; T4—30% CM + 70% CF; T5—60% PM + 40% CF; and T6—30% PM + 70% CF. Results showed that across the seasons, treatment T6 increased the net photosynthesis rate, total biomass, grain yield, and amylose content by 23%, 90%, 95%, and 10%, respectively, compared with control. This increment in net photosynthetic rate and growth was the result of 24%, 14%, 19%, and 20% higher total root length, root surface area, root volume, and root diameter, respectively. Improvements in these attributes further enhanced the grain yield and nitrogen use efficiency of rice. No significant difference between T4 and T6 was observed. The correlation analysis also confirmed that root morphological traits were positively correlated with grain yield, N uptake, and biomass accumulation. Similarly, improvement in grain yield and NUE was also associated with improved soil properties, i.e., bulk density, soil porosity, soil organic carbon, and total N under combined organic and inorganic N fertilizers treatment. Conclusively, the integration of 30% N from PM or CM with 70% N from CF (urea) is a promising option not only for higher grain yield and quality of rice but also for improved soil health. This study provides a sustainable nutrient management strategy to improve crop yield with high nutrient use efficiency.

The excessive use of synthetic nitrogen (N) fertilizers in rice ( Oryza sativa L.) has resulted in high N loss, soil degradation, and environmental pollution in a changing climate. Soil biochar amendment is proposed as a climate change mitigation tool that supports carbon sequestration and reduces N losses and greenhouse gas (GHG) emissions from the soil. The current study evaluated the impact of four different rates of biochar (B) (C/B 0 -0 t ha −1 , B 1 -20 t ha −1 , B 2 -40 t ha −1 , and B 3 -60 t ha −1 ) and two N levels (N 1 ; low (270 kg N ha −1 ) and N 2 ; high (360 kg N ha −1 )), on rice (cultivar Zhenguiai) grown in pots. Significant increases in the average soil microbial biomass N (SMBN) (88%) and carbon (87%) were recorded at the highest rate of 60-ton ha −1 B and 360 kg N ha −1 compared to the control (N 1 C) during both seasons (S1 and S2). The photochemical efficiency (Fv/Fm), quantum yield of the photosystem (PS) II (ΦPS II), electron transport rate (ETR), and photochemical quenching ( qP ) were enhanced at low rates of biochar applications (20 to 40 t B ha −1 ) for high and low N rates across the seasons. Nitrate reductase (NR), glutamine synthetase (GS), and glutamine 2-oxoglutarate aminotransferase (GOGAT) activity were, on average, 39%, 55%, and 63% higher in the N 1 B 3 , N 2 B 2 , and N 2 B 3 treatments, respectively than the N 1 C. The grain quality was higher in the N1B 3 treatment than the N 1 C, i.e., the protein content (PC), amylose content (AC), percent brown rice (BRP), and percent milled rice (MRP) were, on average, 16%, 28%, 4.6%, and 5% higher, respectively in both seasons. The results of this study indicated that biochar addition to the soil in combination with N fertilizers increased the dry matter (DM) content, N uptake, and grain yield of rice by 24%, 27%, and 64%, respectively, compared to the N 1 C.

A high-quality rice population structure serves as the foundation for achieving high yields, with plant spacing and the number of seedlings per hill playing key roles in regulating this structural development. However, the combined effects of seedling number per hill and plant spacing on yield formation and resource allocation in rice ( Oryza sativa L.) are not yet fully understood. This study aimed to assess the effects of coordinated changes in seedling number per hill and plant spacing on source-sink characteristics and yield in rice, while maintaining a constant seedling density. The study evaluated the response of four rice varieties to combined variations in seedling number per hill and plant spacing, all under a baseline seedling density of 60 × 10 4 ha - ¹, over a two-year field experiment. Linear models, mixed-effects models, ridge regression, and structural equation modeling were used to examine the effects of these factors on rice growth, biomass allocation, nitrogen and carbon accumulation, and yield. Results showed that increasing seedlings per hill and plant spacing reduced yield and above-ground biomass (AGB) but increased the harvest index (HI). Single seedlings with narrow spacing produced the highest yield (7.27 t ha - ¹), AGB (16.4 t ha - ¹), and the lowest HI (0.46). The combined effects of seedling number per hill and plant spacing negatively affected tiller number, number of effective panicles, leaf area index, and nutrient accumulation, while positively influencing specific leaf area and panicle biomass allocation. Organic carbon accumulation (43.52%) and biomass accumulation (31.32%) were major contributors to yield variation. Path analysis indicated that 96% of yield variance was accounted for, highlighting the importance of panicle biomass, organic carbon accumulation, and the source-sink balance between stems and panicles. In conclusion, single seedlings with narrow spacing (12.93 cm spacing with 1 seedling per hill) optimize the source-sink balance in rice, compensating for a lower harvest index by enhancing biomass accumulation, thereby increasing yield.

[This corrects the article DOI: 10.3389/fpls.2022.895230.].