Average Rice Grain Research Articles

Factors controlling accumulation and bioavailability of selenium in paddy soils: A case study in Luxi County, China

Selenium (Se) accumulation in rice (Oryza sativa L.) has become a major global concern. Se offers multiple health benefits in humans; however, its inadequate or excessive intake can be harmful. Therefore, determining the factors driving Se abundance and bioavailability in paddy soils is essential to ensure the safety of human Se intake. This study investigated the accumulation, bioavailability, and distribution of Se in 820 paddy soil and rice grain samples from Luxi County, China to assess how soil properties (soil organic matter [SOM], cation exchange capacity [CEC], and pH), geographical factors (parent materials, elevation, and mean annual precipitation [MAP] and temperature [MAT]), and essential micronutrients (copper [Cu], zinc [Zn], and manganese [Mn]) govern Se accumulation and bioavailability in paddy soils. Results showed that the average soil Se content was 0.36 mg kg−1, which was higher than that in China (0.29 mg kg−1). Alternatively, the average rice grain Se content was 0.032 mg kg−1, which was lower than the minimum allowable content in Se-rich rice grains (0.04 mg kg−1). Five studied parent materials all had a significant effect on soil Se content but had little effect on Se bioavailability (p < 0.05). CEC, elevation, and SOM, as well as the soil contents of Cu, Zn, and Mn were positively correlated with soil Se content, but pH, MAP, and MAT were negatively correlated. Correspondingly, Se bioavailability was negatively correlated with SOM and soil Zn content, but positively correlated with MAP and grain contents of Cu, Zn, and Mn. Furthermore, partial least squares path analysis revealed the interactive impacts of the influencing factors on Se accumulation and bioavailability in soils. On this basis, prediction models were established to predict Se accumulation and bioavailability in paddy soils, thereby providing theoretical support for developing efficient control measures to meet Se challenges in agriculture.

Effects of different tillage and residue management systems on soil organic carbon stock and grain yield of rice–wheat double cropping system

Of late, intensive agricultural practices are often associated with many negative implications for soil systems, such as decline in soil organic matter and biological diversity, and increase in the risk of soil erosion, and degradation of soil physical quality. However, conservation agriculture (CA) offers minimum soil disturbance, improving and creating more efficient use of natural resources, enhancing use efficiency of external inputs and increasing soil functioning, organic matter content, and biodiversity. However, CA practices need to be redefined at the specific field level or growing conditions to promote sustainable production system without deteriorating soil health, and to manage profitability. Therefore, a fixed-site field experiment was conducted to evaluate the effects of different tillage and residue management practices; CT0 (puddled transplanted rice followed by conventional tilled wheat sown with residue removal); CTR (puddled transplanted rice followed by conventional tilled wheat sown with residue retention); NT0 (direct seeded rice followed by zero-tilled wheat sown with residue removal); NTR (direct seeded rice followed by zero-tilled wheat sown with residue retention) on soil organic carbon (SOC) stock and grain yield of rice–wheat double cropping system. The results showed that the mean SOC stock increased by 31%, 21.9% and 15.3% and by 35.2%, 22% and 17% under NTR, CTR, and NT0 compared with CT0. Furthermore, the SOC sequestration rate in NTR was significantly higher than other treatments. Particulate organic carbon (POC) concentration was 58.4% higher in 0–15 cm than 15–30 cm soil layer, and the maximum concentration was recorded under NTR and minimum was under CT0. The highest average rice grain yield was recorded under CTR, which was 5.5%, 16.2% and 24.3% higher than CT0, NTR and NT0, respectively. Both NTR and CTR produced more average wheat yield, which was 8.4% and 8.5% higher than CT0 and NT0, respectively. Principal component analysis (PCA) also showed that cumulative cropping system yield and SOC were increased under CTR, NTR as compared to other treatments. Therefore, it can be drawn that residue retention could be a useful management practice to increase SOC stock and grain yield under both tillage practices in the rice–wheat cropping system.

Evaluation of quantitative synchrotron radiation micro-X-ray fluorescence in rice grain.

Concentrations of nutrients and contaminants in rice grain affect human health, specifically through the localization and chemical form of elements. Methods to spatially quantify the concentration and speciation of elements are needed to protect human health and characterize elemental homeostasis in plants. Here, an evaluation was carried out using quantitative synchrotron radiation microprobe X-ray fluorescence (SR-µXRF) imaging by comparing average rice grain concentrations of As, Cu, K, Mn, P, S and Zn measured with rice grain concentrations from acid digestion and ICP-MS analysis for 50 grain samples. Better agreement was found between the two methods for high-Z elements. Regression fits between the two methods allowed quantitative concentration maps of the measured elements. These maps revealed that most elements were concentrated in the bran, although S and Zn permeated into the endosperm. Arsenic was highest in the ovular vascular trace (OVT), with concentrations approaching 100 mg kg-1 in the OVT of a grain from a rice plant grown in As-contaminated soil. Quantitative SR-µXRF is a useful approach for comparison across multiple studies but requires careful consideration of sample preparation and beamline characteristics.

Source Apportionment of Speciated Mercury in Chinese Rice Grain Using a High-Resolution Model.

Rice grain consumption is a primary pathway of human mercury exposure. To trace the source of rice grain mercury in China, we developed a rice paddy mercury transport and transformation model with a grid resolution of 1 km × 1 km by using the unit cell mass conservation method. The simulated total mercury (THg) and methylmercury (MeHg) concentrations in Chinese rice grain ranged from 0.08 to 243.6 and 0.03 to 238.6 μg/kg, respectively, in 2017. Approximately, 81.3% of the national average rice grain THg concentration was due to atmospheric mercury deposition. However, soil heterogeneity, especially the variation in soil mercury, led to the wide rice grain THg distribution across grids. Approximately, 64.8% of the national average rice grain MeHg concentration was due to soil mercury. In situ methylation was the main pathway via which the rice grain MeHg concentration was increased. The coupled impact of high mercury input and methylation potential led to extremely high rice grain MeHg in partial grids among Guizhou province and junctions with surrounding provinces. The spatial variation in soil organic matter significantly impacted the methylation potential among grids, especially in Northeast China. Based on the high-resolution rice grain THg concentration, we identified 0.72% of grids as heavily polluted THg grids (rice grain THg > 20 μg/kg). These grids mainly corresponded to areas in which the human activities of nonferrous metal smelting, cement clinker production, and mercury and other metal mining were conducted. Thus, we recommended measures that are targeted at the control of heavy pollution of rice grain by THg according to the pollution sources. In addition, we observed a wide spatial variation range of MeHg to THg ratios not only in China but also in other regions of the world, which highlights the potential risk of rice intake.

Effects of weed infestation on the productivity of hybrid and inbred rice varieties in Myanmar

AbstractDouble rice‐cropping areas in the dry and wet seasons have been increasing in Myanmar, and hybrid rice has been cultivated throughout the country. However, weeds are often not adequately managed. Therefore, the objective of this study was to investigate the effect of weed infestation on rice production of three hybrid varieties (Palethwe 1, Palethwe 3, and Palethwe Basmati) and three inbred varieties (Manaw Thu Kha, Shwe Thwe Yin, and Sin Thwe Latt) in the dry and wet seasons in a lowland rice field. In the dry and wet seasons, 19 ‐ 20 weed species were naturally infested into the fields. Limnocharis flava was the most abundant weed in both seasons. Weed dry weight and rice grain yield showed a negative linear relationship in both seasons. Manaw Thu Kha showed the highest yield loss in the un‐weeded fields in both seasons, while Sin Thwe Latt and Palethwe Basmati showed the lowest yield loss in the dry season and wet season, respectively. Sin Thwe Latt recorded the lowest yield loss of 30.21% on average in both seasons, and the highest yield loss of 60.37% was recorded for Manaw Thu Kha. The average rice grain yield loss of all the varieties in the un‐weeded fields was 64.37 and 33.66% for the dry and wet seasons, respectively. Thus, the yield loss in the dry season was 1.9‐times greater than that in the wet season. The present research suggests that adequate weed management is necessary for rice cultivation, especially in the dry season in Myanmar.

Improving Rice Yields and Nitrogen Use Efficiency by Optimizing Nitrogen Management and Applications to Rapeseed in Rapeseed-Rice Rotation System

This investigation aims to provide theoretical and practical evidence for the efficient utilization of nitrogen (N) in paddy-upland rapeseed-rice rotation systems because a lack of previous research on such rotation systems leads to inefficient management practices. The effects of the N application rates and the N fertilizer management strategies for rapeseed and rice were examined, respectively, in relation to the photosynthetic productivity and yields of hybrid rice. The results indicated that the leaf area, Pn, with 40% as basal fertilizer, 40% as tillering fertilize, and 20% as panicle fertilizer and a reduced N rate (30 kg/ha) during the rape season, were higher than other nitrogen management strategies trialed, with conventional N rates in the rape season. The average rice grain yield (9545.15 kg/ha) over the two years with 40% as basal fertilizer, 40% as tillering fertilizer, and 20% as panicle fertilizer was higher than other N treatments with the reduced N rates during the rape season. The reduced N rate during the rapeseed season and 40% as basal fertilizer, 40% as tillering fertilizer, and 20% as panicle fertilizer management during the rice season for the rape-rice rotation system exhibited the highest rice yields. Our findings indicated that the N fertilizer management model was a high-yielding, N-saving, and environmentally friendly measure for rape–rice rotation systems in southern China.

Innovative water-saving ground cover rice production system increases yield with slight reduction in grain quality

Ground cover rice production system (GCRPS) is known to increase grain yield and reduce irrigation water and greenhouse gas emission. However, whether this innovative technology affects commercial and nutritional rice quality remains unknown. Thus, a three-year field experiment was conducted to compare three production systems: traditional paddy (Paddy) and GCRPS under two soil moisture conditions, namely, saturated and 80% of soil water-holding capacity combined with three nitrogen fertilizer regimes. We analyzed the grain-milling quality (brown rice rate, milled rice rate and head rice recovery), the appearance quality (chalky rice rate and grain size), eating quality (amylose concentration) and nutritional quality (protein and 15 amino acids concentration). Results showed that compared with Paddy, the average rice grain yield, water and nitrogen use efficiency were significantly higher in GCRPS. The milling quality was improved in GCRPS, whereas the appearance quality decreased. Amylose concentration was 7.6% higher in saturated GCRPS than in Paddy. Moreover, protein concentration was 11.5%–13.1% lower in GCRPS than in Paddy and total amino acid concentration was reduced by 6.9%, whereas protein and total amino acid yield were significantly improved. Meanwhile, the concentrations of six essential amino acids were similar to those in Paddy, whereas non-essential amino acid concentration decreased in GCRPS. Overall, our findings showed that suitable N management practices for GCRPS are to be developed to further enhance the protein and amino acid concentrations.

Tillage practices improve rice yield and soil phosphorus fractions in two typical paddy soils

This research was undertaken (I) to evaluate the status of phosphorus fractions in paddy soils in response to different tillage management practices under different rice-based cropping systems and environments in order to better understand phosphorus behavior in paddy soils and (II) to assess the effects of various tillage practices on crop yield in different soil types and climatic conditions. We selected four tillage treatments, i.e., conventional tillage (T1), conventional tillage with straw return (T2), rotary tillage with straw return (T3), and no-tillage with straw return and autumn plowing with straw return (T4) at Ningxiang and Haerbin, respectively. Soil samples were collected from 20 cm depth, and we investigated soil pH, total P, Olsen P, SOM content, phosphatase activities, phosphorus fractions, and grain yield at the two experimental sites. The results showed that the T4 tillage system led to significantly higher soil organic matter (SOM) content, total P, and Olsen P concentrations at both sites compared with T1. Regardless of the tillage system, the average rice grain yield at Haerbin was 50.3% greater than that at Ningxiang. Phosphomonoesterase (AcP) and phosphodiesterase (DP) enzyme activities were significantly higher, by 39.8% and 62.1% and by 40.3% and 54.6%, under T4 compared to under T1 at Haerbin and Ningxiang, respectively. The organic and inorganic fractions of P were significantly affected by the different tillage systems. Labile and moderately labile P pools were 29.3% and 19.2% higher in Ningxiang and 64.7% and 33.8% higher in Haerbin under T4 compared to T1, and the non-labile P pools were 10.6% and 18.5% lower, respectively. The labile and moderately labile organic P fractions and phosphatase activities showed a significant correlation with SOM and total P concentrations in RDA analysis. Variance partitioning analysis (VPA) showed that different soil properties, climate factors, phosphatase activities, and their interactions were responsible for 7.1%, 6.8%, 1.3%, and 53.7%, respectively, of the variation in grain yield. Different tillage management practices revealed varied effects at both sites for grain yield, P fractions, and phosphatase activities. Tillage management and climatic variations could be the driving factors that influence grain yield in northern and southern parts of China.

Soil organic carbon and its labile fractions in paddy soil as influenced by water regimes and straw management

Understanding the effects of water regimes and straw management on soil organic carbon (SOC) pools is necessary to improve soil C sequestration and soil quality. Based on a long-term field experiment (15 years), we examined impacts of water regimes and straw management methods on total soil organic C (TOC), particulate organic C (POC) and potassium permanganate-oxidizable C (KMnO4–C) at two soil depths. Water regimes consisted of flooding cultivation and non-flooded cultivation. In non-flooded cultivation, limited irrigation was employed to keep the soil moist condition without standing water covering the field during the rice-growing season. It is substantially different from conventional flooded rice cultivation. The two straw management methods were straw mulching and straw removal. The results showed that water management had greater effects on TOC and KMnO4–C than did straw management at 0–10 cm soil layer. Compared to the non-flooded treatment, flooding cultivation resulted in 17.4% higher TOC and 31.4% higher KMnO4–C contents. Correspondingly, straw management showed dominant effects on POC. Straw mulching significantly increased POC content by 13.0% as compared to the straw removal treatment. However, at deeper soil depth (10–20 cm), labile SOC fractions were only affected by water regimes. The higher carbon management index (CMI) values at 0–20 cm were recorded in the flooding condition with straw mulching treatment. This was attributed to the increased carbon pool index (CPI), which contributed to the formation of more stable organic compounds that collectively act as a soil reservoir. The combined non-flooded cultivation and straw mulching method (NFC–SM) produced a similar 15–year average rice grain yield and TOC content in 2016 compared to the traditional flooding cultivation with straw removal treatment (FC–SR). Our data indicated that NFC–SM could be an ideal strategy not only to save water but also to maintain soil fertility.

Comparison of yield and nitrogen use efficiency of different types of nitrogen fertilizers for different rice cropping systems under subtropical monsoon climate in China

Abstract Controlled release urea (CRU) and urea with nitrification inhibitor could improve yields and nitrogen use efficiency (NUE) in a number of production systems. However, their effectiveness will be strongly influenced by environmental conditions. The objective of this research was to evaluate the effects of CRU and urea with nitrification inhibitors on grain yield and nitrogen use efficiency under different rice cropping systems. A five-year experiment on double rice cropping systems and a two-year experiment on single rice cropping systems were conducted using four treatments: not N fertilized (CK), prilled urea with split applications (PU), single basal application of polymer coating of sulfur-coated urea (PSCU) and prilled urea with the nitrification inhibitor 2-chloro, 6-(trichloromethyl) pyridine (NPU). The fertilizers were applied at the rate of 180 kg N ha −1 under a subtropical monsoon climate in China. The results suggest that NPU significantly increased the five-year average grain yield and NUE when compared with the PU treatment by 9.7% and 10.3% for early rice, and 9.6% and 8.8% for late rice, respectively. However, PU treatment produced a similar two-year average rice grain yield and 3.1% higher NUE when compared with the NPU treatments for single rice. PSCU treatment significantly increased average grain yield by 5% and 3.7% compared to the PU treatment of late rice and single rice, respectively. In addition, PSCU treatment resulted in the highest total N uptake and NUE during 2012–2015 for late rice and 2014–2015 for single rice, indicating synchronized N release in accordance with the N requirement of rice. However, the use of PSCU was not effective in improving grain yield or NUE of early rice owing to the delayed release of N during the tillering-heading stage. Overall, our results suggest that urea with nitrification inhibitor is preferable to urea for double rice cropping systems, and that PSCU is more suitable for single rice.

Changes in soil organic carbon fractions under integrated management systems in a low-productivity paddy soil given different organic amendments and chemical fertilizers

Labile soil organic carbon fractions are important indicators of soil C dynamics, which is affected by different management practices. However, few studies have reported the short-term effect of a wide range of organic materials mulching on the distribution of soil total organic C (TOC) and its labile C pools in a low-productivity paddy soil. Our objective was quantify TOC and labile organic C fractions down a 0–30cm soil profile in a 4-year field experiment receiving four organic amendments (spent mushroom compost, green manure, cattle manure and rice straw residues). Soil samples were taken from the 0–5cm, 5–10cm, 10–20cm and 20–30cm soil depths. Soil total organic carbon (TOC), total nitrogen (TN), microbial biomass C (MBC), particulate organic C (POC), potassium permanganate-oxidizable C (KMnO4-C) and dissolved organic C (DOC) were measured. Carbon management index (CMI) was also calculated. Among the four organic amendments, cattle manure showed the most profound effect on TOC, TN and labile organic C fractions and produced the highest 4-year average rice grain yield (9.67tha−1). The cattle manure combined with NPK resulted in the highest level of TOC (19.2gkg−1) and TN (1.86gkg−1) in the surface soil (0–5cm). Additionally, KMnO4-C and MBC concentrations in the cattle manure plus NPK treatment were 1.3 and 1.5 times higher at the 0–5cm depth, 1.4 and 1.6 times higher at the 5–10cm depth, 1.2 and 1.4 times higher at the 10–20cm depth compared to NPK fertilizer alone, respectively. However, POC was not sensitive to different management practices in the deeper soil layer (10–20cm). DOC was not significantly affected by fertilization in the 0–20cm soil layer, suggesting it was unsuitable as an early indicator of soil quality. Overall, the integrated use of cattle manure and NPK fertilizers is the most efficient management practice in improving carbon sequestering under current soil conditions. A long-term assessment is needed to confirm the most effective and sustainable management practice for improving rice grain yield and soil quality.

Effects of Urea and Controlled Release Urea Fertilizers on Methane Emission from Paddy Fields: A Multi-Year Field Study

A four-year (2008–2011) field study was implemented in a major rice-growing region of China to better understand the effect of urea and controlled release fertilier (CRF, thermoplastic resin-coated urea in this study) on CH4 emission from paddy fields. Over the four years, the average CH4 emission during the rice growing seasons was 76.9, 65.8 and 64.9 kg CH4 ha−1 in treatments CK (zero N), U (urea) and C (CRF), respectively. Urea and CRF significantly reduced CH4 emission by 14.4% and 15.6%, and increased average rice grain yield by 25.8% and 19.7% (P < 0.05), respectively, compared with treatment CK. Flooding duration would affect CRF's effect on CH4 emission from paddy fields. Under normal aeration conditions, CH4 emission tended to be 3.9%–15.2% lower in treatment C than in treatment U from 2009 to 2011, while it tended to be 4.2% higher under delayed aeration conditions in 2008. The findings suggest that mid-season aeration (MSA) starting on D30 (30 days after rice transplanting), just like the local practice, would optimize the CRF's effect on CH4 emission from rice fields in China. Over the four years, average rice yield did not differ between treatments U and C, and tended to be 5% lower in treatment C than in treatment U.

Effects of Different Cultivation Methods and Straw Incorporation on Grain Yield and Nutrition Quality of Rice

Plastic film mulching cultivation (PFMC) under non-flooded condition has been considered as a new water-saving technique in rice production, while yield decline from continuous cropping of aerobic rice is a constraint to the widespread adoption of PFMC. Rice straw incorporation has been proposed to counter this negative effect in recent decades. This study examined the effects of three cultivation methods and rice straw incorporation on rice grain yield and quality using Liangyoupeijiu (an indica hybrid). The three cultivation treatments were: conventional flooding cultivation (CFC); non-flooded plastic film mulching cultivation (PFMC); no mulching cultivation in non-flooded condition (NMC). Compared with that under CFC, average rice grain yield under PFMC from 2008 to 2010 was significantly improved by 8.0%, while total amino acids content was decreased by 3.5%, no obvious effect was observed on rice protein, Fe and Zn concentrations in rice; under NMC, the reduction in yield, protein, total amino acids and Fe concentrations were 5.1%, 4.4%, 9.3%, and 11.8%, respectively. With rice straw incorporation, grain yield was improved by 113.6, 142.6, and 522.1 kg ha 1 under CFC, NMC, and PFMC, respectively. Average rice grain yield, Fe and Zn contents in brown rice were significantly improved by 3.3%, 3.1%, and 6.4% with rice straw incorporation. The results of the three years showed the same trend in rice grain yield and nutrition quality. The results indicated that PFMC could improve not only grain yield, but also part of rice nutrition quality. Rice straw incorporation could significantly improved rice grain yield as well as Fe and Zn concentrations in brown rice, which would be a good method to overcome grain yield decline under long term PFMC.

The implications of land preparation, crop establishment method and weed management on rice yield variation in the rice–wheat system in the Indo-Gangetic plains

The implications of adopting alternative seeding methods for rice and wheat establishment were examined at three geographically separate sites in the rice–wheat system of the Indo-Gangetic plains, across northern India. Rice yields in cultivated plots, established by either wet or dry seeding methods, were evaluated in comparison to yields from zero-tillage plots and under conventional transplanting methods. In the same trials, the effects of crop establishment methods in wheat were assessed both on wheat yields and rice yields. Rice crop establishment methods markedly influenced the emerging weed flora and attainable yields were measured in relation to intensity of weed management. Over four years, average rice grain yields in the absence of weed competition were greatest (6.56 t ha −1) under wet seeding (sowing pre-germinated rice seed on puddled soil), and similar to those from transplanted rice (6.17 t ha −1) into puddled soil, and dry seeded rice after dry soil tillage (6.15 t ha −1). Lowest yields were observed from dry seeded rice sown without tillage (5.44 t ha −1). Rice yield losses due to uncontrolled weed growth were least in transplanted rice (12%) but otherwise large (c. 85%) where rice had been sown to dry cultivated fields or to puddled soil, rising to 98% in dry seeded rice sown without soil tillage. Weed competition reduced multiple rice yield components, and weed biomass in wet seeded rice was six-fold greater that in rice transplanted into puddled soil and twice as much again in dry seeded rice sown either after dry tillage or without tillage. Wheat grain yields were significantly higher from crops sown into tilled soil (3.89 t ha −1) than those sown without tillage (3.51 t ha −1), and also were elevated (5% on average) where the soil had been dry cultivated in preparation for the previous rice crops rather than puddled. The method of wheat cultivation did not influence rice yield. Soil infiltration rates in the wheat season were least where the land had been puddled for rice (1.52 mm h −1), and greater where the soil had been dry-tilled (2.63 mm h −1) and greatest after zero-tillage (3.54 mm h −1). These studies demonstrated at research managed sites across a wide geographic area, and on farmers’ fields, that yields of dry seeded rice sown after dry cultivation of soil were broadly comparable with those of transplanted rice, providing weed competition was absent. These results support the proposition that direct seeding of rice could provide an alternative to the conventional practice of transplanting, and help address rising costs and threats to sustainability in the rice–wheat rotation. Further, analysis of patterns of long-term rainfall data indicated that farmers reliant on monsoon rainfall could prepare fields for dry direct seeded rice some 30 days before they could prepare fields for either transplanting or seeding with pre-germinated seed. Dry, direct seeding of rice contributes a valuable component of an adaptive strategy to address monsoonal variability that also may advance the time of wheat establishment and yield. Whilst the results illustrate the robustness, feasibility and significant potential of direct seeded rice, they also highlight the critical nature of effective weed control in successful implementation of direct seeding systems for rice.

Triangular Transplanting Pattern and Split Nitrogen Fertilizer Application Increase Rice Yield and Nitrogen Fertilizer Recovery

Field experiments were conducted to evaluate the effects of improved crop management (OPT) for irrigated rice (Oryza sativa L.) on grain yield and N recovery efficiency in southwestern China. In the OPT treatment, rice seedlings were transplanted in a triangular spatial pattern and the N fertilizer was split, based on the difference between the estimated total N requirement and the soil and environmental N supply. Fine‐tuning of application rates was achieved using leaf greenness measurements. The performance of OPT was tested in two adjacent fields in which the crops preceding rice were wheat (Triticum aestivum L.; Rw) and rapeseed (Brassica napus var. napus; Ro). The OPT and traditional farming practice (TRA) treatments both gave higher average grain yields than zero‐N controls (CK). Rice yields were considerably smaller in Rw than Ro under CK. Compared with TRA, OPT led to significantly higher aboveground N uptake, biomass accumulation, and grain yield in Rw Over the 2 yr of the study, average rice grain yields under OPT increased by 19 and 22% compared with TRA and 30 farmers' fields, respectively. The OPT treatment performed better than TRA in 15N recovery efficiency. Compared with TRA, OPT led to increased 15N fertilizer recovery efficiency from 19% in TRA to 42% in OPT, and decreased loss from 68% in TRA to 39% in OPT. In conclusion, OPT practice is a feasible means to attain increased yield with efficient N use. This study provides guidance for farmers using rice‐based cropping systems, especially in southwestern China.

Interactions between non-flooded mulching cultivation and varying nitrogen inputs in rice–wheat rotations

A 3-year field experiment examined the effects of non-flooded mulching cultivation and traditional flooding and four fertilizer N application rates (0, 75, 150 and 225 kg ha −1 for rice and 0, 60,120, and 180 kg N ha −1 for wheat) on grain yield, N uptake, residual soil N min and the net N balance in a rice–wheat rotation on Chengdu flood plain, southwest China. There were significant grain yield responses to N fertilizer. Nitrogen applications of >150 kg ha −1 for rice and >120 kg ha −1 for wheat gave no increase in crop yield but increased crop N uptake and N balance surplus in both water regimes. Average rice grain yield increased by 14% with plastic film mulching and decreased by 16% with wheat straw mulching at lower N inputs compared with traditional flooding. Rice grain yields under SM were comparable to those under PM and TF at higher N inputs. Plastic film mulching of preceding rice did not affect the yield of succeeding wheat but straw mulching had a residual effect on succeeding wheat. As a result, there was 17–18% higher wheat yield under N0 in SM than those in PM and TF. Combined rice and wheat grain yields under plastic mulching was similar to that of flooding and higher than that of straw mulching across N treatments. Soil mineral N (top 60 cm) after the rice harvest ranged from 50 to 65 kg ha −1 and was unaffected by non-flooded mulching cultivation and N rate. After the wheat harvest, soil N min ranged from 66 to 88 kg N ha −1 and increased with increasing fertilizer N rate. High N inputs led to a positive N balance (160–621 kg ha −1), but low N inputs resulted in a negative balance (−85 to −360 kg ha −1). Across N treatments, the net N balances of SM were highest among the three cultivations systems, resulting from additional applied wheat straw (79 kg ha −1) as mulching materials. There was not clear trend found in net N balance between PM and TF. Results from this study indicate non-flooded mulching cultivation may be utilized as an alternative option for saving water, using efficiently straw and maintaining or improving crop yield in rice–wheat rotation systems. There is the need to evaluate the long-term environmental risks of non-flooded mulching cultivation and improve system productivity (especially with straw mulching) by integrated resource management.

ARROZ DE TERRAS ALTAS EM ROTAÇÃO COM SOJA

The objective of this study was to evaluate the performance of upland rice grown in soils of continued soybean cultivation, under different tillage systems and nutrient doses, and the effects of these treatments on the subsequent soybean yield. The treatments were three doses of macronutrients (zero, 100 kg.ha -1 , and 300 kg.ha -1 of commercial formula 4-30-16), without or with micronutrient fertilization (20 kg.ha -1 of zinc sulfate, 50 kg.ha -1 of FTE BR 12, and 50 kg.ha -1 of iron sulfate). The experiments were carried out under three soil tillage systems (heavy disk harrow, chisel plow, and moldboard plow). A joint analysis showed that the moldboard plow system provided average rice grain yield of 3077 kg.ha -1 , 9% and 26% higher than those of chisel plow (2823 kg.ha -1 ), and heavy disk harrow (2440 kg.ha -1 ), respectively. Macro and micronutrient treatments did not significantly affect rice grain yield. The different soil tillage systems and nutrient doses applied to rice crop did not significantly affect soil macro and micronutrient levels and pH, nor did it affect the soybean yield when the crop was planted in the same area in the succeeding year. Average soybean yield was approximately 2600 kg.ha -1 . As far as profitability and sustainability are concerned, it was recommended that rice grown after soybean crop, under moldboard plowing, should be fertilized with 100 kg.ha -1 of commercial formula 4-30-16, without micronutrient fertilization. KEY-WORDS: Moldboard plow; chisel plow; heavy disk harrow; macronutrient; micronutrient.