Controlled-release Urea Treatments Research Articles

Effects of Long-Term Controlled-Release Urea on Soil Greenhouse Gas Emissions in an Open-Field Lettuce System.

Controlled-release urea (CRU) fertilizers are widely used in agricultural production to reduce conventional nitrogen (N) fertilization-induced agricultural greenhouse gas emissions (GHGs) and improve N use efficiency (NUE). However, the long-term effects of different CRU fertilizers on GHGs and crop yields in vegetable fields remain relatively unexplored. This study investigated the variations in GHG emissions at four growth stages of lettuce in the spring and autumn seasons based on a five-year field experiment in the North China Plain. Four treatments were setup: CK (without N application), U (conventional urea-N application), ON (20% reduction in urea-N application), CRU (20% reduction in polyurethane-coated urea without topdressing), and DCRU (20% reduction in polyurethane-coated urea containing dicyandiamide [DCD] without topdressing). The results show that N application treatments significantly increased the GHG emissions and the lettuce yield and net yield, and DCRU exhibited the lowest N2O and CO2 emissions, the highest lettuce yield and net yield, and the highest lettuce N content of the N application treatments. When compared to U, the N2O emission peak under CRU and DCRU treatments was notably decreased and delayed, and their average N2O emission fluxes were significantly reduced by 10.20-20.72% and 17.51-29.35%, respectively, leading to a significant reduction in mean cumulative N2O emissions during the 2017-2021 period. When compared to U, the CO2 fluxes of DCRU significantly decreased by 8.0-16.54% in the seedling period, and mean cumulative CO2 emission decreased by 9.28%. Moreover, compared to U, the global warming potential (GWP) and greenhouse gas intensity (GHGI) of the DCRU treatment was significantly alleviated by 9.02-17.13% and 16.68-20.36%, respectively. Compared to U, the N content of lettuce under DCRU was significantly increased by 6.48-17.25%, and the lettuce net yield was also significantly increased by 5.41-7.71%. These observations indicated that the simple and efficient N management strategy to strike a balance between enhancing lettuce yields and reduce GHG emissions in open-field lettuce fields could be obtained by applying controlled-release urea containing DCD without topdressing.

Optimizing One-Time Nitrogen Fertilization for Rice Production Using Controlled-Release Urea and Urease Inhibitors

One-time fertilization with controlled-release urea (CRU) is a research hotspot for its lower labor cost and stability of nitrogen (N) supply for rice growth. Yet the fertilizer formulation needs to be further improved to better adjust the N supplement to meet the demand of rice plants and obtain a higher grain yield. Therefore, the effects of novel fertilizer formulations composed of CRU, urease inhibitor (UI) and nitrification inhibitor (NI) on the rice growth and photosynthetic characteristics as well as high-yield formation were tested through a two-year field experiment. The result indicated that the combined use of CRU and UI treatment can achieve higher yields than with CRU at the same N application level. Meanwhile, with a 20% reduction of N use, one-time application of CRU + UI can obtain the same high yield as the conventional split application of urea. Compared with conventional fertilization and CRU treatment, the CRU + UI treatment had suitable leaf area and biomass accumulation at the vegetative growth stage and high effective stem tiller rate. More post-anthesis dry matter accumulation, higher net photosynthesis rate and low senescence rate were guaranteed for its high yield and nitrogen agronomic efficiency.

A Controlled-Release Nanofertilizer Improves Tomato Growth and Minimizes Nitrogen Consumption.

Minimizing the consumption of agrochemicals, particularly nitrogen, is the ultimate goal for achieving sustainable agricultural production with low cost and high economic and environmental returns. The use of biopolymers instead of petroleum-based synthetic polymers for CRFs can significantly improve the sustainability of crop production since biopolymers are biodegradable and not harmful to soil quality. Lignin is one of the most abundant biopolymers that naturally exist.In this study, controlled-release fertilizers were developed using a biobased nanocomposite of lignin and bentonite clay mineral as a coating material for urea to increase nitrogen use efficiency. Five types of controlled-release urea (CRU) were prepared using two ratios of modified bentonite as well as techniques. The efficiency of the five controlled-release nano-urea (CRU) fertilizers in improving the growth of tomato plants was studied under field conditions. The CRU was applied to the tomato plants at three N levels representing 100, 50, and 25% of the recommended dose of conventional urea. The results showed that all CRU treatments at the three N levels significantly enhanced plant growth parameters, including plant height, number of leaves, fresh weight, and dry weight, compared to the control. Additionally, most CRU fertilizers increased total yield and fruit characteristics (weight, length, and diameter) compared to the control. Additionally, marketable yield was improved by CRU fertilizers. Fruit firmness and acidity of CRU treatments at 25 and 50% N levels were much higher than both the 100% CRU treatment and the control. The vitamin C values of all CRU treatments were lower than the control. Nitrogen uptake efficiencies (NUpE) of CRU treatments were 47-88%, which is significantly higher than that of the control (33%). In conclusion, all CRU treatments at an N level of 25% of the recommended dose showed better plant growth, yield, and fruit quality of tomatoes than the conventional fertilizer.

Soil Microbial Co-Occurrence Patterns under Controlled-Release Urea and Fulvic Acid Applications.

The increasing amount of agricultural applications of controlled-release urea (CRU) and fulvic acids (FA) demands a better understanding of FA’s effects on microbially mediated nitrogen (N) nutrient cycling. Herein, a 0–60 day laboratory experiment and a consecutive pot experiment (2016–2018) were carried out to reveal the effects of using CRU on soil microbial N-cycling processes and soil fertility, with and without the application of FA. Compared to the CRU treatment, the CRU+FA treatment boosted wheat yield by 22.1%. To reveal the mechanism of CRU+FA affecting the soil fertility, soil nutrient supply and microbial community were assessed and contrasted in this research. From 0–60 days, compared with the CRU treatment, leaching NO3−-N content of CRU+FA was dramatically decreased by 12.7–84.2% in the 20 cm depth of soil column. Different fertilizers and the day of fertilization both have an impact on the soil microbiota. The most dominant bacterial phyla Actinobacteria and Proteobacteria were increased with CRU+FA treatment during 0–60 days. Network analysis revealed that microbial co-occurrence grew more intensive during the CRU+FA treatment, and the environmental change enhanced the microbial community. The CRU+FA treatment, in particular, significantly decreased the relative abundance of Sphingomonas, Lysobacter and Nitrospira associated with nitrification reactions, Nocardioides and Gaiella related to denitrification reactions. Meanwhile, the CRU+FA treatment grew the relative abundance of Ensifer, Blastococcus, and Pseudolabrys that function in N fixation, and then could reduce NH4+-N and NO3−-N leaching and improve the soil nutrient supply. In conclusion, the synergistic effects of slow nutrition release of CRU and growth promoting of FA could improve the soil microbial community of N cycle, reduce the loss of nutrients, and increase the wheat yield.

Increase in yield and nitrogen use efficiency of double rice with long-term application of controlled-release urea

Controlled-release urea (CRU) has better characteristics than conventional urea for synchronizing nitrogen (N) release with plant uptake. Understanding the effects of CRU on crop yield and N use efficiency (NUE) has long been the key to evaluate the performance of CRU. A long-term experiment over five consecutive years was conducted in Changsha, Hunan Province, China, to investigate the effects of polyethylene-coated urea with a 90-d release period on the yield and NUE of double rice (early and late crops are grown in the same year), the amount of residual soil mineral N and the soil–plant N balance, as well as on the economic benefits. Four N fertilizer treatments including CK (no N fertilizer), U (conventional urea), CRU1 (polyethylene-coated urea with equal N application rate to U) and CRU2 (20% reduction in N application rate of CRU1) were established. The results indicated that CRU1 application increased the yield and NUE of double rice by 11.0 and 13.5%, respectively, compared with U. Higher yield and NUE of late rice were found than in early rice in CRU treatments. Compared with conventional U, the yield and NUE of early rice in the CRU1 treatment were increased by 6.0 and 10.2%, respectively, and those of late rice were increased by 15.4 and 13.8%, respectively. There was no significant difference between CRU1 and CRU2 in double rice yield. Furthermore, CRU treatments (including CRU1 and CRU2) had higher apparent residual Nmin rate (ARNR) and apparent N recovery rate (ANRR), but lower apparent N loss (NS) than the conventional U treatment. Concentrations of NH4+-N and NO3–-N were greater in the surface soil (0–20 cm) and lower in the deeper soil layer (40–60 cm) with CRU treatments than in the U treatment after harvest. Moreover, CRU application produced a greater economic benefit than conventional U application. In general, CRU outperformed U fertilizer in terms of rice yield, NUE, soil–plant N balance, economic benefit, and CRU2 provided greater comprehensive benefits than CRU1. It is suggested that CRU application is beneficial for solving N management challenges in the production of rice.

Optimal Blends of Controlled-Release Urea and Conventional Urea Improved Nitrogen Use Efficiency in Wheat and Maize with Reduced Nitrogen Application

Blending controlled-release urea (CRU) with conventional urea has the potential to be an effective option for improving nitrogen (N) use efficiency (NUE), although determination of optimal blends in combination with a reduced N application rate has not been well studied. A field experiment was conducted to compare the effects of CRU (a mixture of polymer-coated urea and urea with N ratios of 100:00, 75:25, and 50:50 at 144 kg N ha−1, hereafter denoted as CRU1, CRU2, and CRU3, respectively), urea at 180 (U1) and 144 kg N ha−1 (U2) and a control (no N fertilizer applied, CK) on grain yield, NUE, and economic benefits in a wheat–maize rotation system. The CRU treatments were one-time applied, while for the U treatments, fertilizer N was applied in a split application. The results suggest that a one-time application of CRU prior to sowing of both crops fulfilled the demand of crop plants for N across the entire growth period. Relative to U1, the CRU treatments achieved approximately the same grain yield and 4.7–26.6% greater NUE at 20% reduced N application. Moreover, under CRU2, the yield, NUE, and economic benefits were increased by 12.2%, 9.7%, and 19.1%, respectively, for wheat, and under CRU3, they were increased by 10.9%, 20.6%, and 17.3%, respectively, for maize, compared with the U2 treatment. These results demonstrate that a mixture of CRU and urea at a ratio of 75:25 for wheat and 50:50 for maize with a 20% reduction in N application rate can maintain productivity, while enhancing NUE in the North China Plain.

Controlled-release urea improved rice yields by providing nitrogen in synchrony with the nitrogen requirements of plants.

Excessive application of nitrogen (N) fertilizer and low nitrogen-use efficiency (NUE) are prevalent problems in rice production. Controlled-release urea (CRU) is widely adopted to increase rice yields, but the synchronicity of N release from CRU with uptake of N by plants has rarely been studied. A 2-year field experiment involving CRU and urea applications at three different N rates (240, 192 and 144 kg N ha-1 , equal to 100%, 80% and 60% of the recommended rate, respectively) was performed to compare their effects on N uptake, soil N content and rice yields. The successive release curves of CRU in the soil matched the corresponding N uptake curves of rice plants, and significant linear correlations were observed. Grain yield and N uptake under the CRU treatment increased by 5.25-7.88% and 7.13-17.94% than urea treatments, at the same N rate, and no obvious difference was found between CRU60% and Urea100%. CRU80% and CRU60% presented the highest NUE. The contents of ammonium-nitrogen (NH4 + -N), nitrate-nitrogen (NO3 - -N), and total N and the chlorophyll relative value - SPAD (Soil Plant Analysis Development) values - of the leaves under the CRU treatments were significantly higher than those under the urea treatments from heading to harvest. The contents of exchangeable sodium ion (Na+ ) and calcium ion (Ca2+ ) and the cation exchange capacity increased in response to CRU. CRU increased rice yields by providing N strongly in synchrony with the N requirements of the plants, and applying CRU at 192 kg N ha-1 was an effective strategy to conserve N fertilizer, increase soil N contents and enhance NUE. © 2021 Society of Chemical Industry.

控释尿素和普通尿素配比对不同氮效率玉米叶片衰老特性和土壤酶活性的影响

控释尿素和普通尿素配比施用可以同步玉米氮素需求，延缓后期衰老，增加产量。本试验以黄淮海区域两种氮效率玉米作为对象，研究控释尿素和普通尿素不同配比对其叶片衰老特性、土壤酶活性和土壤无机氮的影响。试验选取黄淮海主栽玉米品种豫禾988（氮低效）和郑单958（氮高效）作为试验材料，设置6个施氮处理（CK、N180U、N180C1、N180C2、N180C、N300U），其中CK为不施氮处理，180、300代表施氮水平分别为180 kg/hm²和300 kg/hm²，U代表全尿素处理（基肥：追肥=2：3），C1、C2分别代表控释氮：尿素氮为1：2和2：1（基肥一次施用），C代表全控释尿素处理（基肥一次施用）。2018-2019年结果表明：与CK相比，豫禾988在N180C1和郑单958在N180C2处理下，能够在玉米生育后期显著提高穗位叶超氧化物歧化酶（SOD）和过氧化物酶（POD）活性，降低膜脂过氧化物（MDA）含量，同时也增加了土壤无机氮含量、脲酶和蔗糖酶活性。综上所述，针对不同氮效率玉米品种，通过控释尿素和尿素合理配施，利用速效氮和控释氮的释放来延缓玉米功能叶片衰老，延长功能期，提高生育后期土壤无机氮含量和酶活性，共同促进玉米生长，增加玉米产量，其中豫禾988和郑单958分别在N180C1和N180C2处理下效果最佳。;Mixture of controlled release urea and urea one-application can synchronize the need of nitrogen requirement, postpone leaf senescence and increase yield for summer maize, coupling with labor saving, which will be the most effective way of nitrogen application in the future. In our experiment, two maize cultivars of different nitrogen efficiency were selected to study the effects of different ratios of controlled-release urea and urea on leaf senescence characteristics, soil inorganic nitrogen content, enzyme activity and yield of different maize varieties. Using cultivars YH988 and ZD958, which were mainly planted cultivars in Huang Huaihai Plain as test materials, 6 treatments (CK, N180U, N180C1, N180C2, N180C, and N300U) were set up, of which CK was no nitrogen treatment, 180 and 300 represented nitrogen application levels of 180 kg/hm² and 300 kg/hm², respectively. U stands for total urea treatment (basal nitrogen and top dressing was 2:3), C1 and C2 stand for the controlled release urea:ordinary urea being 1:2 and 2:1 (basal nitrogen one-application), and C stands for full controlled release urea treatment (basal nitrogen one-application). The results during 2018 and 2019 showed that one-off application of the blend of controlled release urea (CRU) and urea (U) before sowing at 180 kg N hm^-2 was able to satisfy the N demand of a summer maize system with varieties YH988 and ZD958 in Huang Huaihai Plain. One-off application a mixture of CRU and urea with 1:2 and 2:1 of cultivars YH988 and ZD958 at 180 kg N hm^-2 achieved the highest yield, which indicated N180C1 and N180C2, respectively. During the maize growth period, comparing with CK treatment, the superoxide dismutase (SOD) and peroxidase (POD) activities of ear leaves increased significantly and the membrane lipid peroxides (MDA) content of ear leaves reduced significantly in treatment N180C1 and N180C2 for cultivars YH988 and ZD958, respectively, while also increasing soil inorganic nitrogen content, urease and sucrose enzyme activity in the post-silking stage for summer maize. In summary, for the two maize cultivars with different nitrogen efficiencies, optimizing the mixture of controlled-release urea and urea can delay the senescence of functional leaves of maize through the complementary effects of the release of urea in the early stage and the release of CRU in the later stage, prolong the functional period, and increase the soil inorganic nitrogen content and enzyme activity in the later growth period. The treatments N180C1 and N180C2 are most suitable for YH988 and ZD958, respectively.

Effects of controlled-release urea combined with fulvic acid on soil inorganic nitrogen, leaf senescence and yield of cotton

A split-plot field experiment was conducted in 2018–2019 to study the effects of nitrogen fertilizer types and fulvic acid (FA) rates on soil nitrogen and cotton growth. The nitrogen fertilizers included controlled-release urea (CRU) and urea, which were applied combined with three FA rates (90, 180 and 270 kg ha-1). The main plot was the nitrogen fertilizer type, and the subplot was the FA rate. The results showed that the lint yield of the FA180 treatment was 5.2–8.6% higher than the FA90 and FA270 treatments. Moreover, moderate FA application markedly improved the cotton leaf SPAD value (chlorophyll relative value), photosynthesis and chlorophyll fluorescence parameters compared with low and high FA rates. Replacing urea with CRU significantly increased the soil inorganic nitrogen and nitrogen use efficiency and also improved cotton fiber quality parameters. Meanwhile, the boll weight and seed yield of the CRU treatments were 1.5–8.4% and 3.3–19.1% higher, respectively, than the urea treatments. The interaction between nitrogen type and FA rate had a positive effect on cotton growth. Thus, the application of CRU combined with 180 kg ha-1 FA on cotton can not only improve the fiber quality and delay leaf senescence but also increase the yield and economic benefit.

Effects of controlled-release urea on nitrogen uptake characteristics and yield of double-cropping rice around Dongting Lake area

<p indent=0mm>The application of slow- and controlled-release fertilizer in rice production plays an important role in promoting the zero growth of fertilizer use and the sustainable development of agriculture in China. In this study, six consecutive years from 2013 to 2018 of controlled-release urea application in double-cropping rice in Hunan province were used to analyze the relationship between N uptake rate and N utilization in the above part of early- and late- rice in the main growth period by controlled-release urea application around the Dongting Lake district, and to explore the reasons for the sustained and stable yield increase of controlled-release urea on rice. The results showed that there was an obvious peak of N uptake rate in each stage of early rice by different N treatments, while N uptake in controlled-release urea (CRU) treatment was relatively delayed. And N accumulation was mainly from panicle initiation stage to heading stage, accounting for 35.31%–42.33%, followed by tillering stage to young panicle differentiation stage and heading stage to milk stage. Two obvious peaks of N uptake rates occurred in late rice from tillering stage to panicle initiation stage and from heading stage to milk stage, and the peak value was the highest at 1.0 CRU treatment. Large amount of N uptake from tillering stage to young panicle differentiation stage and heading stage to milk stage accounted for 35.92%–40.52% and 23.05%–24.58% of total amount of the whole growing period, respectively. Controlled-release urea could also significantly increase the yield of double-cropping rice, especially in early- and late- rice were treated with 0.9 CRU and 0.8 CRU respectively, and the yield increase of late rice was better than that of early rice with reduced application of controlled-release urea, and the N absorption efficiency, N agronomic efficiency and N partial productivity of early- and late- rice were significantly improved. The yield of early- and late-rice treated by CRU was significantly positively correlated with N accumulation and effective panicle number at panicle initiation stage, heading stage, milk stage and waxen stage, and the yield of late rice was significantly positively correlated with panicle length. The N accumulation of early and late rice at the panicle initiation stage was significantly negatively correlated with the agronomic and physiological rates of N fertilizer. The N partial productivity was significantly or significantly negatively correlated with the N accumulation of early rice at the panicle initiation stage, heading stage, milk stage and waxen stage, and significantly negatively correlated with the N accumulation at the heading stage of late rice. Therefore, application of controlled-release urea delayed the N uptake rate and N accumulation in the aboveground part of rice, which was beneficial to the later reproductive growth and seed setting, and could significantly improve the yield and nitrogen utilization efficiency of double-cropping rice. Combined with N absorption characteristics and grain yield of double-cropping rice, it was suggested that controlled release urea with a short release period should be used for early rice around the Dongting Lake area or applied with quick-availability N fertilizer to achieve further increase in yield level.

Impact of controlled-release urea on rice yield, nitrogen use efficiency and soil fertility in a single rice cropping system

Overuse of nitrogen (N) fertilizer has led to low N use efficiency (NUE) and high N loss in single rice cropping systems in southeast China. Application of controlled-release urea (CRU) is considered as an effective N fertilizer practice for improving crop yields and NUE. Here, field experiments were conducted during 2015–2017 to assess the effects of two CRUs (resin-coated urea (RCU) and polyurethane-coated urea (PCU)) on rice yields, NUE and soil fertility at two sites (Lincheng town (LC) and Xintang town (XT)). Four treatments were established at each site: (1) control with no N application (CK), (2) split application of conventional urea (U, 270 kg N ha−1), (3) single basal application of RCU (RCU, 216 kg N ha−1), and (4) single basal application of PCU (PCU, 216 kg N ha−1). The N application rate in the CRU treatment compared to the U treatment was reduced by 20%. However, the results showed that, compared to split application of urea, single basal application of CRU led to similar rice grain yields and aboveground biomass at both sites. No significant difference in the N uptake by rice plant was observed between the U and CRU treatments at either site. There were no significant differences in the N apparent recovery efficiency (NARE) among the U, RCU and PCU treatments, with the exception of that in XT in 2015. Compared to application of U, application of CRU increased the N agronomic efficiency (NAE) and N partial factor productivity (NPFP) by 17.4–52.6% and 23.4–29.8% at the LC site, and 15.0–84.1% and 23.2–33.4% at the XT site, respectively, during 2015–2017. Yield component analysis revealed that greater rice grain yield in response to N fertilizer was attributed mainly to the number of panicles per m2, which increased in the fertilized treatments compared to the CK treatment. The application of CRU did not affect the soil fertility after rice harvest in 2016. Overall, these results suggest that single basal application of CRU constitutes a promising alternative N management practice for reducing N application rates, time- and labor-consuming in rice production in southeast China.

Effects of Mixed Controlled Release Nitrogen Fertilizer with Rice Straw Biochar on Rice Yield and Nitrogen Balance in Northeast China

A 3-year fixed site experiment was carried out on a Planosol in Northeast China to study the effects of biochar and controlled-release nitrogen fertilizer on rice yield, nitrogen-use efficiency, residual nitrogen, and nitrogen balance in soil-crop system. Five treatments were established: control (CK), bare urea (BU), controlled-release urea (CRU), 50% BU + 50% CRU (MBC), and 50% BU + 50% CRU + biochar (MBCB) treatments. The results showed that, compared with the BU treatment, the yield, N-use efficiency (NUE) and N agronomic efficiency (NAE) of the CRU treatment increased by 12.2%, 33.9% and 4.3 kg kg−1, respectively; while the soil residual N and N surplus at harvest decreased by 11.6% and 10.7%, respectively. Compared with the MBC treatment, the yield, NUE and NAE of the MBCB treatment increased by 10.2%, 16.5% and 4.0 kg kg−1, respectively; while the soil residual N and N surplus at harvest decreased by 10.8% and 12.3%, respectively. Therefore, mixed application of bare urea, controlled-release urea and biochar was effective for obtaining high rice yield, and high fertilization efficiency as well as for sustainable agricultural development in Northeast China.

Effect of controlled-release urea fertilizers for oilseed rape (Brassica napus L.) on soil carbon storage and CO2 emission.

Fertilizer-induced CO2 emission is a primary driver of global warming. The experiment was used to study whether controlled-release urea (CRU) application in winter oilseed rape can play a positive role in mitigating CO2 emission and promoting C utilization by soil microorganisms. Five fertilizer types consisted of N0 (0 g N plant-1), conventional CRU application (CRU100%), monotypic CRU at the 80% of conventional rate (CRU80%), co-application of CRU with uncoated urea (CRC), and organic fertilizer (CRO). Results showed that soil CO2 fluxes were significantly affected by N fertilizer types after the start of the stem growing (P < 0.05). CO2 emissions typically peaked during the seed filling period, with the highest emission of 1.99 μmol m-2 s-1 being registered for CRU100%. CRU100% had 25.00%, 30.60%, and 4.17% greater CO2 emissions than CRU80%, CRC, and CRO practices by harvest, respectively. Compared to the conventional CRU treatment, CRU80% led to a lower root volume and root mass ratio than CRU100%, which could partly contribute to the reduced CO2 emission. Conversely, CRU80% performed better in N agronomic efficiency than that of CRU100% treatment. Also, C source utilization by soil microbiomes as well as microbial diversity indices following CRU80% along with CRO applications was substantially higher than that under the conventional CRU supply. These observations suggest that opportunity exists to maintain N balance by N fertilization practices to mitigate CO2 emission from cropland. Further, a close and positive relationship between soil total nitrogen and CO2 emission also supports this. CRO-treated soils substantially elevated the contents of total carbon and readily oxidation carbon over CK. Moreover, the enzyme activity of β-glucosidase in CRO soil was about twice as high as the CRU100%. Consequently, CRU amendments by decreasing CRU rate application and the incorporation of organic fertilizer into CRU have the potential for mitigating of CO2 emission and positive effect on the soil microbial functional diversity to improve nitrogen use efficiency of rapeseed.

The combined application of controlled-release urea and fulvic acid improved the soil nutrient supply and maize yield

ABSTRACT Controlled-release urea (CRU) and fulvic acid (FA) could improve nitrogen (N) use efficiency (NUE) and crop yield. This study aimed to reveal the synergistic interactions between CRU and FA on NUE, soil nutrient supply, and maize (Zea mays L.) yield. Here, we used no fertilizer for the control; low- or full-strength regular urea with or without FA (urea (U), U2/3, U+FA, U2/3+FA); and low or full-strength CRU with or without FA (CRU, CRU2/3, CRU+FA, CRU2/3+FA). Compared with U treatment, the maize yield, NUE and net returns of CRU and CRU+FA treatments were significantly increased, by 6.4%, 37.1%, and 11.5%, and 14.2%, 33.8%, and 24.7%, respectively; SPAD values were significantly increased after CRU, CRU+FA treatment, by 10.4% and 13.6%, respectively, at the 12-leaf collar (V12) stage. After CRU treatment, the NO3 –N content of was significantly increased by 14–28%; meanwhile, CRU+FA treatment increased significantly the NO3 –N content by 15–71% at the V12 and silking stages. When ammonia volatilization was maximal after U+FA treatment, the soil urease activity, nitrification, denitrification, and respiration levels were significantly improved by 25, 262, 370, and 428%, respectively. Based on these results, CRU+FA can be suggested as a new eco-friendly fertilizer that could improve maize yield.

Controlled‐Release Nitrogen Fertilizer Improved Lodging Resistance and Potassium and Silicon Uptake of Direct‐Seeded Rice

ABSTRACTLodging is a severe problem for rice (Oryza sativa L.) because it interferes with mechanical harvesting, and potentially results total crop loss. This study investigated whether a controlled‐release urea (CRU) could reduce lodging, improve the uptake of K and Si, and yields of direct‐seeded rice. The 2‐yr field experiment included four rates of CRU (120, 180, 240, and 360 kg N ha−1), each provided in one application; a conventional urea fertilizer provided in four applications (360 kg N ha−1 total); and a control with no N fertilizer. Results indicated that the N release rates from the CRUs were matched well to N uptakes by rice plants; hence, N use efficiencies were improved. Concentrations of K and Si in rice tissues were much higher for treatments with the full and reduced rates of CRU than for the full rate urea treatment. Lodging of rice only appeared to occur in the urea treatment. Microscopic examination revealed that cells of rice stems provided with CRU treatments were more resistant to lodging than stem cells from plants in the urea treatment.

Impacts of one-off fertilization on nitrogen leaching and economic benefits for rice-rape rotation system

One-off fertilization is a new technology of one-time applying base fertilizer near the rhizosphere during whole crop cultivation period. It has the advantages of simplifying fertilization manage-ment and reducing labor costs, but its impacts on environment, such as leaching characteristics need further analysis. We set five treatments in the typical rice-rape rotation system in the middle and lower reaches of the Yangtze River, including control treatment (CK), farmers' practice treatment (FP), optimal fertilizer treatment (OPT), one-off application of urea fertilizer treatment (UA) and one-off application of controlled release urea treatment (CRF). Using in situ leaching monitoring method, nitrogen (N) leaching characteristics at 90 cm depth of soil in rice-rape rotation system under different treatments were obtained, the impacts of one-off fertilization on N lea-ching were evaluated and its economic benefits were comprehensively analyzed. The results showed that the main forms of N in leachate were different for rape and rice. In the rape season, NO3--N was the major component of leachate, while for rice season NO3--N and NH4+-N were equally important. In the whole rotation period, the inorganic N leaching mainly occurred in the rice season, and compared with FP, OPT and UA, the total amount of inorganic N leached by CRF were significantly reduced by 33.7%, 20.8%, and 20.7%, respectively. However, the effects of different fertilization treatments on N leaching in rape season were not significantly different. Under the same N application rates, compared with OPT, UA ensured the stable yield of rape and rice and significantly increased the NAE in rape season by 15.1%, but failed to improve the NAE in rice season. There was no significant difference between OPT and CRF in rice yield and NAE, but rape yield and NAE of CRF significantly increased by 10.7% and 18.9%, respectively. From the economic front, compared with OPT, UA and CRFincreased rapeseed income by 3660 and 3048 yuan·hm-2, and rice income by 3162 and 2220 yuan·hm-2. Therefore, considering the effects of various fertilizer treatments on N leaching, crop yield, and economic benefits, one-off base fertilization application of controlled release fertilizer technology could ensure stable or increase crop yields, and improve farmers' income, while significantly reduce the inorganic N leaching loss. Such technology is recommended for future rice-rape rotation cultivation.

Application of Controlled-Release Urea Enhances Grain Yield and Nitrogen Use Efficiency in Irrigated Rice in the Yangtze River Basin, China

The use of controlled-release urea (CRU) has been recommended over that of conventional urea to improve rice grain yield and nitrogen use efficiency. However, the underlying agronomical and physiological mechanisms need to be better understood. In this study, field trials over four site-years, and a big container experiment were carried out to explore CRU effects on rice yield and NUE, with the main aims to identify the key yield components contributing to the superior rice yield with CRU use, and to evaluate differences in dry matter, nitrogen (N) accumulation, translocation and yield formation with different N fertilizer practices. Four N treatments were investigated: control with 0 kg N ha−1 (CK), farmers' fertilizer practice (FFP) with 150 kg N ha−1 as urea basal application, modified fertilizer practice (MFP) with 150 kg N ha−1 as split urea application (40% at transplanting, 30% at tillering and 30% at the panicle stages), and CRU treatment with 150 kg N ha−1 as CRU basal application. Results showed that the CRU increased rice yields by 10.8 and 5.6% over FFP and MFP, respectively. The N recovery efficiency and N agronomic efficiency for CRU were significantly higher than that obtained from MFP and FFP treatments. The analysis of yield components revealed that the higher grain yields using CRU were accounted for mainly by increased panicle and spikelet numbers per m2, which resulted from higher N uptake. In addition, results from the container experiment with comparable experimental design to field trials illustrated that both post-anthesis dry matter production and translocation were critical for high grain yields using CRU, while the former seemed more important. Relative to MFP and FFP, CRU maintained higher flag leaf SPAD and photosynthetic rate, as well as higher root oxidation activity (ROA) and N uptake during grain filling. Furthermore, CRU increased the activities of key enzymes involved in N assimilation in flag leaves, including GS, GOGAT, and NR. CRU effects on such underground and aboveground processes were proposed to contribute to high rice yield.

Reducing nitrogen fertilization of intensive kiwifruit orchards decreases nitrate accumulation in soil without compromising crop production

Excessive nitrogen (N) fertilization of high value horticultural crops is a common problem that not only increases the cost to farmers, but also negatively affects crop growth and the environment. A three-year field experiment was conducted in an intensive kiwifruit orchard in Shaanxi Province, China to compare the effects of reduced N fertilization applied as urea (U), and controlled release urea (CRU) on the N nutrition of kiwi vines, fruit yield and quality, and nitrate-N accumulation in the soil profile. The three treatments included a conventional N application rate (CF-U, 900 kg N ha−1 yr−1 as urea), two reduced N fertilization treatments where the amount of N fertilizer applied as U and CRU was reduced by 25% in 2013 and 2014, and by 45% in 2015. The 25 and 45% reduced N treatments had no adverse effects on the N concentrations in leaves and pruning branches and the fruit yield and quality of kiwi vines. However, they significantly enhanced the partial factor productivity of applied N (PFPN) and the economic benefits, and reduced nitrate accumulation in the 0–200 cm soil profile. The same benefits of reduced N fertilization were observed for both the U and CRU treatments, but the CRU treatment had the added benefit of decreasing the loss of nitrate through leaching. We concluded that the current level of N fertilization in kiwi orchards is very excessive, and reducing the N fertilizer rate by 25–45% could not only guarantee fruit yield, but also reduce N accumulation and loss.

Controlled-release urea reduced nitrogen leaching and improved nitrogen use efficiency and yield of direct-seeded rice

The use of controlled-release urea (CRU) has become one of best management practices for increasing crop yield and improving nitrogen (N) use efficiency (NUE). However, the effects of CRU on direct-seeded rice are not well understood while direct-seeding has gradually replaced transplanting due to increasing labor cost and lack of irrigation water. The objective of this two-year field experiment was to compare the effects of the CRU at four rates (120, 180, 240 and 360 kg N ha−1, CRU1, CRU2, CRU3 and CRU4, respectively) with a conventional urea fertilizer (360 kg N ha−1; U) and a control (no N fertilizer applied; CK) on yield, biomass, NUE of direct-seeded rice and soil nutrients. The results indicated that the successive release rates of N from CRU corresponded well to the N requirements of rice. The use of CRU3 and CRU4 increased rice grain yields by 20.8 and 28.7%, respectively, compared with U. In addition, the NUEs were improved by all CRU treatments compared to the U treatment. Concentrations of NO3−-N and NH4+-N in the soil were increased, especially during the later growth stages of the rice, and the leaching of N was reduced with CRU treatments. In conclusion, applying CRU on direct-seeded rice increased the crops yields and NUE, increased nitrogen availability at the late growth stages, and reduced N leaching.

Controlled release urea improved crop yields and mitigated nitrate leaching under cotton-garlic intercropping system in a 4-year field trial

Nitrogen fertilization is important for improving crop yields, but excessive amounts lead to high N losses through nitrate (NO3−-N) leaching. Controlled-release urea (CRU) has been shown to increase crop yields, yet the long term effects of CRU on soil NO3−-N distribution are not well known. A 4-year field experiment applied 50% (100kgha−1), 100% (200kgha−1) and 150% (300kgha−1) of the local practice N rates with CRU and urea was conducted under cotton-garlic intercropping system in Shandong Province, China. The linear increase in garlic yield and curvilinear increase in cotton yield indicates that crop yields increased as the input N rate increased with both urea and CRU while exceeded N application decreased cotton yields. The successive release of N from CRU permitted the meeting of the full N requirements of crops grown. Consequently, the lint cotton yield of CRU treatments was increased by 5.2%-17.3%, and garlic bulb yield increased by 2.0%-7.4%, compared with urea treatment. Although the CRU100% supplied one-third less N than Urea150%, the CRU100% produced −0.6%-5.6% more cotton, and −4.0%-2.6% more garlic than Urea150%. The NO3−-N contents of CRU treatments were augmented in 0–40cm soil, but the opposite trend was found in 60–100cm soil. The organic matter and total N contents in 0–40cm profile were increased with CRU fertilization over 4-year fertilization. However, no prominent difference of available P and K contents in 0–20cm soil was observed between CRU and urea treatments. Thus a one-third decrease in the recommended N application rate of urea is possible with CRU while maintaining crops yield, decreasing NO3−-N leaching to deep soil layer and preserving the soil fertility in North China plain.