Split Application Of Urea Research Articles

Blended controlled-release nitrogen fertilizer increases rice post-anthesis nitrogen accumulation, translocation and nitrogen-use efficiency.

One-time application of blended controlled-release nitrogen fertilizer (CRN) has the potential to solve the difficulty of top-dressing fertilizer in the cultivation of rice and reduce the cost of CRN fertilizer application. However, its effects on rice dry matter and nitrogen (N) accumulation and translocation, yield and N-use efficiency (NUE) remain uncertain. Field experiments were carried out at three sites (Mingguang, Chaohu, and Guichi) in the Yangtze River Delta in China to compare the effects of the conventional split applications of urea and the blended CRN and on post-anthesis dry matter and N accumulation and translocation, yield, and NUE in rice at 0, 60, 120, 180, and 240kg N ha-1. The results showed that at the equal N application rates, compared under the conventional N fertilizer treatment, the blended CRN application significantly increased the rice yield by an average of 0.9-6.9%, mainly due to increase the number of spikelets per panicle. The highest yield achieved with blended CRN treatment occurred at 200kg N ha-1, with an NUE of 45.9%. Moreover, in comparison to the conventional N fertilizer, the blended CRN treatment increased pre-anthesis N translocation (Pre-NT) by 1.0-19.8%, and the contribution of pre-NT to grain N by 0.2-8.7%, and NUE by 3.2-28.4%. Meanwhile, the blended CRN treatment reduced labor costs by 1800 Yuan ha-1 and enhanced the economic gains by 21.5-68.8%. Therefore, one-time application of blended CRN ≤ 200kg N ha-1 application rate improved rice yield, NUE, and economic profit compared to equivalent rates of split applied conventional N fertilizers.

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.

The Long-Term Application of Controlled-Release Nitrogen Fertilizer Maintains a More Stable Bacterial Community and Nitrogen Cycling Functions Than Common Urea in Fluvo-Aquic Soil

Controlled-release nitrogen fertilizer (CRNF) has been proven to surpass common urea by mitigating nutrient losses, enhancing soil quality, and improving crop productivity. However, the long-term effects of CRNF on soil biological properties are not well understood. Here, a 12-year field experiment was conducted with five treatments: no N fertilizer (PK); the split application of urea at the farmer’s practice rate (FP) and the optimal rate (OPT); the one-time application of CRNF at the same rate as the OPT (CRNF); and a 20% reduced rate of the OPT (0.8CRNF). Soil samples were collected during the maize tasseling and filling stages; high-throughput sequencing and the PICRUSt2 method were employed to determine the bacterial community and its functional potential. The results showed that CRNF significantly increased alkaline hydrolysis N by 14.10% and 9.45% compared to OPT during the tasseling and filling stages, respectively. This increase in soil available N resulted in a significant increase in bacterial diversity of 2.09% and 2.35% compared with the FP and OPT, respectively. The bacterial community in the FP and OPT changed markedly between the tasseling and filling stages, with many bacterial species at the ASV and genus levels showing variations in relative abundance. In contrast, CRNF and 0.8CRNF exhibited stable N-cycling functions, as indicated by the lower variations in nitrate reductase and predicted N-cycling functional genes between the tasseling and filling stages. The obtained results suggest that CRNF application can enhance soil N supply, promote the formation of stable bacterial communities, and maintain stable N-cycling functions.

Suitable split nitrogen application increases grain yield and photosynthetic capacity in drip-irrigated winter wheat (Triticum aestivum L.) under different water regimes in the North China Plain.

Chemical fertilizer overuse is a major environmental threat, critically polluting soil and water resources. An optimization of nitrogen (N) fertilizer application in winter wheat (Triticum aestivum L.) in association with various irrigation scheduling is a potential approach in this regard. A 2-year field experiment was carried out to assess the growth, yield and photosynthetic capacity of drip-irrigated winter wheat subjected to various split applications of urea (240kg ha-1, 46% N). The eight treatments were, two irrigation scheduling and six N application modes in which, one slow-release fertilizer (SRF). Irrigation scheduling was based on the difference between actual crop evapotranspiration and precipitation (ETa-P). The two irrigation scheduling were I45 (Irrigation scheduling when ETa-P reaches 45mm) and I30 (Irrigation scheduling when ETa-P reaches 30mm). The six N levels were N0-100 (100% from jointing to booting), N25-75 (25% during sowing and 75% from jointing to booting), N50-50 (50% during sowing and 50% from jointing to booting), N75-25 (75% during sowing and 25% from jointing to booting), N100-0 (100% during sowing), and SRF100 (240kg ha-1, 43% N during sowing). N top-dressing application significantly (P<0.05) influenced wheat growth, aboveground biomass (ABM), grain yield (GY) and its components, photosynthetic and chlorophyll parameters, and plant nutrient content. According to the averages of the two winter wheat-growing seasons, the I45N50-50 and I45SRF100 treatments, respectively had the highest GY (9.83 and 9.5t ha-1), ABM (19.91 and 19.79t ha-1), net photosynthetic rate (35.92 and 34.59 µmol m-2s-1), stomatal conductance (1.387 and 1.223mol m-2s-1), SPAD (69.33 and 64.03), and chlorophyll fluorescence FV/FM (8.901 and 8.922). The present study provided convincing confirmation that N applied equally in splits at basal-top-dressing rates could be a desirable N application mode under drip irrigation system and could economically compete with the costly SRF for winter wheat fertilization. The I45N50-50 treatment offers to farmers an option to sustain wheat production in the NCP.

AEROBIC RICE'S YIELD PERFORMANCE AND NITROGEN USE EFFICIENCY UNDER VARIOUS NITROGEN FERTILIZER RATES

Aerobic rice, a water-saving cultivation system rice could thrive well in rain-fed areas in Sarawak which lacks in drainage and irrigation system, with appropriate fertilizer management practices. Since nitrogen (N) as a major determinant factor in rice yield is required differently based on cultivation system, soil and other in-situ conditions, a study was conducted to determine the optimum N fertilizer rate while assessing nitrogen use efficiency of aerobic rice in Lundu, Sarawak. Four N fertilizer rates (T1=0, T2=100, T3=200 and T4=300 kg N/ha) were tested with split application of urea (46% N) at 23%, 31%, and 46% at 5, 25, and 45 days after emergence (DAE) using MRIA1 variety. The findings indicated that an increase in N fertilizer of more than 100 kg N/ha had no discernible impact on yield. The highest yield recorded was 3.31 t/ha in T2 and decreased to 2.99 t/ha and 2.86 t/ha respectively in T3 and T4, while T1 recorded 1.12 t/ha. Meanwhile, significant differences in partial factor productivity (PFPN), agronomic efficiency (AEN), apparent recovery efficiency (REN) and physiological efficiency (PEN) were observed between the treatments with descending efficiency trends at higher N fertilizer rates. Optimum NUE values were recorded in T2 with PFPN = 29.30 kg/kg; AEN = 14.56 kg/kg; REN = 0.26 kg/kg; and PEN = 55.64 kg/kg. Therefore, it can be concluded that 100 kg N/ha is recommended for aerobic rice cultivation in Tanjung Purun, Lundu, as yield and NUEs were optimized.

Subsurface banding of blended controlled-release urea can optimize rice yields while minimizing yield-scaled greenhouse gas emissions

Controlled-release urea (CRU) is widely reported to supply crop nitrogen (N) demand with one basal application, thus effectively replacing split applications of urea without diminishing grain yield and N use efficiency (NUE). However, its use for replacement for high-yield split applications of urea (CK) for rice is untested. In addition, the degree to which greenhouse gas (GHG) emissions in rice systems are affected when CRU is substituted for CK remains unclear. During 2017 and 2018, we sampled plant growth and gas emissions in a rice paddy field treated with three CRU types (sulfur-coated urea [SCU], polymer-coated urea [PCU], and bulk blended CRU [BBU]) applied via two methods (surface broadcasting on the soil and subsurface banding at 5 cm depth), with CK as a control. The three CRUs led to different soil NH4+-N dynamics, and the N supply pattern under BBU was more beneficial for rice seedling establishment than under SCU and PCU, resulting in grain yield and NUE comparable to those under CK. CRU type showed no significant effect on either CH4 emissions or N2O emissions, and broadcast CRUs exhibited significantly higher total GHG emissions than CK. However, banded CRUs significantly reduced the total GHG emissions in comparison with broadcast CRUs, by 9.2% averaged across the two years. Reduced CH4 emissions, particularly during the period prior to the middle drainage, contributed largely to the GHG difference. With comparably high grain yield and low total GHG emissions, banded BBU showed a low yield-scaled GHG (GHG emissions divided by grain yield) comparable to that under CK in both years. Overall, our study suggested that N management synchronized with rice demand and contributing to a high NUE tended to minimize yield-scaled GHG. Broadcast CRU can hardly substitute for CK in terms of either grain yield or GHG emissions, but banded BBU is a promising N management strategy for sustaining rice production while minimizing environmental impacts.

Effects of mixed fertilizers formed by the compounding of two targeted controlled-release nitrogen fertilizers on yield, nitrogen use efficiency, and ammonia volatilization in double-cropping rice

One-time application of mixed fertilizer formed by the compounding of two controlled-release nitrogen fertilizers (CRUs) with targeted N supply during the periods from transplantation (TS) to panicle initiation (PI) and from PI to heading (HS) is expected to synchronize the double-peak N demand of rice. However, its effects on the yield and N use efficiency (NUE) of labor-intensive double-cropping rice were unknown. Two targeted CRU (CRUA and CRUB) were compounded in five ratios (CRUA: CRUB = 10:0, 7:3, 5:5, 3:7, and 0:10) to form five mixed fertilizers (BBFs): BBF1–5. A field experiment was performed to investigate the characteristics of N supply in early and late seasons under different BBFs and their effects on N uptake, yield, and ammonia volatilization (AV) loss from paddy fields of double-cropping rice. Conventional high-yield fertilization (CK, three split applications of urea) and zero-N treatments were established as controls. The N supply dropped significantly with the increased compound ratio of CRUB during the period from TS to PI, but increased during the period from PI to HS. With the exception of the period from TS to PI in the late rice season, the N uptake of early and late rice maintained close synchronicity with the N supply of BBFs during the double-peak periods. Excessive N supply (BBF1 and BBF2) in the late rice season during the period from TS to PI increased N loss by AV. The effect of BBF on grain yield increase varied widely between seasons, irrespective of year. Among the BBFs, the BBF2 treatment of early rice not only stabilized the spikelets per panicle but also ensured a high number of effective panicles by promoting N uptake during the period from TS to PI and a high grain-filling percentage by appropriately reducing the N supply at the later PI stage, resulting in the highest rice yield. While stabilizing the effective panicle number, the BBF4 treatment of late rice increased the number of spikelets per panicle by promoting N uptake during the period from PI to HS, resulting in the highest rice yield. The two-year average yield and apparent N recovery efficiency of the BBF2 treatment during the early rice season were 9.6 t ha−1 and 45.3%, while those of late rice in BBF4 were 9.6 t ha−1 and 43.0%, respectively. The yield and NUE indexes of BBF2 in early rice and BBF4 in late rice showed no significant difference from those of CK. The AVs of BBF2 during the early rice season and of BBF4 during the late rice season were 50.0% and 76.8% lower, respectively, than those of CK. BBF2 and BBF4 could effectively replace conventional urea split fertilization in early and late rice seasons, ensuring rice yield and NUE and reducing AV loss in paddy fields.

Modeling ammonia volatilization following urea and controlled-release urea application to paddy fields

• The WHCNS model performed well in simulating NH 3 flux measured by a continuous ventilation method. • Urea split application reduced the peak of NH 3 flux but increased total NH 3 loss. • Controlled-release urea application significantly reduced NH 3 loss compared to urea. • The controlled-release urea rate was recommended to reduce N loss without reducing yield. Ammonia volatilization, a main pathway of nitrogen (N) loss in paddy fields, can easily lead to environmental problems, such as haze and water eutrophication. Field measurement of ammonia volatilization is time-consuming and expensive. Soil–crop system models can simulate the effect of different fertilizer management practices on NH 3 volatilization and compensate for the limitations of field measurement. Therefore, the WHCNS (soil Water Heat Carbon Nitrogen Simulator) model was used to evaluate the feasibility of simulating NH 3 volatilization in paddy fields under different N fertilizer types and application methods. The field experiment, including four treatments of farmer’s practice (FP), basal application of urea in one dose (SBN), split application of urea in three doses (SPN), and basal application of controlled-release urea in one dose (CRU), was conducted from 2013 to 2014. All treatments were conducted with a fertilizer rate of 165 kg N ha −1 , except for FP with a rate of 210 kg N ha −1 . The measured dry matter weight, grain yield, N uptake, and NH 3 flux were used to test the WHCNS model. The model evaluation indices of Nash–Sutcliffe efficiency ( NSE ) and index of agreement ( d ) were close to 1 for the measured variables, except for NSE of yield (0.16). The normalized root mean square error ( NRMSE ) of NH 3 flux was slightly over 30%, but lower than 30% for the other items. Results showed that the model can successfully simulate rice yield and NH 3 flux of urea and controlled-release urea under different application methods. The simulated annual average cumulative NH 3 losses of FP, SBN, SPN, and CRU accounted for 18.9%, 17.8%, 20.6%, and 10.1% of their N inputs, respectively. Compared with the FP treatment, the ratios of NH 3 losses of the SBN and CRU treatments were decreased by 1.2%-8.8%. Compared with the SBN treatment (the same rate of 165 kg N ha −1 ), SPN reduced the peak of NH 3 flux but increased the cumulated NH 3 losses and CRU significantly reduced the NH 3 flux and cumulative NH 3 losses. The application rate of controlled-release urea could be further optimized by refined model calculations to reduce NH 3 volatilization and total N loss while maintaining yield.

Effects of Split Application of Urea on Greenhouse Gas and Ammonia Emissions From a Rainfed Maize Field in Northeast China

Split application of nitrogen (N) fertilizers during different crop growth stages to fulfill the crop N requirements reduces soil mineral N concentrations and improves the efficiency of crop N fertilizer use, and can decrease nitrous oxide (N2O) emission from the soil. However, inconsistent results regarding N2O emissions have been reported in rainfed areas. Furthermore, few long-term studies have explained the effects of split N application on soil methane (CH4) flux, thus limiting complete assessment of the effects of split N application on total greenhouse gas (GHG) emissions. Therefore, long-term monitoring is urgently required to understand the impacts of split N application on GHG emissions in rainfed areas. In this study, a 6-year field experiment was conducted in a rainfed maize (Zea mays L.) field in Northeast China. The experiment included three treatments: no N application representing control (CK), single application at the sowing stage of maize (SU), and split N at the sowing and jointing stages at a ratio of 1: 2 (SF). Between the sowing and jointing stages, N2O emissions were significantly higher in SU than in SF. However, high N2O emissions were observed in SF for 1 month after N application at the jointing stage possibly because the time of N application coincided with optimum precipitation and soil temperature conditions, which stimulated N2O emissions. Overall, the total N2O emissions showed no significant difference between SU and SF. During the study period, split application of N fertilizer did not significantly affect the cumulative CH4 flux. Compared to CK, the yield-scaled GWP in SF treatment increased by 18.7% (p &amp;lt; 0.05). Ammonia (NH3) volatilization in SF was 272% higher than that in SU. The findings indicated that split N application exhibited an environmental risk by increasing the yield-scaled GWP and NH3 emissions in the field. Thus, this study suggested that single N application applied in the sowing stage should be employed in rainfed fields to mitigate the yield-scaled GWP and NH3 emissions, and maintain efficient maize yields.

Evaluation of carbon, nitrogen footprint and primary energy demand under different rice production systems

Abstract Ground cover rice production system (GCRPS) has been widely proved to enhance rice yield and save irrigation water. However, information on the environmental impacts and energy consumption of GCRPS remains unknown. In this study, a two-year field experiment was conducted in Hubei Province of China including conventional paddy (W1) and GCRPS (W2, maintaining saturated soil water content; W3, maintaining 80% of the field capacity), factorially combined with different N management practices (N1, zero-N application; N2, single urea application; N3, split application of urea for W1 treatments; manure substitution for W2 and W3 treatments). By combining a soil-crop model simulation with a footprint analysis method, a life cycle inventory was built to evaluate yield-scaled carbon footprint (CF), nitrogen footprint (NF), and primary energy demand (PED) of different rice production systems. Results showed that, compared to conventional flooding paddy, GCRPSs significantly reduced CF, NF, and PED by 31%–35%, 37%–40%, and 17%–18% respectively. Across different N treatments under GCRPS, manure substitution reduced the CF (20%–22%), NF (11%–37%), and PED (25%–27%) compared to the single urea treatments. The hotspot’s contribution of N2O to CF, NH3 to NF, and N-fertilizer production to PED under GCRPS can be reduced by 77%, 33%, and 51% respectively compared to the single urea treatments. Therefore, W3N3 was recommended as the best management practice achieving less CF of 541.4 kg CO2 eq t−1, NF of 2.4 kg N eq t−1, and PED of 2440.0 MJ t−1 meanwhile maintaining high rice yield of 8526 kg ha−1 in the study region.

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.

Feasibility of stabilised nitrogen fertilisers decreasing greenhouse gas emissions under optimal management in sprinkler irrigated conditions

Stabilised nitrogen (N) fertilisers with nitrification and urease inhibitors have been proposed to abate greenhouse gas (GHG) emissions in agrosystems. Nevertheless, differences in their application and in the management of water and nitrogen rates make it difficult to evaluate their actual utility. The aim of this study was to analyse the possibility for GHG emissions reduction in a 3-year rotation (maize-maize-wheat) by substituting the traditional split-urea application to maize by a single side-dress application of stabilised urea fertiliser. The experiment was performed in 24 drainage lysimeters in two contrasting soil types (Shallow and Deep) under efficient irrigation practices and adjusted N rates under Mediterranean conditions. Nitrous oxide (N2O) and methane (CH4) were measured using static closed unvented chambers, and the soil mineral N was monitored through periodic soil samplings. CH4 emissions were generally negligible with occasional tendency the soil acting as a sink more than as a net source. Direct N2O emissions during the whole rotation showed lower values when a nitrification inhibitor (3,4-dimethylpyrazole phosphate) was added than with conventional urea (Deep soil: 73% lower, p < 0.05; Shallow soil: 60% lower, ns). Urease inhibitors (N-(n-butyl) thiophosphoric triamide and monocarbamide dihydrogen sulphate) could not abate direct N2O emissions, and their effect depended on the soil type. However, all stabilised fertilisers mitigated N2O emissions in Deep soil when scaled by grain yield (average 54%). Indirect N2O emissions associated with nitrate leaching were not affected by the treatments but contributed more to total N2O emissions in Shallow soil (12%) than in Deep soil (6%). These results suggest that adequate use of nitrification inhibitors could have environmental benefits without lessening agronomic production.

Effect of Split N-Fertilizer Application on Soil Quality and Maize Yield of Tropical Alfisol

A field experiment was conducted to determine the effect of split application of nitrogen fertilizer on soil properties and maize yield. Two sites at Apatapiti layout, South gate of the Federal University of Technology Akure were used as the experimental sites. The experiment was designed in a randomized-complete-block design arrangement with three replications. The treatments consisted of urea applied at four levels of split application (0kgha-1, 60kgha-1 basal application, 30kgha-1 basal application+ 30kgha-1 applied at 15 days after planting, 30kgha-1basal application + 20kgha-1applied at 15 days after planting + 10kgha-1applied at 30 days after planting). The plot size was 2 m x 2 m with 1 m space between plots and blocks. Maize (Zea mays L. var. TZB-SR) was planted at 75 cm by 25 cm spacing and 10 were sampled per unit for yield parameters. Split application of urea (30kgha-1basal application + 20kgha-1applied at 15 days after planting + 10kgha-1applied at 30 days after planting) significantly (p&gt;0.05) increased N content of the soil. There was no significant (p&gt;0.05) difference with regard to other nutrients. Soil pH was significantly (p&gt;0.05) reduced as a result of urea application in all treatments. Split urea fertilizer application retained a considerable amount of nitrogen in soil even after the harvest of maize. Exchangeable cations were not significantly different from one another as well as CEC. Split application of urea (30kgha-1basal application + 20kgha-1applied at 15 days after planting + 10kgha-1applied at 30 days after planting) gave the highest grain yield of maize for both sites. Also, plant biomass of both split application were better than the basal application and control.

Russet Potato Yield, Quality, and Nitrogen Uptake with Enhanced Efficiency Fertilizers

Core Ideas Irrigated russet potato yield and quality as influenced by the enhanced efficiency fertilizers. Effect of enhanced efficiency fertilizers in improving crop N uptake. Effect of enhanced efficiency fertilizers in improving fertilizer recovery and N use efficiency. Enhanced efficiency fertilizers (EEFs) are supposed to improve nitrogen use efficiency (NUE) of potato (Solanum tuberosum L.) by synchronizing N release from fertilizers and plant uptake. This experiment evaluated the performance of EEFs for tuber yield, quality, N uptake, apparent fertilizer recovery (AFR), and NUE under irrigated conditions. At Inkster, ND, during the summer of 2015 and 2016, six N treatments and three cultivars were laid out in a factorial randomized complete block design with four replications. Three russet potato cultivars (Russet Burbank, Dakota Trailblazer, and ND8068‐5Russ) were treated with six N treatments: (i) grower’s standard (urea) and two EEFs; (ii) SuperU; (iii) ESN; (iv) split application of urea, each at 280 kg N ha−1; (v) urea at 225 kg N ha−1; and (vi) check. The highest marketable tuber yield of 42.3 and 41.6 Mg ha−1 was obtained with urea 225 kg N ha−1 and ESN at 280 kg N ha−1 (38.7 Mg ha−1), respectively, in 2015 and 2016. In 2015, AFR ranged from 33.9 to 39.7%. In 2016, AFR with Russet Burbank reached 66.4%. Yield, quality, and NUE were not significantly improved with EEFs compared with urea or grower’s standard. Cultivar‐specific fertilizer recommendations should be developed.

Yield gap associated with crop management in wheat (Case study: Ardabil province-Parsabad Moghan)

TO INVESTIGATE the factors affecting irrigated wheat yield loss, compared to the attainable yield, a non systematic survey experiment was conducted in 60 fields in the city of Parsabad-Moghan, during two years 2013-2014 and 2014-2015 using Comparative Performance Analysis (CPA). Sampling of wheat fields was performed randomly from 5 different points of each farm using a square meter. All the information about management operations, soil and crop characteristics including seed bed preparation, planting date, varieties and their site preparation, seed rate, planting ways, weeds control ways, amount and timing of herbicides and fungicide use and wheat harvest time were recorded during a seasonal year using questionnaire. At the end of the seasonal year, the actual yield harvested by farmer’s was recorded. Among the various parameters, planting time, spike density, the number of split application of urea, land preparation operations, farmer experience and repeated use of fungicides had significant effects on wheat yield. The results showed that the average actual yield (6431.85kg/ha) and attainable yield (8749.27kg/ha), were different with a gap of 2317.42kg per hectare. The share of each of the factors were: Wheat planting time of yield gap 18%, spike density, 29%, the split application of urea 20%, land preparation operations 4.6%, farmer experience 14.3%, repeated use of fungicides 13.4%. The improvisation cases referred above can reduced yield gap and increase yield to more than 8.7ton/ha.

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.

Combined controlled-released nitrogen fertilizers and deep placement effects of N leaching, rice yield and N recovery in machine-transplanted rice

In the Taihu region of China, overuse of chemical nitrogen (N) fertilizer is often associated with low nitrogen recovery (NRE) and leads to serious groundwater pollution caused by N leaching losses. Controlled-released nitrogen fertilizers (CRNFs) and mechanized deep placement are promising alternatives to broadcasting urea to increase crop yield and NRE in machine-transplanted rice production. However, their interactions with regard to soil N status, N leaching and crop performance are unclear. A two-year (2015 and 2016) field experiment was conducted in a randomized complete block using two fertilization techniques (broadcast and deep placement by mechanical side-dressing fertilization) and three CRNFs (sulphur-coated urea (SCU), polymer-coated urea (PCU) and a bulk blended mixture (BBF)). Conventional high-yield fertilization (four split applications of urea at 216 kg N ha−1 (CK)) and 0–N treatments were established as controls. The results showed that the variation in NH4+-N concentration in the percolation and surface water varied across the different CRNFs, irrespective of the techniques used. NO3− -N concentration in the percolation water varied with water conditions in the field. Deep placement with CRNF correspondingly increased mineral N concentration in percolation at depths of 20 and 60 cm but reduced it in the surface water compared to that of the broadcast, although the benefits varied depending on the CRNF type and growth stage. Deep placement of SCU and PCU significantly increased N leaching and the mineral N in the 40–60 cm soil layer compared to that of the broadcast, due to the intensive N release during tillering and ineffective stage when the rice plant had a weak N uptake capability. Deep placement of SCU had the highest N leaching of 6.65 and 5.34 kg N ha−1 during 2015 and 2016. In contrast, BBF exhibited the lowest N leaching, regardless of fertilization placement, which apparently synchronized N release rates with rice N uptake patterns. In the present study, BBF obtained higher rice yields and N recoveries, without significantly enhancing mineral N leaching losses, when compared to CK. Our results suggest that the use of BBF is a promising alternative to a conventional high-yield fertilization practice, especially if combined with deep placement.

Urea-based fertilization strategies to reduce yield-scaled N oxides and enhance bread-making quality in a rainfed Mediterranean wheat crop

Urea fertilizer applications to calcareous soils can result in significant nitrous oxide (N2O) and nitric oxide (NO) emissions, predominantly via nitrification rather than denitrification. To address this, we explored several mitigation strategies based on improved urea management in a rainfed winter wheat (Triticum aestivum L.) crop during two consecutive cropping seasons with contrasting rainfall quantities and distribution. The strategies we investigated included the split application of urea at top dressing, the use of nitrification inhibitors (e.g. 2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture, DMPSA, and nitrapyrin), the urease inhibitor N-butyl thiophosphorictriamide (NBPT), or the double inhibitor DMPSA + NBPT. Emissions of N2O, NO, methane (CH4), as well as measurements of grain and straw yield and bread-making quality (protein content, reserve protein composition: glutenins and gliadins) were measured. Nitrogen (N) use efficiency (NUE) and N surplus were also calculated. Results were affected by rainfall, since the first cropping season experienced typical rainfall quantity and distribution, whilst the second cropping season was very dry, thus increasing significantly the yield-scaled emissions and N surplus, and markedly decreasing the NUE. In comparison to the single application of urea without inhibitors, all treatments generally decreased surface-scaled and yield-scaled emissions, with urea+DMPSA being the most effective and consistent mitigation option. Split urea and NBPT did not mitigate surface-scaled emissions in the dry cropping season, because of the marked peaks in N oxides after flowering, caused by inefficient crop N uptake. In the typical rainfall cropping season, the use of the double NBPT+DMPSA inhibitor led to the best balance between mitigation of yield-scaled N oxides emissions, N efficiency, crop yield and bread-making quality (i.e. increments in total protein, gliadins and glutenins). We did not observe any effect of nitrification inhibitors on grain yield (except in the dry cropping season) or the composition of gluten proteins. Our results suggest that the use of DMPSA with or without NBPT should be recommended to mitigate yield-scaled emissions of N oxides in rainfed semi-arid crops.

Effect of the Slow-Release Nitrogen Fertilizer Oxamide on Ammonia Volatilization and Nitrogen Use Efficiency in Paddy Soil

The effects of a single basal fertilization with oxamide compared with those of a split application of urea on ammonia volatilization, rice yield, nitrogen (N) accumulation, and N use efficiency were investigated in a field experiment over 2 years. The study consisted of two N fertilizers (oxamide and urea) applied at 157.5 and 225 kg N ha−1 and a no-N Control. Compared with urea, the single application of oxamide produced similar rice yields and reduced approximately 38.3% to 62.7% of the N lost through ammonia volatilization in 2013 and 2014. Oxamide applied at a rate of 225 kg N ha−1 resulted in greater aboveground accumulation of N by rice than the other treatments in both years, and oxamide fertilization resulted in the accumulation of an additional 15.2 kg N ha−1 and 15.3 kg N ha−1 compared to the amounts accumulated under the urea treatments at the same N application rates. N use efficiency was higher under oxamide than under urea treatment. In conclusion, the use of oxamide as a fertilizer can reduce N loss via ammonia volatilization, increase N use efficiency, and maintain a steady rice grain yield.

Improving nitrogen management for zero-tillage rice in China

Zero-tillage has become increasingly attractive in rice production in China. This study was conducted to determine the feasibility of two possible improved N management practices with fewer N applications in zero-tillage rice: (1) two split applications of urea at 75kgNha−1 at mid-tillering and 45kgNha−1 at panicle initiation (U120–2), and (2) a single application of cross-linked polyacrylamide-coated urea (a slow-release fertilizer) at mid-tillering at a rate of 150kgNha−1 (PCU150–1). Three field experiments were conducted to compare grain yield and N-use efficiency among several N treatments: a zero-N control (CK), U120–2, PCU150–1, a single application of urea at mid-tillering at a rate of 150kgNha−1 (U150–1), and a commonly recommended N management practice for conventional tillage rice (three split applications of urea with 75kgNha−1 as basal, 30kgNha−1 at mid-tillering, and 45kgNha−1 at panicle initiation) (U150–3). Treatments with N application (U120–2, PCU150–1, U150–1, and U150–3) produced 1.08–3.16tha−1 higher grain yields than CK. Grain yields under both U120–2 and PCU150–1 were comparable to that in U150–3. Recovery efficiency of N (REN), agronomic N-use efficiency (AEN) and partial factor productivity of applied N (PFPN) were increased under U120–2 and were similar under PCU150–1 to those under U150–3. U150–1 showed lower grain yield, REN, AEN, and PFPN than U150–3. These results suggest that U150–3 can be replaced with U120–2 to achieve both an increase in N-use efficiency and a reduction in number of N applications and or by PCU150–1 to achieve a maximum reduction in number of N applications in zero-tillage rice production in China.