Determination of optimum nitrogen application rates in Zhejiang Province,China, based on rice yields and ecological security

Excessive nitrogen(N) fertilization in intensive agricultural areas such as the plain region of South China has resulted in low nitrogen use efficiency and serious environmental problems. To determine the optimum N application rate, grain yield, apparent nitrogen recovery efficiency(ANRE), apparent N loss, and ammonium(NH_3) volatilization under different N application rates in the three years from 2012 to 2014 were studied. The results showed that the relationship between grain yields and N application rate in the three years were well fitted by quadratic equations. When N application rate reached 197 kg ha~(–1) in 2012, 199 kg ha~(–1) in 2013 and 196 kg ha~(–1) in 2014, the plateau of the grain yields appeared. With the increase of N application rate, the ANRE for rice decreased which could be expressed with sigmoidal equation; when N application rate was 305 kg ha~(–1) in 2012, 275 kg ha~(–1) in 2013 and 312 kg ha~(–1) in 2014, the curves of ANRE appeared turing points. Besides, the relationship between soil Nresidual and N application rate was fitted by the quadratic equation and the maximums of soil Nresidual were reached in the three years with the N application rate of 206, 244 and 170 kg ha~(–1), respectively. Statistical analysis indicated that NH3 volatilization and apparent N loss in three years all increased with the increasing N application rate. When the amount of NH3 volatilization increased to 11.6 kg N ha~(–1) in 2012, 40.5 kg N ha~(–1) in 2013 and 57.0 kg N ha~(–1)in 2014, the apparent N loss in the three years had obvious increase. To determine the optimum N application rate, the average N application on the plateau of the grain yield was considered as the lower limit while the average N application rate at the turning points of ANRE, the residual N in soil and apparent N loss was taken as the upper limit. According to the results in three years, the optimum N application rate for rice in Zhejiang was 197–255 kg ha~(–1).     

Review grain yield and nitrogen use efficiency in rice production regions in China

As one of the staple food crops, rice(Oryza sativa L.) is widely cultivated across China, which plays a critical role in guaranteeing national food security. Most previous studies on grain yield or/and nitrogen use efficiency(NUE) of rice in China often involved site-specific field experiments, or small regions with insufficient data, which limited the representation for the current rice production regions. In this study, a database covering a wide range of climate conditions, soil types and field managements across China, was developed to estimate rice grain yield and NUE in various rice production regions in China and to evaluate the relationships between N rates and grain yield, NUE. According to the database for rice, the values of grain yield, plant N accumulation, N harvest index(HIN), indigenous N supply(INS), internal N efficiency(IE_N), reciprocal internal N efficiency(RIE_N), agronomic N use efficiency(AE_N), partial N factor productivity(PEPN), physiological N efficiency(PE_N), and recover efficiency of applied N(RE_N) averaged 7.69 t ha~(–1), 152 kg ha~(–1), 0.64 kg kg~(–1), 94.1 kg kg~(–1), 53.9 kg kg~(–1), 1.98 kg kg~(–1), 12.6 kg kg~(–1), 48.6 kg kg~(–1), 33.8 kg kg~(–1), and 39.3%, respectively. However, the corresponding values all varied tremendously with large variation. Rice planting regions and N rates had significant influence on grain yield, N uptake and NUE values. Considering all observations, N rates of 200 to 250 kg ha~(–1) commonly achieved higher rice grain yield compared to less than 200 kg N ha~(–1) and more than 250 kg N ha~(–1) at most rice planting regions. At N rates of 200 to 250 kg ha~(–1), significant positive linear relationships were observed between rice grain yield and AE_N, PE_N, RE_N, IE_N, and PFPN, and 46.49, 24.64, 7.94, 17.84, and 88.24% of the variation in AE_N, PE_N, RE_N, IE_N, and PFPN could be explained by grain yield, respectively. In conclusion, in a reasonable range of N application, an increase in grain yield can be achieved accompanying by an acceptable NUE.     

Does nitrogen application rate affect the moisture content of corn grains?

Nitrogen fertilizer application is an important measure to obtain high and stable corn yield, and the moisture content of corn grains is an important factor affecting the quality of mechanical grain harvesting. In this study, four different nitrogen fertilizer treatments from 0 to 450 kg ha~(–1) pure nitrogen were set for a planting density of 12.0×10~4 plants ha~(–1) in 2017 and 2018, and 18 different nitrogen fertilizer treatments from 0 to 765 kg ha~(–1) pure nitrogen were set for planting densities of 7.5×10~4 and 12.0×10~4 plants ha~(–1) in 2019, to investigate the effect of nitrogen application rate on the moisture content of corn grains. Under each treatment, the growth of corn, leaf area index(LAI) of green leaves, grain moisture content, and grain dehydration rate were measured. The results showed that, as nitrogen application increased from 0 to 765 kg ha~(–1), the silking stage was delayed by about 1 day, the maturity stage was delayed by about 1–2 days, and the number of physiologically mature green leaves and LAI increased. At and after physiological maturity, the extreme difference in grain moisture content between different nitrogen application rates was 1.9–4.0%. As the amount of nitrogen application increased, the corn grain dehydration rate after physiological maturity decreased, but it did not reach statistical significance between nitrogen application rate and grain dehydration rate. No significant correlation was observed between LAI at physiological maturity and grain dehydration rate after physiological maturity. In short, nitrogen application affected the grain moisture content of corn at and after physiological maturity, however, the difference in grain moisture content among different nitrogen application rates was small. These results suggest that the effect of nitrogen application on the moisture content of corn grains should not be considered in agricultural production.     

Increased ammonification,nitrogenase, soil respiration and microbial biomass N in the rhizosphere of rice plants inoculated with rhizobacteria

Azospirillum brasilense and Pseudomonas fluorescens are well-known plant growth promoting rhizobacteria. However, the effects of A. brasilense and P. fluorescens on the N cycles in the paddy field and rice plant growth are little known. This study investigated whether and how A. brasilense and P. fluorescens contribute to the N transformations and N supply capacities in the rhizosphere, and clarified the effects of A. brasilense and P. fluorescens on the N application rate in rice cultivation. Inoculations with A. brasilense and P. fluorescens coupled with N application rate trials were conducted in the paddy field in 2016 and 2017. The inoculations of rice seedlings included four treatments: sterile saline solution(M_0), A. brasilense(Mb), P. fluorescens(Mp), and co-inoculation with a mixture of A. brasilense and P. fluorescens(Mbp). The N application rate included four levels: 0 kg N ha~(–1)(N_0), 90 kg N ha~(–1)(N_(90)), 180 kg N ha~(–1)(N_(180)), and 270 kg N ha~(–1)(N_(270)). The results indicated that the Mbp and Mp treatments significantly enhanced the ammonification activities in the rhizosphere compared with the M_0 treatment, especially for higher N applications, while the Mbp and Mb treatments greatly enhanced the nitrogenase activities in the rhizosphere compared with the M_0 treatments, especially for lower N applications. Azospirillum brasilense and P. fluorescens did not participate in the nitrification processes or the denitrification processes in the soil. The soil respiration rate and microbial biomass N were greatly affected by the interactions between the rhizobacteria inoculations and the N fertilizer applications. In the Mbp treatment, N supply capacities and rice grain yields showed no significant differences among the N_(90), N_(180), and N_(270) applications. The N application rate in the study region can be reduced to 90 kg N ha~(–1) for rice seedlings co-inoculated with a mixture of A. brasilense and P. fluorescens.     

Effects of nitrogen level on yield and quality of japonica soft super rice

Although studies on the balance between yield and quality of japonica soft super rice are limited, they are crucial for super rice cultivation. In order to investigate the effects of nitrogen application rate on grain yield and rice quality, two japonica soft super rice varieties, Nanjing 9108(NJ 9108) and Nanjing 5055(NJ 5055), were used under seven N levels with the application rates of 0, 150, 187.5, 225, 262.5, 300, and 337.5 kg ha~(–1). With the increasing nitrogen application level, grain yield of both varieties first increased and then decreased. The highest yield was obtained at 300 kg ha~(–1). The milling quality and protein content increased, while the appearance quality, amylose content, gel consistency, cooking/eating quality, and rice flour viscosity decreased. Milling was significantly negatively related with the eating/cooking quality whereas the appearance was significantly positively related with cooking/eating quality. These results suggest that nitrogen level significantly affects the yield and rice quality of japonica soft super rice. We conclude that the suitable nitrogen application rate for japonica soft super rice, NJ 9108 and NJ 5055, is 270 kg ha~(–1), under which they obtain high yield as well as superior eating/cooking quality.     

Effect of side deep placement of nitrogen on yield and nitrogen use efficiency of single season late japonica rice

Side deep placement of nitrogen plays an important role in improving rice yield and nitrogen use efficiency. Few studies have examined the effects of reducing the times of nitrogen(RTN) application and reducing the nitrogen rate(RNR) of application on rice yield and nitrogen use efficiency under side deep placement of nitrogen in paddy fields. Therefore, a field experiment of RNT and RNR treatments was conducted with nine fertilization modes during the 2018–2019 rice growing seasons in a rice–wheat cropping system of the lower reaches of the Yangtze River, China. Rice yield and nitrogen use efficiency were investigated under side deep placement of nitrogen. We found that under the same nitrogen application rate, the yield of RTN3 increased by 9.64 and 10.18% in rice varieties NJ9108 and NJ5718, respectively, compared with the farmers' fertilizer practices(FFP). The nitrogen accumulation of RTN3 was the highest at heading stage, at 11.30 t ha–1 across 2018 and 2019. Under the same nitrogen application rate, the N agronomic use efficiency(NAE), N physiological efficiency(NPE) and N recovery efficiency(NRE) of RTN3 were 8.1–21.28%, 8.51–41.76% and 0.28–14.52% higher than those of the other fertilization modes, respectively. RNR led to decreases in SPAD value, leaf area index(LAI), dry matter accumulation, nitrogen accumulation, and nitrogen use efficiency. These results suggest that RTN3 increased rice yield and nitrogen use efficiency under the side deep placement of nitrogen, and RNR1 could achieve the goals of saving cost and increasing resource use efficiency. Two fertilization modes RTN3 and RNR1 both could achieve the dual goals of increasing grain yield and resource use efficiency and thus are worth further application and investigation.     

Evaluation of nitrogen requirement and efficiency of rice in the region of Yangtze River Valley based on large-scale field experiments

Overestimation of nitrogen(N) uptake requirement is one of the driving forces of the overuse of N fertilization and the low efficiency of N use in China. In this study, we collected data from 1 844 site-years of rice(Oryza sativa L.) under various rotation cropping systems across the Yangtze River Valley. Selected treatments included without(N0 treatment) and with N application(N treatment) which were recommended by local technicians, with a wide grain range of 1.5–11.9 t ha–1. Across the 1 844 site-years, over 96% of the sites showed yield increase(relative yield105%) with N fertilization, and the increase rates decreased from 78.9 to 16.2% within the lowest range 4.0 to the highest 6.5 t ha–1. To produce one ton of grain, the rice absorbed approximately 17.8 kg N in the N0 treatment and 20.4 kg N in the N treatment. The value of partial factor productivity by N(PFP N) reached a range of 35.2–51.4 kg grain kg–1 with N application under the current recommended N rate. Averaged recovery rate of N(RE N) was above 36.0% in yields below 6.0 t ha–1 and lower than 31.7% in those above 6.0 t ha–1. Soil properties only affected yield increments within low rice yield levels(5.5 t ha–1). There is a poor relationship between N application rates and indigenous nitrogen supply(INS). From these observations and considering the local INS, we concluded there was a great potential for improvement in regional grain yield and N efficiency.     

Effects of nitrogen fertilizer and chemical regulation on spring maize lodging characteristics,grain filling and yield formation under high planting density in Heilongjiang Province,China

Now,lodging is a major constraint factor contributing to yield loss of maize (Zea mays L.) under high planting density.Chemical regulation and nitrogen fertilizer could effectively coordinate the relationship between stem lodging and maize yield,which significantly reduce lodging and improve the grain yield.The purpose of this study was to explore the effects of chemical regulation and different nitrogen application rates on lodging characteristics,grain filling and yield of maize under high density.For this,we established a field study during 2017 and 2018 growing seasons,with three nitrogen levels of N100 (100 kg ha~(–1)),N200 (200 kg ha~(–1)) and N300 (300 kg ha~(–1)) at high planting density (90 000 plants ha~(–1)),and applied plant growth regulator (Yuhuangjin,the mixture of 3% DTA-6 and 27% ethephon) at the 7th leaf.The results showed that chemical control increased the activities of phenylalanine ammonia-lyase (PAL),tyrosine ammonia-lyase (TAL),4-coumarate:Co A ligase (4CL),and cinnamyl alcohol dehydrogenase (CAD),and increased the lignin,cellulose and hemicellulose contents at the bottom of the 3rd internode,which significantly reduced the lodging percentage.The lignin-related enzyme activities,lignin,cellulose and hemicellulose contents decreased with the increase of nitrogen fertilizer,which significantly increased the lodging percentage.The 200 kg ha~(–1) nitrogen application and chemical control increased the number,diameter,angle,volume,and dry weight of brace roots.The 200 kg ha~(–1) nitrogen application and chemical control significantly increased the activities of ADP-glucose pyrophosphorylase (AGPase),soluble starch synthase (SSS) and starch branching enzyme(SBE),which promoted the starch accumulation in grains.Additional,improved the maximum grain filling rate (V_(max)) and mean grain filling rate (V_m),which promoted the grain filling process,significantly increased grain weight and grain number per ear,thus increased the final yield.     

Effect of biochar on grain yield and leaf photosynthetic physiology of soybean cultivars with different phosphorus efficiencies

This study was conducted with two soybean cultivars, Liaodou 13(L13, phosphorus(P)-efficient) and Tiefeng 3(T3, P-inefficient), to investigate the effects of biochar on soybean yield and photosynthetic physiological parameters, at four biochar application rates(0, 1, 5, and 10%, w/w), and two fertilization treatments(0 and 150 kg ha~(–1)). Grain yield, plant biomass, P accumulation, leaf net photosynthetic rate(P_n), chlorophyll index(Chl), nitrogen balance index(NBI), sucrose phosphate synthase(SPS), and sucrose synthase(SS) activities, soluble sugar, sucrose and starch contents, and leaf area duration(LAD) were measured. Biochar had positive effects on P_n, Chl, NBI, SPS, and SS activities, and leaf soluble sugar, sucrose, and starch contents of both genotypes, these effects increased with biochar application rate. L13 benefited more efficiently from biochar than T3 did, as the grain yield of L13 significantly increased by 31.0 and 51.0%, at 5 and 10% biochar, respectively, while that of T3 increased by 40.4 at 10% biochar application rate, as compared with controls. The combined application of biochar and fertilizer boosted the positive effects described, but no difference was found for grain yield in L13 among biochar application rates, while grain yield of T3 continually increased with biochar rate, among which, 1% biochar combined with 150 kg ha~(–1) fertilizer resulted in T3 yield increment of more than 23%, compared with the application of 150 kg ha~(–1) fertilizer alone. Altogether, our results indicated that the application of biochar enhanced carbon assimilation in soybean, resulting in increased biomass accumulation and yield. Differences in genotypic responses to biochar highlight the need to consider specific cultivars and biochar rate, when evaluating the potential responses of crops to biochar.     

Increased plant density and reduced N rate lead to more grain yield and higher resource utilization in summer maize

Planting at an optimum density and supplying adequate nitrogen(N) to achieve higher yields is a common practice in crop production, especially for maize(Zea mays L.); however, excessive N fertilizer supply in maize production results in reduced N use efficiency(NUE) and severe negative impacts on the environment. This research was conducted to determine the effects of increased plant density and reduced N rate on grain yield, total N uptake, NUE, leaf area index(LAI), intercepted photosynthetically active radiation(IPAR), and resource use efficiency in maize. Field experiments were conducted using a popular maize hybrid Zhengdan 958(ZD958) under different combinations of plant densities and N rates to determine an effective approach for maize production with high yield and high resource use efficiency. Increasing plant density was clearly able to promote N absorption and LAI during the entire growth stage, which allowed high total N uptake and interception of radiation to achieve high dry matter accumulation(DMA), grain yield, NUE, and radiation use efficiency(RUE). However, with an increase in plant density, the demand of N increased along with grain yield. Increasing N rate can significantly increase the DMA, grain yield, LAI, IPAR, and RUE. However, this increase was non-linear and due to the input of too much N fertilizers, the efficiency of N use at NCK(320 kg ha~(–1)) was low. An appropriate reduction in N rate can therefore lead to higher NUE despite a slight loss in grain production. Taking into account both the need for high grain yield and resource use efficiency, a 30% reduction in N supply, and an increase in plant density of 3 plants m~(–2), compared to LD(5.25 plants m~(–2)), would lead to an optimal balance between yield and resource use efficiency.     

Combined effect of shading time and nitrogen level on grain filling and grain quality in japonica super rice

There is limited information about the combined effect of shading time and nitrogen(N) on grain filling and quality of rice. Therefore, two japonica super rice cultivars, Nanjing 44 and Ningjing 3, were used to study the effect of shading time and N level on the characteristics of rice panicle and grain filling as well as the corresponding yield and quality. At a low N level(150 kg N ha~(–1), 150 N), grain yield decreased(by 21.07–26.07%) under the treatment of 20 days of shading before heading(BH) compared with the no shading(NS) treatment. These decreases occurred because of shortened panicle length, decreased number of primary and secondary branches, as well as the grain number and weight per panicle. At 150 N, in the treatment of 20 days of shading after heading(AH), grain yield also decreased(by 9.46–10.60%) due to the lower grain weight per panicle. The interaction of shading and N level had a significant effect on the number of primary and secondary branches. A high level of N(300 kg N ha~(–1), 300 N) could offset the negative effect of shading on the number of secondary branches and grain weight per panicle, and consequently increased the grain yield in both shading treatments. In superior grains, compared with 150 N NS, the time to reach 99% of the grain weight(T_(99)) was shortened by 1.6 to 1.7 days, and the grain weight was decreased by 4.18–5.91% in 150 N BH. In 150 N AH, the grain weight was 13.39–13.92% lower than that in 150 N NS due to the slow mean and the maximum grain-filling rate(GR_(mean )and GR_(max)). In inferior grains, grain weight and GR_(mean) had a tendency of 150 N NS150 N BH150 N AH. Under shaded conditions, 300 N decreased the grain weight due to lower GR_(mean) both in superior and inferior grains. Compared with 150 N NS, the milling and appearance qualities as well as eating and cooking quality were all decreased in 150 N BH and 150 N AH. Shading with the high level of 300 N improved the milling quality and decreased the number of chalky rice kernels, but the eating and cooking quality was reduced with increased chalky area and overall chalkiness. Therefore, in the case of short term shading, appropriate N fertilizer could be used to improve the yield and milling quality of rice, but limited application of N fertilizer is recommended to achieve good eating and cooking quality of rice.     

Irrigation water salinity and N fertilization:Effects on ammonia oxidizer abundance,enzyme activity and cotton growth in a drip irrigated cotton field

Use of saline water in irrigated agriculture has become an important means for alleviating water scarcity in arid and semi-arid regions. The objective of this field experiment was to evaluate the effects of irrigation water salinity and N fertilization on soil physicochemical and biological properties related to nitrification and denitrification. A 3×2 factorial design was used with three levels of irrigation water salinity(0.35, 4.61 and 8.04 d S m–1) and two N rates(0 and 360 kg N ha~(–1)). The results indicated that irrigation water salinity and N fertilization had significant effects on many soil physicochemical properties including water content, salinity, p H, NH_4-N concentration, and NO_3-N concentration. The abundance(i.e., gene copy number) of ammonia-oxidizing archaea(AOA) was greater than that of ammonia-oxidizing bacteria(AOB) in all treatments. Irrigation water salinity had no significant effect on the abundance of AOA or AOB in unfertilized plots. However, saline irrigation water(i.e., the 4.61 and 8.04 d S m–1 treatments) reduced AOA abundance, AOB abundance and potential nitrification rate in N fertilized plots. Regardless of N application rate, saline irrigation water increased urease activity but reduced the activities of both nitrate reductase and nitrite reductase. Irrigation with saline irrigation water significantly reduced cotton biomass, N uptake and yield. Nitrogen application exacerbated the negative effect of saline water. These results suggest that brackish water and saline water irrigation could significantly reduce both the abundance of ammonia oxidizers and potential nitrification rates. The AOA may play a more important role than AOB in nitrification in desert soil.     

Effect of wide-narrow row arrangement in mechanical pot-seedling transplanting and plant density on yield formation and grain quality of japonica rice

Mechanical pot-seedling transplanting is an innovatively developed transplanting method that has the potential to replace mechanical carpet-seedling transplanting. However, the initial pot-seedling transplanting machine lacked optimized density spacing and limited yield potential for japonica rice. Therefore, ascertaining the optimized density by wide-narrow rows and the appropriate transplanting method for yield formation and grain quality of japonica rice is of great importance for high-quality rice production. Field experiments were conducted using two japonica rice cultivars Nanjing 9108 and Nanjing 5055 under three transplanting methods in 2016 and 2017: mechanical pot-seedling transplanting with wide-narrow row(K, average row spacing of 30 cm); equidistant row(D, 33 cm×12 cm); and mechanical carpet-seedling transplanting(T, 30 cm×12.4 cm). In addition, five different density treatments were set in K(K1–K5, from 18.62×10~4 to 28.49×10~4 hills ha~(–1)). The results showed that the highest yield was produced by a planting density of 26.88×104 hills ha~(–1) in mechanical pot-seedling transplanting with wide-narrow row with a greater number of total spikelets that resulted from significantly more panicles per area and slightly more grain number per panicle, as compared with equidistant row, and yield among density in wide-narrow row showed a parabolic trend. Compared with mechanical carpet-seedling transplanting, the treatment of the highest yield increased yield significantly, which was mainly attributed to the larger sink size with improved filled-grain percentage and grain weight, higher harvest index, and increased total dry matter accumulation, especially the larger amount accumulated from heading stage to maturity stage. With the density in wide-narrow row decreasing, processing quality, appearance quality, and nutrition quality were all improved, whereas amylose content and the taste value were decreased. Compared with mechanical carpet-seedling transplanting, mechanical pot-seedling transplanting improved processing quality and nutrition quality, but decreased amylose content and deteriorated appearance quality. These results suggested that mechanical pot-seedling transplanting with wide-narrow row coupling produced a suitable planting density of 26.88×10~4 hills ha~(–1) and may be an alternative approach to improving grain yield and quality for japonica rice.     

Charactering protein fraction concentrations as influenced by nitrogen application in low-glutelin rice cultivars

To optimize both grain yield and quality of low-glutelin rice cultivars under N-fertilizer strategies, two-year field experiments involving three low-glutelin rice cultivars(W1240, W1721, W025) and an ordinary rice cultivar(H9405) with five N treatments were carried out to determine the effects of N application rate and genotype on protein fractions contents and Glutelin/Prolamin ratio(Glu/Pro). The difference of protein fraction concentrations affected by N application rate existed in genotypes. Ordinary rice cultivar had a larger increase in glutlein concentration affected by N application rate than low-glutelin rice cultivars did. Glutelin in H9405 had a increase of 30.6 and 41.0% under the N4 treatment(360 kg N ha~(–1)) when compared with N0 treatment(no fertilizer N) in 2010 and 2011 respectively, while all the low-glutelin rice cultivars showed relatively smaller increases for two years. Variance analysis showed no significant effect of N application rate on glutelin in W1240 and W025 while the effects on albumin, globulin and prolamin were significant in low-glutelin rice. What's more, N treatment had no significant i nfluence on Glu/Pro ratios in low-glutelin rice cultivars while a significant increase in Glu/Pro ratio was observed in ordinary rice cultivar. So low-gultelin rice cultivars showed a different pattern from ordinary rice cultivars when influenced by N application rate.     

Optimize nitrogen fertilization location in root-growing zone to increase grain yield and nitrogen use efficiency of transplanted rice in subtropical China

The optimized nitrogen fertilization location differs in different rice-growing regions. We optimized nitrogen deep-point application in root-growing zone(NARZ) for transplanted rice in subtropical China. Field plot experiments were conducted over two years(2014–2015) in a double-rice cropping system to evaluate the effects of nitrogen(N) fertilizer location on grain yield and N use efficiency(NUE). Four different nitrogen deep-point application methods(DN) were compared with traditional broadcast application(BN) using granular urea. The results showed that grain yield, recovery efficiency of N(REN), agronomic efficiency of N(AEN), and partial factor productivity of N(PFP_N) significantly increased 10.3–63.4, 13.7–56.7, 24.7–201.9 and 10.2–63.4%, respectively, in DN treatment compared to BN, respectively. We also find that DN treatments increased grain yield as well as grain N content, and thus grain quality, in comparison with conventional BN treatment. Correlation analysis indicated that significant improvement in grain yield and NUE mainly resulted from increases in productive panicle number and grain N content. In our proposed NARZ method, granular urea should be placed 0 to 5 cm around the rice seeding at a 12-cm depth druing rice transplanting. In NARZ, balanced application of N, P and K further improved grain yield and NUE over treatments with a single N deep-point application. High N uptake by the rice plant did not cause significant soil fertility depletion, demonstrating that this method could guarantee sustainable rice production.     

Increasing photosynthetic performance and post-silking N uptake by moderate decreasing leaf source of maize under high planting density

To date,little attention has been paid to the effects of leaf source reduction on photosynthetic matter production,root function and post-silking N uptake characteristics at different planting densities.In a 2-year field experiment,Xianyu 335,a widely released hybrid in China,was planted at 60 000 plants ha~(–1 )(conventional planting density,CD) and 90 000 plants ha~(–1) (high planting density,HD),respectively.Until all the filaments protruded from the ear,at which point the plants were subjected to the removal of 1/2 (T1),1/3 (T2) and 1/4 (T3) each leaf length per plant,no leaf removal served as the control(CK).We evaluated the leaf source reduction on canopy photosynthetic matter production and N accumulation of different planting densities.Under CD,decreasing leaf source markedly decreased photosynthetic rate (P_n),effective quantum yield of photosystem II (ΦPSII) and the maximal efficiency of photosystem II photochemistry (F_v/F_m) at grain filling stage,reduced post-silking dry matter accumulation,harvest index (HI),and the yield.Compared with the CK,the 2-year average yields of T1,T2 and T3 treatments decreased by 35.4,23.8 and 8.3%,respectively.Meanwhile,decreasing leaf source reduced the root bleeding sap intensity,the content of soluble sugar in the bleeding sap,post-silking N uptake,and N accumulation in grain.The grain N accumulation in T1,T2 and T3 decreased by 26.7,16.5 and 12.8% compared with CK,respectively.Under HD,compared to other treatments,excising T3 markedly improved the leaf P_n,ΦPSII and F_v/F_m at late-grain filling stage,increased the post-silking dry matter accumulation,HI and the grain yield.The yield of T3 was 9.2,35.7 and 20.1% higher than that of CK,T1 and T2 on average,respectively.The T3 treatment also increased the root bleeding sap intensity,the content of soluble sugar in the bleeding sap and post-silking N uptake and N accumulation in grain.Compared with CK,T1 and T2 treatments,the grain N accumulation in T3 increased by 13.1,40.9 and 25.2% on average,respectively.In addition,under the same source reduction treatment,the maize yield of HD was significantly higher than that of CD.Therefore,planting density should be increased in maize production for higher grain yield.Under HD,moderate decreasing leaf source improved photosynthetic performance and increased the post-silking dry matter accumulation and HI,and thus the grain yield.In addition,the improvement of photosynthetic performance improved the root function and promoted postsilking N uptake,which led to the increase of N accumulation in grain.     

How plant density affects maize spike differentiation,kernel set,and grain yield formation in Northeast China?

A two-year field experiment was conducted to evaluate the effects of plant density on tassel and ear differentiation, anthesissilking interval(ASI), and grain yield formation of two types of modern maize hybrids(Zhongdan 909(ZD909) as tolerant hybrid to crowding stress, Jidan 209(JD209) and Neidan 4(ND4) as intolerant hybrids to crowding stress) in Northeast China. Plant densities of 4.50×104(D1), 6.75×104(D2), 9.00×104(D3), 11.25×104(D4), and 13.50×104(D5) plants ha~(-1) had no significant effects on initial time of tassel and ear differentiation of maize. Instead, higher plant density delayed the tassel and ear development during floret differentiation and sexual organ formation stage, subsequently resulting in ASI increments at the rate of 1.2–2.9 days on average for ZD909 in 2013–2014, 0.7–4.2 days for JD209 in 2013, and 0.5–3.7 days for ND4 in 2014, respectively, under the treatments of D2, D3, D4, and D5 compared to that under the D1 treatment. Total florets, silking florets, and silking rates of ear showed slightly decrease trends with the plant density increasing, whereas the normal kernels seriously decreased at the rate of 11.0–44.9% on average for ZD909 in 2013–2014, 2.0–32.6% for JD209 in 2013, and 9.7–28.3% for ND4 in 2014 with the plant density increased compared to that under the D1 treatment due to increased florets abortive rates. It was also observed that 100-kernel weight of ZD909 showed less decrease trend compared that of JD209 and ND4 along with the plant densities increase. As a consequence, ZD909 gained its highest grain yield by 13.7 t ha~(-1) on average at the plant density of 9.00×104 plants ha~(-1), whereas JD209 and ND4 reached their highest grain yields by 11.7 and 10.2 t ha~(-1) at the plant density of 6.75×104 plants ha~(-1), respectively. Our experiment demonstrated that hybrids with lower ASI, higher kernel number potential per ear, and relative constant 100-kernel weight(e.g., ZD909) could achieve higher yield under dense planting in high latitude area(e.g., Northeast China).     

Non-leguminous winter cover crop and nitrogen rate in relation to double rice grain yield and nitrogen uptake in Dongting Lake Plain,Hunan Province,China

Annual ryegrass(Lolium multiflorum Lam.), a non-leguminous winter cover crop, has been adopted to absorb soil native N to minimize N loss from an intensive double rice cropping system in southern China, but a little is known about its effects on rice grain yield and rice N use efficiency. In this study, effects of ryegrass on double rice yield, N uptake and use efficiency were measured under different fertilizer N rates. A 3-year(2009–2011) field experiment arranged in a split-plot design was undertaken. Main plots were ryegrass(RG) as a winter cover crop and winter fallow(WF) without weed. Subplots were three N treatments for each rice season: 0(N_0), 100(N_(100)) and 200 kg N ha–1(N_(200)). In the 3-year experiment, RG reduced grain yield and plant N uptake for early rice(0.4–1.7 t ha–1 for grain yield and 4.6–20.3 kg ha–1 for N uptake) and double rice(0.6–2.0 t ha–1 for grain yield and 6.3–27.0 kg ha–1 for N uptake) when compared with WF among different N rates. Yield and N uptake decrease due to RG was smaller in N_(100) and N_(200) plots than in N_0 plots. The reduction in early rice grain yield in RG plots was associated with decrease number of panicles. Agronomic N use efficiency and fertilizer N recovery efficiency were higher in RG plots than winter fallow for early rice and double rice among different N rates and experimental years. RG tended to have little effect on grain yield, N uptake, agronomic N use efficiency, and fertilizer N recovery efficiency in the late rice season. These results suggest that ryegrass may reduce grain yield while it improves rice N use efficiency in a double rice cropping system.     

Soil mineral nitrogen and yield-scaled soil N_2O emissions lowered by reducing nitrogen application and intercropping with soybean for sweet maize production in southern China

The increasing demand for fresh sweet maize(Zea mays L.saccharata)in southern China has prioritized the need to find solutions to the environmental pollution caused by its continuous production and high inputs of chemical nitrogen fertilizers.A promising method for improving crop production and environmental conditions is to intercrop sweet maize with legumes.Here,a three-year field experiment was conducted to assess the influence of four different cropping systems(sole sweet maize(SS),sole soybean(SB),two rows sweet maize-three rows soybean(S2B3)intercropping,and two rows sweet maize-four rows soybean(S2B4)intercropping),together with two rates of N fertilizer application(300 and 360 kg N ha~(–1))on grain yield,residual soil mineral N,and soil N_2O emissions in southern China.Results showed that in most case,intercropping achieved yield advantages(total land equivalent ratio(TLER=0.87–1.25)was above one).Moreover,intercropping resulted in 39.8%less soil mineral N than SS at the time of crop harvest,averaged over six seasons(spring and autumn in each of the three years of the field experiment).Generally,intercropping and reduced-N application(300 kg N ha~(–1))produced lower cumulative soil N_2O and yield-scaled soil N_2O emissions than SS and conventional-N application(360 kg N ha~(–1)),respectively.S2B4 intercropping with reduced-N rate(300 kg N ha~(–1))showed the lowest cumulative soil N_2O(mean value=0.61 kg ha~(–1))and yield-scaled soil N_2O(mean value=0.04 kg t~(–1))emissions.Overall,intercropping with reduced-N rate maintained sweet maize production,while also reducing environmental impacts.The system of S2B4 intercropping with reduced-N rate may be the most sustainable and environmentally friendly cropping system.     

Effects of Organic Manure Application with Chemical Fertilizers on Nutrient Absorption and Yield of Rice in Hunan of Southern China

To evaluate the effect of organic manure application with chemical fertilizers on rice yield and soil fertility under long-term double-rice cropping system, a six year field experiment was conducted continually in the paddy soil derived from Quaternary red clay in Hunan Province of southern China. Four different treatments, i.e., no nitrogen with chemical P and K （PK）, swine manure only （M）, N, P and K chemical fertilizers only （NPK）, and half chemical fertilizers combined with half swine manure （NPKM） with four replications were included. Each N, P and K application rate was the same at all the treatments （except the N application rate at PK） and N application rate was 150 kg N ha^-1. All fertilizers were applied to soil tillage layer with once application as baseal fertilizers. The nutrients uptake rate, grain yield, nitrogen use efficiency, and soil organic matter content at each treatment were investigated. The NPKM treatment achieved the highest mean annual yield of 12.2 t ha^-1 （68% higher than that of PK）. Higher dry matter accumulation and nutrients absorption were observed during the middle-late growth period in the NPKM treatment, with higher panicle number per unit and filled-grain number per panicle. Its average nitrogen use efficiency was 36.3% and soil organic matter increased by 18.5% during the experimental period in the NPKM treatment, which were significantly higher than those in the NPK treatment. Organic manure application with chemical fertilizers increased the yield and nitrogen use efficiency of rice, reduced the risk of environmental pollution and improved soil fertility greatly. It could be a good practical technique that protects the environment and raises the rice yield in this region.