Faxiang TIAN, Jian ZHU, Yunhe XIE,3, Hua PENG,3, Xionghui JI*

1. Soil and Fertilizer Institute of Hunan Province, Changsha 410125, China;

2. Key Laboratory of Agri-Environment in Midstream of Yangtze Plain, Ministry of Agriculture, Changsha 410125, China;

3. Longping Branch of Central South University, Changsha 410125, China

Nitrogen (N), phosphorus (P),and potassium (K) are three main macronutrients of rice,playing a key role in rice growth[1]. The rational distribution of fertilizers, therefore,improves fertility of paddy field[2-3]and increases biomass if rice organs,accelerating absorption and assimilation of Carbon and nitrogen in rice[4-5]and enhancing crop yield and quali ty[6-7].For example,Li et al.[3]researched that the application of N, P and K significantly improved organic matter and total N contents of soils and balanced fertilization of N,P and K was effective in restoring soil fertility of paddy fields[8].Huang et al.[9]conducted a comparative test on experimental plots and 49 fields for two years and the results showed that the yield of the treatment applied with N,P and K fertilizers grew by 491.0 kg/hm2compared with the treatment as per traditional cultivation,showing significant differences. Peng et al.[10]researched that the increased yield of early rice in the treatment applied with N,P and K was in the range of 8.2%-12.0% and of late rice in the range of 3.7%-12.1% compared with the control. It can be concluded that the application of N,P and K is of great significance for rice production, which guarantees a stable and high yield of rice[11].The formulated compound fertilizer takes advantages in many aspects, covering rich nutrients, rational proportions, high efficiency of fertilizer effect and use rate, and physical property, which is convenient for production, and avoids the blindness ofsingle-nutrient fertilizers. Therefore,the formulated compound fertilizer is much popular among agricultural departments, enterprises and farmers.Nevertheless, the application effects tend to be volatile upon types,the proportions of N, P and K, and prices of fertilizers,soil type,fertilization method and water management. The effect of different formula of NPK and top dressing on rice growth in typical double cropping rice area, which located at Kaihui, Ganshan, Matang and Xinqiang towns, were studied on field experiment in order to select the formula of compound fertilizer and top dressing mode for double cropping of rice production in Hunan.

Materials and Methods

Test site

The test site is located in typical double cropping rice area in Kaihui,Ganshan, Matang and Xinqiang towns,Hunan Province,and soils were paddy soils,sandy mud paddy and alluvial sandy soils developed from Quaternary red clays(Table 1).

Table 1 Soil physical and chemical properties in different experimental sites

Test materials and farming

The early rice included Zhongjiazao No.17 in Ganshan, local rice in Kaihui and Xiangzao indica rice in Yueyang and late rice were Yueyou No.9113 in Ganshan, Dangtaifengyou No.390 in Kaihui,and Yueyou No.9113 in Yueyang, respectively. Besides,early rice in Ganshan was grown in farmlands by transplanting, and seedlings in Kaihui and Matang were cultivated with soft trays by seedling broadcasting. Then, 7 -10 d after transplanting,tillering fertilizer was applied and ear fertilizer applied after 30 d. In contrast, late rice was cultivated in farmlands in Ganshan and Kaihui,by transplanting, and rice seedlings in Xinqiang were cultivated with soft trays by seedling broadcasting. Then, 7-10 d after transplanting, tillering fertilizer was applied and ear fertilizer applied after 30 d. Additionally, the density of early rice reached 375 000 plants/hm2in Ganshan by transplanting, 300 000 plants/hm2in Kaihui by seedling broadcasting, and 552 000 plants/hm2in Yueyang by seedling broadcasting.As for late rice, the transplanting density in Ganshan was 225 000 plants/hm2, 225 000 plants/hm2in Kaihui by seedling broadcasting, and 382 000 plants/hm2in Yueyang by seedling broadcasting.

Test design

The test designed 5 treatments,as follows: Treatment 1 was not applied with fertilizers. Treatment 2 included early rice applied with compound fertilizers (20-10-10)at 375.0 kg/hm2,followed by urea application at 150.0 kg/hm27-10 d after transplanting, and late rice applied with compound fertilizers (20-11-13)at 375.0 kg/hm2,followed by urea application at 146.7 kg/hm27-10 d after transplanting. Treatment 3 included early rice applied with formulated compound fertilizers (18-9-16) at 375.0 kg/hm2,followed by urea application at 150.0 kg/hm27 d after transplanting,and late rice applied with formulated compound fertilizers(18-14-16)at 375.0 kg/hm2,followed by urea application at 195.0 kg/hm27 -10 d after transplanting.Treatment 4 included early rice applied with formulated compound fertilizers(18-14-16) at 375.0 kg/hm2, followed by urea application at 150.0 kg/hm27-10 d after transplanting, and late rice applied with formulated compound fertilizers (18-9-16) at 375.0 kg/hm2,followed by urea application at 195.0 kg/hm27 -10 d after transplanting.Treatment 5 included early rice applied with formulated compound fertilizers(18-14-16) at 375.0 kg/hm2, followed by urea applications both at 75.0 kg/hm27-10 d after transplanting and 25-30 d after transplanting, and late rice applied with formulated compound fertilizers (18-9-16) at 375.0 kg/hm2,followed by urea applications at 90.0 and 105.0 kg/hm27-10 d after transplanting and 25-30 d after transplanting, respectively. The test set three replications, totaling 15 test plots, as per randomized block, and the test regions totaled 30 m2. The protection rows were dug surrounded and ridged in test regions.

Specifically,the compound fertilizers(20-10-10) applied in the control and urea(46%)applied as topdressing were both the fertilizer widely used locally. Besides, compound fertilizer(26-11-13),compound fertilizer (18-14-16) and compound fertilizer (18-9-16)were all provided by SACF.

Test management

In every test plot, fields were ridged in case of water loss or flowing.Furthermore,rice seedlings in different plots were irrigated exclusively, and the ridges should be 20 cm higher than farmlands. Besides, paddy fields were well prepared a week before farming,followed by planning. Then, farmlands were ridged firstly, and again after the ridge hardening,followed by mulching.

Early rice was fertilized after ploughing and urea was applied one week after well mixing of base fertilizer and soils. Late rice was applied with fertilizers after ploughing, followed by ploughing after early rice harvesting.Then,urea was applied after a week.

Irrigation and disease or insect damage prevention work should be the same as local methods. It is notable that farmlands should be dried timely and rice harvesting be conducted on time.

Statistics and analysis

The test data were analyzed with Excel and DPS.

Results and Analysis

The effects of optimized formulated fertilizers on early rice yield

As shown in Fig.1,compared with compound fertilizer (20-10-10), with N reduced by 5.2%, formulated compound fertilizers (18-9-16 and 18-14 -16) were optimized in Ganshan and Kaihui to guarantee a stable yield.In Matang,however,rice yield reduced by 300.0-718.5 kg/hm2, which is possibly caused by P shortage in Matang[12].It is clear that the effects of nitrogen reduction tended to be volatileon yield of early rice upon regions,and it is necessary to apply formulated fertilizers as per local situation. In general, the reduction of N fertilizer would maintain a stable yield for early rice in large scale in Hunan Province.

The investments of N and K kept the same of the treatments applied with optimized formulated compound fertilizers. With available P lower in soils, the application of P fertilizers would increase yield of early rice. For example, rice yields in the treatments(18-14-16) in Ganshan and Matang grew by 172.5 and 405.0 kg/hm2compared with the treatment(18-9-16).In the soils with higher content of available P,however, the yield of early rice changed insignificantly by applying more P fertilizers. For instance, the yield of rice maintained unchanged in Kaihui where the content of available P was 17.4 mg/kg. Therefore, more phosphorus should be applied in the soils with lower P availability for early rice. The proportion of P keeps higher in optimized formulated compound fertilizer which is much suitable for early rice in Hunan Province.

Table 2 The contents,accumulations and use rates of N in early and late rice in mature stage

Effects of optimized formulated fertilizers on yield of late rice

As shown in Fig.2,compared with compound fertilizer (26-11-13), with N reduced by 4.5%, rice yields maintained increasing in the three towns by applying optimized formulated compound fertilizers (18-14-16 and 18-9-16), of which the increased yields tended to be in the range of 225.0-285.0 kg/hm2in the fertilizer (18-14-16) and in the range of 187.5-378.0 kg/hm2by the fertilizer (18 -9 -16).These indicated that the optimized formulated compound fertilizer performed well in increasing yield of late rice.

The yields of late rice in Kaihui and Ganshan showed little differences by two optimized formulated compound fertilizer. In Xinqiang, late rice yield by formulated compound fertilizer(18-9-16) was higher compared with the formulated compound fertilizer(18-14-16). Generally speaking, the optimized formulated compound fertilizer (18-9-16) saves the investment of P, which actually increases farmers’ incomes, so that the fertilizer is suitable for late rice.

Effects of topdressings on tillering and booting stages of early and late rice

It is important for increasing rice yield and N fertilizer use rate to apply additional fertilizer. As shown in Fig.1 and Fig.2, the yields of early and late rice reached the highest in the treatment with twice topdressings in tillering and booting stages, respectively.Compared with the treatment with conventional compound fertilizer, with N fertilizer reduced by 7.5 kg/hm2, the yields of early and late rice grew by 177.0-205.5 and 537.0-756.0 kg/hm2,respectively. On the other hand, given specific quantities of nutrients and additional fertilizers,the yield of early rice in the treatment by twice topdressings in tillering and booting stages enhanced by 187.5-382.5 kg/hm2compared with the treatment with once topdressing in tillering stage and the yield of late rice grew by 258.0-415.5 kg/hm2.

Effects of different treatments on nitrogen content and N fertilizer use rate of early and late rice

As shown in Table 2, compared with the treatment with conventional compound fertilizer, with N fertilizer decreased by 7.5 kg/hm2of early and late rice, N contents of grains and straws changed insignificantly.Specifically,the accumulation of nitrogen declined a little of early rice, but increased of late rice, showing insignificant differences. As for N fertilizer userate, it dropped 0.2-4.6 and 0.9-7.0 points of early rice in Ganshan and Matang, and advanced 8.6-8.9 and 1.6-4.2 points of late rice in Ganshan and Xinqiang. Additionally, the contents of nitrogen in grains and straws,the accumulated quantities of nitrogen,and N fertilizer use rate all showed insignificant differences of the treatments with optimized formulated compound fertilizers.

Provided the quantity of additional fertilizer fixed, the treatment with twice topdressings improved remarkably in terms of N content compared with the treatment with once topdressing.Specifically, N contents of grain and straw of early advanced 0.16 -0.19 and 0.11-0.22 points,respectively;the accumulated quantities of nitrogen grew by 14.8 -31.8 kg/hm2; the use rate of N fertilizer advanced 10.9-24.2 points. In contrast, N contents of grain and straw advanced 0.04 -0.23 and 0.08 -0.10 points; the accumulated quantities of nitrogen increased by 12.9-21.2 kg/hm2; the use rate of N fertilizer advanced 8.3-13.4 points. It is obvious that twice topdressing is conductive to increasing N content,accumulation of nitrogen and use rate of N fertilizer of rice.

Conclusions and Discussions

Compared with conventional compound fertilizer, the optimized formulated compound fertilizer guarantees a stable yield of early rice and increases late rice yield in certain extent with N fertilizer reduced by 7.5 kg/hm2, which suggested that the compound fertilizers(18-14-16 and 18-9-16)are suitable for early and late rice in Hunan Province, respectively. With additional fertilizer quantity fixed, rational application of tillering and earing fertilizers improves yield, N content, nitrogen accumulation and fertilizer use rate of rice.

As testing soil for formulated fertilization advances,market demands is increasing on formulated compound fertilizer, and rational distribution of N,P and K has drawn attention widely.Hence,many researches are conducted on the aspect[13-17]. According to statistics of testing soil for formulated fertilization in 5 years by Hunan Soil and Fertilizer Station, the production of every 100 kg early rice consumes 2.30 kg pure N,0.94 kg P2O5,and 2.73 kg K2O, with a N-P2O5-K2O rate of 1 ∶0.41∶1.19 and of every 100 kg late rice consumes 2.39 kg pure N,0.86 kg P2O5and 2.71 kg K2O,with a N-P2O5-K2O rate of 1∶0.36∶1.13[18]. Most data come from “3415” fertilizer efficiency experiments, so that the data are reliable. It can be concluded from N, P and K proportions that early and late rice both have higher demands on N and K,though the demands tend to be volatile.In the research,both of the optimized formulated fertilizers (18-14-16 and 18-9-16) contain higher contents of N and K,whose N-to-K rate is significantly higher compared with the control(20-10-10 and 26-11-13),incorporating that the fertilizers meet double-cropping rice demands on nutrients, and suitable to be applied in double-cropping fields in Hunan.Additionally,considering from N-P-K proportions proposed by Hunan Soil and Fertilizer Station,early rice have higher demands on P than late rice, and the proportion of P should be improved for early rice with N and K proportions the same.Besides,the growing period of early rice in Hunan generally maintains cold at low temperature, so that activity of soil microbes is poor, and soil phosphorus transforms slowly.Consequently,P availability is lower of most soils[19-22], demanding investment of P. Therefore, the formula of N ∶P2O5∶K2O of 18∶14∶16 is more suitable for early rice in Hunan and the formula of N ∶P2O5∶K2O of 18 ∶9 ∶16 is suitable for late rice.

In addition, planning and management of N fertilizers is an important measure to get a high yield of rice.Zhao et al.[23]explored that the yield,net yield and output-to-input ratio all achieved the highest by three times topdressing, followed by the treatment with twice topdressings. Liu et al.[24]also investigated that with total N fixed,the increase of earing fertilizer increased protein contents of rice, improving rice quality. It is accepted that base fertilizer-tillering fertilizer-earing fertilizer of 4∶3∶3 is optimal, when accumulation of dry matter and dry weight of root reach higher, and dry matter accumulation keeps fast growing in later period[25].The research indicated that combined applications of base fertilizer, tillering fertilizer and earing fertilizer significantly enhanced rice yield,increased N content,and nitrogen accumulation compared withindividual application, as well as use rate of N fertilizer, because tillering fertilizer and earing fertilizer promote rice absorption on nutrients,accelerate tillering and ear development, and increase the number of ear, so that rice yield and N fertilizer use rate can be improved accordingly.

Currently, “once base fertilizer application and once topdressing”dominates double-cropping farmlands in most areas in Hunan Province[26-28],and topdressing is usually conducted 5-7 d after transplanting or seedling broadcasting. Nevertheless, because of such practice,chemical fertilizers,N fertilizer in particular, is too much in early stage,and the number of ineffective tillering increases. What’s worse,early aging might occur in ripening stage when chemical fertilizers are prone to be lost, resulting in waste of chemical fertilizer and low production benefits. Hence, topdressing can be increased to twice in order to accomplish a high yield, which controls excessive growth of rice before earing,and guarantees nutrient supply in later period.

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