Effects of Nitrogen-phosphorus-potassium Combined Fertilization on Rice Yield and Fertilizer Use E

Xiangping WANG Wei ZHOU Pubing ZHENG Guilan HUANG

Abstract    [Objectives]  This study was conducted to explore the rational formula for rice fertilization in Jianghan Plain.

[Methods] An experiment on the  combined  application of nitrogen， phosphorus and potassium fertilizers was carried out in Jianghan Plain， an important rice producing area in Hubei， with a total of five treatments to study the effects of nitrogen， phosphorus and potassium fertilizers on the fertilizer use efficiency and yield of rice.

[Results]  Fertilization had a significant effect on improving rice yield， and nitrogen fertilizer had the greatest effect on rice yield， followed by potassium fertilizer and phosphorous fertilizer.

[Conclusions] This study provides a scientific basis for the application of rice fertilizers and the reduction and efficiency improvement of chemical fertilizers in Jianghan Plain.

Key words   Rice; Nitrogen; Phosphorus; Potassium fertilizers; Fertilizer use efficiency; Yield

Hubei Province is the main rice producing area in China， and the rice area accounts for more than 50% of the cultivated land in the province  [1] . Rice production has low fixed asset investment， high labor cost， unstable land cost， high proportion of chemical fertilizer input， low contribution to scientific and technological progress  [2]  and large differences in the application amounts and formulas of fertilizers used by farmers， which ultimately affects the economic income of farmers  [3-4] . Relevant scholars have done a lot of research on the apparent use efficiency of fertilizers， agronomic efficiency of fertilizers， and physiological use efficiency of fertilizers， accurately analyzed the requirements of different crops for various nutrients， and scientifically guided farmers to apply fertilizers reasonably  [5-7] . Therefore， in this study， the effects of combined application of nitrogen， phosphorus and potassium fertilizers on rice yield and fertilizer use efficiency were investigated in Jianghan Plain， an important rice producing area in Hubei Province， aiming to provide a scientific basis for the application of rice fertilizers and the reduction and efficiency improvement of chemical fertilizers in Jianghan Plain.

Materials and Methods

General situation of the experimental location

The experiment was carried out from May to October 2020 in Gedan Village （30°41′16″ N; 113°35′40″ E）， Huangjiakou Town， Honghu City， southern Jianghan Plain， Hubei Province， and Jiangsikou Office （33°3′3″ N; 113o44′52″ E） in Datong Lake Management Area. The area is an important national commodity grain base， with an altitude of about 25 m， an annual average temperature of 20 ℃， and an annual rainfall of 1 310 mm. The main crops are rice， rape， and wheat. The previous crop in the experimental site was wheat， and the physicochemical properties of soil nutrients before rice planting are shown in Table 1. The contents of soil organic matter， alkali-hydrolyzable nitrogen， available phosphorus and available potassium in the experimental plots were moderately high. Comprehensive analysis of the experimental plots showed medium and high fertility， which could represent the nutrient status and productivity level of local farmland.

The tested rice varieties were Yanliangyou 1618 and Liangyou 240， which were bred by Jiangsu Coastal Agricultural Science  Research  Institute and Anhui Huayun Biotechnology Co.， Ltd. The tested fertilizers were urea （containing N 46%， produced by Hubei Sanning Chemical Co.， Ltd.）， calcium superphosphate （containing P2O5 12%， produced by Yichang Ruishuo Biotechnology Co.， Ltd.）， and potassium chloride （containing K2O 60%， Sinofert Co.， Ltd. distributed Canadian for production）.

Experimental design

The experiment adopted a completely randomized block design， with a total of 5 treatments， each having 3 repetitions. Each plot had an area of 4.0 m×5.0 m. The test density was 175 890 plants/hm 2 in Huangjiakou， where the seeds were sown on May 25， 2020， and the plants were transplanted on June 21 and harvested on October 22. The test density was 176 730 plants/hm 2 in Datong Lake， where the seeds were sown on May 25， 2020， and the plants were transplanted on June 24， and harvested on September 30. The sub-areas were separated by soil ridges and thin films. Each sub-area was provided with a separate irrigation and drainage ditch， and other field management measures were carried out in the same way. The amounts of fertilizers for each treatment in the experiment are shown in Table 2. Fertilizers were mixed  evenly  and applied according to the test requirements. Phosphorus and potassium were applied as the base fertilizer at one time， and 65% of nitrogen fertilizer was applied as the base fertilizer and 35% of nitrogen fertilizer was applied in the tillering stage.

Sample collection and determination

During the rice harvesting period， the yield was measured in different plots. After the yield test， 5 plants with the same growth vigor were taken from each plot to prepare straw and grain samples， respectively.

Method for determination of nitrogen， phosphorus and potassium contents in plants and grains： The samples were dried at  70 ℃，  crushed with a sample mill， and all sieved through a 1 mm sieve to determine the nitrogen， phosphorus and potassium contents of the straw and grains， respectively. After the samples were subjected to the digestion and boiling treatment， the total nitrogen content was determined by the semi-micro Kjeldahl method; the total phosphorus content was determined by the vanadium molybdenum yellow colorimetric method; and the total potassium content was determined by the flame photometer method （determined by the Plant Protection and Soil and Fertilizer Institute of Hubei  Academy  of Agricultural Sciences）.

Calculation of plant nutrient accumulation： N （P2O5， K2O） accumulation=Dry matter×Corresponding N （P2O5， K2O） content （%）.

Calculation formulas and statistical methods

The formulas for calculating the apparent use efficiencies and agronomic efficiencies of fertilizers are as follows：

Agronomic efficiency of fertilizer=（Grain yield in fertilization area-Grain yield in nutrient-deficient area）/Pure nutrient input of fertilizer×100%;

Apparent use efficiency of fertilizer =（Crop nutrient uptake in fertilization area-Crop nutrient uptake in nutrient-deficient  area） /Fertilizer nutrient input×100%.

Excel2003 was used to organize data， and DPS software was used for significance analysis by the Duncan’s new multiple range method.

Results and Analysis

Effects of combined application of nitrogen， phosphorus and potassium fertilizers on rice yield and dry matter weight

It can be seen from Table 3 that the yield of the CK was the lowest and the yield of NPK was the highest. Specifically， the yield of the CK in the Huangjiakou test was only 7 508.9 kg/hm 2; and compared with the CK， the yields of various fertilization treatments increased by 3.64%-20.72%， and the yield of NPK reached 9 065.0 kg/hm 2. In the Datong Lake test， the yield of the CK was only 5 999.0 kg/hm 2. Compared with the CK， the yields of various fertilization treatments increased by 2.38%-49.75%， and the yield of NPK reached 8 983.5 kg/hm 2. In the two tests， compared with the PK treatment， the NPK treatment increased the yield by 1 282.6 and 2 842 kg/hm 2， respectively， and the yield increase rates of nitrogen fertilizer were 14.14% and 31.64%， respectively. Compared with the NK treatment， the NPK treatment increased the yield by 560.9 and 884.5 kg/hm 2， respectively， and the yield increase rates of phosphorus fertilizer were 6.19% and  9.85% ， respectively. Compared with the NP treatment， the NPK treatment increased the yield by 408.8 and 547 kg/hm 2， respectively， and the yield increase rates of potassium fertilizer were  4.51%  and 6.09%， respectively. The yield increase rate of nitrogen fertilizer application was the highest， followed by phosphorus fertilizer application， and that of potassium fertilizer application was the lowest. In the Huangjiakou test， the yield of treatment NPK was significantly higher than that of treatments PK and CK， and the yield of treatment NP was significantly higher than that of the CK， but the differences of yield between treatments NP， NK and PK were not significant. In the Datong Lake test， the yields of treatments NPK， NP and NK were significantly higher than those of treatments PK and CK， and the yield difference between treatments NP and NK was not significant. The yield of rice can be significantly improved by applying nitrogen， phosphorus and potassium fertilizers in a reasonable manner.

It can also be seen from Table 3 that in the Datong Lake test， the dry matter weight of treatment PK increased by 3.64% compared with the CK treatment， and the dry matter weights of other treatments increased by 7.58%-59.12% compared with the CK treatment. It could be seen that fertilization was beneficial to promote the growth and development of rice，  thereby significantly  improving  the dry matter weight of rice. In the two tests， the dry matter weight of rice in the NPK treatment was  22.71%  and  34.74%  higher than the PK treatment， 8.05% and 11.10% higher than the NK treatment， and 5.27% and 7.55% higher than the NP treatment， respectively. From the yield increase rates in the two tests， it could be concluded that nitrogen had the greatest effect on rice yield， followed by phosphorus， and potassium had the least effect.

Xiangping WANG  et al.  Effects of Nitrogen-phosphorus-potassium Combined  Fertilization  on Rice Yield and Fertilizer Use Efficiency in Jianghan Plain

Effects of combined application of nitrogen， phosphorus and potassium fertilizers on nutrient accumulation and distribution in rice

Nitrogen accumulation and distribution

It can be seen from Table 4 that the N accumulation in rice grains and stems and leaves of treatment NPK was significantly higher than that of the CK treatment. In the Huangjiakou test， the N accumulation in grains and stems and leaves and the total N of treatments NPK， NK， NP reached the extremely significant level compared with treatments PK and CK， respectively， but the differences between treatments NPK， NK and NP were not significant. The total amount of N accumulation in the aboveground part of rice was the highest in treatment NPK， and the N accumulation increased by 58.2%， 11.4% and 0.9% after the addition of nitrogen， phosphorus and potassium， respectively. During rice harvesting period， the N accumulation in grains and stems and leaves of treatment NPK accounted for 50.07% and 49.93% of the total N accumulation in aboveground plants， respectively. In the Datong Lake test， the N accumulation in the NPK treatment was significantly higher than that in treatments NK， PK， and CK， and had extremely significant differences from that in treatments PK and CK， and the extremely significant level was reached when comparing treatments PK and CK with treatments NP and NK， but there were no significant differences between treatments NP and NK and between treatments PK and CK. The amounts of N accumulation in stems and leaves of treatments NPK and NP were significantly higher than those of treatments PK and CK， but there were no significant differences  between  treatments NPK， NP， and NK and between treatments NK， PK， and CK. The N accumulation in the aboveground part of treatments NPK and NP had extremely significant differences from treatments PK and CK， and treatment NK was significantly higher than treatments PK and CK， but there were no significant differences between treatments NPK， NP and NK， and treatment PK had no significant difference from the CK. The total amount of N accumulation in the aboveground part of rice was the highest in treatment NPK， and the N accumulation increased by  77.1% ，  22.4%  and 4.6% after the addition of nitrogen， phosphorus and potassium， respectively. During the rice harvesting period， the N accumulation in grains of treatment NPK accounted for 62.34% of the total N accumulation in aboveground plants， and that in stems and leaves only accounted for 37.66%.

P2O5 accumulation and distribution

Table 5 shows that treatment NPK could increase P2O5 accumulation in rice grains and stems and leaves compared with the CK. In the Huangjiakou test， the accumulation of P2O5 in grains of treatment NPK was significantly higher than that of treatments PK and CK， but there were no significant differences between treatments NPK， NP， and NK and between treatments NP， NK， PK， and CK. The accumulation of P2O5 in stems and leaves of treatments NPK and NP was significantly higher than that of treatments PK and CK， and the difference between treatments NPK and CK reached an extremely significant level， but NPK， NP， and NK were not significantly different， and treatments NK， PK and CK were not significant as well. Treatments NPK and NP had extremely significant differences in the total accumulation of P2O5 in the aboveground part from treatments PK and CK， and treatment NPK was significantly higher than treatment NK， but there were no significant differences between treatments NPK and NP， between treatments NP and NK， and between treatments PK and CK. The total accumulation of P2O5 in the aboveground part of rice was the highest in treatment NPK， and the addition of nitrogen， phosphorus and potassium could increase the accumulation of P2O5 by 32.9%， 15.8% and 6.5%， respectively. During the rice harvesting period， the accumulation of P2O5 in grains under treatment NPK accounted for  67.67%  of the total P2O5 accumulation in aboveground plants， and that in stems and leaves accounted for only 32.33%. In the Datong Lake test， the P2O5 accumulation in grains of treatments NPK， NP， and NK had extremely significant differences from that of treatments PK and CK， and treatment NPK was significantly higher than treatments NP and NK， but there were no significant differences between treatments NP and NK and between treatments PK and CK. The accumulation of P2O5 in stems and leaves of treatment NPK had extremely significant differences from that of treatment NK， PK and CK， and was significantly higher than NP， and the difference between treatments NP and CK reached the extremely significant level， but there were no significant differences between treatments NP， NK and PK and between treatments NK， PK and CK. The total accumulation of P2O5 in the aboveground part of treatment NPK had extremely significant differences from that of NP， NK， PK， and CK， and the NP treatment had an extremely significant difference from the CK， and was significantly higher than the PK and CK treatments， but there were no significant differences between treatments NP and NK， between treatments NK and PK and between treatments PK and CK. The total accumulation of P2O5 in the aboveground part of rice was the highest in treatment NPK， and the addition of nitrogen， phosphorus and potassium increased the accumulation of P2O5 by  66.6% ，  27.4%  and 39.6%， respectively. During the rice harvesting period， the accumulation of P2O5 in grains in treatment NPK accounted for 62.90% of the total P2O5 accumulation in the aboveground plants， and that in stems and leaves only accounted for 37.10%.

K2O accumulation and distribution

Table 6 shows that the NPK treatment increased K2O accumulation in rice grains and stems and leaves compared with the CK. In the Huangjiakou test， the accumulation of K2O in grains of treatment NPK reached an extremely significant level compared with treatments PK and CK， and treatment NP was significantly higher than the CK， but there were no significant differences between treatments NPK， NP and NK， between treatments NP， NK and PK， and between treatments NK， PK and CK. For the accumulation of K2O in stems and leaves and the total accumulation of K2O in the aboveground part， treatments NPK， NP and NK were extremely significant different from treatments PK and CK， but there were no significant differences between treatments NPK， NP and NK， and there was no significant difference between treatments PK and CK. Treatment NPK had the highest total accumulation of K2O in the aboveground part， and the addition of nitrogen， phosphorus and potassium could increase the accumulation of K2O by 50.7%， 6.9% and 6.9%， respectively. During the rice harvesting period， the K2O accumulation in grains of treatment NPK only accounted for 7.75% of the total K2O accumulation in the aboveground plants， while the proportion in stems and leaves accounted for 92.25%. In the Datong Lake test， the accumulation of K2O in the grains of treatments NPK and NP reached an extremely significant level compared with treatments PK and CK， but there were no significant differences between treatments NPK and NP， between treatments NP and NK， and between treatments PK and CK. In terms of the K2O accumulation in stems and leaves， treatments NPK， NP and NK reached the extremely significant level compared with treatments PK and CK， treatment NPK was significantly higher than treatment NK， but there were no significant differences between treatments NPK and NP， between treatments NP and NK， and between treatments PK and CK. The total accumulation of K2O in the aboveground part of NPK， NP and NK reached the extremely significant level compared with PK and CK， and the accumulation of K2O in stems and leaves of NPK was significantly higher than that of NP and NK， but the difference between NP and NK was not significant， and the difference between PK and CK was not significant as well.  The total accumulation of K2O in the aboveground part of rice was the highest in treatment NPK， and the addition of nitrogen， phosphorus and potassium could increase the accumulation of K2O by  70.1% ， 20.8% and 15.6%， respectively. During the rice harvesting period， the K2O accumulation in grains of treatment NPK only accounted for 10.46% of the total K2O accumulation in aboveground plants， while the proportion in stems and leaves reached 89.54%.

Effects of combined application of nitrogen， phosphorus and potassium fertilizers on fertilizer use efficiency and the required amounts of fertilizers per unit mass of rice

Fertilizer use efficiency

From Table 7， it can be concluded that in the process of rice cultivation in different experimental areas， the variety and quantity of fertilizers applied were different， and the fertilizer use efficiency was also different. In the Huangjiakou test， the apparent use efficiencies of nitrogen， phosphorus and potassium fertilizers were 31.6%， 26.1%， and 43.9%， respectively. Among them， potassium fertilizer was the highest， followed by nitrogen fertilizer， and phosphorus fertilizer was the lowest. The agronomic efficiencies of nitrogen， phosphorus， and potassium fertilizers were 6.3， 14.0， and 6.4 kg/kg， respectively， and the agronomic efficiency of phosphorus fertilizer was higher than those of nitrogen and potassium fertilizers. In the Datong Lake test， the apparent use efficiencies of nitrogen， phosphorus， and potassium fertilizers were 37.7%， 34.0%， and 46.3%， respectively. Among them， potassium fertilizer was the highest， followed by nitrogen fertilizer， and phosphorus fertilizer was the lowest. The agronomic efficiencies of nitrogen， phosphorus， and potassium fertilizer were 15.4， 14.7， and 5.7 kg/kg， respectively， and the agronomic efficiencies of nitrogen and phosphorus fertilizers were higher than that of potassium fertilizer.

Demands for nitrogen， phosphorus and potassium fertilizers per unit mass of rice

The data in Table 8 show that， in the two tests， the CK treatment had the lowest absorption of N， P2O5 and K2O; the NP treatment had the highest absorption of N， 19.9 and 18.1 kg， respectively; the NPK treatment had the highest absorption of P2O5， 8.5 and 10.6 kg， respectively; and the amount of K2O absorbed by treatment NPK was the highest， 47.3 and 36.7 kg， respectively. The ratios of N， P2O5 and K2O absorbed by  1 000  kg of rice produced by treatment NPK were 1∶ 0.44∶ 2.47 and  1∶ 0.59∶ 2.06， respectively， while the ratios of N， P2O5 and K2O in the CK treatment were 1∶ 0.56∶ 2.74 and 1∶ 0.58∶  2.00， respectively.

Conclusions and Discussion

The experimental study showed that the reasonable distribution ratio of nitrogen， phosphorus and potassium and sufficient fertilizers are beneficial to improve the grain yield of rice. The yield was the highest in treatment NPK and the lowest in the CK in both tests. The yields of various fertilization treatments in the Huangjiakou test increased by 3.64%-20.72% compared with the CK， and the yield of the balanced fertilization treatment （NPK） was the highest， reaching 9 065.0 kg/hm 2; the yields of various  fertilization treatments in the Datong Lake test increased by 2.38%-49.75%  compared with the CK， and the balanced fertilization treatment （NPK） had the highest yield， reaching 8 983.5 kg/hm 2. It shows that scientific combination of nitrogen， phosphorus and potassium fertilizers can significantly increase the yield of rice during rice cultivation in Jianghan Plain， and the technical guidance based on rice soil testing and formula fertilization should be strengthened.

The agronomic efficiency and apparent use efficiency of fertilizers are important indicators to measure the use efficiency of fertilizers. In the two tests in this area， the apparent use efficiencies of nitrogen fertilizer were 31.6% and 37.7%， respectively; the apparent use efficiencies of phosphorus fertilizer were 26.1% and 34.0%， respectively; and the apparent use efficiencies of potassium fertilizer were 43.9% and 46.3%， respectively. The apparent use efficiency of potassium fertilizer was the highest， followed by nitrogen fertilizer， and that of phosphorus fertilizer was the lowest， but there were certain differences between plots with different fertility and between different rice varieties. In the two tests， the  agronomic efficiencies of nitrogen fertilizer were 6.3 and 15.4 kg/kg，  respectively， the agronomic efficiencies of phosphate fertilizer were 14.0 and 15.4 kg/kg， respectively， and the agronomic efficiencies of potassium fertilizer were 6.4 and 5.7 kg/kg， respectively， respectively. The agronomic efficiency of phosphate fertilizer was significantly higher than that of potassium fertilizer.

The dry matter accumulation and nutrient accumulation of rice provide important basis for formulating fertilizer application  amounts  and reasonable ratios. In the two tests in this area， it could be concluded from the yield increase rate that nitrogen had the greatest impact on rice yield， followed by phosphorus and potassium; and according to the proportion of K2O accumulation， the K2O accumulation in stems and leaves accounted for most of the total K2O accumulation in aboveground plants， indicating that the application of potassium fertilizer can be greatly reduced by returning straw to the field.

In this study， when the rice variety Yanliangyou 1618 was grown in the Jianghan Plain， when the fertilizing amounts of N，  P2O5， and K2O were 202.5， 40.05， and 63.6 kg/hm 2， respectively， the yield could reach 9 065.0 kg/hm 2. Under these conditions，  the amounts of N， P2O5 and K2O that needed to be absorbed per 100 kg of rice produced were 1.92， 0.85， and 4.73 kg， respectively， and the ratio of the three was 1∶ 0.44∶ 2.47. When planting the rice variety Liangyou 240， when the fertilizing amounts of N， P2O5， and K2O were 184.5， 60.0， and 96.0 kg/hm 2， respectively， the yield could reach 8 983.5 kg/hm 2. Under these conditions， the amounts of N， P2O5， and K2O needed to be absorbed per 100 kg of rice produced were 1.78， 1.06 and 3.67 kg， respectively， and the ratio of the three was 1∶ 0.59∶ 2.06.

References

[1]  CAO CG， CAI ML， ZHANG SS，  et al.  The rice production present situation and technical countermeasures of Hubei Province[J]. Hubei Agricultural Sciences， 2004（4）： 28-30. （in Chinese）.

[2] LI JJ， LI JP. International comparison of rice production cost and benefit and China’s development prospects[J]. China Rice， 2021（4）： 2-10. （in Chinese）.

[3] LIU LJ， SANG DZ， LIU CL，  et al.  Effects of real-time and site-specific nitrogen managements on rice yield and nitrogen use efficiency[J]. Scientia Agricultura Sinica， 2003， 36（12）： 1456-1461. （in Chinese）.

[4] WANG WN， WANG YY， YAO ZQ，  et al.  Effect of "3414" fertilization experiment and fertilizer recommendation on mid-season rice[J]. Hubei Agricultural Sciences， 2008， 47（12）： 1416-1419. （in Chinese）.

[5] KUMAR P， PANDEY SK， SINGH BP，  et al.  Influence of source and time of potassium application on potato growth，yield，economics and crisp quality[J]. Potato Research， 2007（50）： 1-13.

[6] BELANGER JR， WALSH JE. Tuber growth and biomass partitioning of two potato cultivars grown under different N fertilization rates with and without irrigation[J]. Amer J of Potato Res， 2001（78）： 109-117.

[7] ZHANG FS， WANG JQ， ZHANG WF，  et al.  Nutrient use efficiencies of major cereal crops in china and measures for improvement[J]. Acta Pedologica Sinica， 2008， 45（5）： 915-924. （in Chinese）.

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