Effect of Nitrogen and Density Interaction on Yield Formation of Late Japonica Rice Under Different Transplanting Dates

Chengfang HE Liquan LI Renchun ZHENG Hongjie ZHU

Abstract [Objectives] This study was conducted to clarify the appropriate nitrogen fertilizer amount and transplanting density that should be selected for different transplanting dates.

[Methods]The effects of nitrogen fertilizer rate and transplanting density on the traits and yield of late japonica rice in the Jianghuai rice-wheat cropping area under different transplanting dates （transplanting at an appropriate time and delayed transplanting） were studied.

[Results] The transplanting date significantly affected the heading， maturity and whole growth period of rice， and when the transplanting date of early-maturing late japonica rice was delayed by 15 d， the growth period was shortened by about 10 d. Nitrogen and density interaction obviously affected the dry matter accumulation and effective tillers of rice， and the dry matter production and effective tiller number of rice treated with B1N2 were greater than other treatments. Under the timely transplanting date， the best nitrogen and density combination was 225-300 kg/hm2 and 250 500 holes/hm and the nitrogen use efficiency was ideal. It suggests that under the condition of transplanting rice in a timely manner， applying nitrogen fertilizer at an appropriate rate while ensuring a reasonable population density is conducive to the coordination of the number of stems and tillers， the number of grains per panicle， etc.， thereby ensuring the best formation of yield factors in the middle and late stages of rice growth.

[Conclusions]This study provides technical support and theoretical reference for reasonable nitrogen and density interaction of rice.

Key words Transplanting date; Nitrogen and density interaction; Late japonica rice; Nitrogen use efficiency

Received： April 6， 2021  Accepted： May 10， 2021

Supported by Major National Research and Development Program （2016YFD0300206-2）.

Chengfang HE （1973-）， female， P. R. China， associate researcher， devoted to research about agricultural ecological environment.

*Corresponding author. E-mail： hechengfang@aaas.org.cn.

Rice is the main food crop in China. Rice yield is affected by the genotypes of varieties， and the cultivation technology， planting environment and interaction effects are also important factors[1-2]. Among the high-yield cultivation techniques of rice， seeding at an appropriate time is an important guarantee for making full use of light and heat resources to improve overall quality and increase yield[3]. Xie et al.[4] believe that the selection of varieties should be determined according to different sowing dates， in order to give full play to the production potential of  varieties， which is the basis for high yield and quality of rice. Nitrogen fertilizer is one of the important factors affecting the growth and yield of rice. A large number of previous studies have proved that under the same amount of nitrogen fertilizer， different application methods also have greater impacts on rice growth and yield. Jin et al.[5-7] studied the effects of nitrogen fertilizer types and fertilization methods on rice. Anhui Province is one of the key areas for the country to promote the "Change of Indica to Japonica". In the Jianghuai rice-wheat cropping area， the sowing date is set by simple planting methods such as machine transplanting and direct seeding. Late sowing is beneficial to the improvement of rice quality， but as the postponement of the sowing date， the growth period of varieties with longer growth period is shortened， and the yield and quality gradually decrease[8]. In this study， the effects of nitrogen application rate and transplanting density on the physiological characteristics and yield of rice under the conditions of proper and delayed transplanting were investigated， so as to provide technical and theoretical reference for the reasonable nitrogen and density interaction of rice under the new form of diversified rice cultivation methods.

Materials and Methods

Materials

The experiment was conducted in the National Modern Agriculture Demonstration Park Base in Lujiang County， Hefei City， Anhui Province from May to October 2018 （117°01′ E， 30°57′ N）. The experimental soil was paddy soil with following basic physical and chemical properties： organic matter content 21.38 g/kg， total nitrogen content 1.47 g/kg， alkali-hydrolyzable nitrogen content 147.5 mg/kg， available phosphorus content 32.57 mg/kg， available potassium content 124.45 mg/kg， soil pH 6.45. The tested variety was Zhendao 18， which is an early-maturing late japonica rice species.

Experimental design

The experiment adopted raising seedlings for artificial transplanting. The age of transplanted seedlings was 30 d. The transplanting dates were suitable transplanting （B1： June 20） and postponed transplanting （B2： July 5）. Three planting densities were set： M1： 217 500 holes/hm2 （row plant spacing 20 cm×23 cm）， M2： 250 500 holes/hm2 （row plant spacing 20 cm×20 cm）， and M3： 291 000 holes/hm2 （row plant spacing 20 cm×17cm）. The four nitrogen fertilizer application rates were N0： 0， N1： 225， N2： 300， and N3： 375 kg/hm2. A three-factor split block design was adopted， with transplanting period as the main plot， the amount of nitrogen fertilizer as the split plot， and planting density as the small split plot. Each treatment was repeated 3 times. In the field test， the bottom of the plow pan was wrapped with double-layer plastic film to prevent lateral seepage of fertilizer and water， and a protection zone was set up in the test area. Wheat stalks were returned to the field， and seedlings were hand-planted according to 3-4 per hole during transplanting. Phosphorus and potassium fertilizers were applied at a rate of 135 kg/hm2. In terms of the nitrogen fertilizer application， the ratio of base and tiller fertilizer to panicle fertilizer was 6∶4. All phosphate fertilizer was applied as the base fertilizer. The potassium fertilizer was applied as the base fertilizer and panicle fertilizer equally. The prevention and control of diseases， pests and weeds was carried out at the right time.

Determination items and methods

The main growth periods such as the sowing date， transplanting date， jointing date， booting date， full heading date and maturation date were recorded. When the rice was mature， 10 consecutive rows were selected in each plot， with 10 holes in each row （continuous points）， for the determination of the number of effective panicles （panicles）， the number of grains per panicle （grains）， and 1 000-seed weight （g）， etc.， and then， yield structure analysis was carried out.

Results and Analysis

Effects of nitrogen and density interaction on the growth period of late japonica rice under different transplanting dates

Research has found that reasonable arrangement of sowing date can promote rice growth and development， effectively coordinate rice yield components， and increase rice yield. It can be seen from Table 1 that as the transplanting date was postponed， the temperature gradually increased， the growth process from sowing to maturity of rice was accelerated， the accumulated temperature during the growth period was reduced[9]， and the growth period of rice was correspondingly delayed. The transplanting date of the early-maturing late japonica rice Zhendao 18 was delayed by 15 d， and the growth period was shortened by about 10 d， which was consistent with the research conclusions of Xu et al.[10].

Effects of nitrogen and density interaction on tillering dynamics of late japonica rice under different sowing dates

It can be seen from Table 2 that the tiller dynamics of the rice population decreased with the delay of the transplanting date. Under the same sowing date， the nitrogen and density interaction significantly affected the number of tillers of the rice population. The average number of tillers in the peak tiller period under the condition of suitable transplanting （B1） increased by 59.16%-104.91% in the fertilization treatments compared with N0， and the number of tillers in the peak tiller period under the condition of postponed transplanting （B2） increased by 53.508%-86.15% in the fertilization treatments compared with N0. The number of tillers of the rice population increased first and then decreased with the increase in the amount of nitrogen fertilizer， and N3 and N1 had similar effects on the tillering of rice. Excessive increase in the amount of nitrogen fertilizer was not conducive to the dynamic development of the stems and tillers of the rice population， and although there were more seedlings in the early and mid stages， the final effective panicle number and the percentage of productive tillers were relatively low. The reasonable amount of nitrogen fertilizer was conducive to the formation of a reasonable population structure， and the number of effective ears and the percentage of productive tillers were relatively high.

Effects of nitrogen and density interaction on dry matter production of late japonica rice under different sowing dates

Table 3 shows that the dry matter production of rice decreased with the postponement of the transplanting date. Under the same sowing date， increasing the transplanting density could increase the dry matter accumulation of rice， and the dry matter accumulation had an increasing trend with the increase of density. Nitrogen fertilizer obviously affected the dry matter accumulation of rice， and the dry matter production of rice in B1N2 treatment was greater than other treatments. It indicated that reasonable application of nitrogen fertilizer in rice was beneficial to the accumulation of dry matter in the later stage.

Effects of nitrogen and density interaction on yield components of late japonica rice under different sowing dates

It can be seen from Table 4 that rice yield decreased with the delay of transplanting date.  Under the same transplanting date， the effective panicle number of the nitrogen deficiency treatment （N0） was significantly lower than those of other treatments. As the amount of nitrogen fertilizer increased， the yield of rice had an increasing trend. However， when the amount of nitrogen fertilizer application could ensure the normal growth of the population， increasing the cultivation density was not conducive to the increase of rice yield. In this study， the rice yield of the B1N2M2 treatment was the highest. It showed that under the conditions of transplanting rice at the right time， ensuring reasonable population density and applying an appropriate amount of nitrogen fertilizer at the same time were conducive to the coordination of the number of stems and tillers， the number of grains per panicle， and the 1 000-seed weight of the rice population， thereby ensuring the best formation of yield factors in the middle and late stages of rice growth.

Effects of nitrogen fertilizer treatments on nitrogen use efficiency of late japonica rice under different sowing dates

The nitrogen use efficiency of late japonica rice in this study gradually decreased with the increase of nitrogen fertilizer application. Under the condition of suitable transplanting （B1）， the nitrogen use efficiency of N3 （375 kg/hm2） dropped to 18.26%， and under the condition of postponed transplanting （B2）， the nitrogen use efficiency of N3 （375 kg/hm2） dropped to 13.12% （Table 5）， indicating that excessive application of nitrogen fertilizer reduced the use efficiency of nitrogen fertilizer. The N2 （300 kg/hm2） treatment had lower nitrogen use efficiency than the N1 （225 kg/hm2） treatment under the same sowing date， indicating that the nitrogen uptake by rice could increase yield formation to a certain extent. The nitrogen application rate of 225-300 kg of nitrogen fertilizer was ideal in this study.

Conclusions and Discussion

Transplanting date affects the growth rate of rice， which in turn affects the number of days in the whole growth period， and the dry matter of rice decreases with the delay of the transplanting date. Nitrogen fertilizer is a key factor affecting the growth of rice. Within a reasonable application range of nitrogen fertilizer， it can promote rice tillering， increase the number of effective panicles， and increase yield[11-12]. In this study， suitable nitrogen and density interaction facilitated dry matter accumulation in the later stage， had a greater impact on the effective panicle number of late japonica rice， but no significant effect on the 1 000-seed weight. Reasonable application of nitrogen fertilizer created a reasonable population structure， which had relatively high number of effective panicles and percentage of productive tillers， and the number of stems and tillers in the rice population was suitable and there were few ineffective tillers， which was beneficial to the light and ventilation conditions of the population[12] and increased the accumulation of dry matter in the middle and late stages of growth. Under the conditions of high nitrogen and high density， the dynamic development of stems and tillers of the rice population was affected. Although the number of tillers increased in the early and mid stages， it intensified individual competition， affected photosynthetic efficiency， and affected the differentiation of spikelets， and the final percentage of productive tillers was relatively low[13-14]. Therefore， appropriate nitrogen fertilizer amount and transplanting density are beneficial to the coordination of individuals and the growth environment of the population， and can ensure good light and ventilation conditions， enhance light energy interception， improve leaf area efficiency and increase percentage of productive tillers while ensuring sufficient effective panicles. In this study， under timely transplanting， the best nitrogen and density combination was 225-300 kg/hm2 and 250 500 holes/hm and the nitrogen use efficiency was ideal.

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