Impact of fertilization with reducing in nitrogen and phosphorous application on growth, yield and biomass accumulation of rice (Oryza sativa L.) under a dual cropping system.

The current farming system in China is heavily reliant on synthetic fertilizers, which adversely affect soil quality and crop production. Therefore, the aim of this study was to assess the effect of different nitrogen (N) and phosphorous (P) fertilizer application rate on the growth, yield, and yield components of rice cultivars in the Binyang, Beiliu and Liucheng sites of southern China in the early (March to July) and late season (August to December). The study consisted of three fertilization regimes-CK (N0P0); N180P90 (180 kg N + 90 kg P2O5 ha-1) and N90P45 (90 kg N ha-1 + 45 kg P2O5)-conducted at each of three different experimental sites with four cultivars (Baixang 139, Y Liangyou 1, Guiyu 9, and Teyou 582). Results showed that the leaf area index (LAI) was 38.8% found higher in Guiyu 9 compared with Baxiang at reduced fertilization (N90P45). N90P45 resulted higher dry matter production at the heading (9411.2 kg ha-1) and maturity (15319.5 kg ha-1) stages in Teyou 582 at Beiliu. Fertilization (N180P90) had higher effective panicle number (4,158,800 panicle ha-1) and grains panicle-1 (113.84 grains) compared with other treatments. Teyou 582 treated with N90P45 and Y Liangyou 1 treated with N180P90 improved seed setting rate average by 82.91% and 72.17% compared with other treatments at Beiliu in both seasons, respectively. N0P0 and N90P45 increased the thousand-grain weight (TGW) of Y Liangyou 1 at Binyang (27.07 g) and Liucheng (27.84 g) during the early and late seasons, respectively. In Beiliu, the N90P45 treatment (6611.7 kg ha-1) of Teyou 582 increased grain yield compared with other treatments. Overall, our results suggested that reducing N and P at the ratio of 90:45 kg ha-1 in Teyou 582 and Y Liangyou 1 could increase rice grain yield and yield components.

Introduction

The n class="Chemical">an class="Disease">steady risepan>> of fertilizer use in global agriculture over the past century has made a major contribution to the development of modern farming. It has improved overall global agricultural productivity, crop yields, ann>d soil fertility. As a result of increased fertilizer use, agriculture production, crop yield and soil fertility were increased globally (Wehmeyer, de Guia & Connor, 2020). Since its introduction during the Green Revolution in the 1960s, synthetic fertilizer has been an essential factor of Asian agriculture (Lu & Tian, 2017). China used 26.7% of global fertilizers in 2014, resulting in China the world’s largest consumer of fertilizer (Heffer, Gruère & Roberts, 2014). A study reported that farmers in China reached an extremely high average NPK fertilizer application rate of 559.8 kg ha−1 (Wehmeyer, de Guia & Connor, 2020). In particular, the use of N fertilizer in an class="Species">rice cultivation usually overtakes 250 kg ha−1 (Ali et al., 2020), which is approximately higher than the global average.

The increase in the world population has led to increases in the demn class="Chemical">and for food. However, meetinpan>g this inpan>creased demn class="Chemical">and by enhancing crop production in current conventional farming systems is a major challenge. Nitrogen (N) has a significant effect on plant growth anpan>pan>>d production under various environmental conditions (Ullah et al., 2021; Leghari et al., 2016). The application of N through chemical fertilizer is the primary source of N in crop production (Tao et al., 2015; Ali et al., 2019), yet the excessive use of chemical fertilizer adversely affects soil health, the environment, ann>d crop production (Ali et al., 2020). Furthermore, the overuse of N fertilization enhances plant growth (Iqbal et al., 2020) and decreases grain quality (Iqbal et al., 2021) and grain yield (Zörb et al., 2010). The constant increase in N fertilizer application in paddy rice production in China has led to low N use efficiency. According to the Chinese Ministry of Agriculture in 2015, the utilization rates of N, phosphorus (P), and potassium (K) fertilizers in three major cereal crops (i.e., rice, wheat, and maize) are only 33%, 24%, and 42%, respectively (Bai et al., 2016). The excessive application of N fertilizer and the low N use efficiency in paddy fields leads to a large loss of N fertilizer. The annual planting area of rice in China is 30 million hectares (Gao et al., 2014). According to Beckinghausen et al. (2020), at least 1.8 million tons of N fertilizer (pure N) are wasted every year. This is a major global challenge to feed the growing global population by increasing crop yield and quality while minimizing environmental costs. P fertilization plays a critically important role in improving an class="Species">rice yield. However, its utilization efficiency during agricultural consumption is low in China, which results in a serious wastage of pan> class="Chemical">phosphate rock resources (Li et al., 2014). Excessive fertilizer application not only leads to waste but also increases the planting costs of producers. Currently, approximately 67% of the world’s cultivated land can be found lacking in P (Dhillon et al., 2017). P deficiency in China is particularly severe, with approximately two-thirds of the cultivated land lacking P (Zhou et al., 2017a). Given that soil P deficiency is one of the main factors limiting crop yields, there is a need for more work to maximize P utilization efficiency.

n class="Chemical">an class="Species">Ricepan>> is the staple food of more thann> half of the world’s population and almost 60% of China (Zhao et al., 2020). Rice yield is mainly associated with N and P application rate (Iqbal et al., 2019), but N and P management is often modified depending on rice type, cultivar, geographic zone, and other crop practices (Angus et al., 1994; Hirzel et al., 2020). Additionally, an class="Species">rice yield canpan> be induced through variety selection and improvements in cultivation technology (Cai, Liang & Wan, 2010). The selection of hybrid cultivars has a higher return compared with conventional pan> class="Species">rice (Lin et al., 2020). Furthermore, rice yield is associated with the photosynthetic products of leaves and the photosynthetic attributes rates (Acevedo-Siaca et al., 2020). Thus, increasing plant biomass is a direct way to improve rice yield, as rice cultivars with higher biomass, higher leaf area index, and high biological yield are considered more desirable.

Identifying N and P-efficienpan>t cultivars requiring minimal fertilizer application is importpan> class="Chemical">ant for improving the yield and quality of an class="Species">rice as well as for environmental protection (Zhou et al., 2017b). The objective of this study was to assess differences in the growth, biomass accumulation, and grain yield of cultivars under high and low N anpan>pan>>d P fertilization rates at different experimental sites.

Materials and Methods

Experimental sites and weather

The field experiments were conducted at three ln class="Chemical">ocationpan>s: (1) Binpan>yn class="Chemical">ang, Nanning, China (23°0635″N, 108°5912″E); (2) Beiliu, Yulin, China (22°4419″N, 110°1032″E); and (3) Liucheng, Liuzhou, China (24°44197″N, 109°0418″E) during the early (March to July) and late season (August to December) in 2019. The basic soil physicochemical properties of the experimental fields before the experiments are shown in Table 1.

Table 1

Basic physical and chemical properties of soil in the experimental site.

Site	pH	OC (g kg−1)	TN (g kg−1)	AN (mg kg−1)	AP (mg kg−1)	AK (mg kg−1)
Binyang	5.28	33.47	2.07	147	124.13	194
Beiliu	4.89	22.76	1.31	161	380.12	115
Liucheng	8.08	42.35	2.74	206.5	104.5	81

Note:

OC, organic carbon; TN, total nitrogen; AN, available nitrogen; AP, available phosphorous; AK, available potassium.

n class="Chemical">OC, pan> class="Chemical">an class="Chemical">organic carbon; TN, total anpan>pan>> class="Chemical">nitrogen; AN, available nitrogen; AP, available phosphorous; AK, available potassium.

The soils of Binyn class="Chemical">ang n class="Chemical">and Beiliu are relatively acidic, and the soil of Liucheng is relatively alkaline (Table 1). The content of an class="Chemical">organic carbon and available N is higher in Liucheng soil than in Binyanpan>pan>>g ann>d Beiliu soils. The content of available P is higher in Beiliu soil compared with the soils of Binyang and Liucheng. Our previous study at the same experimental sites was conducted with the same cultivars, which show no significant effect among experimental sites for an class="Species">rice yield. However, their results were significant among the treatments across the experimental sites (Xie et al., 2021).

Figure 1 shows the temperature of the experimental sites collected from ln class="Chemical">ocal metrological stations. The maximum temperature in August pan> class="Chemical">an average 28 °C, and the minimum temperature in December an average 10 °C. Figure 2 shows that the average rainfall of the three sites was concentrated in the early season (March to July) and late season (August to December).

Figure 1

Average temperature of Binyang, Liucheng and Beiliu throughout the growing season.

Figure 2

Average rain fall of Binyang, Liucheng and Beiliu throughout the growing season.

Experimental design and field management

The experiments were performed in a split-plot factorial design consisting of 12 treatments. Plots (3.6 m × 5.6 m) had n class="Chemical">an area of 20.16 m2. Three seedlinpan>gs were planted per hill, the hill to hill distance was 14 cm, and the row-to-row distance was 30 cm. Each plot contained 12 rows, 40 hills, and 1,440 seedlings. The cultivars were randomly arranged and were not separated. Four different cultivars selected from a previous experiment (Li et al., 2019) were tested, including two hybrid rice cultivars (Teyou 582 and Y Liangyou 1) and two conventional rice cultivars (Baixiang 139 and Guiyu 9). Three fertilization levels were set for each cultivar: (1) F1: 180 kg N ha−1 + 90 kg P2O5 ha−1 + 180 kg K2O ha−1 (N180P90), (2) F2: 90 kg N ha−1 + 45 kg P2O5 ha−1 + 180 kg K2O ha−1 (N90P45), and (3) F3: 0 kg N ha−1 + 0 kg P2O5 ha−1 + 180 kg K2O ha−1 (N0P0).

The 25-day-old seedlings were mn class="Chemical">anually transplanted to the experimental fields. The sources of N, P, and K were urea, superphosphate, and potassium chloride, respectively. Urea and potassium chloride were applied in splits (50% as a basal fertilizer, 30% at the tillering stage, and 20% at the panicle initiation stage), whereas all superphosphate was used as basal fertilizer. Uniform flood water approximately 4 cm deep was continued from transplanting until physiological maturity in each plot. Throughout the growing season, standard agricultural practices including irrigation, herbicide application, and insecticide application were performed in the same manner for all plots.

Sampling and measurements

Soil sampling and analysis

Prior to experiments, soil samples were rn class="Chemical">andomly collected from up to 20 cm depth, air-dried, n class="Chemical">and passed through a 2-mm sieve. Soil pH was assessed after shaking the soil with distilled water at a 1:2.5 (w/v) solid-to-water ratio for 1 h using a digital pH meter (Thunderbolt PHS-3C, Shangai, China) (Cambardella et al., 2001). Total organic carbon was measured following the procedure of (Rich & Black, 1994). Total nitrogen (TN) was analyzed using the micro-Kjeldahl procedure (Jackson, 1956). Next, 200-mg soil samples were digested using the salicylic acid–sulfuric acid–hydrogen peroxide method (Ohyma et al., 1991), and available nitrogen (AN) was extracted from the soil samples using the hot water extraction method (Curtin et al., 2006). Available phosphorous (AP) was determined by Olsen’s method with 0.5 M NaHCO3 solution adjusted to pH 8.5 (Olsen, 1964). Available K was determined by placing the soil samples in 100-mL polyethylene bottles and adding 50 mL of the ammonium acetate/acetic acid solution (AK). AP was determined by the method as previously described by Leaf (1958).

Leaf area index

During the heading n class="Chemical">and maturity stages of pan> class="Chemical">an class="Species">rice, five representative anpan>pan>> class="Species">rice samples were taken from each treatment plot, prepared for preservation, and brought to the laboratory to determine the rice leaf area using the length-width coefficient method (Xie et al., 2021).

Dry matter accumulation

To measure n class="Chemical">an class="Disease">dry matter accumulationpan>> (DM), samples were rann>domly collected at the heading and maturity stages. The above-ground plants were washed with water and divided into three parts—stem, leaf, and panicle—and were dried in an oven at 70 °C for 48 h. Finally, the samples were weighed with a digital lab scale.

Growth, yield, and yield components

Five n class="Chemical">an class="Species">ricepan>> tillers were selected rann>domly to determine the number of filled grains per panicle, the number of grains blighted, seed setting rate, and thousand-grain weight (TGW). All of the plants in the plot were harvested, threshed, dried, and weighed. The moisture content of 100-g grains was measured and converted into standard yield based on 15% an class="Chemical">water content.

Statistical analysis

The data were n class="Chemical">analyzed using Statistix 8.0 software (Miller Lpan> class="Chemical">anding Rd Tallahassee, FL 32312). After checking the data for normality, data were analyzed using two-way an class="Chemical">ANOVAs. The least significant difference (LSD) tests at (P < 0.05) were performed to assess significant differences among treatments (Steel, Torrie & Dickey, 1996).

Results

Significant and non signifant data

The significn class="Chemical">ant level of pan> class="Chemical">an class="Species">rice traits as influenced by experimental sites (E), treatments (T), varieties (V), E × T, E × V anpan>pan>>d E × T × V is shown in Table 2. All interactions were found non-significann>t, except E × T × V for grain yield. Among the treatments, an class="Species">rice grain yield, grains panicle−1 and Seed setting rate were found non-significant during the early season, whereas during late season seed setting rate and thousand-grain weight were recorded non-significant. In the case of different varieties (V) all data were found significant during the early season and during late season, leaf area, an class="Disease">dry matter and grain yield were found non-significant (Table 2).

Table 2

Analysis of variance for leaf area, dry matter, grain yield, effective panicle numbers, grains panicle−1, seed setting rate, thousand-grain weight, as affected by experimental sites (E), treatments (T) and varieties (V) early and late sowing sea.

Rice traits	Experimental sites (E)	Treatments(T)	Varieties (V)	ExT	ExV	TxV
Early Season
Leaf area	**	*	*	*	*	ns
Dry matter	**	*	*	ns	*	ns
Grain yield	**	ns	**	**	**	ns
Effective panicle numbers	**	**	**	ns	**	ns
Grains panicle−1	**	ns	**	ns	*	ns
Seed setting rate	ns	ns	*	ns	**	ns
Thousand-grain weight	**	ns	**	ns	ns	ns
Late season						ns
Leaf area	**	**	ns	ns	ns	ns
Dry matter	**	**	ns	ns	*	ns
Grain yield	**	**	ns	**	**	ns
Effective panicle numbers	**	*	**	ns	ns	ns
Grains panicle−1	**	**	*	ns	**	ns
Seed setting rate	**	ns	*	ns	ns	ns
Thousand-grain weight	ns	ns	**	ns	**	ns

Note:

ns stands for non-significant, while *, **, and *** stand for significance at the 5, 1, and 0.1% levels of probability.

ns stands for non-signpan>ificpan> class="Chemical">ant, while *, **, and *** stand for significance at the 5, 1, and 0.1% levels of probability.

Effects of N and P levels on leaf area index

The leaf area index (LAI) of n class="Chemical">an class="Species">ricepan>> was significann>tly affected by fertilizer rate, experimental sites, and cultivar during both seasons (Table 3). LAI was 21.5% and 52.1% higher in Binyang and Beiliu, respectively, across both seasons compared with Liucheng. The LAI was highest for Guiyu 9 during the early season, which was 38.8% higher compared with Baixiang 139; during the late season, the LAI was highest for Teyou 582, which was 17.8% higher compared with Guiyu 9. Y Liangyou 1 under N180P90 resulted in higher LAI (3.85 m−2) across seasons compared with the rest of the treatments. However, the lowest value of LAI (0.85 m−2) was observed for Y Liangyou 1 at Binyang under N0P0 treatment.

Table 3

Leaf area index (LAI) at ripening stage of different rice cultivars under different nitrogen and phosphorus rate in the early season of 2019.

Season	Site	Treatment	Baixiang139	Guiyu 9	Y Liangyou 1	Teyou 582	Average
Early		N180P90	3.00 ± 0.99abc	3.85 ± 0.18a	2.75 ± 0.72abc	2.66 ± 0.63bc	3.07
	Binyang	N90P45	2.71 ± 0.81bc	3.38 ± 0.12ab	2.42 ± 0.14bc	2.95 ± 0.94abc	2.87
		N0P0	2.32 ± 0.64bc	2.83 ± 0.43abc	2.12 ± 0.42c	2.25 ± 0.22c	2.38
		Average	2.68	3.35	2.43	2.62	2.77
		N180P90	2.37 ± 0.58abc	3.61 ± 0.62a	2.40 ± 0.62abc	2.52 ± 0.78abc	2.73
	Beiliu	N90P45	1.84 ± 0.51bc	3.25 ± 0.49ab	2.17 ± 1.20abc	1.87 ± 0.16bc	2.28
		N0P0	1.26 ± 0.35c	2.46 ± 0.95abc	1.97 ± 0.29abc	1.58 ± 0.28c	1.82
		Average	1.82	3.11	2.18	1.99	2.28
		N180P90	2.39 ± 0.34ab	3.38 ± 0.53ab	3.85 ± 1.53a	3.14 ± 1.25ab	3.19
	Liucheng	N90P45	2.12 ± 0.90ab	2.65 ± 0.79ab	2.70 ± 0.86ab	2.18 ± 0.29ab	2.41
		N0P0	1.56 ± 0.29b	1.75 ± 0.20ab	1.20 ± 0.33b	1.78 ± 0.58ab	1.57
		Average	2.02	2.59	2.58	2.37	2.39
Late		N180P90	2.63 ± 0.30ab	1.12 ± 0.49cd	2.24 ± 1.04abc	2.97 ± 0.49a	2.24
	Binyang	N90P45	1.89 ± 1.80abcd	1.42 ± 0.81bcd	1.36 ± 0.09bcd	1.61 ± 1.01bcd	1.57
		N0P0	1.41 ± 0.42bcd	0.97 ± 0.16cd	0.85 ± 0.13d	1.36 ± 0.28bcd	1.15
		Average	1.98	1.17	1.48	1.98	1.65
		N180P90	3.12 ± 0.25ab	2.96 ± 0.67ab	3.30 ± 1.03a	3.07 ± 0.74ab	3.11
	Beiliu	N90P45	2.47 ± 0.27abc	2.56 ± 1.08abc	2.39 ± 0.53abc	3.16 ± 1.05ab	2.65
		N0P0	2.03 ± 0.21abc	1.75 ± 0.49bc	1.36 ± 0.43c	1.90 ± 0.46abc	1.76
		Average	2.54	2.42	2.35	2.71	2.51
		N180P90	2.64 ± 0.44ab	3.16 ± 0.35a	2.78 ± 0.49ab	2.40 ± 0.82abc	2.75
	Liucheng	N90P45	1.93 ± 0.20bcd	1.96 ± 0.96bcd	1.98 ± 0.08bcd	2.42 ± 0.63abc	2.07
		N0P0	1.39 ± 0.23d	1.49 ± 0.26d	1.61 ± 0.33cd	1.59 ± 0.21cd	1.52
		Average	1.99	2.2	2.12	2.14	2.11

Note:

Values in columns with different letters showed significant differences (P < 0.05). ± Value represents the SE value among the replications.

Values in columns with different letters showed significn class="Chemical">ant differenpan>ces (P < 0.05). ± Value represenpan>ts the SE value among the replications.

Effects of N and P levels on DM

In the early season, N and P fertilizers, site, pan> class="Chemical">and cultivar significantly affected DM during both seasons and regimes (Tables 4 and 5). The highest DM was observed at Liucheng and Beiliu, respectively, which had 23.5% and 11.7% higher DM compared withBeiliu. Y Liangyou 1 resulted in 20.8% and 21.2% higher DM compared with Baixiang 139 at the heading and maturity stages, respectively.

Table 4

Dry matter accumulation at heading and maturity stage of different rice cultivars under different nitrogen and phosphorus rate in the early season of 2019 (kg/ha).

Site	Treatment	Baixiang139	Guiyu 9	Y Liangyou 1	Teyou 582	Average
		Heading
	N180P90	6,697.1 ± 403.93abc	6,888.6 ± 386.41abc	8,055.0 ± 986.89ab	8,541.9 ± 855.01a	7,545.7
Binyang	N90P45	6,360.5 ± 900.03abc	7,584.9 ± 1,127.33ab	8,051.0 ± 1,260.84ab	7,777.7 ± 512.36ab	7,443.5
	N0P0	4,948.1 ± 1,725.84c	6,117.8 ± 368.12bc	5,949.5 ± 574.96bc	7,280.3 ± 538.57ab	6,073.9
	Average	6,001.9	6,863.8	7,351.8	7,866.6	7,021
	N180P90	8,069.3 ± 1,280.14ab	10,228.5 ± 1,520.39a	8,925.3 ± 970.03a	8,710.4 ± 147.70ab	8,983.4
Beiliu	N90P45	8,660.4 ± 1,502.70ab	9,158.9 ± 759.78a	7,923.9 ± 1,201.95ab	9,411.2 ± 1,088.72a	8,788.6
	N0P0	4,942.7 ± 217.27b	7,701.6 ± 1,371.37ab	7,140.3 ± 783.79ab	7,222.8 ± 184.64ab	6,751.9
	Average	7,224.1	9,029.7	7,996.5	8,448.1	8,174.6
	N180P90	6,367.8 ± 745.71ab	7,467.0 ± 1,093.67ab	8,109.8 ± 1,340.07a	6,471.5 ± 2,637.84ab	7,104
Liucheng	N90P45	6,194.9 ± 1,013.22ab	6,937.2 ± 603.47ab	8,369.0 ± 513.12a	6,946.4 ± 71.40ab	7,111.9
	N0P0	4,424.4 ± 864.94b	6,289.4 ± 975.70ab	5,945.0 ± 795.21ab	5,883.0 ± 748.81ab	5,635.5
	Average	5,662.4	6,897.9	7,474.6	6,433.6	6,617.1
		Maturity
	N180P90	9,752.1 ± 760.60bc	10,694.0 ± 712.45abc	14,656.8 ± 1,973.58a	12,380.1 ± 1,746.95ab	11,870.8
Binyang	N90P45	9,707.7 ± 1,305.80bc	11,627.9 ± 77.92abc	13,238.9 ± 301.60ab	13,948.5 ± 3,501.99a	12,130.8
	N0P0	8,323.4 ± 1,305.58c	9,735.8 ± 371.20bc	11,190.9 ± 1,874.89abc	10,950.9 ± 538.05abc	10,050.3
	Average	9,261.1	10,685.9	13,028.9	12,426.5	11,350.6
	N180P90	14,076.9 ± 2,167.13ab	12,074.9 ± 1,237.51ab	14,144.1 ± 2,887.99ab	13,709.1 ± 1,391.80ab	13,501.3
Beiliu	N90P45	13,116.5 ± 3,666.66ab	11,549.3 ± 2,110.37ab	15,319.5 ± 1,724.47a	13,655.0 ± 1,257.55ab	13,410.1
	N0P0	9,356.4 ± 1,084.59b	10,661.9 ± 2,503.85ab	12,306.8 ± 1,875.56b	12,212.4 ± 2,576.85ab	11,134.4
	Average	12,183.3	11,428.7	13,923.5	13,192.2	12,681.9
	N180P90	11,717.1 ± 339.72abcd	12,961.8 ± 1,772.77abc	14,030.4 ± 1,539.90ab	14,958.0 ± 1,137.26a	13,416.8
Liucheng	N90P45	10,587.0 ± 1,710.58abcd	12,929.3 ± 1,700.94abc	12,189.2 ± 1,372.23abcd	12,437.0 ± 923.96abcd	12,035.6
	N0P0	8,496.6 ± 2,145.74cd	9,628.7 ± 2,049.71bcd	8,253.8 ± 1,621.48d	10,361.0 ± 2,802.33bcd	9,185
	Average	10,266.9	11,839.9	11,491.1	12,585.3	11,545.8

Note:

Values in columns with different letters showed significant differences (P < 0.05).

Table 5

Dry matter accumulation at heading and maturity stage of different rice cultivars under different nitrogen and phosphorus rate in the late season of 2019 (kg ha−1).

Site	Treatment	Baixiang139	Guiyu 9	Y Liangyou 1	Teyou 582	Average
	Heading
	N180P90	9,686.6 ± 741.43ab	10,083.6 ± 955.38a	8,549.0 ± 1,741.78abcd	8,936.7 ± 1,678.65abc	9,314
Binyang	N90P45	8,323.7 ± 1,235.71abcd	7,611.9 ± 92.63abcde	6,798.6 ± 1,063.82bcde	9,067.8 ± 1,465.35abc	7,950.5
	N0P0	5,498.1 ± 1,852.39de	6,083.0 ± 1,192.46cde	4,362.2 ± 468.44e	6,779.3 ± 2,028.19bcde	5,680.7
	Average	7,836.1	7,926.2	6,569.9	8,261.3	7,648.4
	N180P90	8,043.2 ± 2,367.80a	7,131.8 ± 418.48ab	7,910.0 ± 1,069.79a	7,913.7 ± 720.96a	7,749.7
Beiliu	N90P45	7,280.7 ± 762.72ab	7,215 ± 831.09ab	7,186.4 ± 83.32ab	7,427.9 ± 936.24ab	7,277.5
	N0P0	5,069.4 ± 291.30b	5,706.5 ± 637.24ab	6,271.5 ± 369.49ab	5,836.8 ± 1,025.77ab	5,721.1
	Average	6,797.8	6,684.4	7,122.6	7,059.5	6,916.1
	N180P90	9,364.8 ± 962.94ab	10,149.6 ± 296.78a	9,913.4 ± 567.71ab	9,693.2 ± 626.09ab	9,780.3
Liucheng	N90P45	7,658.4 ± 1,957.01ab	9,905.1 ± 1,565.78ab	9,691.8 ± 385.80ab	9,447.6 ± 873.91ab	9,175.7
	N0P0	7,574.7 ± 726.67ab	7,327.8 ± 555.09b	8,510.7 ± 485.66ab	7,537.1 ± 1,164.75ab	7,737.6
	Average	8,199.3	9,127.5	9,372	8,892.6	8,897.9
	Maturity
	N180P90	11,818.8 ± 2,372.51ab	9,754.1 ± 750.08abcd	11,454.3 ± 1,363.42ab	12,077.1 ± 3,098.66a	11,276.1
Binyang	N90P45	8,922.5 ± 1,348.79abcde	9,304.5 ± 358.40abcde	8,993.4 ± 585.10abcde	10,953.5 ± 2,187.7abc	9,543.5
	N0P0	6,789.5 ± 1,366.36de	7,367.7 ± 856.38cde	5,617.5 ± 274.53e	8,122.4 ± 1,714.71bcde	6,974.3
	Average	9,176.9	8,808.8	8,688.4	10,384.3	9,264.6
	N180P90	12,020.7 ± 557.22ab	11,372.7 ± 1,048.47abc	13,421.7 ± 1,356.26a	10,044.3 ± 839.54abcd	11,714.9
Beiliu	N90P45	10,467.9 ± 1,468.12abcd	9,393.2 ± 2,763.04bcd	10,796.1 ± 287.97abcd	12,324.6 ± 1,343.67ab	10,745.4
	N0P0	8,660.9 ± 531.44bcd	7,445.4 ± 1,992.97d	7,758.9 ± 2,549.71cd	7,197.45 ± 1,338.98d	7,765.7
	Average	10,383.2	9,403.8	10,658.9	9,855.5	10,075.3
	N180P90	11,552.4 ± 1,724.73abc	11,865.2 ± 1,080.48abc	13,414.1 ± 2,210.51a	12,579.8 ± 1,813.34ab	12,352.9
Liucheng	N90P45	9,900.2 ± 609.73abc	9,977.3 ± 1,427.54abc	12,352.2 ± 862.57abc	11,979.9 ± 1,079.22abc	11,052.4
	N0P0	9,110.1 ± 1,233.77bc	8,817.8 ± 700.49c	11,366.9 ± 782.50abc	10,807.1 ± 1,033.32abc	10,025.5
	Average	10,187.6	10,220.1	12,377.7	11,788.9	11,143.6

Note:

Values in columns with different letters showed significant differences (P < 0.05).

Values in columns with different letters showed significn class="Chemical">ant differenpan>ces (P < 0.05).

Values in columns with different letters showed significn class="Chemical">ant differenpan>ces (P < 0.05).

The highest values of n class="Disease">DM at the heading (9,411.2 kg ha−1) stages were recorded for Teyou 582 treated with N90P45 at Beiliu. However, the lowest pan> class="Disease">DM at the heading (4,424.4 kg ha−1) and maturity (8,253.8 kg ha−1) stages were recorded for Baixiang 139 and Y Liangyou 1 under N0P0 at Liucheng during the early season.

During the heading stage of late n class="Chemical">an class="Species">ricepan>>, the DM of Liucheng among different treatments was 28.7% higher thapan class="Chemical">nn> that of Beiliu, and the DM of Liucheng among different treatments during the maturity period was 20.3% higher than that of Binyang (Table 5). Teyou 582 had 6% and 12.6% higher DM in the late-season compared with Baixiang 139 and Guiyu 9 at the heading and maturity stages, respectively. N180P90 led to higher DM (10,083.6 kg ha−1 and 13,421.7 kg ha−1) in Guiyu 9 and Y Liangyou 1 at Binyang and Beiliu, respectively, compared with the other cultivars and experimental sites. However, the lowest DM (4,362.2 kg ha−1 and 5,617.5 kg ha−1) during the late season was observed for Y Liangyou 1 at Binyang under N0P0 treatment.

Yield and yield components

Effective panicle numbers

Lower rates of N n class="Chemical">and P fertilizationpan> signpan>ificantly improved crop growth, grain yield, and yield components during both seasons (Tables 6 and 7). During the early an class="Species">rice period, the effective panicle number of Beiliu between different treatments was 28.6% higher than that of Liucheng. Compared with Teyou 582, the effective panicle number of Baixianpan>pan>>g 139 increased by 40.3%. Furthermore, Baixiann>g 139 treated with N180P90 led to a higher panicle number (4,158,800 panicle ha−1) compared with the other treatments in Beiliu. Teyou 582 had the lowest number of panicles (1.6508 million panicle ha−1) under N90P45 treatment at Liucheng.

Table 6

Effects of N and P application rates on yield components in early season in different rice cultivars.

Site	Cultivars	Treatments	Effective	Grain	Seed setting	TGW	Grain yield
			panicles	panicle−1	rate (%)	(g)	(kg ha−1)
Binyang	Baixiang 139	N180P90	300.99 ± 14.52a	125.47 ± 4.88cd	73.9 ± 0.01ab	18.36 ± 0.22d	5,153.6 ± 135.15e
		N90P45	312.08 ± 10.98a	115.25 ± 7.86d	81.11 ± 0.08a	18.70 ± 0.68d	5,015.1 ± 56.03e
		N0P0	256.63 ± 47.52ab	125.64 ± 3.07bcd	78.88 ± 0.04ab	18.14 ± 0.06d	4,900.7 ± 83.57e
	Guiyu 9	N180P90	270.89 ± 17.14a	132.97 ± 14.54bcd	56.73 ± 0.05c	22.54 ± 0.94c	5,130.5 ± 169.89e
		N90P45	267.72 ± 2.74ab	150.48 ± 2.97abcd	55.47 ± 0.05c	22.96 ± 0.67c	5,020.4 ± 206.09e
		N0P0	256.63 ± 4.75ab	121.74 ± 6.81d	65.60 ± 0.01bc	22.02 ± 0.97c	4,318.1 ± 126.76f
	Y Liangyou 1	N180P90	281.98 ± 26.17a	133.13 ± 13.95bcd	80.93 ± 0.06a	27.00 ± 0.93a	6,333.2 ± 100.02bc
		N90P45	251.88 ± 45.34ab	154.08 ± 46.56abcd	81.58 ± 0.11a	26.48 ± 0.76a	7,231.1 ± 163.02a
		N0P0	242.38 ± 20.72ab	129.11 ± 12.16bcd	78.52 ± 0.09ab	27.07 ± 0.21a	6,635.3 ± 300.98b
	Teyou 582	N180P90	250.3 ± 21.43ab	172.22 ± 11.78abc	72.30 ± 0.09ab	24.74 ± 1.07b	6,258.0 ± 287.70c
		N90P45	251.88 ± 28.91ab	187.86 ± 30.59a	77.47 ± 0.02ab	24.73 ± 0.85b	5,794.1 ± 56.80d
		N0P0	199.6 ± 12.57b	174.66 ± 9.22ab	77.91 ± 0.06ab	25.85 ± 0.27ab	5,641.8 ± 215.56d
Beiliu	Baixiang 139	N180P90	415.88 ± 30.61a	120.52 ± 15.15c	81.08 ± 0.03a	17.62 ± 0.48d	5,125.4 ± 960.29bcd
		N90P45	361.91 ± 43.64ab	133.77 ± 19.06c	80.18 ± 0.03a	17.82 ± 0.18d	5,723.4 ± 307.21abc
		N0P0	287.3 ± 11.00bc	120.36 ± 13.32c	80.02 ± 0.07a	17.57 ± 0.22d	5,179.5 ± 254.63bcd
	Guiyu 9	N180P90	304.76 ± 33.33bc	113.84 ± 10.48c	53.61 ± 0.03bc	22.34 ± 1.95c	4,763.7 ± 212.57cd
		N90P45	282.54 ± 2.75c	119.83 ± 10.88c	45.55 ± 0.13c	21.47 ± 1.46c	4,605.9 ± 216.53d
		N0P0	277.78 ± 58.77c	115.3 ± 21.09c	49.54 ± 0.17c	21.75 ± 0.31c	4,799.0 ± 167.32bcd
	Y Liangyou 1	N180P90	273.02 ± 11.98c	138.01 ± 24.85c	74.34 ± 0.08a	25.83 ± 0.75ab	5,843.3 ± 138.81ab
		N90P45	261.91 ± 19.05c	159.62 ± 22.51abc	82.29 ± 0.01a	26.06 ± 0.73ab	6,546.8 ± 64.57a
		N0P0	233.33 ± 16.50cd	143.82 ± 15.93bc	70.86 ± 0.04ab	26.95 ± 0.46a	6,361.8 ± 432.49a
	Teyou 582	N180P90	253.97 ± 29.10c	194.53 ± 25.84a	74.39 ± 0.11a	22.30 ± 0.63c	6,377.3 ± 286.02a
		N90P45	231.75 ± 21.99cd	186.71 ± 30.66ab	82.91 ± 0.10a	23.87 ± 1.47bc	6,611.7 ± 196.59a
		N0P0	174.60 ± 58.19d	200.89 ± 4.37a	80.81 ± 0.09a	25.15 ± 0.65ab	6,545.9 ± 285.52a
Liucheng	Baixiang 139	N180P90	293.65 ± 11.00a	139.05 ± 1.85bc	74.86 ± 0.08abc	17.39 ± 0.44e	4,305.6 ± 120.33bcd
		N90P45	269.84 ± 11.98ab	142.15 ± 19.57bc	75.93 ± 0.04abc	17.12 ± 0.33e	4,474.2 ± 676.31abc
		N0P0	209.52 ± 31.23cde	140.94 ± 11.65bc	82.4 ± 0.05a	17.05 ± 0.79e	3,482.3 ± 214.63d
	Guiyu 9	N180P90	241.27 ± 11.98abc	154.18 ± 31.29bc	66.09 ± 0.03bc	21.12 ± 0.83d	4,137.0 ± 310.68cd
		N90P45	212.70 ± 13.75bcde	187.91 ± 17.81ab	69.25 ± 0.03abc	20.89 ± 0.53d	4,166.7 ± 467.74cd
		N0P0	201.59 ± 13.75cde	148.17 ± 18.52bc	66.11 ± 0.09bc	20.76 ± 0.42d	3,740.1 ± 274.88cd
	Y Liangyou 1	N180P90	228.57 ± 16.50bcd	163.91 ± 15.73bc	63.53 ± 0.08c	25.29 ± 0.37a	5,198.4 ± 61.91ab
		N90P45	212.7 ± 11.98bcde	160.49 ± 9.62bc	66.37 ± 0.11bc	25.58 ± 0.66a	5,238.2 ± 337.98ab
		N0P0	173.02 ± 2.75de	132.53 ± 23.66c	73.57 ± 0.04abc	24.49 ± 0.86ab	4,414.8 ± 474.65abcd
	Teyou 582	N180P90	225.40 ± 45.01bcd	215.94 ± 43.82a	80.16 ± 0.03ab	22.93 ± 0.25c	5,287.8 ± 574.25a
		N90P45	165.08 ± 14.55e	228.4 ± 28.65a	82.41 ± 0.04a	22.98 ± 0.23c	4,613.1 ± 658.10abc
		N0P0	177.78 ± 32.41de	177.28 ± 18.54abc	81.55 ± 0.04a	23.48 ± 0.25bc	4,652.9 ± 725.56abc

Note:

Values in columns with different letters showed significant differences (P < 0.05).

Table 7

Effects of N and P application rates on yield components of late rice in different rice cultivars.

Site	Cultivars	Treatments	Effective	Total grains	Seed setting	TGW(g)	Actual output
			panicles	per panicle	rate (%)		(kg ha−1)
Binyang	Baixiang 139	N180P90	358.02 ± 42.60a	127.46 ± 13.76de	42.51 ± 0.07bc	18.29 ± 0.62c	2,980.5 ± 611.19abcd
		N90P45	266.14 ± 41.43b	135.35 ± 8.44cde	56.56 ± 0.03ab	19.39 ± 0.72c	3,588.3 ± 196.74a
		N0P0	237.62 ± 49.62bc	108.11 ± 2.68ef	58.89 ± 0.03a	18.22 ± 0.27c	1,941.9 ± 235.31e
	Guiyu 9	N180P90	185.35 ± 20.72bcd	179.85 ± 12.97a	45.48 ± 0.07abc	22.84 ± 0.78b	2,423.3 ± 314.67cde
		N90P45	199.60 ± 12.57bcd	163.09 ± 18.72abc	40.32 ± 0.04c	22.54 ± 1.41b	2,659.7 ± 373.08cde
		N0P0	148.91 ± 23.44d	169.73 ± 9.45ab	45.48 ± 0.08abc	22.08 ± 0.76b	2,254.4 ± 329.29de
	Y Liangyou 1	N180P90	237.62 ± 28.91bc	144.4 ± 6.94bcd	48.50 ± 0.08abc	26.01 ± 2.01a	3,453.3 ± 345.73ab
		N90P45	217.03 ± 15.28bcd	121.18 ± 0.95def	51.57 ± 0.01abc	25.64 ± 0.34a	3,318.2 ± 140.99ab
		N0P0	169.51 ± 2.74cd	94.79 ± 2.28f	55.83 ± 0.07ab	25.2 ± 0.53a	2,338.8 ± 168.62cde
	Teyou 582	N180P90	201.19 ± 48.08bcd	169.47 ± 5.71ab	53.86 ± 0.08abc	25.36 ± 0.29a	3,174.6 ± 373.46abc
		N90P45	202.77 ± 38.12bcd	160.91 ± 8.82abc	56.55 ± 0.02ab	25.43 ± 0.48a	3,065.0 ± 292.12abcd
		N0P0	177.43 ± 38.41cd	135.42 ± 16.04cde	51.64 ± 0.04abc	25.17 ± 0.45a	2,794.7 ± 402.43abcd
Beiliu	Baixiang 139	N180P90	292.06 ± 32.41a	142.67 ± 17.66bc	65.95 ± 0.02abc	18.81 ± 0.21e	5,537.1 ± 138.45bc
		N90P45	292.06 ± 50.92a	127.88 ± 15.63c	70.95 ± 0.03ab	18.23 ± 0.13e	4,725 ± 175.89d
		N0P0	261.91 ± 21.82ab	121.83 ± 8.16c	71.30 ± 0.04a	17.50 ± 0.07e	4,005.2 ± 57.62ef
	Guiyu 9	N180P90	192.06 ± 11.00bcd	188.24 ± 13.79ab	57.39 ± 0.06d	23.42 ± 0.79cd	4,974.2 ± 166.89cd
		N90P45	188.89 ± 49.56bcd	154.21 ± 19.85abc	60.58 ± 0.07abc	22.52 ± 1.47d	4,365.2 ± 476.59de
		N0P0	141.27 ± 27.08d	162.36 ± 24.28abc	58.05 ± 0.04d	22.73 ± 0.84d	3,590 ± 136.54f
	Y Liangyou 1	N180P90	228.57 ± 34.34abc	150.19 ± 27.02bc	72.17 ± 0.21a	26.99 ± 0.57a	6,284.7 ± 126.86a
		N90P45	204.76 ± 12.60bcd	145.69 ± 7.03bc	71.31 ± 0.06a	26.01 ± 0.96ab	6,063.2 ± 628.91ab
		N0P0	155.56 ± 43.21cd	136.51 ± 12.52c	68.53 ± 0.04abc	26.78 ± 0.51a	4,623.5 ± 413.43de
	Teyou 582	N180P90	176.19 ± 4.76cd	164.21 ± 8.90abc	59.45 ± 0.07bc	26.42 ± 0.31ab	5,795.6 ± 265.96ab
		N90P45	179.37 ± 2.75cd	199.60 ± 31.25a	66.41 ± 0.04abc	26.40 ± 0.18ab	5,435.6 ± 680.58bc
		N0P0	144.45 ± 7.27d	153.27 ± 23.63abc	66.08 ± 0.07abc	24.85 ± 0.87bc	4,466.6 ± 130.83de
Liucheng	Baixiang 139	N180P90	311.11 ± 58.77a	147.50 ± 7.62c	51.90 ± 0.01abc	18.91 ± 0.42f	5,353.1 ± 1,126.45abcd
		N90P45	290.48 ± 17.17ab	141.00 ± 11.00c	51.38 ± 0.04abc	18.65 ± 0.26f	5,144.6 ± 387.28abcd
		N0P0	258.73 ± 31.71abc	137.41 ± 9.72c	55.07 ± 0.04abc	19.36 ± 0.81ef	4,808.7 ± 366.91cd
	Guiyu 9	N180P90	226.99 ± 23.49bc	177.65 ± 61.01bc	44.80 ± 0.07c	21.33 ± 1.60def	5,436.6 ± 723.10abcd
		N90P45	217.46 ± 35.10bc	141.81 ± 13.45c	49.10 ± 0.09bc	22.22 ± 2.37cde	5,081.4 ± 852.28bcd
		N0P0	190.48 ± 16.50c	147.47 ± 15.62c	50.84 ± 0.07abc	22.00 ± 1.03cde	4,350.9 ± 198.15d
	Y Liangyou 1	N180P90	255.56 ± 26.23abc	151.68 ± 7.80c	58.76 ± 0.01ab	26.41 ± 1.63ab	7,047.3 ± 410.20a
		N90P45	239.68 ± 30.60abc	155.58 ± 8.97c	51.79 ± 0.02abc	27.84 ± 0.39a	6,762.3 ± 694.85ab
		N0P0	246.03 ± 11.00abc	140.36 ± 18.53c	59.94 ± 0.01ab	26.8 ± 0.46ab	5,973.8 ± 335.22abcd
	Teyou 582	N180P90	188.89 ± 39.65c	243.15 ± 11.39a	53.96 ± 0.07abc	23.86 ± 0.29bcd	6,596.6 ± 941.22abc
		N90P45	179.37 ± 27.08cd	223.49 ± 14.31ab	54.33 ± 0.06abc	24.55 ± 0.24bc	6,824.4 ± 192.24ab
		N0P0	188.89 ± 19.25c	188.14 ± 8.51abc	62.56 ± 0.02a	23.89 ± 1.11bcd	5,370.5 ± 543.71abcd

Note:

Values in columns with different letters showed significant differences (P < 0.05). ± Values represent SE among the replications.

Values in columns with different letters showed significn class="Chemical">ant differenpan>ces (P < 0.05).

Values in columns with different letters showed significn class="Chemical">ant differenpan>ces (P < 0.05). ± Values represenpan>t SE among the replications.

In the Liucheng test site, the effective pn class="Chemical">anicle number of Baixiang 139 increased by 56.7% compared with Guiyu 9 (Tables 6 and 7). Furthermore, Baixiang 139 treated with N180P90 in Binyang had significantly more panicles (3.5802 million panicle ha−1) compared with other treatments. However, the panicle number of Teyou 582 at Beiliu was low (1.4445 million ear ha−1) under N0P0 treatment.

Grains panicle−1

The number of grains pn class="Chemical">anicle−1 amonpan>g differenpan>t treatmenpan>ts was 28.6% n class="Chemical">and 16.7% higher in Liucheng compared with Binyang during the early and late seasons, respectively. Teyou 582 had a 49.5% higher number of grains per panicle compared with Baixiang 139 during the early season (Tables 6 and 7). In addition, Teyou 582 had considerably more (228.4 grains) total grains panicle−1 treated with N90P45 compared with treatments at Liucheng during the early season. Guiyu 9 treated with N180P90 had significantly more grains panicle−1 at Beiliu (113.84 grains) and Liucheng (243.15 grains) during the early and late seasons, respectively. The number of grains panicle−1 of Guiyu 9 was 37.7% higher compared with Baixiang 139 during the late season. However, Y Liangyou 1 at Binyang had a low number of grains panicle−1 (94 grains panicle−1) under the N0P0 treatment during the late season.

Seed setting rate

The seed setting rate was 3.1% higher in Liucheng thn class="Chemical">an inpan> Beiliu durinpan>g the early seasonpan> across fertilizer treatmenpan>ts (Tables 6 n class="Chemical">and 7). During the late season, the seed setting rate at Beiliu was 29.8% higher compared with Binyang, followed by Liucheng. Teyou 582 had a 34.5% higher seed setting rate than Guiyu 9 during the early season, and Y Liangyou 1 had a 19.1% higher seed setting rate than Teyou 582 during the late season. Teyou 582 treated with N90P45 and Y Liangyou 1 treated with N180P90 had seed setting rates that were 82.91% and 72.17% higher compared with other treatments at Beiliu in the early and late seasons, respectively. The lowest seed setting rate was recorded in Guiyu 9 (at Beiliu) and Teyou 582 (at Binyang) under N90P45 treatment during the early and late seasons, respectively.

Thousand-grain weight

TGW of Binyn class="Chemical">ang betweenpan> differenpan>t treatmenpan>ts durinpan>g the early seasonpan> was 7.5% higher thpan> class="Chemical">an that of Liucheng, and TGW of Beiliu between different treatments during the late season was 1.8% higher than that of Liucheng.Y Liangyou 1 had 44% higher TGW compared with Baixiang during both seasons (Tables 6 and 7). N0P0 and N90P45 increased the TGW of Y Liangyou 1 at Binyang (27.07 g) and Liucheng (27.84 g) during the early and late seasons, respectively. Lower TGW values (17.05 and 17.5 gm) were observed in Baixiang 139 at Liucheng and Beiliu during the early and late seasons, respectively, under N0P0.

Grain yield

The yield of Beiliu among different treatments during the early season was 27.5% higher compared with Liucheng (Tables 6 n class="Chemical">and 7). Compared with Guiyu 9, the yield of Y Lipan> class="Chemical">angyou 1 was increased by 32.3%. In Beiliu, the N90P45 treatment (6,611.7 kg ha−1) of Teyou 582 increased production compared with the other treatments. In Liucheng, the grain yield of Baixiang 139 was lower (3,482.3 kg ha−1) under N0P0 treatment.

Relationships between DM accumulation, LAI, effective panicle number, total number of grains per panicle, and grain yield of rice

n class="Chemical">an class="Species">Ricepan>> yield is strongly related to yield components ann>d growth attributes (Iqbal et al., 2020). In this study, the correlation analysis showed that DM (0.65**), LAI (0.6**), and effective panicle number (0.56*) were strongly positively correlated with grain yield (Table 8). Total grains panicle−1, seed setting rate, and TGW were moderately positively correlated with grain yield. Furthermore, effective panicle number was also strongly positively correlated with DM (0.83**) and LAI (0.6**). DM was significantly correlated with LAI (0.78**) and total grains panicle−1 (0.52*).

Table 8

Correlation between rice yield and yield components.

Index	Grain yield	LAI	DM	EP	TGPP	SSR
LAI	0.6**
DM	0.65**	0.78**
Effective panicles (EP)	0.56*	0.6**	0.83**
Total grains panicle−1	0.35	0.44	0.52*	0.03
Seed setting rate	0.41	0.36	0.3	0.25	−0.1
TGW	0.13	0.07	−0.21	−0.04	−0.21	−0.4

Note:

Significant correlation (P < 0.05).

Extremely significant correlation (P < 0.01).

LAI, leaf area index; DM, dry matter; TGW, thousand grain weight; EP, Effective panicles

Significn class="Chemical">ant correlationpan> (P < 0.05).

Extremely significn class="Chemical">ant correlationpan> (P < 0.01).

LAI, leaf area index; n class="Disease">DM, pan> class="Chemical">an class="Disease">dry matter; TGW, thousanpan>pan>>d grain weight; EP, Effective papan class="Chemical">nn>icles

Discussion

n class="Chemical">an class="Chemical">Nitrogenpan>pan>> (N) ann>d an class="Chemical">phosphorous (P) fertilizers are key to the “green revolution,” which has converted approximately half of the world’s land to agriculture (Melillo, 2012; Iqbal et al., 2021). Previously it is well reported that using synthetic fertilizers in conventional farming improved crop growth and yield. Increasing the rate of N and P fertilizer application has been reported the main strategy for increasing grain yield (Leghari et al., 2016; Ali et al., 2019; Iqbal et al., 2021). However, the overuse of N and P can lead to the eutrophication of an class="Chemical">water bodies, high pan> class="Chemical">nitrate content in water bodies, and deterioration of rice quality (Carpenter et al., 1998; Ullah et al., 2020). Furthermore, the consequences of N and P losses from paddy fields, such as through runoff and leaching, can span multiple organizational levels and scales in time and space and thus threaten critical ecosystem services (Fowler et al., 2013; Guignard et al., 2017; Ullah et al., 2020). Although previous work indicates that increasing P and N fertilization can increase crop growth, yield, and yield attributes, and few studies have examined the extent to which the levels of P and N fertilizers could be reduced at different sites and with different cultivars in southern China. Thus our studies provided the response of different cultivars to the reduction of fertilizer use in South China at three different experimental sites.

Leaf area index (LAI) n class="Chemical">and pan> class="Chemical">an class="Disease">dry matter (DM) are directly associated with the grain yield of anpan>pan>> class="Species">rice (Iqbal et al., 2019; Ali et al., 2020). Our results showed that the LAI was increased under moderate amounts of fertilization (N90P45) of a hybrid cultivar (Guiyu 9) compared with conventional rice cultivars. Likewise, moderate fertilization (N90P45) led to higher DM of a hybrid variety (Teyou 582) at Beiliu. These increases can be explained by the characteristics of hybrid cultivars, which can use less N and P while maintaining LAI and DM in paddy fields. These cultivars require less N and P for their growth and development (Li et al., 2019). Our results are consistent with those of Ali et al. (2020), showing that proper N application can increase the number of tillers and LAI of rice and promote its growth but that the excessive application of N fertilizer increases the number of ineffective tillers and reduces the utilization of N (Xie et al., 2021). However, several studies have reported that reducing N and P fertilizer application reduces rice growth traits (Jiang et al., 2021; Murthy et al., 2015) and alters rice flowering days (Ye et al., 2019). Similar to our findings, another study reported that reducing N application rate increases rice grain yield and N use efficiency (Wei et al., 2021), although their study used dense planting techniques. In addition Zhang et al. (2014) documented that regulating fertilization rate such as reducing and postponing N doses could sustain plant growth and yield. In general, our results suggest that rice LAI can be enhanced with the use of hybrid cultivars treated with moderate amounts of fertilizer.

Furthermore, our results indicated that effective pn class="Chemical">anicle number n class="Chemical">and grains per panicle were highest under N180P90 fertilization of Baixiang 139 and Guiyu 9, respectively. Seed setting rate, TGW, and grain yield were highest under moderate fertilization (N90P45) in Beiliu with the cultivar Teyou 582; furthermore, Y Liangyou 1 led to a higher grain yield compared with Guiyu 9 in Liucheng. Overall, the hybrid cultivar Teyou 582 increased the grain yield and yield attributes under reduced fertilization rates (N90P45); however, there were no significant differences in grain yield and yield attributes between moderate and high applications of N and P fertilizer. This result might stem from the properties of Teyou 582, a hybrid cultivar that can grow better and produce higher yields with less fertilizer. These results are consistent with those of (Ma et al., 2019) showing that optimal applications of N and P enhanced grain yield and quality by improving N uptake. Furthermore, similar to our finding reported that using low fertilizer rates improves rice yield with other agronomic techniques such as selection of verities (Ju et al., 2015), dense planting (Wei et al., 2021), coupling with organic manure (Iqbal et al., 2019) or combined with biochar amendment (Ali et al., 2020) whereas other studies (Wang et al., 2011) have found that moderate application rates of N lead to increases in nitrate content in the 0–60 cm soil layer, N uptake amount, grain yield, and apparent recovery fraction of applied fertilizer N in wheat (Cheng et al., 2020; Tadesse et al., 2020) also showed that moderate amounts of N and P can enhance grain yield compared with higher amounts of N and P in wheat and rice.

Conclusion

Based on our results, we concluded that n class="Chemical">an class="Species">ricepan>> grain yield cann> be increased under lower fertilization rate using hybrid cultivars. Our results suggested that low fertilization rates of 90 kg N ha−1 and 45 kg P ha−1 can increase grain yield and yield attributes in hybrid cultivars. However, hybrid and conventional cultivars of rice lead to similar yields under higher fertilization rates. Thus, the use of rice hybrid cultivars under a reduced fertilization rate might allow higher grain yields with a lower environmental cost. In order to confirm the potential of these cultivars, further studies are needed to determine the quality, initial photosynthetic rates, root attributes, and chlorophyll fluorescence of these cultivars under reduced fertilization rates.

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