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

Introduction

The steady rise 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, and 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 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 demand for food. However, meeting this increased demand by enhancing crop production in current conventional farming systems is a major challenge. Nitrogen (N) has a significant effect on plant growth and 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, and 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 rice yield. However, its utilization efficiency during agricultural consumption is low in China, which results in a serious wastage of 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.

Rice is the staple food of more than 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, rice yield can 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 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-efficient cultivars requiring minimal fertilizer application is important for improving the yield and quality of 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 and P fertilization rates at different experimental sites.

Materials and Methods

Experimental sites and weather

The field experiments were conducted at three locations: (1) Binyang, 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

DOI: 10.7717/peerj.11668/table-1

Note:

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

The soils of Binyang and Beiliu are relatively acidic, and the soil of Liucheng is relatively alkaline (Table 1). The content of organic carbon and available N is higher in Liucheng soil than in Binyang and 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 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 local metrological stations. The maximum temperature in August 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).

Results

Discussion

Nitrogen (N) and 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 water bodies, high 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) and dry matter (DM) are directly associated with the grain yield of 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 panicle number 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 rice grain yield can 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.

Supplemental Information