Plastic film mulching affects the critical nitrogen dilution curve of drip-irrigated maize
Introduction
Nitrogen application is widely used for improving grain production. Insufficient N application causes low grain yields, while superfluous N inputs do not generally result in a substantial increase in grain production. Superfluous N-fertilizer application can result in increased production costs and detrimental environmental issues (Chen et al., 2014), such as increased greenhouse gas emissions (Godfray et al., 2010) and water eutrophication (Hansen et al., 2019). As a result, an agronomic diagnostic method for detecting N deficiencies and excesses in crops is important for enhancing profits and reducing environmental problems.
There is general agreement that an allometric relationship exists between biomass and plant tissue N concentration (Wang et al., 2018). The critical N dilution curve (CNDC) on basis of this relationship is a potential tool to diagnose N status of plants. The CNDCs are on the basis of the concept of critical N concentration (Nc), which is the minimum N concentration to maintain the maximum crop growth rate (Lemaire and Gastal, 1997). Greenwood et al. (1990) divided plants into C3 and C4 plants, and determined the respective CNDCs (Nc = 5.7DM−0.5 for C3 plants; Nc = 4.1DM−0.5 for C4 plants). Lemaire and Gastal (1997) modified the Greenwood models based on multiple experiments. Recently, CNDCs have been determined for maize (Plénet and Lemaire, 1999; Ziadi et al., 2008; Li et al., 2015), wheat (Justes et al., 1994; Yao et al., 2014), rice (Ata-Ul-Karim et al., 2013), and cotton (Xue et al., 2006), thereby justifying CNDC as a good tool for diagnosing crop N status.
Plastic film mulching is a common method to improve soil hydrothermal conditions, thereby enhancing crop production (Ramakrishna et al., 2006; Li et al., 2013). Drip irrigation can precisely supply water and nutrient for root absorption (Bozkurt et al., 2006). Therefore, mulched drip irrigation is widely adopted for enhancing soil temperature and utilization efficiency of water and fertilizer in cold and arid climates, such as found in Northwest China (Ning et al., 2015). Crops in this region are generally irrigated and fertilized with a fertigation system (Wang et al., 2014). Therefore, instead of focusing on soil water and nutrient availability, the production goal should be on obtaining high water and fertilizer utilization efficiencies with the fertigation system.
Past research has shown that plastic film mulching accelerates accumulation of leaf area (Li et al., 1999) while drip irrigation reduces root growth (Li, 2006; Asady and Smucker, 1989). Additionally, favorable soil water and N environment bring about a thick stem diameter (Fernández and Cuevas, 2010; Jing et al., 2014) which can result in more maize root primordia on the upper stem nodes (Pellerin, 1994). These combined effects may cause root to shoot ratio regulation with subsequent effects on root absorption (Li, 2006; Jones, 2012; Wang et al., 2019) and root-shoot carbohydrate competition (Palta et al., 2011). We hypothesize that mulched drip irrigation should change CNDCs of crops compared with CNDCs of crops in un-mulched fields by crop morphology regulation. However, previously reported CNDCs have all been based on un-mulched crops (Plénet and Lemaire, 1999; Yue et al., 2014), while CNDCs of crops under mulched drip irrigation production have not been investigated.
Mulched drip irrigation is practiced widely in arid Northwest China (Wu et al., 2015). The objectives were to (1) determine the CNDCs of drip-irrigated maize with and without mulching, and (2) investigate how plastic film mulching affects soil NO3−-N concentration (Nsoil) and crop morphological characteristics (including root to shoot ratio and basal stem diameter), and thus on changes to CNDCs of drip-irrigated maize. The results will provide an efficient tool for N application in maize grain production with drip irrigation and with mulched drip irrigation.
Section snippets
Location
A three-year field study was carried out from 2014 to 2016 in the Hetao Irrigation District. The climate is temperate zone continental monsoon and the soil classification is Ustepts in this study area (Table 1). The detailed information can be found in Zhou et al. (2020).
Field management and treatments
After plowing to a 5 cm depth, drip irrigation systems were installed and fertilizer treatments (see details later) were band-applied along each drip lateral line. Immediately following fertilization application, the soil for
Soil NO3−-N concentration, crop N concentration, aboveground dry biomass, and grain yield
The mean values of Nsoil in the root zone (0–120 cm), Ncrop, DM and final grain yields as affected by years, N treatments, and mulching treatments are shown in Table 2. Nsoil, Ncrop, DM, and grain yields were not different between the three years (P > 0.05). Increasing N application rate significantly increased Nsoil, DM, and grain yields (P < 0.05), whereas, the Ncrop was significantly affected when N application rate was below 200 kg N ha−1 (P < 0.05). Plastic film mulching showed no
Soil NO3−-N concentration, N concentration, aboveground dry biomass, and grain yields
In this study, N application rate (N50, N125, N200, N275, N350) was the most significant factor influencing Nsoil, followed by mulching and then the inter-annual variability (Table 2). The N application rates used in this study covered a wide range (from 50 to 350 kg N ha−1), and were a major source of N inputs into the soil. Drip irrigations scheduled by monitoring soil water to maintain water content near field capacity tended to reduce percolation of irrigation water and NO3--N below the
Conclusion
Critical nitrogen dilution curves effectively described the Nc-DM allometric relationship of drip-irrigated maize under both plastic film mulching and non-mulching conditions. The effect of mulching on the morphological index (especially the root to shoot ratio) of maize was an important biological mechanism to regulate the Nc-DM allometric relationship. The NNI calculated from the CNDC can be a reliable N diagnosis tool during the growing stages of drip-irrigated maize under both mulching and
Author statement
All authors approve the submitted manuscript.
Lifeng Zhou did the experiment, analyzed data, and wrote the manuscript. Hao Feng developed scientific questions and objectives. Wenzhi Zhao did the revising and editing. All authors contributed to the discussion of developing the manuscript by providing comments.
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgements
This work was founded by the "Light of West China" Program of the Chinese Academy of Sciences (CAS), the Strategic Priority Research Program of the CAS (XDA23060302), and the State Key Program of National Natural Science of China (41630861).
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