ZHANG Miao-miao ,DANG Peng-fei ,Ll Yu-ze ,QIN Xiao-liang# ,Kadambot H.M.SlDDlQUE

1 College of Agronomy/Key Laboratory of Crop Physio-ecology and Tillage Science in Northwestern Loess Plateau, Northwest A&F University, Yangling 712100, P.R.China

2 The UWA Institute of Agriculture and School of Agriculture &Environment, The University of Western Australia, Perth WA 6001,Australia

Abstract Plastic film mulch systems are used widely in arid areas,and the associated tillage measures affect soil properties,root and crop growth,and nutrient uptake.However,much debate surrounds the most suitable tillage method for plastic film mulch systems.We conducted a two-year field experiment to explore the impact of three tillage treatments -rotary tillage before ridge–furrow plastic film mulch (MR),no-tillage before ridge–furrow plastic film mulch (MZ),and plow tillage before ridge–furrow plastic film mulch (MP) -on soil total nitrogen,available nitrogen,root stratification structure,nitrogen transfer and utilization,and maize yield.The results showed that MP had better soil quality than either MR or MZ over 2019 and 2020,with higher nitrate-nitrogen and total nitrogen in the 0–40 cm soil layer.MP improved the soil physicochemical properties more than the other treatments,producing significantly higher root numbers and root biomass for the aerial and underground nodal roots than MR and MZ.At harvest,MP had the highest root biomass density,root length density,and root surface area density in the different soil layers (0–20,20–40,and 0–40 cm).Significant correlations occurred between root biomass and aboveground nitrogen accumulation during maize growth.During grain filling,MP had the greatest nitrogen transfer amount,significantly increasing root and aboveground nitrogen transfer by 19.63–45.82% and 11.15–24.56%,respectively,relative to the other treatments.MP significantly produced 1.36–26.73%higher grain yields and a higher grain crude protein content at harvest than MR and MZ.MP also had higher values for the nitrogen harvest index,nitrogen uptake efficiency,and partial factor productivity of nitrogen fertilizer than MR and MZ.In conclusion,plow tillage combined with a ridge–furrow plastic film mulch system facilitated maize root development and improved nitrogen utilization,thereby increasing maize yield more than the other treatments.

Keywords: maize,tillage,plastic film mulch,root,nitrogen transfer

1.lntroduction

Dryland farming in Northwest China encompasses 55% of the country’s total cultivated land area (Wanget al.2011),yet much of the land is hilly and deficient in soil nutrients.Tillage practices play important roles in agricultural production,affecting soil properties,root and crop growth,and nutrient uptake (Caiet al.2014;Wanget al.2015).Reasonable tillage measures increase nitrogen accumulation,improve fertilizer use efficiency (Liet al.2019;Omaraet al.2019),and enhance the capacity for sustainable agricultural development.

Plastic film mulch systems are widely used in arid areas to increase crop water and nitrogen absorption and utilization (Liu X Eet al.2015;Maet al.2018;Chenet al.2021;Zhanget al.2022).In China,the plastic film mulched area has increased from about 11.7×104ha in 1982 to 18.7×106ha in 2017 (Fuet al.2021).Much debate surrounds the most suitable tillage method for plastic film mulch systems to sustain soil fertility and productivity while increasing crop yields.Rotary tillage is commonly adopted under plastic-mulched farmland in the dryland areas of Northwest China.However,a recent study showed that plow tillage before plastic film mulch produced higher soil total nitrogen,soil organ carbon,and yields than rotary tillage (Liet al.2019).Other studies have reported that notillage improves the soil physical,biological,and chemical properties (Guoet al.2020;Daiet al.2021),minimizing agroecosystem disturbance and protecting the soil structure,while increasing maize yields (Zhanget al.2015).However,some studies found that no-tillage produced lower maize yields than plow tillage due to reduced soil water storage during the fallow period (Vitaet al.2007;Martínezet al.2008;Zhanget al.2017).Hence,the effects of no-tillage and traditional tillage with film mulch on soil fertility and yield needs further investigation.

Nitrogen is the primary factor limiting yield,with efficient nitrogen uptake and transport benefiting yield (Ladhaet al.2005;Zhouet al.2016;Li G Het al.2021).The nitrogen recovery efficiency of plastic film mulch systems in China ranges from 19–33% (Liu X Eet al.2015;Wang S Jet al.2016),which is less than in the United States and Europe(Ladhaet al.2005).A reasonable root distribution can improve the synergy between the root and aboveground parts of the plants (Liuet al.2007),with modified root traits synergistically improving resource use efficiency and maize yield (Jinet al.2014).Reasonable tillage measures can promote nutrient absorption from the deep soil by promoting root growth and extension (Liu X Wet al.2015;Kanget al.2019) and delaying root senescence,laying the foundation for high and stable crop yields(Morriset al.2007;Wanget al.2014).Tillage practices can regulate root growth and development by changing soil environmental factors (Liet al.2009;Luoet al.2014).Studies have shown that plow tillage improved soil porosity by altering soil bulk density (Xu and Mermoud 2001),improving crop root growth,deep root distribution,plant nutrient absorption,and grain yield (McGarryet al.2000).Another study reported that rotary tillage increased nutrient uptake by improving root biomass,enhancing lodging resistance,and thus increasing maize biomass and grain yield (Bianet al.2016).Plastic film mulch also has significant positive effects on root weight density and root length density (Gaoet al.2014;Li Y Z et al.2021),but it is unclear whether interactions occur between mulch and tillage on root traits.An appropriate combination of tillage and a plastic film mulch system may improve root traits,nitrogen accumulation,and fertilizer absorption and utilization in the semiarid areas of China (Liu X Wet al.2015;Liet al.2019).

Many studies have focused on the consequences of different tillage practices on soil total nitrogen,available nitrogen,and crop yield (Xu and Mermoud 2001;Córdovaet al.2018;Xieet al.2020).Dry matter accumulation and distribution are important characteristics of the‘source–sink’ relationship for crop grain yield formation(Dordas 2012).Increased nitrogen accumulation after silking is the main driver of increased maize yield (Zhouet al.2016),with the translocation of vegetative nitrogen before silking providing 25–82% of maize grain nitrogen(Lemaire and Gastal 2009;Chenet al.2014).However,few studies have investigated the impact of different tillage practices on nitrogen transport during grain filling under ridge–furrow plastic film mulch (RFPM) conditions.Different tillage methods affect the distribution and transfer of nutrients between underground roots and the aboveground plant parts,affecting crop yield and resource use efficiency (Zhanget al.2020).Therefore,investigating nitrogen accumulation and transport from different organs to grain in mulched maize under different tillage measures will help to optimize nitrogen management and increase maize yield (Wang Y Wet al.2016;Zhanget al.2020).

In this study,we combined different tillage measures(rotary tillage,no-tillage,and plow tillage) with RFPM to: 1) explore the impact of tillage on soil total nitrogen,available nitrogen,and nitrogen utilization under RFPM;2)evaluate the performance of maize roots under different tillage measures with RFPM and the contribution of roots to nitrogen uptake;and 3) study the impact of different tillage measures with RFPM on nitrogen transfer,grain yield,and grain quality.

2.Materials and methods

2.1.Study site

This experiment was conducted in 2019 and 2020 at the Agricultural Ecology Experimental Station of Changwu,China Academy of Sciences (35°12′N,107°40′E,1 200 m a.s.l.).The annual average precipitation and temperature are 537.5 mm and 10.1°C (1999–2019),respectively,the frost-free period is 171 d,and the groundwater depth is 70 m.The soil is black loess,and the top 20 cm of soil comprises 17.19% of the soil water content,and contains 11.56 g kg–1organic matter,46.66 mg kg–1available nitrogen,16.94 mg kg–1available phosphorus,and 122.35 mg kg–1available potassium.The annual precipitation levels in 2019 and 2020 were 674 and 522.8 mm,respectively;and the precipitation amounts during the maize growing period were 507.2 mm in 2019 and 419.4 mm in 2020 (Fig.1).

Fig.1 Precipitation (mm) and daily average temperatures (°C) at the experimental site in the 2019 and 2020 maize growing seasons.

2.2.Experimental design

A continuous tillage trial was established in 2017 using a completely randomized design with three replicates the following three treatments: (1) rotary tillage before RFPM(MR),(2) no-tillage before RFPM (MZ),and (3) plow tillage before RFPM (MP).Each plot was 50 m2(10 m×5 m).For the RFPM,each furrow was 50 cm wide,and each ridge was 50 cm wide and 15 cm high.According to the local planting pattern,urea (225 kg N ha–1) was applied once before sowing.The soil was not tilled under MZ,tilled to 10 cm depth under MR,and plowed to 25 cm depth under MP,after fertilization but before being ridged,and mulched with 0.08 mm thick plastic film.Maize variety Shandan 650 was sown (82 000 plants ha–1) at 5 cm depth on the ridge and furrow junctions with a spotting machine.The study site is in a rainfed agricultural area with no irrigation.

2.3.Measurement indexes and methods

Aboveground biomass,root morphology,and root:shoot ratioFive representative maize plants were collected randomly from each plot at about 20,40,60,80,100,and 140 days after sowing (DAS) in 2019 and 2020 to measure aboveground biomass.Roots from each plot were sampled at about 20,40,60,80,100,and 140 DAS in 2019 and 2020 using the soil monolith excavation method (Gajriet al.1994).Soil monoliths -25 cm (toward mid-row)×15 cm (along the row)×20 cm(depth) interval -were excavated to a 40-cm depth from each plot to determine the horizontal and vertical root distribution in a representative unit soil strip.Each monolith was placed in a plastic sample bag and immediately taken to the laboratory,where the roots in each monolith were rinsed slowly with a low-pressure water stream to remove impurities and the complete root systems in each soil layer were obtained.After counting root numbers for the aerial and underground nodal roots,the roots were scanned (Epson V700,Indonesia).Root images were analyzed to determine root length and surface area using WinRHIZO Software (version 5.0,Canada).The roots were oven-dried at 105°C for 1 h and then at 80°C for 48 h before weighing.Root biomass density (RBD,mg cm–3),root length density (RLD,cm cm–3),and root surface area density (RSD,cm2cm–3)were calculated as the ratios of biomass,length,and surface area of the root system in each soil layer to the volume in the respective soil column (Li Q Qet al.2010).The root:shoot ratio was calculated as the ratio of root biomass to aboveground biomass.

Yield and yield componentsAt physiological maturity in both years,20 healthy maize ears were randomly collected in each plot to measure yield per hectare,ear length (length from base to top of ear,cm),ear diameter (diameter at the middle of the ear,cm),row number per ear,kernel number per row,bare tip length (length of the unfruitful part at the top of ear,cm),and 100-grain weight (g).

Nitrogen accumulation in different organs and total soil nitrogen at different depthsFive representative maize plants,collected randomly from each plot at about 20,40,60,80,and 100 DAS in 2019 and 2020,were divided into the different organs (e.g.,roots,stems,and leaves),which were then crushed and sieved to determine total nitrogen content by Kjeldahl distillation.At each growth stage,the nitrogen accumulation amount in each organ was the product of total nitrogen content and organ biomass.The nitrogen transfer amount for each organ (kg ha–1) was calculated as: nitrogen accumulation amount within an organ at flowering-nitrogen accumulation amount within the same organ at harvest.

At harvest in 2019 and 2020,five soil samples were collected in 20 cm intervals from the 0–100 cm soil layer in each plot and mixed as one soil sample,which was then divided into two subsamples.Fresh soil was used to measure nitrate and ammonium nitrogen,which were extracted with 1 mol L–1KCl,and determined using an AA3 flow analyzer.The other subsample of each soil was air-dried naturally indoors to measure total soil nitrogen by Kjeldahl distillation.

Nitrogen-relatedindices Nitrogen harvest index (NHI,%) was calculated as:

whereGNAandANAare nitrogen accumulation (kg ha–1) in maize grain and the aboveground plant parts,respectively.

Nitrogen uptake efficiency (NupE,kg kg–1) was calculated as:

where F is total nitrogen fertilizer inputs (kg ha–1).

Partial factor productivity of nitrogen fertilizer (PFPN,kg kg–1) was calculated as:

Water use efficiencySoil water content (SWC,%) was measured in 20 cm increments from 0–200 cm depth using the weight-loss method.Soil water storage (SWS,mm) was calculated as:

where h is soil layer depth and p is soil bulk density (g cm–3).

Maize water use efficiency (WUE) was calculated as:

where SWS1(mm),SWS2(mm),and P (mm) are soil water storage before sowing,soil water storage at harvest,and precipitation from sowing to harvest;I is total irrigation quota measured by water meters (mm);U is upward flow into the root zone (likely negligible as the groundwater table remained at～80 m below the surface at the experimental site);F is downward drainage out of the root zone (likely negligible as the experimental soil had high water holding capacity,with little drainage assumed below 200 cm);and R is runoff (mm),which was negligible due to the absence of any irrigation and the flat terrain.

2.4.Statistical analyses

All data were analyzed using SPSS 22.0 Software,with figures were drawn with Sigmaplot 12 Software.One-way ANOVA was used to determine differences between treatments MR,MZ,and MP,with the least significant difference used to check for significant treatment differences in maize yield,aboveground biomass,root traits,soil properties,WUE,plant total nitrogen,and nitrogen-related indices (P<0.05).Spearman’s correlation tests were conducted to investigate associations between aboveground nitrogen accumulation and root biomass.

3.Results

3.1.Maize yield and yield components

MP had significantly (P<0.05) more kernels per row,higher 100-grain weights and shorter bald tip lengths than MR and MZ.As a result,MP increased the maize grain yield by 1.36–26.73% relative to MR and MZ,producing 6.45 and 5.55% higher yields than MZ in 2019 and 2020,respectively (Table 1).

Table 1 Yield and yield components of maize under rotary tillage (MR),no-tillage (MZ),and plow tillage (MP) before a ridge–furrow plastic film mulch system in 2019 and 2020

3.2.Aboveground biomass,root biomass,and root:shoot ratios at different growth stages

MP had the highest aboveground biomass at each growth stage,and the values were significantly (P<0.05) higher than those of MR,which had the lowest aboveground biomass among the three treatments (Fig.2-A).Root biomass reached its maximum at about 80 DAS and then decreased until harvest.MP had the highest root biomass at all growth stages,followed by MZ and MR (Fig.2-B).The maize root:shoot ratio decreased with maize growth,and the ratios of MP were higher than those of MR and MZ at the timepoints before 80 DAS (Fig.2-C).

Fig.2 Changes in (A) aboveground biomass,(B) root biomass,and (C) root:shoot ratio of maize under rotary tillage (MR),notillage (MZ),and plow tillage (MP) before a ridge–furrow plastic film mulch system in 2019 and 2020.Bars indicate least significant differences among MR,MZ,and MP at P<0.05 (n=3).＊ and ＊＊ denote significant differences at the P<0.05 and P<0.01 probability levels,respectively.

3.3.Root morphology

The different tillage measures under RFPM significantly(P<0.05) impacted root number and biomass for aerial roots and underground node roots.MP had the highest root numbers and biomass for aerial roots and underground node roots,followed by MZ and MR (Fig.3).In both years,the tillage measures affected RBD,RLD,and RSD in the 0–40 cm soil layer at harvest (P<0.05;Table 2).MP produced 12.34–36.26,12.28–133.91,and 12.30–108.06% higher RBD,RLD,and RSD at 0–20 cm,respectively,than MR and MZ.The corresponding values of the differences in the other two soil layers were 26.74–136.94,9.81–45.50,and 12.08–45.22% higher in the 20–40 cm soil layer,and 15.64–39.94,15.63–97.45,and 15.64–82.05% higher in the 0–40 cm soil layer.MZ produced higher RBD,RLD,and RSD than MR in the 0–20 cm soil layer (by 20.90–21.29,107.27–108.32,and 84.74–85.14%) and 0–40 cm soil layer (by 14.11–16.36,61.09–64.26,and 48.35–51.29%),but MR had higher values than MZ in the 20–40 cm soil layer (by 11.98–45.22,11.96–32.50,and 12.62–29.57%) (P<0.05;Table 2).

Table 2 Root biomass density,root length density,and root surface area density of different soil layers (0–20,20–40,and 0–40 cm)at harvest under rotary tillage (MR),no-tillage (MZ),and plow tillage (MP) before a ridge–furrow plastic film mulch system at harvest in 2019 and 2020

Fig.3 Root number and biomass for underground node roots (A and C) and aerial roots (B and D) at harvest under rotary tillage(MR),no-tillage (MZ),and plow tillage (MP) before a ridge–furrow plastic film mulch system in 2019 and 2020.Bars indicate least significant differences among MR,MZ,and MP at P<0.05 (n=3).Values followed by different letters indicate significant differences among treatments at P<0.05.

3.4.Change in total nitrogen content and nitrogen accumulation in maize roots and aboveground parts over time

Aboveground nitrogen accumulation increased with plant growth in both growing seasons,increasing rapidly in the first 80 DAS and then slowly after 80 DAS.Compared with MZ and MR,MP increased the aboveground nitrogen accumulation in maize (Fig.4-A).Root nitrogen accumulation increased rapidly,reaching its maximum at 80 DAS,and then it decreased rapidly.MP significantly(P<0.05) increased root nitrogen accumulation,with no significant difference between MR and MZ in either growing season (Fig.4-B).

Fig.4 Changes in (A) aboveground nitrogen (N) accumulation and (B) root N accumulation of maize grown under rotary tillage(MR),no-tillage (MZ),and plow tillage (MP) before a ridge–furrow plastic film mulch system in 2019 and 2020.Bars indicate least significant differences among MR,MZ,and MP at P<0.05 (n=3).＊ and ＊＊ denote significant differences at the P<0.05 and P<0.01 probability levels,respectively.

In both growing seasons,significant (P<0.05) positive correlations occurred between aboveground nitrogen accumulation and root biomass at each growth stage(R2>0.6;P<0.05;Fig.5).

Fig.5 Relationship between root biomass and aboveground nitrogen accumulation at 20,40,60,80,100,and 140 days after sowing (DAS) in 2019 and 2020.＊＊ denotes significant differences at the P<0.01 probability level.

3.5.Nitrogen transfer from roots,leaves,stems,cobs,and bracts to grain during grain filling

The aboveground organ and root contributions to the grain nitrogen transfer content were 86–89% and 11–14%,respectively,with root nitrogen transfer representing about one-eighth to one-sixth of the aboveground organs.MP significantly (P<0.05) increased the nitrogen transfer amount from roots by 19.63–45.82% relative to the other treatments,with no significant differences between MR and MZ (Table 3).Leaves had the highest nitrogen transfer amount to grain,followed by cobs,bracts,and roots,while stems had the lowest nitrogen transfer amount.During grain filling,MP had the largest nitrogen transfer amount among the different organs,with 11.15–24.56% more aboveground nitrogen transfer than the other two treatments.In addition,MR had 6.41 and 7.91%more aboveground nitrogen transfer than MZ during grain filling in 2019 and 2020,respectively (Table 3).

Table 3 Root and aboveground nitrogen transfer amount (kg N ha–1) under rotary tillage (MR),no-tillage (MZ),and plow tillage(MP) before a ridge–furrow plastic film mulch system in 2019 and 2020

3.6.NHl,NupE,PFPN,WUE,and grain quality of spring maize at harvest

NHI and PFPN performed similarly.MP had higher NHI and PFPN than MR and MZ,while MR had higher NHI and PFPN than MZ.MP significantly (P<0.05) improved NupE relative to both MR and MZ (Table 4).MP had the highest WUE,and it was significantly (P<0.05) higher than MZ,which had the lowest WUE of the three treatments(Table 4).MP also produced significantly (P<0.05) higher crude protein than MR and MZ (Table 5).

Table 4 Nitrogen harvest index (NHI),nitrogen uptake efficiency(NupE),partial factor productivity of nitrogen fertilizer (PFPN),and water use efficiency (WUE) at harvest of spring maize under rotary tillage (MR),no-tillage (MZ),and plow tillage (MP) before a ridge–furrow plastic film mulch system in 2019 and 2020

Table 5 Crude protein,starch crude fiber,crude fat content,and moisture of maize grain under rotary tillage (MR),no-tillage(MZ),and plow tillage (MP) before a ridge–furrow plastic film mulch system at harvest in 2019 and 2020

3.7.Soil total nitrogen,nitrate-nitrogen,and ammonium nitrogen contents at harvest

The impact of the different treatments on soil characteristics was concentrated mainly in the 0–40 cm soil layer in 2019 and the 0–60 cm soil layer in 2020(Fig.6).MP had higher total nitrogen,nitrate,and ammonium nitrogen contents in the upper soil layer than the other treatments,with MR significantly (P<0.05) higher than MZ (Fig.6).

Fig.6 Changes in soil total nitrogen (A),soil nitrate-nitrogen (B),and soil ammonium nitrogen (C) under rotary tillage (MR),notillage (MZ),and plow tillage (MP) before a ridge–furrow plastic film mulch system in the 2019 and 2020 maize growing seasons.Bars indicate least significant differences among MR,MZ,and MP at P<0.05 (n=3).＊ and ＊＊ denote significant differences at the P<0.05 and P<0.01 probability levels,respectively.

4.Discussion

4.1.Effect of tillage on TN,soil nitrate-nitrogen,and ammonium nitrogen

No-tillage is considered to be a sustainable development strategy for increasing surface TN,available nitrogen content,and crop production (Maoet al.2010;Maet al.2015).However,we found that MP had better soil quality than either MR or MZ over two years,with higher nitratenitrogen content and TN in the 0–40 cm soil layer (Fig.6).Improvements in soil nutrients were conducive to increases in the crude protein content in maize grain and grain yield(Tables 1 and 5),which could be associated with the different mulch practices.While numerous studies have investigated soil nitrogen content under different tillage practices (Raperet al.2005;Muet al.2016),few have been conducted under RFPM conditions.Moreover,tillage measures under RFPM can change the spatial distribution of fertilizer and affect fertilizer use efficiency by changing the soil physicochemical processes (Zhanget al.2011;Liet al.2019);for example,MZ concentrated the fertilizer and soil nutrients in the surface layer in the ridges.However,MP transferred more nutrients to the deep soil than MZ,reducing nitrogen gas losses and improving nitrogen utilization efficiency.Alternatively,while no-tillage has become popular in agricultural production for its environmental advantages in reducing soil disturbance(Allettoet al.2011),the disturbance of ridging on the surface soil increases soil available water and improves the soil physicochemical properties (Caiet al.2012;Azizet al.2013).

4.2.Effect of tillage on maize root development,aboveground nitrogen accumulation,nitrogen use efficiency,and maize yield

Roots link soil properties with aboveground crop growth(Coelho and Or 1999;Jiaet al.2018;Shaoet al.2021;Huiet al.2022).Tillage can affect crop root growth and yield formation by influencing soil structure (Sunet al.2018;Sessitschet al.2019;Schwartzet al.2020).Compared to rotary and no-tillage,plow tillage decreases soil bulk density and improves deep root distribution(McGarryet al.2000;Xu and Mermoud 2001).In this study,plow tillage improved the soil physicochemical properties relative to the other treatments,increasing root biomass (Figs.2 and 6).Root biomass was significantly(P<0.05) correlated with aboveground nitrogen accumulation during maize growth (Fig.5).The larger root biomass (Fig.2),as well as RBD,RLD,and RSD(Table 3) under MP suggest better nutrient absorption ability than MR and MZ,which increased aboveground biomass and nitrogen accumulation (Figs.2 and 4),resulting in better NupE and maize yield (Table 1).While several studies have reported more positive effects of notillage on crop yield than traditional tillage (Heet al.2011;Zhanget al.2015),we found that MP had the highest yield and nitrogen use efficiency among the three tillage treatments (Tables 1 and 4).

Root characteristics such as root mass,root volume,and root number are closely related to root lodging resistance (Kamaraet al.2003;Sposaroet al.2008).Lodging typically reduces maize yields by 5–25%,or even up to 100% in some years (Li Net al.2010;Liuet al.2021).Larger root systems will improve root anchorage,reducing the risk of lodging (Manzuret al.2014).We showed that MP produced the highest aerial root biomass and root numbers (Fig.3),and it had the highest RBD,RLD,and RSD in the 0–20 and 20–40 cm soil layers,relative to MR and MZ,which could also help to reduce the likelihood of maize lodging.

4.3.Effect of tillage on nitrogen transfer and grain quality during grain filling

Grain filling is an important growth stage for the maize grain to absorb nitrogen (Masvayaet al.2017).Improving nitrogen translocation from vegetative organs makes full use of the nitrogen,increasing grain nitrogen accumulation and nitrogen use efficiency (Masclaux-Daubresseet al.2010).Tillage measures can improve soil moisture during grain filling,thereby altering nitrogen transfer in the different aboveground parts (Wanget al.2020).In our study,MP significantly (P<0.05) increased aboveground nitrogen transfer by 11.15–24.55% relative to MR and MZ (Table 3),increasing the NHI at harvest(Table 4).Crop roots are the key to improving nutrient uptake rate and thus crop yield (Wanget al.2015).However,the root system is also a crucial storage organ,and that role has not attracted enough attention.The nitrogen transfer amounts from roots to grain ranged from 17.9–29.7 kg N ha–1during grain filling,exceeding the nitrogen transfer from stems to grain (Fig.4-A;Table 3).MP transferred the most nitrogen from roots to grain from flowering to maturity,in amounts 24.77–47.84% higher than MR and MZ (Table 3).As a result,MP had a 13.67–24.75% higher total nitrogen transfer amount than MR and MZ,increasing both grain yield and crude protein content(Tables 1,3,and 5).Studies have predicted that 84% of China’s maize grain will be used for feed production by 2030 (Chen and Lu 2019).Adopting plow tillage before ridge–furrow plastic film mulch can increase the grain protein content,improving the feed conversion efficiency.

5.Conclusion

Plow and rotary tillage are common practices in the semiarid areas of Northwest China.This study showed that plow tillage is more suitable than rotary tillage and notillage before RFPM,improving root biomass,RBD,RLD,and RSD and increasing NupE and nitrogen transfer from the aboveground organs and roots to grain during grain filling,thus contributing to higher maize yields and crude protein contents.Therefore,marketing efforts to guide farmers to combine film mulch with plow tillage measures should be increased,in order to increase maize yield and reduce nitrogen losses and non-point source pollution.In conclusion,this study’s findings provide a reference for developing high-yielding maize with high nitrogen use efficiency for sustainable agricultural development.

Acknowledgements

Financial support was provided by the National Natural Science Foundation of China (31701384 and 32071980).

Declaration of competing interest

The authors declare that they have no conflict of interest.