Nanotechnology in precision agriculture: Advancing towards sustainable crop production.

Nanotechnology offers many potential solutions for sustainable agroecosystem, including improvement in nutrient use efficiency, efficacy of pest management, and minimizing the adverse environmental effects of agricultural production. Herein, we first highlighted the integrated application of nanotechnology and precision agriculture for sustainable productivity. Application of nanoparticle mediated material and advanced biosensors in precision agriculture is only possible by nanochips or nanosensors. Nanosensors offers the measurement of various stresses, soil quality parameters and detection of heavy metals along with the enhanced data collection, enabling precise decision-making and resource management in agricultural systems. Nanoencapsulation of conventional chemical fertilizers (known as nanofertilizers), and pesticides (known as nanopesticides) helps in sustained and slow release of chemicals to soils and results in precise dosage to plants. Further, nano-based disease detection kits are popular tools for early and speedy detection of viral diseases. Many other innovative approaches including biosynthesized nanoparticles have been evaluated and proposed at various scales, but in fact there are some barriers for practical application of nanotechnology in soil-plant system, including safety and regulatory concerns, efficient delivery at field levels, and consumer acceptance. Finally, we outlined the policy options and actions required for sustainable agricultural productivity, and proposed various research pathways that may help to overcome the upcoming challenges regarding practical implications of nanotechnology.

Developing a tactical irrigation and nitrogen fertilizer management strategy for winter wheat through drip irrigation.

Introduction: Agricultural activities in the North China Plain are often challenged by inadequate irrigation and nutrient supply. Inadequate and improper resource utilization may impose negative impacts on agricultural sustainability. To counteract the negative impacts, a deeper understanding of the different resource management strategies is an essential prerequisite to assess the resource saving potential of crops. Methods: We explored plausible adaptation strategies including drip irrigation lateral spacings of 40 and 80 cm (hereafter referred to as LS40 and LS80, respectively), irrigating winter wheat after soil water consumption of 20 and 35 mm (hereafter represented as IS20 and IS35, respectively), and nitrogen fertilization scheme of a) applying 50% nitrogen as a basal dose and 50% as a top-dressing dose (NS50:50), b) 25% nitrogen as a basal dose and 75% as a topdressing dose (NS25:75), and c) no nitrogen application as a basal dose and 100% application as a top-dressing dose (NS0:100). Results and discussion: The consecutive 2 years (2017-2018 and 2018-2019) of field study results show that growing winter wheat under LS40 enhanced the water use efficiency (WUE), grain yield, 1,000-grain weight, and number of grains per spike by 15.04%, 6.95%, 5.67%, and 21.59% during the 2017-2018 season, respectively. Additionally, the corresponding values during the 2018-2019 season were 12.70%, 7.17%, 2.66%, and 19.25%, respectively. Irrigation scheduling of IS35 treatment improved all the growth-related and yield parameters of winter wheat. Further, treating 25% nitrogen as a basal dose and application of 75% as a top-dressing dose positively influenced the winter wheat yield. While NS0:100 increased the plant height, leaf area index (LAI), and aboveground biomass as compared to the other application strategies, but high nitrogen was observed in deeper soil layers. Regarding soil environment, the lowest soil moisture and nitrate nitrogen contents were observed in LS80 during both growing seasons. Overall, coupling the IS35 with NS25:75 under 40-cm lateral spacing is a suitable choice for sustainable winter wheat production in theNorth China Plain. The results of our study may be helpful in advancing the knowledge of the farmer community for winter wheat production. The findings can also aid in advancing new insights among scientists working on soil water and nitrogen distribution in drip irrigation for better productivity.

The Effects of Foliar Supplementation of Silicon on Physiological and Biochemical Responses of Winter Wheat to Drought Stress during Different Growth Stages.

Drought is one of the major environmental stresses, resulting in serious yield reductions in wheat production. Silicon (Si) has been considered beneficial to enhancing wheat resistance to drought stress. However, few studies have explored the mediated effects of foliar supplementation of Si on drought stress imposed at different wheat growth stages. Therefore, a field experiment was carried out to investigate the effects of Si supplementation on the physiological and biochemical responses of wheat to drought stress imposed at the jointing (D-jointing), anthesis (D-anthesis) and filling (D-filling) stages. Our results showed that a moderate water deficit markedly decreased the dry matter accumulation, leaf relative water content (LRWC), photosynthetic rate (Pn), stomatal conductance (Sc), transpiration rate (Tr) and antioxidant activity [peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT)]. On the contrary, it remarkably increased the content of osmolytes (proline, soluble sugar, soluble protein) and lipid peroxidation. The grain yields of D-jointing, D-anthesis and D-filling treatments were 9.59%, 13.9% and 18.9% lower, respectively, compared to the control treatment (CK). However, foliar supplementation of Si at the anthesis and filling stages significantly improved plant growth under drought stress due to the increased Si content. Consequently, the improvement in antioxidant activity and soluble sugar, and the reduction in the content of ROS, increased the LRWC, chlorophyll content, Pn, Sc and Tr, and ultimately boosted wheat yield by 5.71% and 8.9%, respectively, in comparison with the non-Si-treated plants subjected to water stress at the anthesis and filling stages. However, the mitigating effect of Si application was not significant at the jointing stage. It was concluded that foliar supplementation of Si, especially at the reproductive stage, was effective in alleviating drought-induced yield reduction.

A Review on Regulation of Irrigation Management on Wheat Physiology, Grain Yield, and Quality.

Irrigation has been pivotal in sustaining wheat as a major food crop in the world and is increasingly important as an adaptation response to climate change. In the context of agricultural production responding to climate change, improved irrigation management plays a significant role in increasing water productivity (WP) and maintaining the sustainable development of water resources. Considering that wheat is a major crop cultivated in arid and semi-arid regions, which consumes high amounts of irrigation water, developing wheat irrigation management with high efficiency is urgently required. Both irrigation scheduling and irrigation methods intricately influence wheat physiology, affect plant growth and development, and regulate grain yield and quality. In this frame, this review aims to provide a critical analysis of the regulation mechanism of irrigation management on wheat physiology, plant growth and yield formation, and grain quality. Considering the key traits involved in wheat water uptake and utilization efficiency, we suggest a series of future perspectives that could enhance the irrigation efficiency of wheat.

Interactive effects of irrigation system and level on grain yield, crop water use, and greenhouse gas emissions of summer maize in North China Plain.

Irrigation management is one of most critical factors influencing soil N2O and CO2 emissions in dryland agriculture. To explore the effects of irrigation systems and levels on the mitigation of N2O and CO2 emissions from maize fields and to determine the balance among greenhouse gases (GHG) emission, water-saving and grain yield, a two-year field experiment was conducted in the North China Plain (NCP) during the growing seasons of 2018 and 2019. Two irrigation systems (i.e., flood irrigation, FI, and drip irrigation, DI) were adopted with four irrigation levels in each system, including 65 mm/event (sufficient irrigation, CK), 50 mm/event (decreased by 23 %), 35 mm/event (by 46 %) and 20 mm/event (by 69 %), respectively. The results showed that both irrigation systems and levels had significant effects on soil N2O and CO2 emissions (P < 0.05). Nitrous oxide (N2O) and CO2 emissions peaked following irrigation or irrigation + fertilization events during sowing to early filling stage (R1), with the peak values increasing with irrigation levels. Meanwhile, peak values from FI were higher than those from DI at 50 mm and 65 mm irrigation levels. The average cumulative N2O and CO2 emissions of DI treatments were 14.9 % and 6.23 % lower than those of FI treatments (P < 0.05), respectively. Soil moisture was identified as one of the most crucial factors influencing N2O and CO2 fluxes. Deficit irrigation efficiently deceased cumulative N2O and CO2 emissions, but moderate to severe deficit irrigation brought significant reduction in grain yield. Drip irrigation with a slight deficit irrigation level (decreased by 23 %) obtained the best economic and environmental benefits, which achieved the dual goal of lower GHG emissions but higher WUE without sacrificing grain yield.

The end-use quality of wheat can be enhanced by optimal water management without incurring yield loss.

In China, water-saving irrigation is playing important roles in ensuring food security, and improving wheat quality. A barrel experiment was conducted with three winter wheat (Triticum aestivum L.) genotypes and two irrigation pattens to examine the effects of regulated deficit irrigation (RDI) on wheat grain yield, water-use efficiency (WUE), and grain quality. In order to accurately control the soil water content, wheat was planted in the iron barrels set under a rainproof shelter, and the soil water content in the iron barrel was controlled by gravity method. The mechanisms whereby water management influences the end-use functional properties of wheat grain were also investigated. The results revealed that RDI improved the end-use functional properties of wheat and WUE, without significant yield loss (less than 3%). Moderate water deficit (60% to 65% field capacity) before jointing and during the late grain-filling stage combined with a slight water deficit (65% to 70% field capacity) from jointing to booting increased grain quality and WUE. The observed non-significant reduction in wheat yield associated with RDI may be attributed to higher rate of photosynthesis during the early stage of grain development and higher rate of transfer of carbohydrates from vegetative organs to grains during the later stage. By triggering an earlier rapid transfer of nitrogen deposited in vegetative organs, RDI enhances grain nitrogen content, which in turn could enhance dough elasticity, given the positive correlation between grain nitrogen content and dough midline peak value. Our results also indicate that the effects of RDI on grain quality are genotype dependent. Therefore, the grain end-use quality of some specific wheat genotypes may be enhanced without incurring yield loss by an optimal water management.

Estimating the Impacts of Plant Internal Nitrogen Deficit at Key Top Dressing Stages on Corn Productivity and Intercepted Photosynthetic Active Radiation.

Accurate and timely appraisal of plant nitrogen (N) demand is imperative to regulate the canopy structure and corn production. The strength and time of plant N deficit can be quantified by critical N concentration. The study was aimed to analyze nitrogen nutrition index (NNI), nitrogen deficit content (NDC), plant nitrogen productivity (PNP), and a fraction of intercepted photosynthetic active radiation (FIPAR) across different N treatments and to develop NNI-NDC, NNI-PNP, NNI-FIPAR, NDC-PNP, and NDC-FIPAR relationships from V6 to V12 stages of corn to quantify the suitable PNP and FIPAR values under the optimal plant N condition. Four multi-N rates (0, 75, 90, 150, 180, 225, 270, and 300 kg N ha-1) field experiments were conducted with two cultivars of corn in Henan province of China. Results indicated that N fertilization affected yield, plant biomass, plant N content, and leaf area index. The values of NNI and NDC were from 0.54 to 1.28 kg ha-1 and from -28.13 to 21.99 kg ha-1 under the different treatments of N rate, respectively. The NDC and NNI showed significantly negative relationships from V6 to V12 stages. The values of PNP and FIPAR increased gradually with the crop growth process. The PNP values gradually declined while the FIPAR values of every leaf layer increased with the increase of N supply. The NDC-PNP and NNI-FIPAR relationships were significantly positive; however, the relationships between NNI-PNP and NDC-FIPAR were significantly negative during the vegetative period of corn. The coefficient of determination (R 2) based on NNI was better than that on NDC. The FIPAR values were ~0.35, 0.67, and 0.76% at the upper, middle, and bottom of leaf layers, respectively, and PNP values were ~39, 44, and 51 kg kg-1 at V6, V9, and V12 stages, respectively, when NNI and NDC values were equal to 1 and 0 kg ha-1, respectively. This study described the quantitative information about the effect of a plant's internal N deficit on plant N productivity and canopy light intercept. The projected results would assist in predicting the appropriate plant growth status during key N top-dressing stages of corn, which can optimize N application and improve N use efficiency.

Suitable split nitrogen application increases grain yield and photosynthetic capacity in drip-irrigated winter wheat (Triticum aestivum L.) under different water regimes in the North China Plain.

Chemical fertilizer overuse is a major environmental threat, critically polluting soil and water resources. An optimization of nitrogen (N) fertilizer application in winter wheat (Triticum aestivum L.) in association with various irrigation scheduling is a potential approach in this regard. A 2-year field experiment was carried out to assess the growth, yield and photosynthetic capacity of drip-irrigated winter wheat subjected to various split applications of urea (240 kg ha-1, 46% N). The eight treatments were, two irrigation scheduling and six N application modes in which, one slow-release fertilizer (SRF). Irrigation scheduling was based on the difference between actual crop evapotranspiration and precipitation (ETa-P). The two irrigation scheduling were I45 (Irrigation scheduling when ETa-P reaches 45 mm) and I30 (Irrigation scheduling when ETa-P reaches 30 mm). The six N levels were N0-100 (100% from jointing to booting), N25-75 (25% during sowing and 75% from jointing to booting), N50-50 (50% during sowing and 50% from jointing to booting), N75-25 (75% during sowing and 25% from jointing to booting), N100-0 (100% during sowing), and SRF100 (240 kg ha-1, 43% N during sowing). N top-dressing application significantly (P<0.05) influenced wheat growth, aboveground biomass (ABM), grain yield (GY) and its components, photosynthetic and chlorophyll parameters, and plant nutrient content. According to the averages of the two winter wheat-growing seasons, the I45N50-50 and I45SRF100 treatments, respectively had the highest GY (9.83 and 9.5 t ha-1), ABM (19.91 and 19.79 t ha-1), net photosynthetic rate (35.92 and 34.59 µmol m-2s-1), stomatal conductance (1.387 and 1.223 mol m-2s-1), SPAD (69.33 and 64.03), and chlorophyll fluorescence FV/FM (8.901 and 8.922). The present study provided convincing confirmation that N applied equally in splits at basal-top-dressing rates could be a desirable N application mode under drip irrigation system and could economically compete with the costly SRF for winter wheat fertilization. The I45N50-50 treatment offers to farmers an option to sustain wheat production in the NCP.

Coordination of leaf hydraulic, anatomical, and economical traits in tomato seedlings acclimation to long-term drought.

BACKGROUND: Leaf hydraulic and economics traits are critical for balancing plant water and CO2 exchange, and their relationship has been widely studied. Leaf anatomical traits determine the efficiency of CO2 diffusion within mesophyll structure. However, it remains unclear whether leaf anatomical traits are associated with leaf hydraulic and economics traits acclimation to long-term drought. RESULTS: To address this knowledge gap, eight hydraulic traits, including stomatal and venation structures, four economics traits, including leaf dry mass per area (LMA) and the ratio between palisade and spongy mesophyll thickness (PT/ST), and four anatomical traits related to CO2 diffusion were measured in tomato seedlings under the long-term drought conditions. Redundancy analysis indicated that the long-term drought decreased stomatal conductance (gs) mainly due to a synchronized reduction in hydraulic structure such as leaf hydraulic conductance (Kleaf) and major vein width. Simultaneously, stomatal aperture on the adaxial surface and minor vein density (VDminor) also contributed a lot to this reduction. The decreases in mesophyll thickness (Tmes) and chlorophyll surface area exposed to leaf intercellular air spaces (Sc/S) were primarily responsible for the decline of mesophyll conductance (gm) thereby affecting photosynthesis. Drought increased leaf density (LD) thus limited CO2 diffusion. In addition, LMA may not be important in regulating gm in tomato under drought. Principal component analysis revealed that main anatomical traits such as Tmes and Sc/S were positively correlated to Kleaf, VDminor and leaf thickness (LT), while negatively associated with PT/ST. CONCLUSIONS: These findings indicated that leaf anatomy plays an important role in maintaining the balance between water supply and CO2 diffusion responses to drought. There was a strong coordination between leaf hydraulic, anatomical, and economical traits in tomato seedlings acclimation to long-term drought.

Suitable nitrogen application mode and lateral spacing for drip-irrigated winter wheat in North China Plain.

To propose an appropriate nitrogen application mode and suitable drip irrigation lateral spacing, a field experiment was conducted during 2017-2018 and 2018-2019 growing seasons to quantify the different drip irrigation lateral spacings and nitrogen fertigation strategies effects on winter wheat growth, yield, and water use efficiency (WUE) in the North China Plain (NCP). The experiment consisted of three drip irrigation lateral spacing (LS) (40, 60, and 80 cm, referred to as D40, D60, and D80 respectively) and three percentage splits of nitrogen application modes (NAM) (basal and top dressing application ratio as 50:50 (N50:50), 25:75 (N25:75), and 0:100 (N0-100) respectively). The experimental findings depicted that yield and its components, and WUE were markedly affected by LS and NAM. Fertigation of winter wheat at N25:75 NAM notably (P<0.05) increased the grain yield by 4.88%, 1.83% and 8.03%, 4.61%, and WUE by 3.10%, 3.18% and 5.37%, 7.82%, compared with those at NAM N50:50 and N0:100 in 2017-2018 and 2018-2019 growing seasons, respectively. LS D40 appeared very fruitful in terms of soil moisture and nitrogen distribution, WUE, grain yield, and yield components than that of other LS levels. The maximum grain yield (8.73 and 9.40 t ha-1) and WUE (1.70 and 1.95 kg m-3) were obtained under D40N25:75 during both growing seasons, which mainly due to that all main yield components in D40N25:75 treatment, such as spikes per unit area, 1000-grain weight, and grains per spike were significantly higher as compared to other treatments. The outcomes of this research may provide a scientific basis of lateral spacing and nitrogen fertigation management for the production of drip-irrigated winter wheat in NCP.

Corrigendum: Role of Hydraulic Signal and ABA in Decrease of Leaf Stomatal and Mesophyll Conductance in Soil Drought-Stressed Tomato.

[This corrects the article DOI: 10.3389/fpls.2021.653186.].

Role of Hydraulic Signal and ABA in Decrease of Leaf Stomatal and Mesophyll Conductance in Soil Drought-Stressed Tomato.

Drought reduces leaf stomatal conductance (gs) and mesophyll conductance (gm). Both hydraulic signals and chemical signals (mainly abscisic acid, ABA) are involved in regulating gs. However, it remains unclear what role the endogenous ABA plays in gm under decreasing soil moisture. In this study, the responses of gs and gm to ABA were investigated under progressive soil drying conditions and their impacts on net photosynthesis (An) and intrinsic water use efficiency (WUEi) were also analyzed. Experimental tomato plants were cultivated in pots in an environment-controlled greenhouse. Reductions of gs and gm induced a 68-78% decline of An under drought conditions. While soil water potential (Ψsoil) was over -1.01 MPa, gs reduced as leaf water potential (Ψleaf) decreased, but ABA and gm kept unchanged, which indicating gs was more sensitive to drought than gm. During Ψsoil reduction from -1.01 to -1.44 MPa, Ψleaf still kept decreasing, and both gs and gm decreased concurrently following to the sustained increases of ABA content in shoot sap. The gm was positively correlated to gs during a drying process. Compared to gs or gm, WUEi was strongly correlated with gm/gs. WUEi improved within Ψsoil range between -0.83 and -1.15 MPa. In summary, gs showed a higher sensitivity to drought than gm. Under moderate and severe drought at Ψsoil ≤ -1.01 MPa, furthermore from hydraulic signals, ABA was also involved in this co-ordination reductions of gs and gm and thereby regulated An and WUEi.

Estimating the Growth Indices and Nitrogen Status Based on Color Digital Image Analysis During Early Growth Period of Winter Wheat.

The non-destructive estimation of plant nitrogen (N) status is imperative for timely and in-season crop N management. The objectives of this study were to use canopy cover (CC) to establish the empirical relations between plant growth indices [shoot dry matter (SDM), leaf area index (LAI), shoot N accumulation (SNA), shoot nitrogen concentration (SNC)], and CC as well as to test the feasibility of using CC to assess N nutrition index (NNI) from Feekes 3 to Feekes 6 stages of winter wheat. Four multi-locational (2 sites), multi-cultivars (four cultivars), and multi-N rates (0-300 kg N ha-1) field experiments were carried out during 2016 to 2018 seasons. The digital images of the canopy were captured by a digital camera from Feekes 3 to Feekes 6 stages of winter wheat, while SDM, LAI, SNA, and SNC were measured by destructive plant sampling. CC was calculated from digital images developed by self-programmed software. CC showed significant correlations with growth indices (SDM, LAI, and SNA) across the different cultivars and N treatments, except for SNC. However, the stability of these empirical models was affected by cultivar characteristics and N application rates. Plant N status of winter wheat was assessed using CC through two methods (direct and indirect methods). The direct and indirect methods failed to develop a unified linear regression to estimate NNI owing to the high dispersion of winter wheat SNC during its early growth stages. The relationships of CC with SDM, SNC and NNI developed at individual growth stages of winter wheat using both methods were highly significant. The relationships developed at individual growth stages did not need to consider the effect of N dilution process, yet their stability is influenced by cultivar characteristics. This study revealed that CC has larger limitation to be used as a proxy to manage the crop growth and N nutrition during the early growth period of winter wheat despite it is an easily measured index.

Leaf Gas Exchange of Tomato Depends on Abscisic Acid and Jasmonic Acid in Response to Neighboring Plants under Different Soil Nitrogen Regimes.

High planting density and nitrogen shortage are two important limiting factors for crop yield. Phytohormones, abscisic acid (ABA), and jasmonic acid (JA), play important roles in plant growth. A pot experiment was conducted to reveal the role of ABA and JA in regulating leaf gas exchange and growth in response to the neighborhood of plants under different nitrogen regimes. The experiment included two factors: two planting densities per pot (a single plant or four competing plants) and two N application levels per pot (1 and 15 mmol·L-1). Compared to when a single plant was grown per pot, neighboring competition decreased stomatal conductance (gs), transpiration (Tr) and net photosynthesis (Pn). Shoot ABA and JA and the shoot-to-root ratio increased in response to neighbors. Both gs and Pn were negatively related to shoot ABA and JA. In addition, N shortage stimulated the accumulation of ABA in roots, especially for competing plants, whereas root JA in competing plants did not increase in N15. Pearson's correlation coefficient (R2) of gs to ABA and gs to JA was higher in N1 than in N15. As compared to the absolute value of slope of gs to shoot ABA in N15, it increased in N1. Furthermore, the stomatal limitation and non-stomatal limitation of competing plants in N1 were much higher than in other treatments. It was concluded that the accumulations of ABA and JA in shoots play a coordinating role in regulating gs and Pn in response to neighbors; N shortage could intensify the impact of competition on limiting carbon fixation and plant growth directly.

Simple Assessment of Nitrogen Nutrition Index in Summer Maize by Using Chlorophyll Meter Readings.

Rapid and non-destructive diagnostic tools to accurately assess crop nitrogen nutrition index (NNI) are imperative for improving crop nitrogen (N) diagnosis and sustaining crop production. This study was aimed to develop the relationships among NNI, leaf N gradient, chlorophyll meter (CM) readings gradient, and positional differences chlorophyll meter index [PDCMI, the ratio of CM readings between different leaf layers (LLs) of crop canopy] and to validate the accuracy and stability of these relationships across the different LLs, years, sites, and cultivars. Six multi-N rates (0-320 kg ha-1) field experiments were conducted with four summer maize cultivars (Zhengdan958, Denghai605, Xundan20, and Denghai661) at two different sites located in China. Six summer maize plants per plot were harvested at each sampling stage to assess NNI, leaf N concentration and CM readings of different LLs during the vegetative growth period. The results showed that the leaf N gradient, CM readings gradient and PDCMI of different LLs decreased, while the NNI values increased with increasing N supply. The leaf N gradient and CM readings gradient increased gradually from top to bottom of the canopy and CM readings of the bottom LL were more sensitive to changes in plant N concentration. The significantly positive relationship between NNI and CM readings of different LLs (LL1 to LL3) was observed, yet these relationships varied across the years. In contrast, the relationships between NNI and PDCMI of different LLs (LL1 to LL3) were significantly negative. The strongest relationship between PDCMI and NNI which was stable across the cultivars and years was observed for PDCMI1-3 (NNI = -5.74 × PDCMI1-3+1.5, R2 = 0.76**). Additionally, the models developed in this study were validated with the data acquired from two independent experiments to assess their accuracy of prediction. The root mean square error value of 0.1 indicated that the most accurate and robust relationship was observed between PDCMI1-3 and NNI. The projected results would help to develop a simple, non-destructive and reliable approach to accurately assess the crop N status for precisely managing N application during the growth period of summer maize crop.

Suitable indicators using stem diameter variation-derived indices to monitor the water status of greenhouse tomato plants.

It is very important to seek a simple nondestructive method to continuously measure plant water status for irrigation scheduling. Changes in stem diameter in response to plant water status and soil water content (SWC) were experimentally investigated during the growing seasons of 2011/2012 and 2012/2013 in pot-cultivated tomato (Lycopersicon esculentum L.) plants in a plastic greenhouse. This study was conducted to determine suitable SDV (stem diameter variation)-derived indices as indicators of tomato plant water status for irrigation scheduling. The experiment was designed as a two-factor randomized block using the SWC and growth stages as variables. The SWC was controlled at 70-80% (well-watered), 60-70% (slightly deficit watered), 50-60% (moderately deficit watered) of the field capacity (FC), and the prescribed growing stages were vegetative, flowering and fruit-forming, and harvesting stages. Regression analysis showed that the SD6 (the difference between the stem diameter value at 06:00 am and the initial sensor reading) was closely related to the SWC (p<0.01) during rapid vegetative growth, whereas the MDS (the maximum daily shrinkage) was closely related to the SWC (p<0.01) during slow vegetative growth. Our results suggest that SDV-derived indicators can be used for determining plant water status and for scheduling irrigation at different growth/developmental stages.

Impacts of Steel-Slag-Based Silicate Fertilizer on Soil Acidity and Silicon Availability and Metals-Immobilization in a Paddy Soil.

Slag-based silicate fertilizer has been widely used to improve soil silicon- availability and crop productivity. A consecutive early rice-late rice rotation experiment was conducted to test the impacts of steel slag on soil pH, silicon availability, rice growth and metals-immobilization in paddy soil. Our results show that application of slag at a rate above higher or equal to 1 600 mg plant-available SiO2 per kg soil increased soil pH, dry weight of rice straw and grain, plant-available Si concentration and Si concentration in rice shoots compared with the control treatment. No significant accumulation of total cadmium (Cd) and lead (Pb) was noted in soil; rather, the exchangeable fraction of Cd significantly decreased. The cadmium concentrations in rice grains decreased significantly compared with the control treatment. In conclusion, application of steel slag reduced soil acidity, increased plant-availability of silicon, promoted rice growth and inhibited Cd transport to rice grain in the soil-plant system.

In situ stabilization of heavy metals in multiple-metal contaminated paddy soil using different steel slag-based silicon fertilizer.

Steel slag has been widely used as amendment and silicon fertilizer to alleviate the mobility and bioavailability of heavy metals in soil. The objective of this study was to evaluate the influence of particle size, composition, and application rate of slag on metal immobilization in acidic soil, metals uptake by rice and rice growth. The results indicated that application of slag increased soil pH, plant-available silicon concentrations in soil, and decreased the bioavailability of metals compared with control treatment, whereas pulverous slag (S1) was more effective than granular slag (S2 and S3). The acid-extractable fraction of Cd in the spiked soil was significantly decreased with application of S1 at rates of 1 and 3 %, acid-extractable fractions of Cu and Zn were decreased when treated at 3 %. Use of S1 at both rates resulted in significantly lower Cd, Cu, and Zn concentrations in rice tissues than in controls by 82.6-92.9, 88.4-95.6, and 67.4-81.4 %, respectively. However, use of pulverous slag at 1 % significantly promotes rice growth, restricted rice growth when treated at 3 %. Thus, the results explained that reduced particle size and suitable application rate of slag could be beneficial to rice growth and metals stabilization.

Yield Response of Spring Maize to Inter-Row Subsoiling and Soil Water Deficit in Northern China.

BACKGROUND: Long-term tillage has been shown to induce water stress episode during crop growth period due to low water retention capacity. It is unclear whether integrated water conservation tillage systems, such asspringdeepinter-row subsoiling with annual or biennial repetitions, can be developed to alleviate this issue while improve crop productivity. METHODS: Experimentswere carried out in a spring maize cropping system on Calcaric-fluvicCambisolsatJiaozuoexperimentstation, northern China, in 2009 to 2014. Effects of threesubsoiling depths (i.e., 30 cm, 40 cm, and 50 cm) in combination with annual and biennial repetitionswasdetermined in two single-years (i.e., 2012 and 2014)againstthe conventional tillage. The objectives were to investigateyield response to subsoiling depths and soil water deficit(SWD), and to identify the most effective subsoiling treatment using a systematic assessment. RESULTS: Annualsubsoiling to 50 cm (AS-50) increased soil water storage (SWS, mm) by an average of8% in 0-20 cm soil depth, 19% in 20-80 cm depth, and 10% in 80-120 cm depth, followed by AS-40 and BS-50, whereas AS-30 and BS-30 showed much less effects in increasing SWS across the 0-120 cm soil profile, compared to the CK. AS-50 significantly reduced soil water deficit (SWD, mm) by an average of123% during sowing to jointing, 318% during jointing to filling, and 221% during filling to maturity, compared to the CK, followed by AS-40 and BS-50. An integrated effect on increasing SWS and reducing SWD helped AS-50 boost grain yield by an average of 31% and biomass yield by 30%, compared to the CK. A power function for subsoiling depth and a negative linear function for SWD were used to fit the measured yields, showing the deepest subsoiling depth (50 cm) with the lowest SWD contributed to the highest yield. Systematic assessment showed that AS-50 received the highest evaluation index (0.69 out of 1.0) among all treatments. CONCLUSION: Deepinter-row subsoilingwith annual repetition significantly boosts yield by alleviating SWD in critical growth period and increasing SWS in 20-80 cm soil depth. The results allow us to conclude that AS-50 can be adopted as an effective approach to increase crop productivity, alleviate water stress, and improve soil water availability for spring maize in northern China.

[Differences in root developmenly of winter wheat cultivars in Huang-Huai Plain, China].

Selecting one presently popularized winter wheat cultivar (Zhengmai 9023) and two cultivars (Abo and Fengchan 3) introduced in the 1950s and 1960s in Huang-Huai Plain as test materials, and by using minirhizotron technique, this paper studied the live root length, root diameter distribution, and net root growth rate of the cultivars. Fine roots with a diameter from 0.05 mm to 0.25 mm occupied the majority of the whole root system, and the fine roots with a diameter less than 0.5 mm accounted for 98% of the live root length. The average root diameter varied with plant growth, the variation range being 0.15 - 0.22 mm, and no significant difference was observe among the cultivars. The live root length was significantly positively correlated root number, suggesting that root number was the main factor for the increase of live root length. The most vigorous growth period of the roots was from reviving to jointing stage, and Abo and Fengchan 3 had a longer period increased root vitality, as compared with Zhengmai 9023. For Zhengmai 9023, its fine roots with a diameter more than 0.1 mm had an increasing proportion after jointing stage, which was helpful for improving plant resistance, root activity, and grain-filling at late growth stages.