Interaction effect of nitrogen form and planting density on plant growth and nutrient uptake in maize seedlings

High planting density is essential to increasing maize grain yield.However,single plants suffer from insufficient light under high planting density.Ammonium(NH_4^+)assimilation consumes less energy converted from radiation than nitrateIt is hypothesized that a mixed NO_3~–/NH_4^+supply is more important to improving plant growth and population productivity under high vs.low planting density.Maize plants were grown under hydroponic conditions at two planting densities(low density:only).A significant interaction effect was found between planting density and N form on plant biomass.Compared to nitrate only,75/25NO_3~–/NH_4^+increased per-plant biomass by 44%under low density,but by 81%under high density.Treatment with 75/25NO_3~–/NH_4^+increased plant ATP,photosynthetic rate,and carbon amount per plant by 31,7,and 44%under low density,respectively,but by 51,23,and 95%under high density.Accordingly,carbon level per plant under 75/25NO_3~–/NH_4^+was improved,which increased leaf area,specific leaf weight and total root length,especially for high planting density,increased by 57,17 and 63%,respectively.Furthermore,under low density,75/25NO_3~–/NH_4^+increased nitrogen uptake rate,while under high density,75/25NO_3~–/NH_4^+increased nitrogen,phosphorus,copper and iron uptake rates.By increasing energy use efficiency,an optimum NO_3~–/NH_4^+ratio can improve plant growth and nutrient uptake efficiency,especially under high planting density.In summary,an appropriate supply of NH_4^+in addition to nitrate can greatly improve plant growth and promote population productivity of maize under high planting density,and therefore a mixed N form is recommended for high-yielding maize management in the field.

Increasing nitrogen absorption and assimilation ability under mixed NO_(3)^(–)and NH_(4)^(+) supply is a driver to promote growth of maize seedlings

Compared with sole nitrate (NO_(3)^(-)) or sole ammonium (NH_(4)^(+)) supply,mixed nitrogen (N) supply may promote growth of maize seedlings.Previous study suggested that mixed N supply not only increased photosynthesis rate,but also enhanced leaf growth by increasing auxin synthesis to build a large sink for C and N utilization.However,whether this process depends on N absorption is unknown.Here,maize seedlings were grown hydroponically with three N forms (NO_(3)^(-)only,75/25 NO_(3)^(-)/NH_(4)^(+) and NH_(4)^(+) only).The study results suggested that maize growth rate and N content of shoots under mixed N supply was little different to that under sole NO_(3)^(-)supply at 0–3 d,but was higher than under sole NO_(3)^(-)supply at 6–9 d.^(15)N influx rate under mixed N supply was greater than under sole NO_(3)^(-) or NH_(4)^(+) supply at 6–9 d,although NO_(3)^(-) and NH_(4)^(+) influx under mixed N supply were reduced compared to sole NO_(3)^(-) and NH_(4)^(+) supply,respectively.qRT-PCR determination suggested that the increased N absorption under mixed N supply may be related to the higher expression of NO_(3)^(-) transporters in roots,such as ZmNRT1.1A,ZmNRT1.1B,ZmNRT1.1C,ZmNRT1.2 and ZmNRT1.3,or NH_(4)^(+) absorption transporters,such as Zm AMT1.1A,especially the latter.Furthermore,plants had higher nitrate reductase (NR)glutamine synthase (GS) activity and amino acid content under mixed N supply than when under sole NO_(3)^(-) supply.The experiments with inhibitors of NR reductase and GS synthase further confirmed that N assimilation ability under mixed N supply was necessary to promote maize growth,especially for the reduction of NO_(3)^(-) by NR reductase.This research suggested that the increased processes of NO_(3)^(-)and NH_(4)^(+) assimilation by improving N-absorption ability of roots under mixed N supply may be the main driving force to increase maize growth.

A cluster of mutagenesis revealed an osmotic regulatory role of the OsPIP1 genes in enhancing rice salt tolerance

Aquaporins play important regulatory roles in improving plant abiotic stress tolerance.To better understand whether the Os PIP1 genes collectively dominate the osmotic regulation in rice under salt stress,a cluster editing of the Os PIP1;1,Os PIP1;2 and Os PIP1;3 genes in rice was performed by CRISPR/Cas9 system.Sequencing showed that two mutants with Cas9-free,line 14 and line 18 were successfully edited.Briefly,line 14 deleted a single C base in both the Os PIP1;1 and Os PIP1;3 genes,and inserted a single T base in the Os PIP1;2 gene,respectively.While line 18 demonstrated an insertion of a single A base in the Os PIP1;1gene and a single T base in both the Os PIP1;2 and Os PIP1;3 genes,respectively.Multiplex editing of the Os PIP1 genes significantly inhibited photosynthetic rate and accumulation of compatible metabolites,but increased MDA contents and osmotic potentials in the mutants,thus delaying rice growth under salt stress.Functional loss of the Os PIP1 genes obviously suppressed the expressions of the Os PIP1,Os SOS1,Os CIPK24 and Os CBL4 genes,and increased the influxes of Na+and effluxes of K^(+)/H^(+)in the roots,thus accumulating more Na+in rice mutants under salt stress.This study suggests that the Os PIP1 genes are essential modulators collectively contributing to the enhancement of rice salt stress tolerance,and multiplex editing of the Os PIP1 genes provides insight into the osmotic regulation of the PIP genes.

Effect of Different Fertilizer Formulations on Growth and Chlorophyll Content of Greenhouse Grown Macadamia Plants in a Micro Drip-Irrigation System

A greenhouse experiment was conducted at Mahidol University, Thailand from January to May 2009. Macadamia plants were planted in pots with mixed substrate of soil： sand： coconut-coir： rice-husk： charcoal; 3.0： 1.0： 0.5： 1.0, respectively. Micro drip-irrigation system was operated 10：00 to 16：00 h daily with a controller scheduled to pump 12 minutes at 12 intervals. The study showed that application of Enshi tablet （18 tablets/plant/year） in a drip-irrigation system enhances growth of Macadamia compared to the application of OsmocoteTM tablet, Modified-enshi and Enshi solution. Significant variation in chlorophyll （a ＋ b） content was observed in Enshi tablet treatment. Soil chemical analyses indicated that the nutrient content in Enshi tablet appeared low compared to other formulations but nutrient removal was considerably brought down by the system, which gives a balance between nutrient removals by crops and addition through fertilizers. Hence, application of Enshi tablet is suggested for Macadamia in a drip-irrigation system.

Lateral root elongation in maize is related to auxin synthesis and transportation mediated by N metabolism under a mixed NO_(3)^(–) and NH_(4)^(+) supply

A mixed nitrate (NO_(3)^(–)) and ammonium (NH_(4)^(+)) supply can promote root growth in maize (Zea mays),however,the changes in root morphology and the related physiological mechanism under different N forms are still unclear.Here,maize seedlings were grown hydroponically with three N supplied in three different forms (NO_(3)^(–)only,75/25 NO_(3)^(–)/NH_(4)^(+)and NH_(4)^(+)only).Compared with sole NO_(3)^(–)or NH_(4)^(+),the mixed N supply increased the total root length of maize but did not affect the number of axial roots.The main reason was the increased total lateral root length,while the average lateral root (LR) length in each axle was only slightly increased.In addition,the average LR density of 2nd whorl crown root under mixed N was also increased.Compared with sole nitrate,mixed N could improve the N metabolism of roots (such as the N influx rate,nitrate reductase (NR) and glutamine synthase (GS)enzyme activities and total amino content of the roots).Experiments with exogenously added NR and GS inhibitors suggested that the increase in the average LR length under mixed N was related to the process of N assimilation,and whether the NR mediated NO synthesis participates in this process needs further exploration.Meanwhile,an investigation of the changes in root-shoot ratio and carbon (C) concentration showed that C transportation from shoots to roots may not be the key factor in mediating lateral root elongation,and the changes in the sugar concentration in roots further proved this conclusion.Furthermore,the synthesis and transportation of auxin in axial roots may play a key role in lateral root elongation,in which the expression of ZmPIN1B and ZmPIN9 may be involved in this pathway.This study preliminarily clarified the changes in root morphology and explored the possible physiological mechanism under a mixed N supply in maize,which may provide some theoretical basis for the cultivation of crop varieties with high N efficiency.

Science and Technology Backyard: A novel approach to empower smallholder farmers for sustainable intensification of agriculture in China

Sustainable feeding of the growing population in China without ecological destabilization is a grand challenge. In this populous country where agriculture is dominated by smallholder farming, developing innovative technology and translating scientific knowledge into action for smallholder farmers is a crucial step in addressing this challenge. Here, we present a novel approach for technology innovation and dissemination to achieve sustainable intensification in the fields of smallholder farmers. The Science and Technology Backyard(STB) is a hub in a rural area that links knowledge with practices to promote technology innovation and exchange. In this study, the framework and functions of STB are introduced, and the key implications for sustainable intensification across millions of smallholder farmers are explicitly stated:(i) develop innovative technology based on stated demands of farmers;(ii) disseminate technology by innovative social service models though combined top-down approaches with bottom-up measures to enable smallholders in rural areas. This paper provides a perspective on transformation of small-scale agriculture toward sustainable intensification in China and useful knowledge applicable to other developing countries.

The transformation of agriculture in China: Looking back and looking forward

China’s grain yield increased from 1 t hain 1961 to 6 t hain 2015, while successfully feeding not only its large population but also supplying agricultural products all over the world. These achievements were greatly supported by modern technology and distinct governmental policy. However, China’s grain production has been causing a number of problems mainly related to declining natural resources and a lack of environmental protection. Due to the growing population and changing dietary requirements, increasing food production must be achieved by increasing resource use efficiency while minimizing environmental costs. We propose two novel development pathways that can potentially sustain agricultural crop production in the next few decades:(i) enhancing nutrient use efficiency with zero increase in chemical fertilizer input until 2020 and(ii) concurrently increasing grain yield and nutrient use efficiency for sustainable intensification with integrated nutrient management after 2020. This paper provides a perspective on further agricultural developments and challenges, and useful knowledge of our valuable experiences for other developing countries.

Effect of Inoculation with Arbuscular Mycorrhizal Fungus on Nitrogen and Phosphorus Utilization in Upland Rice-Mungbean Intercropping System

The effect of arbuscular mycorrhiza fungi （AMF） on plant growth and nutrition utilization in upland rice and mungbean intercropping system was studied. A pot experiment was conducted in the greenhouse and AMF colonization rates of rice and mungbean roots, plant nutrient contents, the ability of nitrogen fixation, and nutrient contents changed in the soil were analyzed. The results were obtained as follows： the rates of AMF colonization of rice and mungbean roots were reached to 14.47 and 92.2% in intercopping system, and increased by 4.11 and 11.95% compared with that of in monocropping; the nirtrogen contents of mungbean and rice were increased by 83.72 and 64.83% in shoots, and 53.76 and 41.29% in roots, respectively, while the contents of iron in shoot and root of mungbean were increased by 223.08 and 60.19%, respectively. In the intercropping system with inoculation of AMF, the biomass of mungbean increased by 288.8%. However, the biomass of rice was not significantly changed among all treatments with or without inoculation of AMF recorded. The number and dry weight of nodules were significantly increased either when mungbean was intercropped with rice or inoculated with AMF. When compared with that of monocropping without AMF inoculation, the contents of nitrogen, phosphorus and iron in nodules of intercropping mungbean with inoculation increased by 80.14, 69.54 and 39.62%, respectively. Additionally, intercropping with AMF inoculation significantly increased soil nitrogen content, but reduced soil phosphorus content. We concluded that upland rice-mungbean intercropping system and inoculation with AMF improved the nutrient uptake, the ability of nitrogen fixation and the growth of mungbean.

Effects of Glomus mosseae on the toxicity of heavy metals to Vicia faba

A glasshouse pot experiment was conducted to investigate effects of the arbuscular mycorrhizal fungus Glomus mosseae on the growth of Vicia faba and toxicity induced by heavy metals （HMs） （Cu, Zn, Pb and Cd） in a field soil contaminated by a mixture of these metals. There was also uninoculation treatment （NM） simultaneously. Mycorrhizal （GM） plants have significantly increased growth and tolerance to toxicity induced by heavy metals compared with NM plants. P uptake was significantly increased in GM plants. Mycorrhizal symbiosis reduced the transportation of HMs fi＇om root to shoot by immobilizing HMs in the mycorrhizal, shown by increasing the ratios of HMs from root to shoot. Oxidative stress, which can induce DNA damage, is an important mechanism of heavy metal toxicity. GM treatment decreased oxidative stress by intricating antioxidative systems such as peroxidases and non-enzymic systems including soluble protein. The DNA damage induced by heavy metals was detected using comet assay, which showed DNA damage in the plants was decreased by the GM treatment.

Effect of long-term fertilization on soil nitrate distribution

A thirteen years long-term field fertilizer experiment was conducted to monitor the effect of different fertilization on soil nitrate distribution. The results showed: (1) Applying relative excessive N fertilizer could result large quantities of NO3- residue and NO3- movement downward in soil profiles; amending phosphate fertilizer or organic manure with nitrogen fertilizer together could significantly improve the status of NO3- leaching downward due to the balanced uptake of nutrients by crops. ( 2) Appropriate amounts of nitrogen fertilizer which was equal or smaller than the optimal fertilization rate could not result in more NO3- leaching in Northern China. (3) Precipitation influenced the amounts and depth of soil NO3- leaching: NO3- could move to 80 cm depth or below at autumn or at the next spring when rainfall was higher during the rainy season through July to September in North China.

Involvement of Plasma Membrane H+-ATPase in Adaption of Rice to Ammonium Nutrient

The preference of paddy rice for NH4+ rather than NO3ˉ is associated with its tolerance to low pH since a rhizosphere acidification occurs during NH4+ absorption.However,the adaptation of rice root to low pH has not been fully elucidated.The plasma membrane H+-ATPase is a universal electronic H+ pump,which uses ATP as energy source to pump H+ across the plasma membranes into the apoplast.The key function of this enzyme is to keep pH homeostasis of plant cells and generate a H+ electrochemical gradient,thereby providing the driving force for the active influx and efflux of ions and metabolites across the plasma membrane.This study investigated the acclimation of plasma membrane H+-ATPase of rice root to low pH.This mechanism might be partly responsible for the preference of rice plants to NH4+ nutrition.

Comparison of N uptake and internal use efficiency in two tobacco varieties

To explain the observation in field experiments that tobacco variety CB-1 was more nitrogen(N)-efficient than K326, the influence of two N levels on growth, N uptake and N flow within plants of the two tobacco varieties was studied. Xylem sap from the upper and lower leaves of both tobacco varieties cultured in quartz sand was collected by application of pressure to the root system. CB-1 took up more N with smaller roots at both high(HN, 10 mmol L-1) and low(LN, 1 mmol L-1) N levels, and built up more new tissues in upper leaves especially at LN level,than K326. Both varieties showed luxury N uptake, and CB-1 accumulated significantly less NO-3in new tissues than K326, when grown at the HN level. At both N levels, the amount of xylem-transported N and phloem-cycled N from shoot to root in K326 was greater than those in CB-1, indicating higher N use efficiency in CB-1 shoots than in K326 shoots. The major nitrogenous compound in the xylem sap was NO-3irrespective of N level and variety. Low N supply did not cause more NO-3reduction in the root. The results indicated that the N-efficient tobacco variety CB-1 was more efficient in both N uptake by smaller roots and N utilization in shoots, especially when grown at the LN level.

Transcriptional Regulation of Expression of the Maize Aldehyde Dehydrogenase 7 Gene (ZmALDH7B6) in Response to Abiotic Stresses

Aldehyde dehydrogenases（ALDHs） represent a large protein family, which includes several members that catalyze the oxidation of an aldehyde to its corresponding carboxylic acid in plants. Genes encoding members of the ALDH7 subfamily have been suggested to play important roles in various stress adaptations in plants. In this study, quantitative RT-PCR analysis revealed that a maize ALDH7 subfamily member（ZmALDH7B6） was constitutively expressed in various organs, including roots, leaves, immature ears, tassels, and developing seeds. The abundance of ZmALDH7B6 mRNA transcripts in maize roots was increased by ammonium, NaCl, and mannitol treatments. To further analyze tissue-specific and stress-induced expression patterns, the 1.5-kb 5′-flanking ZmALDH7B6 promoter region was fused to the β-glucuronidase（GUS） reporter gene and introduced into maize plants. In roots of independent transgenic lines, there was significant induction of GUS activity in response to ammonium supply, confirming ammonium-dependent expression of ZmALDH7B6 at the transcript level. Histochemical staining showed that GUS activity driven by the ZmALDH7B6 promoter was mainly localized in the vascular tissues of maize roots. These results suggested that ZmALDH7B6 is induced by multiple environmental stresses in maize roots, and may play a role in detoxifying aldehydes, particularly in vascular tissue.

Phenotypic characterization and genetic mapping of the dwarf mutant m34 in maize

Plant height is one of the most important agronomic traits associated with yield in maize.In this study,a gibberellins(GA)-insensitive dwarf mutant,m34,was screened from inbred line Ye478 by treatment with the chemical mutagen ethylmethanesulfonate(EMS).Compared to Ye478,m34 showed a dwarf phenotype with shorter internodes,and smaller leaf length and width,but with similar leaf number.Furthermore,m34 exhibited smaller guard cells in internodes than Ye478,suggesting that smaller cells might contribute to its dwarf phenotype.Genetic analysis indicated that the m34 dwarf phenotype was controlled by a recessive nuclear gene.An F2 population derived from a cross between m34 and B73 was used for mutational gene cloning and this gene was mapped to a chromosome region between umc2189 and umc1553 in chromosome 1 bin1.10,which harbored a previously identified dwarf gene Zm VP8.Sequencing analysis showed a nucleotide substitution(G1606 to A1606)in the sixth exon of ZmVP8,which resulted in an amino acid change(E531 to K531)from Ye478 to m34.This amino acid change resulted in anα-helix changing to aβ-sheet in the secondary protein structure and the‘SPEC’domain changed to a‘BOT1NT’domain in the tertiary protein structure.Taken together,these results suggested that m34 is a novel allelic mutant originally derived from Ye478 that is useful for further ZmVP8 functional analysis in maize.

Identification of two glycerophosphodiester phosphodiesterase genes in maize leaf phosphorus remobilization

Phosphate deficiency is one of the leading causes of crop productivity loss.Phospholipid degradation liberates phosphate to cope with phosphate deficiency.Glycerophosphodiester phosphodiesterases(GPX-PDEs)hydrolyse the intermediate products of phospholipid catabolism glycerophosphodiesters into glycerol-3-phosphate,a precursor of phosphate.However,the function of GPX-PDEs in phosphate remobilization in maize remains unclear.In the present study,we characterized two phosphate deficiency-inducible GPX-PDE genes,ZmGPX-PDE1 and ZmGPX-PDE5,in maize leaves.ZmGPX-PDE1 and ZmGPX-PDE5 were transcriptionally regulated by ZmPHR1,a well-described phosphate starvation-responsive transcription factor of the MYB family.Complementation of the yeast GPX-PDE mutant gde1Δindicated that ZmGPX-PDE1 and ZmGPX-PDE5 functioned as GPX-PDEs,suggesting their roles in phosphate recycling from glycerophosphodiesters.In vitro enzyme assays showed that ZmGPX-PDE1 and ZmGPX-PDE5 catalysed glycerophosphodiester degradation with different substrate preferences for glycerophosphoinositol and glycerophosphocholine,respectively.ZmGPX-PDE1 was upregulated during leaf senescence,and more remarkably,loss of ZmGPXPDE1 inmaize compromised the remobilization of phosphorus fromsenescing leaves to young leaves,resulting in a stay-green phenotype under phosphate starvation.These results suggest that ZmGPX-PDE1 catalyses the degradation of glycerophosphodiesters in maize,promoting phosphate recycling from senescing leaves to new leaves.This mechanism is crucial for improving phosphorus utilization efficiency in crops.

Characterization of Quantitative Trait Loci for Grain Minerals in Hexaploid Wheat (Triticum aestivum L.)

Wheat is an important source of essential minerals for human body. Breeding wheat with high grain mineral concentration thus benefits human health. The objective of present study was to identify quantitative trait loci （QTLs） controlling grain mineral concentration and to evaluate the relation between nitrogen （N） and other essential minerals in winter wheat. Wheat grains were harvested from field experiment which conducted in China and analyzed for this purpose. Forty-three QTLs controlling grain mineral concentration and nitrogen-related traits were detected by using a double haploid （DH） population derived from winter wheat varieties Hanxuan 10 and Lumai 14. Chromosomes 4D and 5A might be very important in controlling mineral status in wheat grains. Significant positive correlations were found between grain nitrogen concentration （GNC） and nutrients Fe, Mn, Cu, Mg concentrations （FeGC, MnGC, CuGC, MgGC）. Flag leafN concentration at anthesis （FLNC） significantly and positively correlated with GNC, FeGC, MnGC, and CuGC. The study extended our knowledge on minerals in wheat grains and suggested which interactions between minerals should be considered in future breeding program.

Responses of Aerobic Rice (Oryza sativa L.) to Iron Deficiency

Aerobic rice has the advantage of saving water. Most published work has focused on improving its yield, while few reported on its micronutrient status. In fact, Fe deficiency is a common nutritional problem in the production of aerobic rice. Short- term hydroponic culture experiments were conducted to study the response of aerobic rice to Fe deficiency and the effect of root exudates from Fe-deficient wheat on its Fe uptake ability. The results indicate that the amount of phytosiderophores （PS） released from aerobic rice did not increase under Fe deficient conditions. The Fe（III） reducing capacity of Fe-deficient aerobic rice did not increase and the solution pH did not decrease significantly. What＇s more, no obvious swelling was observed in the root tips. Aerobic rice did not show special responses to improve their Fe nutrition under Fe deficiency as both strategy I and II plants though they were very sensitive to Fe deficiency. This may be a reason which causes Fe deficiency problem in aerobic rice. However, root exudates from Fe-deficient wheat （PSw） could improve its Fe nutrition in the presence of insoluble Fe（OH）3. This suggests that aerobic rice could utilize Fe activated by PSw.

Influence of phosphocompost application on phosphorus availability and uptake by maize grown in red soil of Ishigaki Island, Japan

Phospho compost application is important with respect to soil fertility and plant nutrition. Therefore, the objective was to evaluate the influence of phospho compost application on P availability and uptake by maize in red soil. The phosphorus applied in the form of phospho compost, as compare to rock phosphate and super phosphate at a rate of 50 and 100 mg P2O5 Kg-1 soil. The application was done as spot and mix application. Results indicate that, spot application of 100 mg P2O5 kg-1 soil as phospho compost (b) registered significantly higher P uptake (2.1 and 5.31 mg·pot-1) and available soil P (19.1 and 21.0 mg·kg-1) as compare to Rock Phosphate alone (0.60 and 0.97 mg·pot-1) and (5.6 and 6.0 mg·kg-1) at 30 and 60 day after sowing, respectively. The probable chelating effect from phospho composting increased the phosphorus use efficiency and resulted into higher relative agronomic efficiency in phospho compost (b) spot application (40%) over mix application (15%). The dry matter yield had positive and significant correlation with available P in soil and P uptake by maize plants at 30 and 60 day after sowing. Results concluded that phospho compost enriched with FYM was most effective in increasing phosphorus availability in red soil and increasing dry matter yield of maize plants.

Management Options and Soil Types Differentially Affect Weeds in Maize Fields of Kakamega, Western Kenya

Maize production in Kenya is constrained by weed infestation and nutrient deficiencies. Field studies were conducted during the 2008/2009 cropping seasons to investigate weeds in maize fields on three dominant soil types in Western Kenya. Weeds were inventoried and their composition was compared using Jaccard＇s index. The economic importance of weed species （potential to reduce yields and the difficulty to control them by manual weeding） was assessed through participatory surveys. Finally, field trials assessed the effects of management options （farmer＇s practice, clean weeding, green manure, zero-tillage ＋ cover crop and zero-tillage） on weed biomass and species composition. Across the three soil types, 55 weed species in 21 families were identified. Soil types influenced species composition as confirmed by Jaccard＇s similarity indices of 0.50, 0.58 and 0.62 for Nitisol vs. Acrisol, Ferralsol vs. Acrisol and Nitisol vs. Ferralsol, respectively. The economically important weeds were Commelina benghalensis, Cynodon nlemfuensis, Bidens pilosa, Galinsoga parviflora and Leonotis nepetifolia. Management options significantly （P 〈 0.05） reduced weed biomass, irrespective of soil type and seasons. Maize biomass response was highest （7-16 Mg ha1） in zero-tillage and zero-tillage ＋ cover crop and lowest （2-8 Mg ha1） in farmer＇s practice. Significantly negative relationships （P 〈 0.01, r2 = 0.37 - 0.51） were established between leaf area index of maize and weed biomass across the soils. Zero-tillage combined with the use of a cover crop had the lowest weed biomass （〈 30% of the farmer practice） and thus appears to be a promising strategy combining soil fertility improvement with weed suppression in smallholder maize farming systems of Western Kenya.

Spatiotemporal variation and evaluation of agriculture green development: a case study of Hainan Province, China

The realization of green and sustainable development of agriculture is the common pursuit all over the world. Agriculture green development(AGD)program has been proposed as a sustainable development strategy in China,but insufficient is known about the quantitative evaluation of spatiotemporal variation in AGD at the regional scale. This study aimed to assess spatiotemporal patterns in AGD at the county/city-based regional level. For this purpose, a systematic index evaluation system was developed to assess the performance of socioeconomic, food production and environmental components in a key economic region(Hainan Province) of China. Hainan improved its AGD index(representing the overall performance toward achieving AGD) from 38.8 in 1988 to 40.9 in 2019. The socioeconomic development and agricultural productivity have improved with time;environmental quality declined due to overuse of chemicals from 1988 to 2013, but steadily improved after 2013, indicating positive effects of reducing chemical input. There was a higher AGD index in the coastal vs. central regions and the southern vs. northern regions. Scenarios featuring improved nutrient management or optimized diet structure and reduced waste improved economic benefits and social productivity while concurrently reducing environmental degradation. These results provide new insights for the future development of green and sustainable agriculture and formulation of agricultural policies in Hainan Province of China and even other developing countries that are facing or will soon face similar challenges.