Citrus Yield Research Articles

Effect of different spring and summer fertilization proportions on fruit yield, quality, and nutrient use efficiency of Newhall orange (Citrus sinensis Osbeck) orchard in Ganzhou province

The amount and time of fertilization play an important role in the quality and yield of citrus. Moreover, twice fertilization in the spring (March) and summer (July) are generally applied in citrus orchards, of which the appropriate proportion is unclear, especially in Ganzhou. Therefore, the two-year field experiment containing three proportions (60/40, 80/20, 100/0) of spring and summer fertilization was carried out with a 15-year-old Newhall orange orchard to recommend the optimum fertilization proportion for orchard. Results showed that variations of soil available N, P, K concentrations resulting from different spring and summer fertilization proportion significantly affected orange fruit quality and yield. The soil available nitrogen (N), phosphorus (P), and potassium (K) concentrations fertilized with a proportion of 80/20 spring and summer were higher overall the year. The spring and summer fertilizer application with 80/20 increased fruit yield by 35.14%, and had higher total soluble solids and lower titrated acid. Moreover, the only one-time fertilization exhibited almost the same fruit yield, fruit N, P, K removal, but lower fruit titrated acid content and higher solid acid ratio. The present study results demonstrated that increasing the proportion of spring fertilization particularly the proportion of 80/20 could be a recommended dose for obtaining higher fruit yield and quality.

Citrus green fruit detection via improved feature network extraction.

It is crucial to accurately determine the green fruit stage of citrus and formulate detailed fruit conservation and flower thinning plans to increase the yield of citrus. However, the color of citrus green fruits is similar to the background, which results in poor segmentation accuracy. At present, when deep learning and other technologies are applied in agriculture for crop yield estimation and picking tasks, the accuracy of recognition reaches 88%, and the area enclosed by the PR curve and the coordinate axis reaches 0.95, which basically meets the application requirements.To solve these problems, this study proposes a citrus green fruit detection method that is based on improved Mask-RCNN (Mask-Region Convolutional Neural Network) feature network extraction. First, the backbone networks are able to integrate low, medium and high level features and then perform end-to-end classification. They have excellent feature extraction capability for image classification tasks. Deep and shallow feature fusion is used to fuse the ResNet(Residual network) in the Mask-RCNN network. This strategy involves assembling multiple identical backbones using composite connections between adjacent backbones to form a more powerful backbone. This is helpful for increasing the amount of feature information that is extracted at each stage in the backbone network. Second, in neural networks, the feature map contains the feature information of the image, and the number of channels is positively related to the number of feature maps. The more channels, the more convolutional layers are needed, and the more computation is required, so a combined connection block is introduced to reduce the number of channels and improve the model accuracy. To test the method, a visual image dataset of citrus green fruits is collected and established through multisource channels such as handheld camera shooting and cloud platform acquisition. The performance of the improved citrus green fruit detection technology is compared with those of other detection methods on our dataset. The results show that compared with Mask-RCNN model, the average detection accuracy of the improved Mask-RCNN model is 95.36%, increased by 1.42%, and the area surrounded by precision-recall curve and coordinate axis is 0.9673, increased by 0.3%. This research is meaningful for reducing the effect of the image background on the detection accuracy and can provide a constructive reference for the intelligent production of citrus.

A Novel bHLH Transcription Factor PtrbHLH66 from Trifoliate Orange Positively Regulates Plant Drought Tolerance by Mediating Root Growth and ROS Scavenging

Drought limits citrus yield and fruit quality worldwide. The basic helix-loop-helix (bHLH) transcription factors (TFs) are involved in plant response to drought stress. However, few bHLH TFs related to drought response have been functionally characterized in citrus. In this study, a bHLH family gene, named PtrbHLH66, was cloned from trifoliate orange. PtrbHLH66 contained a highly conserved bHLH domain and was clustered closely with bHLH66 homologs from other plant species. PtrbHLH66 was localized to the nucleus and had transcriptional activation activity. The expression of PtrbHLH66 was significantly induced by polyethylene glycol 6000 (PEG6000) and abscisic acid (ABA) treatments. Ectopic expression of PtrbHLH66 promoted the seed germination and root growth, increased the proline and ABA contents and the activities of antioxidant enzymes, but reduced the accumulation of malondialdehyde (MDA) and reactive oxygen species (ROS) under drought stress, resulting in enhanced drought tolerance of transgenic Arabidopsis. In contrast, silencing the PtrbHLH66 homolog in lemon plants showed the opposite effects. Furthermore, under drought stress, the transcript levels of 15 genes involved in ABA biosynthesis, proline biosynthesis, ROS scavenging and drought response were obviously upregulated in PtrbHLH66 ectopic-expressing Arabidopsis but downregulated in PtrbHLH66 homolog silencing lemon. Thus, our results suggested that PtrbHLH66 acted as a positive regulator of plant drought resistance by regulating root growth and ROS scavenging.

Ineffectiveness of applying additional insecticide sprays at the border of the citrus block for the control of Huanglongbing.

Huanglongbing (HLB), mainly associated with the bacterium 'Candidatus Liberibacter asiaticus', is a devastating disease that causes negative impacts on citrus yield and fruit quality. One of the main HLB control measures is based on preventive insecticide sprays, aiming to control its vector, the Asian citrus psyllid (ACP) Diaphorina citri. In blocks on the orchard's periphery, the ACP population is more concentrated in trees closer to the block's edge and gradually decreasing towards its interior. This spread pattern of ACP has motivated growers to perform, empirically based, additional insecticide applications at the border of the block ('AB'), as an additional measure to spraying insecticides in the entire block ('EB'). Hence, this work aimed (i) to evaluate the coverage and efficiency of AB, comparing tree canopy volume, and planting direction; and (ii) to compare ACP population and HLB incidence between blocks treated under EB, and blocks that received 'EB + AB'. Regardless of the operational situation, as the distance increased from the orchard's edge (0m) to the interior, spray coverage exponentially decayed from an average of 21% to less than 1% of coverage, and ACP mortality exponentially decayed from 83% to 7%. In general, the spray coverage and ACP mortality were suitable only for the tree canopy face directly sprayed at the orchard's edge (0m). After 5.5 years, a higher ACP population and number of symptomatic trees were detected in 'EB + AB'. As the 'EB + AB' had no effect in reducing ACP population, or HLB incidence, this additional spraying had no benefit in HLB management. © 2022 Society of Chemical Industry.

Terahertz spectroscopic monitoring and analysis of citrus leaf water status under low temperature stress

Low temperature stress, in the form of chilling and freezing, is one of the major environmental factors impacting on citrus yield, which changes plant's water state and results in the crops' sub-health or injury. The innovative terahertz (THz) spectroscopy and imaging based sensing technology has been shown to be a suitable tool for plant leaf water status determination, due to THz radiation's innate sensitivity to hydrogen bond vibration in aqueous solutions, which is usually related to plant phenotype change. We demonstrate experimentally that the THz absorption coefficient of leaf could be used for distinguishing plant's physiological stress status, exhibiting clear decreasing or increasing trend under chilling or freezing stress respectively. The underlying rationale might be that membrane damage shows a diverse pattern, changing the intra- or extra-cellular liquid environments, likely being linked to the various THz spectral characteristics. There were different adaptations in leaf morphology, leading to different leaf density, which in turn affects the water volume fraction. Moreover, different patterns of the dynamic equilibrium state of free water and bound water under chilling and freezing treatment were revealed by THz spectroscopy. Here, THz spectroscopic monitoring has shown unique potential for judging citrus's low temperature stress state through bio-water detection and discrimination.

Spatiotemporal prediction and optimization of environmental suitability in citrus-producing areas

The increasing need for citrus has driven the rapid expansion of citrus planting areas. However, not all areas are suitable for growing citrus. It is necessary to understand the future changing trend of environmental suitability in citrus-producing areas. Here, based on the soil nutrient data of citrus cultivation from 2006 to 2018, the spatiotemporal kriging method was used to predict the spatiotemporal distribution of soil nutrients in Zigui County, Hubei Province. Then, geographical and meteorological conditions were combined to evaluate the suitability for citrus cultivation at temporal and spatial levels, and the results were verified by the yield and quality data of citrus. The results showed that from 2018 to 2027, the overall suitability of the citrus-producing area displayed a gradually rising trend, with the “suitable” producing area increasing from 4.5% to 20.16%. The validation results indicated that the mean relative errors of spatiotemporal predictors were less than 30% except for the effective iron. Correlation analysis revealed that the proportion of “moderately suitable” and “suitable” orchards had significant positive correlations with annual yield. The low suitability of Maoping town was mainly attributed to its soil acidification and available P content, and that of Shazhenxi town was ascribed to its low soil contents of available P and N. The optimal fertilization scheme was constructed by an artificial neural network to optimize the fertilization status of some citrus producing areas. This study has created a dynamic assessment of the environmental suitability of citrus production areas to support improvements in citrus production.

Salt Tolerance Indicators in ‘Tahiti’ Acid Lime Grafted on 13 Rootstocks

The citrus yield is limited by soil and/or water salinity, but appropriate rootstocks can ensure the sustainability of the production system. Therefore, the objective of the present research was to evaluate the salt content in the soil and the production and physiological aspects of the ‘Tahiti’ acid lime combined with thirteen rootstocks, irrigated with saline water in the first two production years to identify indicators of salt tolerance. The rootstocks evaluated were: ‘Santa Cruz Rangpur’ lime, ‘Indio’, ‘Riverside’ and ‘San Diego’ citrandarins, ‘Sunki Tropical’ mandarin, and eight hybrids, obtained from the Citrus Breeding Program of Embrapa Cassava and Fruits. The waters used had three saline levels: 0.14, 2.40, and 4.80 dS m−1, in a randomized block adopting a split-plot design, with rootstocks in the plots and saline waters in the subplots, with four replicates. From August 2019 to February 2021, fruit harvests and agronomic traits were measured. At the end of each production year, the soil characteristics, leaf gas exchange, and chlorophyll a fluorescence analysis were performed. It was concluded that: (1) the effects of water salinity on citrus are of osmotic nature, reducing gas exchange, (2) the salinity did not significantly damage the photosynthetic apparatus until the second year of production, and (3) using more stable, salt-tolerant rootstocks makes it possible to cultivate ‘Tahiti’ acid lime under irrigation with waters of 2.4 dS m−1 electrical conductivity.

Exploring the Impact of Farmer Field Schools on the Adoption of Sustainable Agricultural Practices and Farm Production: A Case of Pakistani Citrus Growers

In the wake of recent climate changes, extension services have become crucial drivers in disseminating information about the latest agriculture technologies and facilitating sustainable agricultural productivity. Pakistan’s traditional extension cannot yield the expected outcomes which corroborate the introduction of a participatory approach, mainly in farmers’ field schools. Using farm-level data from Punjab province, the current study examined the impact of farmers’ field schools (FFS) on adopting sustainable agriculture practices (SAPs) and citrus yield. The study employed recursive bivariate probit and propensity score matching to explore the objectives. The findings revealed that FFS participants had a higher SAPs adoption than non-participants, demonstrating the positive impact of FFS on the uptake of SAPs. Moreover, the treatment effect showed that FFS participants had a higher yield than the non-participants. The results suggest strengthening and enhancing FFS reach among citrus growers.

Tree-level citrus yield prediction utilizing ground and aerial machine vision and machine learning

Yield prediction of citrus provides critical information before harvest to growers and allied industry to predict the resources required for workers, storage, and transportation of the harvest. In this study, three machine learning (ML) based models were developed for tree-level citrus yield prediction: (i) Model-1 utilized UAV imagery; (ii) Model-2 utilized UAV imagery and ground-based fruit detection and counts from images taken from one side of the tree; and (iii) Model-3 utilized UAV imagery and ground-based fruit detection and counts from images taken from two sides of the tree. The UAV images were used as input to a novel cloud-based technology, Agroview, to get the tree health, height, and canopy area information. The multispectral bands and the tree structural parameters were the input for Model-1. Two images per tree were captured from the ground using an RGB camera (one from each side) and were used for fruit count using an object detection algorithm, YOLOv3. Harvest data was collected manually per tree (fruit count and weight). Four ML algorithms - gradient boosting regression (GBR), random forest regression (RFR), linear regression (LR), and partial least squares regression (PLSR) were used to generate the models. Model-2 (MAPE of 23.45%) performed similarly to Model-3 (MAPE of 25.72%) and significantly better than Model-1 (MAPE of 35.59%). Model-2 was selected as the best model because of its low MAPE value in predicting yield at the tree level, and data collection simplicity (compared to Model-3).

Does Service Utilization Improve Members’ Welfare? Evidence from Citrus Cooperatives in China

Farmers’ professional cooperatives (hereinafter referred to as “cooperatives”) are an important carrier for small farmers to organically connect to the big market. Under the background of frequent phenomena such as generalization of cooperatives, cooperative alienation, empty shelled cooperatives and involution of cooperatives in China, whether cooperatives can improve members’ welfare has attracted the attention of all walks of life. Service is the essential attribute of cooperatives, and the key to the functioning of cooperatives is the services utilization by members (hereinafter referred to as “service utilization”). Therefore, examining the impact of service utilization on members’ welfare has important theoretical and practical significance, which helps to scientifically evaluate of the current value of cooperatives in China and then objectively respond to questions about the development of cooperatives. Thus, this study takes the micro-survey data of 74 citrus cooperatives and 524 citrus members in Citrus County, Sichuan Province, China as examples, and uses the endogenous switching model to empirically analyze the impact of service utilization on members’ welfare. The results show that the level of service utilization is not high, and only half of the members use cooperative services. However, service utilization can significantly improve members’ welfare. Specifically, the average treatment effect of service utilization on citrus yields, net returns and household income is respectively 285.446 kg/mu, 1290 yuan/mu and 4980 yuan/person. Simultaneously, service utilization can increase citrus yields, net returns and household income by 13.49%, 18.32% and 17.99% on average. Finally, some countermeasures and suggestions are put forward, such as actively publicizing cooperative’s services, guiding members to use cooperative’s services, improving the standardization level of cooperatives and strengthening policy support for cooperatives.

Transcriptome and Physiological Analyses of a Navel Orange Mutant with Improved Drought Tolerance and Water Use Efficiency Caused by Increases of Cuticular Wax Accumulation and ROS Scavenging Capacity.

Drought is one of the main abiotic stresses limiting the quality and yield of citrus. Cuticular waxes play an important role in regulating plant drought tolerance and water use efficiency (WUE). However, the contribution of cuticular waxes to drought tolerance, WUE and the underlying molecular mechanism is still largely unknown in citrus. ‘Longhuihong’ (MT) is a bud mutant of ‘Newhall’ navel orange with curly and bright leaves. In this study, significant increases in the amounts of total waxes and aliphatic wax compounds, including n-alkanes, n-primary alcohols and n-aldehydes, were overserved in MT leaves, which led to the decrease in cuticular permeability and finally resulted in the improvements in drought tolerance and WUE. Compared to WT leaves, MT leaves possessed much lower contents of malondialdehyde (MDA) and hydrogen peroxide (H2O2), significantly higher levels of proline and soluble sugar, and enhanced superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities under drought stress, which might reduce reactive oxygen species (ROS) damage, improve osmotic regulation and cell membrane stability, and finally, enhance MT tolerance to drought stress. Transcriptome sequencing results showed that seven structural genes were involved in wax biosynthesis and export, MAPK cascade, and ROS scavenging, and seven genes encoding transcription factors might play an important role in promoting cuticular wax accumulation, improving drought tolerance and WUE in MT plants. Our results not only confirmed the important role of cuticular waxes in regulating citrus drought resistance and WUE but also provided various candidate genes for improving citrus drought tolerance and WUE.

Citrus Canker—Distribution, Taxonomy, Epidemiology, Disease Cycle, Pathogen Biology, Detection, and Management: A Critical Review and Future Research Agenda

Xanthomonas citri subsp. citri, a causative agent of the citrus canker (CC) disease, belongs to one of the essential groups of the bacterial phytopathogen family, Xanthomonadaceae. It has been a potential threat to the globally significant citrus fruit crop, which has remained under investigation for disease management and epidemiology since the 1980s. In Pakistan, the average yield of citrus is 11 t/ha, which is lower than other countries, including China, Brazil, and India, having average productions of 27, 26, and 22 tons/hectare, respectively. Citrus canker is one of the most devastating diseases, posing a significant threat to crop yield and fruit quality. To date, five distinct types (or forms) of the citrus canker have been recognized; the Asiatic (Canker A) form is most destructive and affects most citrus cultivars. Severe infection outcomes include dieback, defoliation, severely blemished fruit, premature fruit drop, and reduced fruit quality. The infection increases under humid, warm, cloudy climate, wind, and heavy rainfall. The analysis of plasmid and chromosomal DNA of X. citri subsp. citri depicted an evolutionary relationship among pathovars of Xanthomonas. The extensive study on the genome of X. citri subsp. citri has contributed to the current knowledge of plant host recognition of pathogens, host specificities, dissemination, and propagation. Regulatory programs, i.e., quarantine or exclusion, continued to be practiced, prohibiting infected citrus plant material into the existing stock. Other measures include removal of inoculums sources, resistant hosts, protective copper-containing sprays, and windbreak systems. In this review, we explored the latest trends in the areas of epidemiology, pathogenome, detection, host–pathogen interaction, biofilm formation, and management of X. citri subsp. citri.

Boron-deficiency and aluminum toxicity activate antioxidant defense and disorganize the cell wall composition and architecture in trifoliate orange leaf

Boron (B)-deficiency and aluminum (Al) phytotoxicity are two main factors that influence the yield and quality of citrus. In this study, we investigated the effects of B-deficiency, Al stress, and double stress of B-deficiency and Al toxicity on antioxidant enzyme system and cell wall components in leaf of trifoliate orange seedlings. Boron deprivation and Al toxicity severely induced morphological and anatomical changes in leaves in terms of higher lipid peroxidation, inhibited photosynthesis and impeded seedling growth, and the damages was more pronounced by double stress. Boron-deficiency disturbed the distribution pattern of pectin in leaves, suppressing the content of alkali-soluble pectin and two types of 2-keto-3-deoxyoctanoic acid (KDO), thus reduced the binding of B to the leaf cell wall. Meanwhile, exposure of Al stress alone resulted in increased content of chelator-soluble pectin and alkali-soluble pectin, whilst an opposite trend was detected in the degree of methylation of the above two pectins. Transmission electron microscope (TEM) micrographs of –B and –B +Al-treated leaves showed destruction of chloroplasts and a distinct thickening of cell wall. Fourier-transform infrared spectroscopy (FTIR) and 13C-nuclear magnetic resonance spectroscopy (13C NMR) in conjunction with X-ray diffraction (XRD) exhibited cellulose accumulation while its crystallinity was reduced by Al toxicity and double stress. Taken together, our results reveal that B-deficiency and Al toxicity caused oxidative damage to plants, changed the pectin content and characteristics, and altered the cell wall components and architecture, which could be a major cause of deleterious seedling growth.

Evaluation of disease alert systems for postbloom fruit drop of citrus in Florida and economic impact of adopting the Citrus Advisory System

Gama, A. B., Peres, N. A., Singerman, A., and Dewdney, M. M. 2021. Evaluation of disease alert systems for postbloom fruit drop of citrus in Florida and economic impact of adopting the Citrus Advisory System. Crop Protec. XX: xx-xx.Postbloom fruit drop of citrus (PFD) is caused by Colletotrichum abscissum in the Colletotrichum acutatum species complex. PFD does not occur annually but some growers tend to apply fungicides during flowering every year, wasting resources and negatively impacting the environment. Due to its sporadicity, the Fungicide Application Decision system (PFD-FAD) and the Citrus Advisory System (CAS) were developed in Florida and Brazil in 2001 and 2017, respectively, to aid in PFD management. Our objectives were to compare the recommendations from CAS and PFD-FAD, a weekly fungicide treatment schedule, and a nontreated control. We also aimed to assess the economic impact of adopting CAS over the other fungicide schedule treatments with low- and high-risk aversion profile scenarios. Weather conditions were not favorable to PFD in seven field trials. We performed one fungicide application based on CAS over four seasons. An average of approximately 2 and 3 fungicide applications per trial was performed based on PFD-FAD and the weekly treatments, respectively. Average cost to manage PFD following CAS, PFD-FAD, and the weekly treatments were, respectively, $17.52, $186.87, and $272.35. The reduction in management costs related to CAS also translates to reduced use of commercial fungicide formulations in small properties by 382 and 573 L compared to PFD-FAD and the weekly treatments, respectively. CAS recommendations greatly reduced production costs and fungicide usage without compromising disease control and citrus yield in years of low weather favorability for PFD in Florida.

Correlation of Soil Characteristics and Citrus Leaf Nutrients Contents in Current Scenario of Layyah District

Soil with low fertility is a big problem for achieving citrus productivity. In this regard, the management of macro and micronutrients is essential. Macro and micronutrient deficiency decreased the yield and the quality of citrus fruit. It is the need of the hour to classify the soil fertility status under changing climatic scenarios. The current soil fertility survey was conducted to examine the macro and micronutrient status in the citrus production area. In soil, three depths (0–15, 15–30, and 30–45 cm) were taken for sampling. For leaves, 4–6-months-old non-bearing twigs were sampled from 20 trees per orchard at breast height. Results showed that soil pH (7.1–8.4) was slightly alkaline, electrical conductivity (EC) was non-saline (<4 dSm−1), soil organic matter (SOM) was deficient (<0.86%), and calcium carbonate (CaCO3) was slight calcareous (<8%), at 0–15, 15–30, and 30–45 cm depths. The majority of soil samples were low in nitrogen (N) contents at all depths, i.e., (<0.043) 0–15 (85%), 15–30 (97%), and 30–45 (100%) cm depths. Phosphorus (P) was medium (7–15 mg kg−1) at 0–15 cm (60%) but low (<7 mg kg−1) at 15–30 (63%) and 30–45 cm (82%) depths. Potassium (K) was medium (80–180 mg kg−1) at 0–15 (69%), 15–30 (69%), and 30–45 cm (10%) depths. Boron (B) and manganese (Mn) were medium, and Cu was high in 0.15 cm, but all were low at 15–30 and 30–45 cm depths. Iron (Fe) and zinc (Zn) were low at depths of 0–15, 15–30, and 30–45 cm. Most citrus leaves were deficient in N (94%), Fe (76%), Zn (67%), and B (67%). In conclusion, soil fertilization is not sufficient for optimum citrus yield because of alkaline pH and slight calcareous soil conditions in this region. Foliar application of nutrients is suggested instead of only soil fertilization, for better nutrient management in citrus orchards.

Tree-Level Citrus Yield Prediction Utilizing Ground and Aerial Machine Vision and Machine Learning

Tree-Level Citrus Yield Prediction Utilizing Ground and Aerial Machine Vision and Machine Learning

Citrus Yield Response and Irrigation Water Use Efficiency under Partial Root Drying Irrigation in a Pilot Exploitation in the Triffa Plain (Eastern Morocco)

Citrus Yield Response and Irrigation Water Use Efficiency under Partial Root Drying Irrigation in a Pilot Exploitation in the Triffa Plain (Eastern Morocco)

Innovations in healthy citrus garden management to reduce major pests and diseases and increase incomes of citrus farmers

Healthy citrus garden management is an effort to optimize citrus yields. The research aims to suppress major pests and diseases and increase yields and incomes of citrus farmers. The research was conducted in Kintamani, Bali in January 2017-December 2020. The study was conducted in pairs in the form of 1 block of garden technology innovation treatment of healthy citrus gardens and 1 block of farmers' existing gardens. Plant samples per block were determined by purposive sampling. The results showed that the treatment had a significant effect on the abundance of fruit fly populations, diplodia infection, crop yields and farm income. There was a decrease in fruit fly population abundance and diplodia infection by 9.20 and 33.60%, the average citrus fruit yield was 23.71 t/ha. / year, there is an increase in citrus farming income by 97.19%/ha/year due to the innovation of healthy citrus gardens. Based on the calculation results, the R/C ratio and MBCR values were 1.96 and 2.55 for innovations with components of healthy citrus garden management. It is concluded that the technological innovation of healthy citrus gardens is feasible to be developed with the same type of agroecosystem.

Increasing yield and quality of citrus by pruning and fertilization

Pruning and fertilization are factors that can determine the production and quality of citrus. The objective of this study was to determine the effect of pruning intensity and fertilizer doses of N (nitrogen), P (phosporus), and K (potassium) on citrus production and quality. The study was carried out in a citrus orchard in Central Java, Indonesia, over the course of two seasons, 2016-17 and 2017-18.The experiment was conducted as a two-factorial, completely randomized block design where the first factor was pruning intensity, namely 0, 5, 10, and 15 % of the total number of branches per tree while the second factor was doses of N, P, and K fertilizers, namely 0, 2, and 4 % of the weight of harvested citrus fruit in the previous season. The result showed that increasing doses of N, P, K fertilizers from 0 to 4 % increased fruit set, harvested fruits, fruit size, content of vitamin C, sugar, and soluble solid. The highest fruit set, weight of harvested fruits, and content of vitamin C were achieved by pruning intensity of 10 %.

Effects of Chemical Fertilizer Combined with Organic Fertilizer Application on Soil Properties, Citrus Growth Physiology, and Yield

Chemical fertilizer has been excessively used for high yield of citrus around the world, especially in China; meanwhile, it deteriorates the citrus orchard soil environment. To resolve the conflict, the use of organic fertilizer provides a promising solution. However, the data about organic fertilizer used in citrus orchard is rarely available. Here, four treatments including CK (no fertilizer), CF (chemical fertilizer), OF + CF (chemical fertilizer reduction combined with organic fertilizer; application of N, P2O5, K2O fertilizer and organic fertilizer is 0.564, 0.236, 0.336 and 10 kg/plant), and BF + CF (chemical fertilizer reduction combined with bioorganic fertilizer; application of N, P2O5, K2O fertilizer and bioorganic fertilizer is 0.508, 0.320, 0.310 and 10 kg/plant) were performed in a ‘Ponkan’ (Citrus reticulata Blanco) orchard to evaluate the effect of organic fertilizer on citrus yield, growth, soil properties etc. when nutrients of fertilizer of each treatment were equal except CK. The data obtained in 2019 and 2020 showed that both OF + CF and BF + CF were beneficial to improve soil fertility (soil physicochemical and microbe properties) and citrus growth physiology (growth, nutrient and photosynthesis), alleviate NO3−-N leaching, and promote yields. Comprehensive evaluation indicated that BF + CF was more effective than OF + CF. Together, organic fertilizer has the potential to substitute partial chemical fertilizer with improvement in soil properties, growth physiology, and yield of citrus.