Dual benefits of long-term ecological agricultural engineering: Mitigation of nutrient losses and improvement of soil quality

Temporal variation of microbial nutrient limitation in citrus plantations: Insights from soil enzyme stoichiometry

Soil enzyme carbon (C): nitrogen (N): phosphorous (P) stoichiometry and their vector model has been widely used to elucidate the balance between microbial nutrient requirements and soil nutrient availability. However, limited knowledge is available on the dynamics of soil enzyme stoichiometry and microbial nutrient limitation following afforestation, especially in the economic forest. In this study, the effects of citrus plantation on C: N: P stoichiometry were assessed through a comparative study between cropland and citrus plantations with varying durations of afforestation (i.e., 3, 15, 25, and 35 years). It was found that the C, N, and P contents in the soil (SOC, STN, and STP), microbial biomass (MBC, MBN, and MBP), as well as the activities of C-, N-, and P-acquiring enzymes (BG, NAG, and AP), were 1.02-2.51 times higher than those in cropland. Additionally, C, N, and P contents in soil and microbial biomass increased consistently with increasing afforestation time. While the activities of C-, N-, and P-acquiring enzymes increased from 3 years to 25 years and then significantly decreased. In addition to NAG: AP, the stoichiometry of C, N, and P in soil (SOC: STN, SOC: STP, and STN: STP) and microbial biomass (MBC: MBN, MBC: MBP, and MBN: MBP), along with BG: NAG, exhibited a decline of 7.69-27.38% compared to cropland. Moreover, the majority of the C: N: P stoichiometry in soil, microbial biomass, and enzymes consistently decreased with increasing afforestation time, except for SOC: STN and NAG: AP, which exhibited an opposite trend. Furthermore, a significant decrease in microbial carbon limitation and an increase in microbial nitrogen limitation were observed with increasing afforestation time. Collectively, the dynamic of microbial nutrient limitation was primarily influenced by the interaction between soil nutrients and edaphic factors. The findings suggest that with the increasing duration of citrus plantation, it is crucial to focus on nitrogen (N) fertilization while maintaining a delicate balance between fertilization strategies and soil acidity levels.

Dynamic Monitoring of Nutrition Inputs and Fertility Evaluation during a Decade in the Main Peach-Producing Areas of Shandong Province, China

The main peach-producing area in Shandong is an important peach fruit-producing area in China. Understanding the nutritional properties of the soil in peach orchards helps us to understand the evolution of soil properties and adjust management methods in a timely manner. This study focuses on 52 peach orchards in the main peach-producing area in Shandong as the research object. The spatiotemporal changes in soil traits and their influential factors were studied in depth, and the changes in soil fertility were effectively evaluated. The results showed that the input of nitrogen, phosphorus and potassium from organic fertilizer in 2021 was significantly higher than that in 2011, while the input of fertilizer in 2011 was significantly higher than that in 2021. Compared with traditional parks, both organic fertilizer inputs and chemical fertilizer inputs in demonstration parks showed a significant downwards trend. There was no significant change in pH values between 2011 and 2021. In 2021, the soil organic matter (SOM) contents of the 0-20 cm and 20-40 cm layers were 24.17 g·kg^-1 and 23.38 g·kg^-1, respectively, an increase of 29.3% and 78.47% over the values measured in 2011. Compared with 2011, the content of soil alkaloid nitrogen (AN) decreased significantly in 2021, and the contents of available phosphorus (AP) and available potassium (AK) in the soil increased significantly. According to the calculation results of the comprehensive fertility index (IFI) value, we found that in 2021, compared with 2011, the quality of soil fertility improved, most of which was at the medium and high levels. The research results show that the fertilizer-saving and synergistic approach in peach orchards in China significantly improved the soil nutrition. In the future, research on suitable comprehensive technologies should be strengthened in the management of peach orchards.

Findings on agricultural cleaner production in the three Gorges Reservoir Area

The 'rural revitalization strategy' is important to achieve sustainable development in the Three Gorges Reservoir Area (TGRA), the largest reservoir in China, located in the poverty alleviation region of the Qinling-Daba mountains, and characterized as mountainous and hilly dominated by backwards resettlements. Pig farming around the reservoir area is a key industry, accounting for 0.90% of the arable land area in the country, while the annual pig market represents a 1.37% share of the national figure. Here, 12 study sites were investigated on-site for understanding agricultural green development in the TGRA. We found two main prevailing models: one of ecological circulation (EC), based on animal husbandry and recycling. Of the 12 site, six cases of the ecological circulation model relied on pig husbandry, combined with cropping (grains/fruits/vegetables) by eco-industrial chains, such as pig-biogas-fruit (grain/vegetables), to prevent environmental pollution, while promoting agricultural economic growth by recycling fecal residues and wastewater (FSW) from pig-husbandry facilities to the fields. Our analysis predicted that a farm holding 10,000 pigs may save inorganic nitrogen and phosphorus fertilizers by as much as 74.36 and 11.15 ton·a^-1, respectively. On the other hand, five cases of ecological models oriented towards agritourism provided tourists with high-quality ecological products while coordinating environment protection with economic development. In addition, 11 research points applied water and fertilizer integration system for the purpose of saving water. However, lack of sufficient supporting arable land made intensive pig farming a risk of ecological degradation. Green control technologies are rarely used leading to an increase in the type and amount of pesticides. Our study has theoretical and practical significance for decision-makers to promote agricultural cleaner production (ACP).

Impacts of droughts on agricultural and ecological systems based on integrated model in shallow groundwater area

Agricultural and ecological developments are increasingly paid attention in light of climate change. It is expected to comprehensively macroscopically control agricultural and ecological developments in shallow groundwater area that ecology is closely related to agricultural development. This study synthesizes multi models, including process-based crop growth model, water status model of shelterbelt, and vegetation-soil-groundwater interactions to identify responses of crops, shelterbelt, and natural vegetation to different level droughts. Obtained results show that the rank of vulnerabilities to droughts is: maize (the most vulnerable crop) > wheat > sunflower > shelterbelt (the least vulnerable vegetation). Under three drought scenarios, the natural vegetation biomass is all in stable states that fluctuations of groundwater salinity and precipitation cannot largely change the natural vegetation biomass. The natural vegetation biomass in equilibrium states is decreased by 4.08 % and 9.19 % respectively when available irrigation water is reduced to 70 % and 50 % levels. The results indicate that controlling and decreasing initial soil salt content before crop growth may be an effective way to avoid the decrease in the yield loss caused by salinization. It is suggested that vulnerable crops and the possible evolution of natural vegetation towards degradation in extreme droughts should be concerned and taken certain measures. This study also implies that optimizing planting structure is a possible strategy to improve adaptabilities to droughts and decrease economic losses. The established model contributes to provide an effective approach to handle large-scale decision-making problems about comprehensively developing agriculture and ecology in changing environments. Obtained results can provide reference strategies for managers to achieve sustainable development.

Optimization of Reclamation Measures in a Mining Area by Analysis of Variations in Soil Nutrient Grades under Different Types of Land Usage—A Case Study of Pingshuo Coal Mine, China

The development of reclaimed mine soils is normally spatially heterogeneous, making the fine management and utilization of reclaimed mined lands difficult. Soil nutrient grading can provide a scientific basis for the precise regulation of soil nutrients, but few related studies are available in reclaimed mined areas. This study aimed to quantify the spatiotemporal variations in soil nutrient grades under different land-use types in a reclaimed mined area on the Loess Plateau, China. The study area was graded by four soil nutrients (soil available potassium (SAK), soil available phosphorus (SAP), soil total nitrogen (STN), and soil organic matter (SOM)), and the variation features of soil nutrient grades in the initial stage of reclamation under four land-use types (i.e., cultivated land, grassland, forestland, and barren land) were systematically characterized by geostatistical analysis, pedodiversity analysis, and correspondence analysis. The results show that during the initial five years after reclamation, the soil nutrient grades of most reclaimed areas increased from Grade V and VI to Grade I–IV, while the improvements were significantly heterogeneous. Notably, the four land-use types had distinct variation characteristics. The barren land had the lowest SAP level, whereas it had the highest proportion, and medium–high grades of SAK, STN, and SOM (88.3, 100.0, and 100.0%, respectively). In terms of quantitative structure, it had the lowest richness index (S′, 2.5) and Shannon’s entropy index (H′, 0.7) and the highest evenness index (E′, 0.8). These results suggest that the barren land had relatively high and balanced nutrients, with the highest homogeneity among the four land-use types. The grassland had considerable improvement in all nutrients (especially SAP; 95.6% of the area had high SAP grades); however, its improvement was the most heterogeneous (S′ = 4.5, E′ = 0.7). As the second-most heterogeneous land-use type (S′ = 4.0, E′ = 0.8), the forestland had relatively low STN, SAP, and SAK levels due to high nutrient uptake and storage by tree species, but it had the highest proportion of area that reached high SOM grades (36.4%) and medium to high SOM grades (100.0%) due to its high community productivity. The cultivated land, which received fertilization for an additional three years, was the most imbalanced in terms of nutrients. It had the highest proportion of area that reached high SAP grades (98.0%); in contrast, its area proportions of low-grade SAK and SOM (69.0 and 32.9%, respectively) were the highest among the four land-use types. Based on the above comprehensive characterization of soil nutrient grade variation, guidance was given for fine management of reclaimed mined land and the optimization of reclamation measures.

High-frequency monitoring of neonicotinoids dynamics in soil-water systems during hydrological processes

Neonicotinoids pollution poses a serious threat to aquatic ecosystems. However, there is currently little knowledge about how neonicotinoids are transferred from the agricultural environment to the aquatic environment. Here, we conducted in situ high-frequency monitoring of neonicotinoids in soil-water systems along the hydrological flow path during rainfall to explore the horizontal and vertical transport mechanisms of neonicotinoids. The collected samples included 240 surface runoff, 128 subsurface runoff, 60 eroded sediment, 120 soil and 144 soil solution, which were used to analyse neonicotinoids concentrations. Surface runoff, subsurface runoff and eroded sediment were the three main paths for the horizontal migration of neonicotinoids. In the CK (citrus orchards without grass cover) and grass-covered citrus orchards, there are 15.89% and 2.29% of the applied neonicotinoids were transported with surface runoff, respectively. While in the CK and grass-covered citrus orchards, there are only 1.23% and 0.19% of the applied neonicotinoids were transported with eroded sediment and subsurface runoff. Although the amount of neonicotinoids lost along with eroded sediment was small, the concentration of neonicotinoids in eroded sediment was two orders of magnitude higher than the concentration of neonicotinoids in sediments of the surface water. Meanwhile, neonicotinoids migrated vertically in soil due to water infiltration. In the CK and grass-covered citrus orchards, there are 57.64% and 24.36% of the applied neonicotinoids were retained in soil and soil solution, respectively, and their concentration decreased as soil depth increased. Another noteworthy phenomenon is that more neonicotinoids migrated to deeper soil layers under grass cover compared with no grass cover because grass roots promoted the formation of cracks and vertical preferential flow. Our results are expected to improve the accuracy of neonicotinoids pollution prediction by considering migration paths, including surface and subsurface runoff and eroded sediment.

Choline-based deep eutectic solvent combined with EDTA-2Na as novel soil washing agent for lead removal in contaminated soil

Lead-contaminated soil was cleaned through ethylene-diamine-teraacetic acid disodium salt (EDTA-2Na) combined with diluted deep eutectic solvent (DES) which was prepared by mixing choline chloride with ethylene glycol. The influences of leaching temperature, leaching time, liquid-solid (L/S) ratio, concentration of EDTA-2Na, water-DES ratio, and the molar ratio of choline chloride-ethylene glycol (Ch-E) on the leaching rate of lead were investigated. The mineral phases of the soil and DES before and after washing were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The changes to the DESs before and after dissolving lead nitrate (Pb(NO₃)₂) were analyzed by high resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR). Hydrogen bonds and EDTA-2Na in the Ch-M system resulted in the conversion of Pb(NO₃)₂ to other complex ions such as [Pb·Ch-E]^- and [Pb·EDTA-2Na]^- and other complex ions due to the dissolution of the washing agent. The results showed that the soil mineral phase did not change significantly and up to 95.79% of Pb could be washed under temperature, time, L/S ratio, EDTA-2Na concentration, DES/water ratio, Ch-E molar ratio, and stirring speed conditions of 40 °C, 2 h, 6, 0.02 M, 2, 0.75 and 300 rpm, respectively. The hydrogen bonds and EDTA-2Na may play a key role in the remediation of lead-contaminated soil by a washing agent. This research describes a rapid, efficient, and environmentally friendly method for remediation of lead-contaminated soil.

Assessment of Potato Farmland Soil Nutrient Based on MDS-SQI Model in the Loess Plateau

Soil nutrients are essential nutrients provided by soil for plant growth. Most researchers focus on the coupling effect of nutrients with potato yield and quality. There are few studies on the evaluation of soil nutrients in potato fields. The purpose of this study is to investigate the soil nutrients of potato farmland and the soil vertical nutrient distributions, and then to provide a theoretical and experimental basis for the fertilizer management practices for potatoes in Loess Plateau. Eight physical and chemical soil indexes were selected in the study area, and 810 farmland soil samples from the potato agriculture product areas were analyzed in Northern Shaanxi. The paper established the minimum data set (MDS) for the quality diagnosis of the cultivated layer for farmland by principal component analysis (PCA), respectively, and furthermore, analyzed the soil nutrient characteristics of the cultivated layer adopted soil quality index (SQI). The results showed that the MDS on soil quality diagnosis of the cultivated layer for farmland soil included such indicators as the soil organic matter content, soil available potassium content, and soil available phosphorus content. The comprehensive index value of the soil quality was between 0.064 and 0.302. The SPSS average clustering process used to classify SQI was divided into three grades: class I (36.2%) was defined as suitable soil fertility (SQI < 0.122), class II (55.6%) was defined as moderate soil fertility (0.122 < SQI < 0.18), and class III (8.2%) was defined as poor soil fertility (SQI > 0.186). The comprehensive quality of the potato farmland soils was generally low. The proportion of soil nutrients in the SQI composition ranged from large to small as the soil available potassium content = soil available phosphorus content > soil organic matter content, which became the limiting factor of the soil organic matter content in this area. This study revolves around the 0 to 60 cm soil layer; the soil fertility decreased gradually with the soil depth, and had significant differences between the respective soil layers. In order to improve the soil nutrient accumulation and potato yield in potato farmland in northern Shaanxi, it is suggested to increase the fertilization depth (20 to 40 cm) and further study the ratio of nitrogen, phosphorus, and potassium fertilizer.