Soil Olsen-P Research Articles

Aeration treatment promotes transformation of soil phosphorus fractions to plant-available phosphorus by modulating rice rhizosphere microbiota

Microorganisms play an important role in affecting the content of available phosphorus (P) in plant rhizosphere soil. However, the effect of aeration on available P in rice rhizosphere soil and its microbial mechanism remain unclear. This study aimed to elucidate the effects of aeration strategies on available P and P-solubilizing microorganisms in rhizosphere soil, employing three different aeration methods (continuous flooding (CF), continuous flooding and aeration (CFA), and alternate wetting and drying (AWD)). We analyzed the bacterial and fungal community structures in rice rhizosphere soil via Illumina sequencing techniques and quantified the abundance of P transformation functional genes related to inorganic P solubilization (pqqC) and organic P mineralization (phoC, phoD, and appA) through quantitative PCR. Our findings revealed that the AWD treatment significantly increased soil pH and Eh; Both AWD and CFA treatments markedly increased soil Olsen-P content at the tillering and heading stages, as well as the microbial carbon-to-phosphorus ratio (MBC/MBP) at the heading and maturity stages. Cluster analysis showed distinct bacterial communities at the heading and maturity stages under AWD, which differed from those in other treatments. Fungal communities at the tillering and heading stages under CFA and AWD grouped together. AWD and CFA treatments consistently enhanced labile-P in the rhizosphere soil throughout the entire growth stages, while reducing moderately labile-P during the tillering and heading stages. Compared to CF, at the heading and maturity stages, the copy numbers of pqqC, phoD, phoC, and appA were higher under AWD compared to other treatments. In conclusion, this study posits that the increase in Olsen-P in paddy fields due to aeration results from improved oxygen conditions in the rhizosphere, alterations in pH and Eh, effects on microbial stoichiometry, and adjustments in the abundance and composition of P-solubilizing microorganisms, thereby promoting P transformation. This conclusion provides new insights into the conversion of soil P Fractions into plant-available forms.

Long-Term Amendment with Sewage Sludge: Effects on Nutrient Value and Trace-Metal Content in Different Parts of Maize Plants

Agricultural soils play a key role in the achievement of a circular nutrient economy. The use of sewage sludges as fertilizers is important for such an achievement, assisting in the maintenance of soil health and nutritional crop value. This study was established, after 23 years of a fertilization experiment, in calcareous soil under a maize monoculture. The treatments included mineral fertilization as a control (MIN, 225 kg N ha−1) and two sludge treatments, where doses followed a threshold sludge nitrogen criterion (SNC, 170 kg org-N ha−1) or a threshold soil phosphorus criterion (SPC; when the soil Olsen-P value exceeded 40–60 kg P ha−1, the sludge application was stopped). A detailed study was performed on Cd, Cu, F, Mn, Pb, and Zn soil extractable with diethylenetriaminepentaacetic acid (DTPA), as well as the nutrient and heavy metal concentration of different fractions of the maize plant (grain, cob, and the rest of the plant). Extractions were also quantified. No biomass-yield differences were observed in the different parts of the maize plant in the year of sampling. Sludges increased the soil DTPA extraction of Cd, Cu, Fe, and Zn and diminished Mn extraction, without differences in extractable Pb. The SNC, when compared with MIN, showed increased P cob concentrations, and in grain, it showed increased Fe, Cr, and Co concentrations. The SPC figures of the studied parameters were, in general, between both treatments (MIN and SNC), although Cr extractions in grain diminished vs. SNC. Based on the results, the SPC can be recommended as it also avoids excessive available-P build up.

Differential responses of soil phosphorus fractions to varied nitrogen compound additions in a meadow steppe

Nitrogen (N) addition can greatly influence soil inorganic phosphorus (Pi) and organic phosphorus (Po) transformations. However, whether and how the N compound forms may differentially affect the soil P fractions remain unclear. Here, we investigated the responses of soil Pi (labile Pi, moderately-occluded Pi, and recalcitrant Pi) and Po fractions (labile Po and stable Po) to varying addition rates of three N compounds ((NH4)2SO4, NH4NO3, and urea) in a meadow steppe in northern China. Our studies revealed that with increasing N addition rate, soil labile and moderately-occluded Pi increased, accompanied by decreases in soil recalcitrant Pi. This shift was attributed to N-induced soil acidification, which accelerated the conversion of recalcitrant Pi into labile and moderately-occluded Pi. Soil labile Po decreased with increasing rate of N addition, whilst soil stable Po was not affected. Regardless of the compound forms, N addition increased soil Olsen-P, suggesting a potential alleviation of P limitation in this grassland ecosystem. The effect of N addition on soil labile Pi was significantly greater with addition of urea than with addition of either (NH4)2SO4 or NH4NO3, indicating that urea was more efficient in enhancing soil P availability. Addition of (NH4)2SO4 imposed a more pronounced positive effect on soil moderately-occluded Pi than the addition of either NH4NO3 or urea, mainly due to the greater mobilization of recalcitrant Pi as a result of higher soil acidification strength of (NH4)2SO4. These findings underscore the importance of considering the distinct effects of different N compounds when studying grassland soil P dynamics and availability in response to N addition.

The effect of combined application of biochar and phosphate fertilizers on phosphorus transformation in saline-alkali soil and its microbiological mechanism

This study investigated the effects of combining Phragmites australis-based biochar, prepared at 400 °C, with various types of phosphate fertilizers—soluble, insoluble, and organic—on the content and transformation of phosphorus fractions in saline-alkali soil. Additionally, we explored microbiological mechanisms driving these transformations. The results showed that this combination significantly increased the concentrations of dicalcium phosphate (Ca2P), octacalcium phosphate (Ca8P), aluminum phosphate (AlP), moderately labile organic phosphorus (MLOP), and resistant organic phosphorus (MROP) in soil. Conversely, the levels of hydroxyapatite (Ca10P) and highly resistant organic phosphorus (HROP) decreased. The increase in labile organic phosphorus (LOP) content or decrease in iron phosphate (FeP) was found to effectively enhance the availability of Olsen phosphorus (Olsen-P) in soil. Furthermore, the study revealed that biochar mixed with organic phosphate fertilizers increased the activity of soil acid phosphatase (ACP) and neutral phosphatase (NEP), while reducing alkaline phosphatase (ALP) activity. In contrast, biochar combined with soluble and insoluble phosphate fertilizers decreased the activity of ACP (22.59 % and 28.57 %, respectively) and NEP (62.50 % and 11.11 %, respectively), with the combination with insoluble fertilizers also reducing ALP activity by 55.84 %, whereas the soluble combination increased it by 190.34 %. Additionally, the co-application of biochar and phosphate fertilizers altered the composition and abundance of the gene phoD-harboring microbial community, enhancing the abundance of Proteobacteria and reducing that of Actinobacteria. Correlation analysis between phoD-functional microbial species and various phosphorus fractions showed that Rhodopseudomonas was significantly associated with several phosphorus components, exhibiting a positive correlation with Ca2P, Ca8P, AlP, LOP, MLOP, and MROP, but a negative relationship with Ca10P. These findings suggest that the combined application of biochar and phosphate fertilizers could change the abundance of Rhodopseudomonas, potentially influencing phosphorus cycling in the soil. This research provides a strong scientific foundation for the efficient combined use of biochar and phosphate fertilizers in managing saline-alkali soil.

Normalized difference vegetation index analysis reveals increase of biomass production and stability during the conversion from conventional to organic farming.

Monitoring agriculture by remote sensing enables large-scale evaluation of biomass production across space and time. The normalized difference vegetation index (NDVI) is used as a proxy for green biomass. Here, we used satellite-derived NDVI of arable farms in the Netherlands to evaluate changes in biomass following conversion from conventional to organic farming. We compared NDVI and the stability of NDVI across 72 fields on sand and marine clay soils. Thirty-six of these fields had been converted into organic agriculture between 0 and 50 years ago (with 2017 as reference year), while the other 36 were paired control fields where conventional farming continued. We used high-resolution images from the Sentinel-2 satellite to obtain NDVI estimates across 5 years (January 2016-October 2020). Overall, NDVI did not differ between conventional and organic management during the time series, but NDVI stability was significantly higher under organic management. NDVI was lower under organic management in sandy, but not in clay, soils. Organic farms that had been converted less than ~19 years ago had lower NDVI than conventional farms. However, the difference diminished over time and eventually turned positive after ~19 years since the conversion. NDVI, averaged across the 5 years of study, was positively correlated to soil Olsen-P measured from soil samples collected in 2017. We conclude that NDVI in organic fields was more stable than in conventional fields, and that the lower biomass in the early years since the transition to organic agriculture can be overcome with time. Our study also indicates the role of soil P bioavailability for plant biomass production across the examined fields, and the benefit of combining remote sensing with on-site soil measurements to develop a more mechanistic understanding that may help us navigate the transition to a more sustainable type of agriculture.

Manure application influences microbial stoichiometry and alters microbial life strategies to regulate phosphorus bioavailability in low-P paddy soil

Microbial stoichiometry is pivotal in the soil elements cycle within terrestrial ecosystems. However, the impact of microbial stoichiometry on the phosphorus (P) pool transformation in low-P paddy soil, especially with manure addition, remains poorly understood. This study aimed to elucidate the response mechanism of microbial stoichiometry in regulating P pool transformation in two low-P paddy soils during a 60-day flooding-drought incubation. The results demonstrated that pig manure and vermicompost application significantly increased soil Olsen-P by 202–309 %, and microbial biomass P (MBP) by 54.4–79.3 % compared to no fertilization. Additionally, vermicompost treatment increased moderately labile organic P (MLPo) by 133–257 % and decreased fulvic acidassociated organic P (FAPo) by 10.5–25.4 % in Acrisol-flooding, Acrisol-drought, and Ultisol-drought, indicating that manure application improved the transformation of FAPo to MLPo. The microbial biomass carbon (MBC)/MBP ratio was lowest under Acrisol-flooding and highest under Ultisol-drought, suggesting that microorganisms adjust high ratios for stoichiometric stability and enhanced MBP utilization under deficient resource conditions. Manure treatments increased alkaline phosphatase (ALP) by 5.33–12.9 % under flooding conditions, indicating microorganisms facilitate the mineralization of soil organic P (Po). Compared to Acrisol-flooding, both ALP and β-1,4-glucosidase (BG) significantly increased by 103 % and 259 %, respectively, under Ultisol-drought, along with a positive correlation between BG and MLPo, implying that microorganisms enhance soil organic matter mineralization in resource-limited conditions by increasing C-acquiring enzymes and releasing Po. Additionally, the microbial community composition shifted from r-strategists to K-strategists, primarily by decreasing Proteobacteria and increasing Acidobacteria under resource deficiency and drought. The r-strategists directly mineralize Po by maintaining a low MBC/MBP and high ALP, while K-strategists indirectly mineralize Po by maintaining a high MBC/MBP and high BG. The findings suggest that manure application altered the resource status of low-P paddy soils, changed microbial stoichiometry, and influenced soil P availability through adjustments in microbial activity and extracellular enzyme production.

Shallow groundwater table fluctuations promote the accumulation and loss of phosphorus from surface soil to deeper soil in croplands around plateau lakes in Southwest China

The continuous excessive application of phosphorus (P) fertilizers in intensive agricultural production leads to a large accumulation of P in surface soils, increasing the risk of soil P loss by runoff and leaching. However, there are few studies on the accumulation and loss of P from surface soil to deep soil profiles driven by shallow groundwater table (SGT) fluctuations. This study used the intensive cropland around 7 plateau lakes in Yunnan Province as an example and conducted in situ monitoring of P storage in the soil profile and SGT during the rainy season (RS) and dry season (DS) as well as simulation experiments on soil P loss. The aim was to study the spatiotemporal variation in P accumulation in the soil profile of cropland driven by SGT fluctuations in the RS and DS and estimate the P loss in the soil profile driven by SGT fluctuations. The results showed that fluctuations in the SGT promoted P accumulation from the surface soil to deeper soil. The proportions of P stored in various forms in the 30–60 cm and 60–100 cm soil layers in the RS were greater than those in the DS, while the average proportion in the 0–30 cm soil layer in the DS was as high as 48%. Compared with those in the DS, the maximum decreases in the proportion of P stored as TP and Olsen-P in the 0–100 cm soil layer in the RS were 16% and 58%, respectively, due to the rise in the SGT (SGT <30 cm), while the soil TP storage decreased by only 1% when the SGT was maintained at 60–100 cm. The critical thresholds for soil Olsen-P and TP gradually decreased with increasing soil depth, and the risk of P loss in deeper soil increased. The loss of soil P was increased by fluctuations in the SGT. Based on the cropland area around the 7 plateau lakes, P storage, and SGT fluctuations, the average loss intensity and loss amount of TP in the 0–100 cm soil layer around the 7 plateau lakes were estimated to be 25 kg/ha and 56 t, respectively. Therefore, reducing exogenous P inputs, improving soil endogenous P utilization efficiency and maintaining deep soil P retention are the basic strategies for preventing and controlling P accumulation and loss in deep soil caused by SGT fluctuations.

Differential Effects of Nitrogen and Phosphorus Fertilization Rates and Fertilizer Placement Methods on P Accumulations in Maize.

Crop production in Afghanistan suffers from limited phosphorus (P) availability, which severely hinders national agriculture sustainability. This study hypothesized that deep fertilizer placement could significantly enhance the uptake of immobile P and, thus, tissue P accumulation and crop yield. A two-year pot experiment growing two maize (Zea mays) hybrid cultivars (Xida-789 and Xida-211) was, therefore, conducted to test these hypotheses under three contrasting fertilizer placement methods (broadcast, side band, and deep band). In doing so, P concentrations in both maize tissues and soils were compared at 45, 60, and 115 days after sowing (DAS) under nine combinations of nitrogen (N) and P fertilizer rates (kg ha-1: N112P45, N112P60, N112P75, N150P45, N150P60, N150P75, N187P45, N187P60, N187P75). Results have shown that deep band placement significantly increased P uptake efficiency, leading to greater P concentration and accumulation in maize tissues compared to the other two fertilization methods. This improved P uptake was attributed to several factors associated with deep placement, including reduced P fixation, enhanced root access to P, and moisture availability for P uptake. Additionally, deep band placement combined with higher N application rates (N187 and N150) further enhanced plant P uptake by promoting P availability and utilization mechanisms. Deep band placement also resulted in significantly higher total soil P, Olsen-P, and P use efficiency than broadcast and side band methods, indicating a more efficient P fertilization strategy for maize that can improve growth and yield. This study also found positive correlations between P concentration in plant organs and soil Olsen-P, highlighting the importance of adequate soil P levels for optimal plant growth. Overall, our results have shown that deep band fertilizer placement emerged as a superior strategy for enhancing P uptake efficiency, utilization, and maize productivity compared to broadcast and side band placement. The outcome generated from the deep band fertilization by this greenhouse study can be recommended for field practices to optimize P fertilizer use and improve maize production while minimizing potential environmental P losses associated with broadcast fertilization.

Phosphorus fertilizer management for high yields in intensive winter wheat-summer maize rotation system: Integrating phosphorus budget and soil available phosphorus

Overuse of phosphorus (P) fertilizer in crop cultivation accelerates the consistent increase in soil P accumulation and increases the risk of P leaching from the agricultural system. The long-term implications of balanced P management on soil P availability and crop P uptake are still unknown. A three-year field experiment with six different P rates was conducted to determine the effect of a balanced P application strategy on crop yield, P uptake, soil P accumulation, and P transformation in a winter wheat-summer maize rotation system. The results found that the yield and P uptake of summer maize and wheat increased linearly with P fertilization up to 12.5 kg P ha–1, after which they stabilized, and the critical threshold is 50 kg P ha–1 for winter wheat. The soil P budget under agronomic thresholds from 2017 to 2020 was observed as –2.99 to –11.04 kg P ha−1 for maize but 15.1–24.5 kg P ha–1 for wheat. Excessive P fertilization accelerated the downward movement of soil P and stocked it in the deep soil in the form of soil labile P and moderately labile P, increasing the risk of soil P leaching. The annual application of 600 kg ha–1 P fertilizer substantially increased the total P concentration by 30%–99% from deep soil to topsoil compared to the no P treatment, while the 75 kg ha–1 and 150 kg ha–1 P fertilizer treatments did not affect soil P accumulation along the soil profile. Soil Olsen-P concentration to meet crop yield requirements is still far from meeting the critical environmental threshold of 47.6 mg kg–1 and increased slightly by an annual 2.39 mg kg–1 under the balanced P fertilization strategy. An annual negative soil P budget of 3–11 kg ha–1 for summer maize could sustain optimal yields and P use efficiency. Winter wheat cultivation required additional P application to reach the agronomic threshold, set at 15–25 kg ha–1 annually. In conclusion, balanced P fertilization can reduce soil P surplus and subsoil P stock while maintaining crop yields.

Reduction of chemical phosphate fertilizer application in a rice–rapeseed cropping system through continuous straw return

Context or problemStraw return has the potential to significantly contribute to nutrient recycling and utilization, thus reducing the reliance on chemical fertilizers. Extensive research has focused on nitrogen and potassium fertilizer management and the associated potential for reduction through straw return. However, the potential effect of straw return on reducing phosphorus (P) fertilizer application has been relatively overlooked due to the inherently low P content in straw.Objective or research questionThis study aimed to determine the potential benefits and underlying mechanism of reducing chemical P fertilizer application through straw return in a rice–rapeseed cropping system. MethodsWe conducted a five-year field experiment in a rice–rapeseed cropping system to investigate the effects of chemical P fertilizer reduction through straw return. Six fertilization treatments were investigated: no chemical P fertilization, 30, 60, 90, 120, and 60 kg P2O5 ha−1 with 6000 kg ha−1 straw return. ResultsThe result showed that continuous straw return increased yield, P uptake and P utilization during rice and rapeseed seasons. According to the P uptake level, the benefits from straw return were tantamount to applying 69.8–88.0 kg ha−1 of P fertilizer, which exceeded the actual amount of P input (64.5–70.3 kg ha−1) from fertilizer and straw. Straw C input mainly increased the content of soil microbial biomass C and P (MBC and MBP), which enhanced the supply capacity of available P, thereby increasing crop P uptake and reducing P fertilizer. The rapeseed season showed a higher chemical P fertilizer reduction rate (31.8%) than the rice season (14.0%). Moreover, rapeseed P uptake was more sensitive to soil Olsen-P, MBP and MBC than rice. The substitution efficiency of P fertilizer through the priming effect of straw C was higher in the rapeseed season (7.5 kg P2O5/1000 kg C) than in the rice season (2.1 kg P2O5/1000 kg C). ConclusionsOverall, under the rice–rapeseed cropping system, straw return increased soil MBC and MBP, thereby enhancing the supply capacity of available P. The C priming effect induced by straw return can partially reduce P fertilizer application. Compared with the rice season, straw return significantly substituted P fertilizer in the rapeseed season. IMplications or significanceThis study articulately delineates the role of straw return in enhancing soil P availability and crop P uptake and further highlights the potential of straw return as a strategy to reduce dependence on chemical P fertilizers in the rice–rapeseed cropping system.

Soil nitrogen availability and microbial carbon use efficiency are dependent more on chemical fertilization than winter drought in a maize-soybean rotation system.

Soil nitrogen (N) availability is one of the limiting factors of crop productivity, and it is strongly influenced by global change and agricultural management practices. However, very few studies have assessed how the winter drought affected soil N availability during the subsequent growing season under chemical fertilization. We conducted a field investigation involving snow removal to simulate winter drought conditions in a Mollisol cropland in Northeast China as part of a 6-year fertilization experiment, and we examined soil physicochemical properties, microbial characteristics, and N availability. Our results demonstrated that chemical fertilization significantly increased soil ammonium and total N availability by 42.9 and 90.3%, respectively; a combined winter drought and fertilization treatment exhibited the highest soil N availability at the end of the growing season. As the growing season continued, the variation in soil N availability was explained more by fertilization than by winter drought. The Mantel test further indicated that soil Olsen-P content and microbial carbon use efficiency (CUE) were significantly related to soil ammonium availability. A microbial community structure explained the largest fraction of the variation in soil nitrate availability. Microbial CUE showed the strongest correlation with soil N availability, followed by soil available C:P and bacteria:fungi ratios under winter drought and chemical fertilization conditions. Overall, we clarified that, despite the weak effect of the winter drought on soil N availability, it cannot be ignored. Our study also identified the important role of soil microorganisms in soil N transformations, even in seasonally snow-covered northern croplands.

Optimizing Phosphorus Fertilizer Use on the Loess Plateau: Impact on Soil Properties and Crop Production Efficiency

Various phosphorus (P) fertilizers are commonly utilized in agricultural production on the Loess Plateau. However, there exists a widespread issue of improper matching between P fertilizers, crop types, and soil types. This study proposes a scientifically based approach to managing phosphate fertilizer through a matching experiment. A field experiment was conducted to investigate the effects of different P fertilizers on soil P profiles in a wheat–corn rotation between October 2017 and September 2021. The experiment adopted a randomized block design. P fertilizer was applied as a basal fertilizer at rates of 115 kg P2O5 ha−1 during the wheat season and 90 kg P2O5 ha−1 during the maize season. Nitrogen (N) fertilizer application rates were 120 kg N ha−1 for wheat and 180 kg N ha−1 for maize. N fertilizer was divided into two applications, with 60% applied at pre-planting and 40% at the jointing stage of wheat or the V12 stage of maize. P fertilizer variants utilized in the study included ammonium dihydrogen, ammonium phosphate, calcium-magnesia phosphate fertilizer, calcium superphosphate, and ammonium polyphosphate. The transformation process of phosphate was examined, revealing that the commonly considered dominant diammonium phosphate fertilizer was not the optimal choice in this production system. Ammonium polyphosphate, calcium superphosphate, and ammonium dihydrogen were deemed more suitable for application in Loess soil. Furthermore, an analysis was conducted on the relationship between P fractions, soil properties, and soil Olsen-P. This research emphasizes the significance of strategic phosphate fertilizer use in agriculture to ensure efficient production and to help address the global P scarcity.

Contrasting fertilization response of soil phosphorus forms and functional bacteria in two newly reclaimed vegetable soils

Fertilization is a pervasive approach to agricultural production enhancing vegetable nutrients such as phosphorus (P) absorption. However, unreasonable fertilization strategies result in high levels of residual P in vegetable planting systems. To better understand the mechanisms of soil phosphorus dynamics responding to inorganic/organic fertilization, we conducted a 3-year field experiment in two newly reclaimed vegetable fields in southern China. The results revealed that soil Olsen-P in CF (mineral fertilization) and OF (Combined application of organic and inorganic fertilizers) increased by approximately 210.6 % and 183.6 %, respectively, while stable P proportion decreased by approximately 9.2 % and 18.1 %, respectively, compared with CK. Combined application of organic and inorganic fertilizer increased the proportion of moderately labile P (NaOH-P) by 1–6 % in comparison with chemical fertilizer and facilitated the conversion from diester-P to monoester-P, indicating that applying pig manure enhanced the potential soil P bioavailability. Besides, organic-inorganic fertilization shaped a bacterial community with more connectivity and stability and changed keystone taxa related to the P transformation of the network. Phenylobacterium, Solirubrobacter, and Modestobacter were regarded as core genera for mobilizing soil phosphorus. However, residual P content in newly reclaimed soils under fertilization, especially for chemical fertilizer, remained non-negligible and may cause potential environmental risks. The partial least squares path modeling results demonstrated that fertilization management had both direct and indirect positive effects on P fraction through the improvement of soil nutrients e.g. total N and soil organic carbon, and bacterial community, while soil properties mainly determined the variation of soil P species. Our results provide comprehensive insights into the current status of legacy P forms and the vital role of fertilizer, key soil properties and bacteria in P dynamics in newly reclaimed vegetable field.

Effects of microplastic properties and dissolved organic matter on phosphorus availability in soil and aqueous mediums

Plastic mulching films and phosphate fertilizers have been widely used to improve agricultural soil productivity. Microplastics (MP) and phosphorus (P) significantly accumulate in agricultural soil and water bodies. However, the effects of residual MP on P availability in soil and aqueous mediums remain unclear. In this study, available P (Olsen-P) in soils and P adsorption capacity in aqueous medium were determined to examine the influence of MP properties on P availability in laboratory. In agricultural soils, Olsen-P was significantly affected by MP types. Conventional MP (mulching film particles), such as polyethylene (PE) and polyvinyl chloride (PVC), and biodegradable MP, such as polylactic acid (PLA), substantially reduced soil Olsen-P by 9.7–38.6% and 38.4–73.6%, respectively. The size and concentration of MP strongly affected soil Olsen-P, with smaller (25 μm) and more concentrated (5%) MP causing greater reductions in Olsen-P. In the soil contaminated with MP, increased fulvic acid content significantly increased Olsen-P levels. Microplastics exhibited strong P adsorption capacities, leading to decreased P availability in aqueous medium. Conventional MP exhibited a higher P adsorption capacity than biodegradable MP, with P distribution coefficients (Kd values) ordered as PVC (5.19 L kg−1) > PE (4.23 L kg−1) > PLA (2.48 L kg−1). Notably, the Kd values increased with decreasing sizes of conventional MP, whereas the opposite trend was observed for PLA. The presence of fulvic acid affected the adsorption of P by MP in aqueous medium. Increased fulvic acid content reduced P adsorption capacity of MP, thus enhancing P availability. Our findings contribute to a better understanding of P dynamics in MP-contaminated agricultural soil and aqueous medium, which could aid in formulating sustainable agricultural practices and effective environmental management strategies for plastic mulching films and P contamination.

Serendipita indica is a biostimulant that improves tea growth at low P levels by modulating P acquisition and hormone levels

Serendipita indica (S.i.) exhibits mycorrhizal fungus-like characteristics, while it is unclear how S.i. improves root growth of tea seedlings at low phosphorus (P) levels. This study investigated the effects of S.i. on biomass production, auxin and cytokinin levels, root P levels, soil Olsen-P levels, soil phosphatase activities, and root P transporter (PT) gene expression in tea (Camellia sinensis) seedlings at normal (50 mM P) and low (0.5 mM P) P levels. S.i. colonized tea roots. S.i. inoculation significantly increased shoot and root biomass production at low and normal P levels, as well as root indolebutyric acid, isopentenyladenine, and trans-zetin levels at low P levels. Furthermore, S.i. inoculation significantly raised root P and soil Olsen-P levels at low and normal P levels, accompanied with an increase in soil acid and neutral phosphatase activities at low P levels. S.i. inoculation increased root CsPT1 expression at low P levels. In summary, S.i. can be considered as a biostimulant to improve tea growth and root P acquisition at low P levels.

Differential effects of cow dung and its biochar on Populus euphratica soil phosphorus effectiveness, bacterial community diversity and functional genes for phosphorus conversion.

Continuous monoculture leading to soil nutrient depletion may cause a decline in plantation productivity. Cow dung is typically used as a cheap renewable resource to improve soil nutrient status. In this study, our purpose was to compare the effects of different cow dung return methods (direct return and carbonization return) on soil microbial communities and phosphorus availability in the root zone (rhizosphere soil and non-rhizosphere soil) of P.euphratica seedlings in forest gardens and to explore possible chemical and microbial mechanisms. Field experiments were conducted. Two-year-old P.euphratica seedlings were planted in the soil together with 7.5 t hm-2 of cow dung and biochar made from the same amount of cow dung. Our findings indicated that the available phosphorus content in soil subjected to biochar treatment was considerably greater than that directly treated with cow dung, leading to an increase in the phosphorus level of both aboveground and underground components of P.euphratica seedlings. The content of Olsen-P in rhizosphere and non-rhizosphere soil increased by 134% and 110%, respectively.This was primarily a result of the direct and indirect impact of biochar on soil characteristics. Biochar increased the biodiversity of rhizosphere and non-rhizosphere soil bacteria compared with the direct return of cow dung. The Shannon diversity index of carbonized cow manure returning to field is 1.11 times and 1.10 times of that of direct cow manure returning to field and control, and the Chao1 diversity index is 1.20 times and 1.15 times of that of direct cow manure returning to field and control.Compared to the direct addition of cow dung, the addition of biochar increased the copy number of the phosphorus functional genes phoC and pqqc in the rhizosphere soil. In the biochar treatment, the abundance of the phosphate-solubilizing bacteria Sphingomonas and Lactobacillus was significantly higher than that in the other treatments, it is relative abundance was 4.83% and 2.62%, respectively, which indirectly improved soil phosphorus availability. The results indicated that different cow dung return methods may exert different effects on phosphorus availability in rhizosphere and non-rhizosphere soils via chemical and microbial pathways. These findings indicated that, compared to the direct return of cow dung, biochar return may exert a more significant impact on the availability of phosphorus in both rhizosphere and non-rhizosphere soils, as well as on the growth of P.euphratica seedlings and the microbial community.

Changes in the Soil Phosphorus Supply with Rice Straw Return in Cold Region

Most phosphorus (P) in soil exists in nonlabile forms, leading to poor soil P supply capacity and limiting crop growth. This study evaluated the effect of 10 years of rice straw return on rice yield, soil P budget, P fractions, and phosphatase activity to establish the relationship between soil P fractions and related microbial communities. Four treatments, i.e., no rice straw return (S0), low amount of rice straw return (S1), high amount of rice straw return (S2), and abandoned farmland (AL), were used in the evaluation. The results showed that rice straw return had no effect on the rice yield and P uptake, and the P budget was positive in the S2 treatment. Rice straw return increased the phosphatase activity and content of soil Olsen-P, total P, NaHCO3-, and NaOH-extractable P, and the phosphatase activity and P fractions were both increased with the amount of straw returned. There was a positive correlation between most soil P fractions and active organic carbon fractions. Rice straw return changed the composition and abundance of soil phosphate-solubilizing bacteria (PSB). The findings showed that straw return decreased the proportion of soil nonlabile P, enhancing the soil P supply capacity, and they further showed that the abundance of PSB was not consistent with soil P content.

Mapping Cropland Soil Nutrients Contents Based on Multi-Spectral Remote Sensing and Machine Learning

Nitrogen (N) and phosphorus (P) are primary indicators of soil nutrients in agriculture. Accurate management of these nutrients is essential for ensuring food security. High-resolution, multi-spectral remote sensing images can provide crucial information for mapping soil nutrients at the field scale. This study compares the capabilities of ZH-1 and Sentinel-2 satellite data, along with different spectral indices, in mapping soil nutrients (total N and Olsen-P) using two machine learning algorithms, random forest (RF) and XGBoost (XGB). Two agricultural fields in Suihua City were selected as the study areas for this investigation. The results showed that Sentinel-2 data performed best in computing the total N content in soil using the RF model (R2 = 0.74, RMSE = 0.10 g/kg). However, for the soil Olsen-P content, the XGBoost model performed better with ZH-1 data (R2 = 0.75, RMSE = 9.79 mg/kg) than the RF model. This study demonstrates that both ZH-1 and Sentinel-2 satellite data perform well in terms of accurately mapping soil total N and Olsen-P contents using machine learning. Due to its higher spectral and spatial resolution, ZH-1 remote sensing data provides more detailed information on soil nutrient content during Olsen-P inversion and exhibits comparable accuracy.

Combining field data and modeling to better understand maize growth response to phosphorus (P) fertilizer application and soil P dynamics in calcareous soils

We used field experimental data to evaluate the ability of the agricultural production system model (APSIM) to simulate soil P availability, maize biomass and grain yield in response to P fertilizer applications on a fluvo-aquic soil in the North China Plain. Crop and soil data from a 2-year experiment with three P fertilizer application rates (0, 75 and 300 kg P2O5 ha−1) were used to calibrate the model. Sensitivity analysis was carried out to investigate the influence of APSIM SoilP parameters on the simulated P availability in soil and maize growth. Crop and soil P parameters were then derived by matching or relating the simulation results to observed crop biomass, yield, P uptake and Olsen-P in soil. The re-parameterized model was further validated against 2 years of independent data at the same sites. The re-parameterized model enabled good simulation of the maize leaf area index (LAI), biomass, grain yield, P uptake, and grain P content in response to different levels of P additions against both the calibration and validation datasets. Our results showed that APSIM needs to be re-parameterized for simulation of maize LAI dynamics through modification of leaf size curve and a reduction in the rate of leaf senescence for modern stay-green maize cultivars in China. The P concentration limits (maximum and minimum P concentrations in organs) at different stages also need to be adjusted. Our results further showed a curvilinear relationship between the measured Olsen-P concentration and simulated labile P content, which could facilitate the initialization of APSIM P pools in the NCP with Olsen-P measurements in future studies. It remains difficult to parameterize the APSIM SoilP module due to the conceptual nature of the pools and simplified conceptualization of key P transformation processes. A fundamental understanding still needs to be developed for modelling and predicting the fate of applied P fertilizers in soils with contrasting physical and chemical characteristics.

Alfalfa stand age at termination influences soil properties, root characteristics, and subsequent maize yield

Alfalfa (Medicago sativa L.)–maize (Zea mays L.) rotation is an important cropping practice to improve crop production and soil fertility, but the effects of the alfalfa stand age on the performances of the following maize remain unexplored. It is not clear how different alfalfa stand ages at termination influence soil properties, root characteristics, and yield of subsequent maize. The aim of this study was to evaluate how alfalfa influences soil characteristics, which in turn influence the root and aboveground growth and grain yield of the following maize crop. A field experiment from 2014 to 2019 was conducted at the Lishu Experimental Station, Jilin Province, China. The field treatments included six years of continuous maize (CM), six years of continuous alfalfa (CA), three years of alfalfa followed by two years of maize (3A2M), four years of alfalfa followed by two years of maize (4A2M), and five years of alfalfa followed by one year of maize (5A1M). Only the yield for the first-year maize after alfalfa in the 3A2M, 4A2M, and 5A1M treatments significantly increased by 8 %, 23 %, and 13 %, respectively. Root biomass (RB) of CA treatment gradually increased from 2014, reaching its maximum value of 5866 kg ha−1 in 2019, which was 35 % greater than the RB accumulation under CM in the 0–60 cm soil layer. Compared with the CM treatment, 3A2M and 4A2M treatments increased RB, while 3A2M, 4A2M, and 5A2M increased root length density (RLD), root surface area density (RSAD), and root volume density (RVD) of first-year maize after alfalfa. The 4A2M treatment also increased RLD, RSAD, and RVD in the 0–60 cm soil layer of second-year maize and reduced the soil bulk density (BD) in the 0–20 cm soil layer of first-year maize after alfalfa. Only 4A2M and 5A1M treatments significantly increased soil Olsen-P and soil organic carbon by first-year maize after alfalfa. The redundancy analysis results showed that the soil water content in the critical period and soil Olsen-P were the primary factors, which explained 33.8 % and 13.0 % of variation in maize root characteristics (P < 0.01), respectively. Structural equation modeling indicated that sowing alfalfa influenced the subsequent maize yield by influencing the soil Olsen-P, soil mineral nitrogen before sowing, and root characteristics. Therefore, keeping alfalfa for at least four years should be the recommended practice owing to its ability to improve the soil properties, root growth, and subsequent maize yield.