Effect of Land Cover Change on Soil Phosphorus Fractions in Southeastern Horqin Sandy Land, Northern China

In the past 50 years, large areas of the Horqin sandy land were afforested to prevent desertification. Although the afforestation policy appears successful, many people now doubt whether it is suitable to plant trees with high density on the poor soils in semiarid regions. Little is known about the impacts of afforestation on the sandy soil properties, although the evaluation of these impacts is fundamental to judge the rationality of afforestation policy. Soil phosphorus （P） fractions, acid phosphomonoesterase activities, and other soil chemical properties were compared among five adjoining typical ecosystems on poor sandy soils in southeastern Horqin sandy land. The ecosystems studied are natural elm savanna, degraded grassland, Mongolian pine （Pinus sylvestris var. mongolica） plantation, Chinese pine （Pinus tabulaeformis） plantation, and mixed plantation of Mongolian pine and poplar （Populus simonii）. The results showed that organic P dominated soil P （47%-65%） was the principal source of available P. The degradation of elm savanna to grassland significantly reduced soil pH and resulted in an overall reduction in soil fertility, although slightly increased labile inorganic P. Grassland afforestation had no significant influence on soil pH, organic carbon, and total N but significantly reduced total P. Impacts of grassland afforestation on soil P fractions depended on tree species. Natural elm savanna had higher soil P conserving ability than artificial plantations. Therefore, with the aim of developing a sustainable ecosystem, we suggested that vegetations with low nutrient demand （particularly P） and efficient nutrient cycling would be more suitable for ecosystem restoration in the semiarid region.

Critical Soil Phosphorus Values for Yield Reduction in Intensive Agricultural Systems

Phosphorus(P)is an essential element for agricultural production.Over-fertilization during decades caused an accumulation of P in soils leading to eutrophication in regions characterized by intensive agriculture.These environmental concerns together with the non-renewability of P resources have led to a more sustainable P use.Knowledge about the P need of crops is essential for a sustainable agriculture thereby minimizing P losses to the environment without lowering the yield substantially.Therefore,in this study,critical soil P values for yield reduction(PCrit)were determined based on fertilizer trials conducted between 1970 and 1988 and more recent fertilizer trials(2016-2017).At rotational level a common PCrit value of 109 mg P/kg dry soil(in an ammonium lactate and acetate extract)was determined.Crop specific PCrit values were also determined for seven crops(potato,winter wheat,barley,rye,maize,sugar beet and temporary grassland).These critical values ranged from 59 mg P/kg dry soil to 164 mg P/kg dry soil with winter wheat the least and maize the most sensitive towards P deficiency.The diversity in PCrit values among crops can mainly be explained by the root intensity but also rooting depth,exudation of organic acids and phosphatases may influence the PCrit value.The soil pH also influenced the P availability significantly.Soils with a favorable pH had a significantly higher availability(i.e.,lower PCrit value)for all crops compared to soils with a suboptimal pH.Critical soil P values might help to set up new or to evaluate current soil P in target zones used for P fertilizer recommendations.

Long-term phosphorus accumulation and agronomic and environmtal critical phosphorus levels in Haplic Luvisol soil, northern China

Sufficient soil phosphorus （P） content is essential for achieving optimal crop yields, but accumulation of P in the soil due to excessive P applications can cause a risk of P loss and contribute to eutrophication of surface waters. Determination of a critical soil P value is fundamental for making appropriate P fertilization recommendations to ensure safety of both environment and crop production. In this study, agronomic and environmental critical P levels were determined by using linear-linear and linear-plateau models, and two segment linear model, for a maize （Zea mays L.）-winter wheat （Triticum aestivum L.） rotation system based on a 22-yr field experiment on a Haplic Luvisol soil in northern China. This study included six treatments： control （unfertilized）, no P （NoP）, application of mineral P fertilizer （MinP）, MinP plus return of maize straw （MinP＋StrP）, MinP plus low rate of farmyard swine manure （MinP＋L.Man） and MinP plus high rate of manure （MinP＋ H.Man）. Based on the two models, the mean agronomic critical levels of soil Olsen-P for optimal maize and wheat yields were 12.3 and 12.8 mg kg-1, respectively. The environmental critical P value as an indicator for P leaching was 30.6 mg Olsen-P kg-1, which was 2.4 times higher than the agronomic critical P value （on average 12.5 mg P kg-1）. It was calculated that soil OIsen-P content would reach the environmental critical P value in 41 years in the MinP treatment, but in only 5-6 years in the two manure treatments. Application of manure could significantly raise soil Olsen-P content and cause an obvious risk of P leaching. In conclusion, the threshold range of soil Olsen-P is from 12.5 to 30.6 mg P kg-1 to optimize crop yields and meanwhile maintain relatively low risk of P leaching in Haplic Luvisol soil, northern China.

Phosphorus fractions of fertiliser-derived P in an allophanic soil under Pinus radiata seedlings grown with broom and ryegrass

Changes in phosphorus （P） fractions in a P deficient allophanic soil under P. radiata seedlings grown with broom （Cytisus scoparius L.） and ryegrass （Lolium multiflorum） in pots were studied 14 months after the application of triple superphosphate at the rates of 0, 50, and 100 pg.g^-1, to determine the fate of fertiliser-derived P in the rhizosphere soils. Application of P fertiliser increased NaOH-Pi, NaOH-Po, and H2SO4-Pi concentrations in the soil, but decreased the residual-P concentration. The resin-Pi concentration, which is ex- tremely low in this soil （1 to μgg^-1 ）, remained the same. The majority of the added fertiliser P was however recovered in the NaOH-Pi fraction （40%-49%）. This is due to the high P fixation in this soil （92%）. The second highest P recovery was in NaOH-Po fraction （7%-19%）. Under P deficient condition or addition at the rate of 0 μg.g^-6, the NaOH-Pi concentration in the radiata rhizosphere soil was lower than that in the bulk soil and broom and grass rhizosphere soils. This may be due to higher oxalate production by the roots and mycorrhiza under P deficient conditions which released some ＆the P fixed to the soils in the rhizosphere, which needs to be tested in future studies.

Bioavailable phosphorus distribution in alpine meadow soil is affected by topography in the Tian Shan Mountains

Phosphorus(P) bioavailability is an important factor in alpine meadows and plays an important role in the response to climate change and the maintenance of ecosystem functioning.However,little is known about how environmental factors,such as elevation and slope aspect,affect soil P bioavailability.We explored the effects of elevational gradient and slope aspect on different forms of P and P availability in the alpine meadows on the southern slope of the Tian Shan Mountain range.Total P was found to be 851.9-1556.7 mg·kg^(-1) at different elevational gradients and 437.5-1547.0 mg·kg^(-1) at different slope aspects,and highest at 3337 and 3652 m.a.s.l.,but little differences between slope aspects.Olsen P and Labile P linearly increased with the elevational gradient.The valley and the base of the shady slope had higher contents of H_2O-Po.NaHCO_3-Pi,and NaHCO_3-Po,and high-active organic P(NaHCO_3-Po,NaOH-Po,and H_2O-Po) was positively correlated with soil total carbon(TC),total nitrogen(TN),soil organic carbon(SOC),and aboveground biomass(AGB),but was negatively correlated with pH,aluminum(Al),and calcium(Ca) at different elevational gradients.High-active bioavailable P(H_2OPi,H_2O-Po,NaHCO_3-Pi,and NaHCO_3-Po) was positively correlated with soil SOC and AGB and was negatively correlated with pH at different slope aspects.Our results suggest that soil P availability in alpine meadows is significantly controlled by topographical factors and the valleys and base of shady slopes are reservoirs of high-active bioavailable P.

Soil phosphorus determines the distinct assembly strategies for abundant and rare bacterial communities during successional reforestation

Uncovering the mechanisms underlying the diversity patterns of abundant and rare species is crucial for terrestrial biodiversity maintenance.However,the response of abundant and rare community assembly to ecological succession has not been explored,particularly considering soil profiles.Here 300 soil samples were collected from reforestation ecosystems from depths of up to 300 cm and horizontal distances of 30–90 cm from a tree.We revealed that soil phosphorus not only affected alpha diversity and community structure,but also mediated the balance of stochastic and deterministic processes for abundant and rare sub-communities,which exhibited contrasting assembly strategies.The abundant sub-community changed from variable selection to stochasticity with the increase of phosphorus,while the rare sub-community shifted from homogeneous selection to stochasticity.Dispersal limitation was the main assembly process in the abundant sub-community,while the rare sub-community was governed primarily by homogeneous selection.Moreover,the relative influence of deterministic processes increased with succession for both sub-communities.At the scale of a single tree,stochastic processes increased with soil depth in rare sub-community,while deterministic processes increased with the radius from a single tree in the abundant subcommunity.Overall,our results highlight the importance of the soil phosphorus-driven assembly process in understanding the re-assembly and maintenance of soil bacterial diversity.

Phosphorus fractions of fertiliser-derived P in an allophanic soil under Pinus radiata seedlings grown with broom and ryegrass

Changes in phosphorus (P) fractions in a P deficient allophanic soil under P. radiata seedlings grown with broom (Cytisus scoparius L.) and ryegrass (Lolium multiflorum) in pots were studied 14 months after the application of triple superphosphate at the rates of 0, 50, and 100 μg·g-1, to determine the fate of fertiliser-derived P in the rhizosphere soils. Application of P fertiliser increased NaOH-Pi, NaOH-Po, and H2SO4-Pi concentrations in the soil, but decreased the residual-P concentration. The resin-Pi concentration, which is extremely low in this soil (1 to 3 μg·g-1 ), remained the same. The majority of the added fertiliser P was however recovered in the NaOH-Pi fraction (40%?49%). This is due to the high P fixation in this soil (92%). The second highest P recovery was in NaOH-Po fraction (7%?19%). Under P deficient condition or addition at the rate of 0 μg·g-1, the NaOH-Pi concentration in the radiata rhizosphere soil was lower than that in the bulk soil and broom and grass rhizosphere soils. This may be due to higher oxalate production by the roots and mycorrhiza under P deficient conditions which released some of the P fixed to the soils in the rhizosphere, which needs to be tested in future studies.

Effects of Two Chelating Agents on Availability of Calcium and Phosphorus in Black Soil of Vegetable Fields

To explore the effects of the two chelating agents on the availability of calcium and phosphorus in black soil of vegetable fields and the growth of cabbage(Brassica pekinensis Rupr.)seedlings,humic acid(F)and ethylene diamine tetraacetic acid disodium salt(EDTA)were used as experiment materials,and two factors and three levels completely randomized experiment of the nine treatments was set.The experiments were carried out by soil incubation experiment and pot experiment to investigate the effects of the two chelating agents with different ratios and their interaction on soil and cabbage.The results showed that there were very significant differences among soil pH,soil available phosphorus content,cabbage biomass,calcium and phosphorus accumulation of cabbage under the interaction of the two chelating agents.It could improve pH of the soil and reduce the electric conductivity(EC)value of soil,when applied chelating agents of different proportions.The EC value of soil fluctuated during the incubation period.There were significant differences between pH and EC in the early incubation period,but there was no significant difference in the later stage.And there were significant differences between soil available calcium and available phosphorus content;there were significant differences between cabbage biomass and the accumulation of calcium and phosphorus in cabbage,and the data of F2E2 treatment were significantly higher than those of other treatments.In summary,under the conditions of the experiment,the available phosphorus content of black soil in vegetable fields,the biomass and accumulation of calcium and phosphorus in cabbage increased significantly in F2E2 treatment(appied 675 kg•hm-2 of lime,300 kg•hm-2 of humic acid and 150 kg•hm-2 of EDTA).

An Evaluation of Manure Management Strategies, Phosphorus Surface Runoff Potential and Water Usage at an Arkansas Discovery Dairy Farm

Manure management is an essential component of dairy production. Nutrient-laden, field-applied dairy manure often serves as a fertilizer source, but can also pose environmental threats if not properly managed. The Haak dairy farm, located in Decatur, Arkansas, was granted a permit by the Arkansas Department of Environmental Quality (ADEQ) to employ a unique method in treating and storing cattle manure generated during the milking process. This method includes minimizing water use in wash water, dry scraping solids to combine with sawdust for composting and pumping effluent underground into a sloped concrete basin that serves as secondary solid separator before transporting the manure effluent into an interception trench and an adjacent grassed field to facilitate manure nutrient uptake and retention. The Arkansas Discovery Farm program (ADF) is conducting research to evaluate the environmental performance of the dairy’s milk center wash water treatment system (MCWW) by statistical analysis, characterization of phosphorus (P) migration in soil downslope from the inception trench, temperature measurements, and nutrient analysis of a stored dry stack manure/sawdust mixture. Goals included determining possible composting effectiveness along with comparisons to untreated dairy manure and quantifying the use of on-farm water. Results from this research demonstrated that: 1) The MCWW was effective at retaining manure-derived nutrients and reducing field nutrient migration as the MCWW interception trench had significantly higher total nitrogen (TN) (804.2 to 4.1), total phosphorus (TP) (135.6 to 1.5), and water extractable phosphorus (WEP) (55.0 to 1.0) concentrations in milligrams per liter (mg⋅L-1) than the downhill freshwater pond respectively;2) temperature readings of the manure dry stack indicated heightened levels of microbial and thermal activity, but did not reach a standard composting temperature of 54°C;3) manure dry stack nutrient content was typically higher than untreated dairy manure when measured on a “dry basis” in ppm, but was lower on an “as is basis” in ppm and kg/metric ton;and 4) water meter readings showed that the greatest use of on-farm water was for farm-wide cattle drinking (18.77), followed by water used in the milking center (3.45) and then followed by human usage (0.02) measured in cubic meters per day (m3⋅d-1). These results demonstrate that practical innovations in agricultural engineering and environmental science, such as the Haak dairy’s manure treatment system, can effectively reduce environmental hazards that accompany the management of manure at this dairy operation.

Soil Nutrient Variance by Slope Position in a Mollisol Farmland Area of Northeast China

In order to generate scientifically-based comparative information to improve fertilization efficiency and reduce nutrient loss, 610 samples of 122 soil profiles were collected at the 0–60 cm depth to compare soil nutrient contents including soil organic matter(SOM), total nitrogen(TN), total phosphorus(TP), available phosphorus(AP), and available potassium(AK) among different slope positions in a Mollisol farmland area of Northeast China. The contents of SOM and TN typically decreased with increased soil depth at back and bottom slope. Soil loss and deposition tended to decrease SOM and TN at the 0–20 cm soil depth on both the back slope and the slope bottom. The TP firstly decreased from 0–20 cm to 30–40 cm, and then not constantly increased at the back slope and the bottom slope. Due to the characteristics of soil nutrients and crop absorption, the contents of both AP and AK were typically the highest at the summit, followed by the slope bottom and the back slope in the 0–20 cm layer. Generally, in order to sustain the high soil productivity and protect the environment, attention should be paid to soil conservation on back slope; in addition, additional N and P fertilizer is necessary on the back slope.

Effects of Introduction of Two Kinds of Legume Species on Soil Quality in Semiarid Loess Plateau

[Objective] The study aimed to find an efficient and sustainable way to improve the degraded soil quality in the semiarid Loess Plateau. [Method] This study was done with three treatments： （1） the perennial legume species alfalfa （Medicago sativa L.） （AF） planted at a density of 22.5 kg/hm 2 ; （2） the biennial legume species sweetclover （Melilotus officinalis L.） （SF） planted at a density of 11.3 kg/hm 2 ; and （3） natural regeneration （NR）. [Result] It is found that NR helped improve deep soil water but with the lowest aboveground biomass. In contrast, AF has the lowest soil water content but with the highest aboveground biomass. Furthermore, in contrast to SF, NR and AF have a higher soil organic carbon and total nitrogen. However, there were no significant differences on soil total and available phosphorus, and soil microbial biomass among all the treatments. As the experiment lasts, AP decreased significantly in all treatments in comparison with their initial values at the beginning of the experiment in 2003. [Conclusion] NR was the best way to restore the deep soil water among all the treatments, and phosphorus fertilizer was necessary for the sustainable development of agricultural production. This research provides a valuable example of soil quality restoration in semiarid regions.

Effects of soil nutrients and climate factors on belowground biomass in an alpine meadow in the source region of the Yangtze-Yellow rivers, Tibetan Plateau of China

Improving our knowledge of the effects of environmental factors （e.g. soil conditions, precipitation and temperature） on belowground biomass in an alpine grassland is essential for understanding the consequences of carbon storage in this biome. The object of this study is to investigate the relative importance of soil nutrients and climate factors on belowground biomass in an alpine meadow in the source region of the Yangtze and Yellow rivers, Tibetan Plateau. Soil organic carbon （SOC）, total nitrogen （TN） and total phosphorous （TP） contents and belowground biomass were measured at 22 sampling sites across an alpine meadow on the Tibetan Plateau. We analyzed the data by using the redundancy analysis to determine the main environmental factors affecting the belowground biomass and the contribution of each factor. The results showed that SOC, TN and TP were the main factors that influenced belowground biomass, and the contribution of SOC, TN and TP on biomass was in the range of 47.87%-72.06% at soil depths of 0-30 cm. Moreover, the combined contribution of annual mean temperature （AMT） and mean annual precipitation （MAP） on belowground biomass ranged from 0.92% to 4.10%. A potential mechanism for the differences in belowground biomass was caused by the variations in soil nitrogen and phosphorous, which were coupled with SOC. A significant correlation was observed between MAP and soil nutrients （SOC, TN and TP） at the soil depth of 0-10 cm （P〈0.05）. We concluded that precipitation is an important driving force in regulating ecosystem functioning as reflected in variations of soil nutrients （SOC, TN and TP） and dynamics of belowground biomass in alpine grassland ecosystems.

Evaluation of H3A for Determination of Plant Available P vs. FeAlO Strips

Phosphorus is an essential nutrient for plant growth but in excess is a source of environmental pollution. Fertilizer additions of P are recommended based on soil tests;however, the commonly applied P extractants are often applied outside of their design criteria (specifically soil pH). As a result, soil tests can produce inaccurate estimates of plant available P in the soil, which either increases P loss in runoff, contributing to eutrophication, or decreases crop production contributing to economic loss. In this study, 200 diverse soils from across the US were extracted with Mehlich 3, water, H3A-3, and FeAlO strips. Comparison with FeAlO was critical, as this method is accepted as the “gold standard” for plant-available P, but it is rarely used in commercial labs because of time and financial constraints. H3A-3 produced mean, median, standard deviations that are very similar to FeAlO strip results and low relative errors (<10%), as well as highly correlated regression relationships (r2 > 0.96 with slopes 0.95 - 0.98). Although Mehlich 3 and water were correlated with FeAlO, Mehlich 3 (strongly acidic) extracted much more P than FeAlO, and water (low buffering capacity) extracted much less P across the range of soil pH values. Thus, H3A-3 provides an improved methodology to accurately determine plant-available P by mimicking root exudate action in the soil, while avoiding the time-consuming and costly FeAlO procedure. In the face of high-profile water quality impairments with enormous economic costs, such advancements are critical to balance agronomic production with environmental concerns.

Effect of crevice density on biological soil crust development on rock cut slope in mountainous regions,Sichuan,China

Background The rock cut slope(RCS)could cause damage to regional ecological functions and landscapes and requires recovery.Biological soil crusts(BSCs)are pioneer and dominant colonizers during the initial recovery stage.To accelerate the natural recovery of RCS,the development process and influencing agents of BSC should be revealed.Thus,the area index of crevices(IR),BSC coverage(COV)and biomass(BM),soil weight(SW),and major soil nutrients[organic carbon(OC),total nitrogen(TN)and total phosphorus(TP)]content,collected from 164 quadrats on 13 RCSs in the mountainous area of west Sichuan Province,China,were measured,to explore the effect of crevice of RCS on BSC development.Results Soil OC,TN and TP on RCSs ranged from 18.61 to 123.03 g kg^(-1),0.96 to 6.02 g kg^(-1)and 0.52 to 2.46 g kg^(-1),respectively,and were approximately to or higher than those on natural slopes.The OC,TN and TP contents in soils elevated unsystematically with recovery time of RCSs.BSCs on RCS distributed along crevices generally and firstly.During the first 13 years of natural recovery,COV,BM and SW ranged from 6.5 to 28.2%,14.43 to 67.25 g m^(-2),and 127.69 to 1277.74 g m^(-2),respectively.COV,BM and SW increased linearly with IR on RCSs.The positive correlation between COV and BM and IR was insignificantly impacted by bedrock,slope aspect and altitude within the recovery time less than 13 years.COV and BM on RCSs increased significantly when the recovery time is more than 27 years.Conclusions Crevice on RCSs could be a major environmental factor which is conducive to BSC development and soil accumulation through creating a space for water and soil particle.Furthermore,with the increase of recovery time of RCSs,BSCs may grow and reach a stable state with the promotion of soil nutrients,plant growth and microbial activity.These results provide a development process of BSC that from inside to outside the crevices on RCSs.In the areas with stable rock strata and a low risk of geological disasters,purposeful improvement in crevice density on RCS may effectively accelerate BSC development.

Seven years of biochar amendment has a negligible effect on soil available P and a progressive effect on organic C in paddy soils

Little attention has been paid to how long-term application of crop straw and its biochar affects soil phosphorus(P)transformation and carbon(C)fractions.We conducted a 7-year field experiment including control treatment(chemical fertilizer only,CK),straw return(2.25 t ha^(−1)),and different amounts of biochar addition(11.25 t ha^(−1)(0.5%BC)and 22.5 t ha^(−1)(1.0%BC),to investigate influence of these amendments on soil C structure,P fractions,and their interaction with microorganisms.The 13C nuclear magnetic resonance and soil P sequence fractionation were applied to capture changes of soil C compositions and P pool.Compared to CK,straw and biochar amendments decreased alkyl C/O-alkyl C,which is conducive to increased soil organic C.The 0.5%BC and 1.0%BC treatments enhanced recalcitrant aromatic C by 69.0%and 131%,respectively.Compared to CK(101.2±33.32 mg kg^(−1)),the 0.5%BC and 1.0%BC treatments had a negligible effect on soil available P,while negative effects were observed in straw treatment(59.79±9.023 mg kg^(−1)).Straw and biochar amendments increased primary P and occluded P,whereas had negligible effect on organic P.Redundancy analysis and correlation analysis indi-cated that C compositions and P pool correlated to microbial community composition and enzyme activities,and aromatic C was the most related factor.Moreover,structural equation modeling indicated available P was most related to phosphatase activity and C composition.Our findings reveal the changes of soil P and C response under long-term crop straw and its biochar amendment,and can contribute toward improving understanding of the effect of biochar and straw return in future agriculture management.

Changes in soil biochemical properties following replacement of Banj oak forest with Chir pine in Central Himalaya,India

Introduction:In Central Himalaya,anthropogenic activities have led to the widespread replacement of Banj oak(Quercus leucotrichophora)forest by Chir pine(Pinus roxburghii)for decades.This study was conducted to determine how natural Banj oak,Chir pine,and mixed oak-pine forest would differ in soil microbial biomass and soil nutrients.Soil microbial biomass nitrogen(SMBN)and phosphorus(SMBP),soil organic carbon(SOC)total nitrogen(TN),and total phosphorus(TP)in the 0 to 15 cm soil layer were investigated in the Central Himalayan region in the stands of Banj oak,mixed oak-pine,and Chir pine forest.Results:The SMBN and SMBP were significantly higher in Banj oak and mixed oak-pine forest as compared to Chir pine forest.The ratios of SMBN to TN(SMBN/TN)and SMBP to TP(SMBP/TP)were significantly higher in the Chir pine forest,indicating that in this forest,the proportion of microbial biomass N and P to total soil N and P was higher as compared to Banj oak forest.A similar pattern of variation was found in relation to season across the forests,all with an apparent peak in the rainy season.Conclusion:These results indicate that low microbial biomass N and P may be one of the reasons to create a nutrient poor site in Chir pine forest.The collection of pine litter by local people also impairs the return of nutrients to the soil and makes it difficult for Banj oak to re-invade areas occupied by Chir pine.This calls for cautions in large-scale conversions of the Banj oak forests to coniferous plantations as a forest management practice on concerns of sustaining soil productivity.

Red soil for sediment capping to control the internal nutrient release under flow conditions

Nitrogen （N） and phosphorus （P） released from the sediment to the surface water is a major source of water quality impairment. Therefore, inhibiting sediment nutrient release seems necessary. In this study, red soil （RS） was employed to control the nutrients released from a black-odorous river sediment under flow conditions. The N and P that were released were effectively controlled by RS capping. Continuous-flow incubations showed that the reduction efficiencies of total N （TN）, ammonium （NH4＋-N）, total P （TP） and soluble reactive P （SRP） of the overlying water by RS capping were 77%, 63%, 77% and 92%, respectively, and nitrification and denitrification occurred concurrently in the RS system. An increase in the water velocity coincided with a decrease in the nutrient release rate as a result of intensive water aeration.