Assembly and co-occurrence patterns of rhizosphere bacterial communities are closely linked to soil fertility during continuous cropping of cut chrysanthemum (Chrysanthemum morifolium Ramat).

AIMS: Continuous cropping is known to have profound effects on the soil microbial community in different planting systems. However, we lack an understanding of how different years of continuous cropping affects rhizosphere soil bacterial community co-occurrence pattern and assembly processes in the cut chrysanthemum (Chrysanthemum morifolium Ramat.) field. METHODS AND RESULTS: We collected the soils from cut chrysanthemum rhizospheres with planting for 1 year (PY1) and continuous cropping for 6 years (CY6) and 12 years (CY12). Real-time quantitative PCR and flow cytometry (FCM) techniques were used to test the 16S rRNA gene copy number and bacterial cell count, respectively. The bacterial community structure was analysed by using high-throughput sequencing technology. The CY12 had a significantly decreased soil fertility index and rhizosphere bacterial living cell counts and gene copy numbers compared to CY6 and PY1 (P < 0.05). The rhizosphere bacterial community dissimilarity increased as the continuous cropping years increased. Three main ecological clusters (modules #1, #2, and #3) were observed in the bacterial co-occurrence network across all samples, and only the relative abundance of module #1 (enriched in the CY12) was significantly correlated with soil fertility (P < 0.05). Moreover, the rhizosphere bacterial community assembly was primarily governed by the deterministic process under 12 years of continuous cropping. CONCLUSIONS: Soil fertility decline correlates with ecological network modularization and the deterministic assembly process of the rhizosphere bacterial community of cut chrysanthemum during continuous cropping.

Response of abundance, diversity, and network of rhizosphere fungal community to monoculture of cut chrysanthemum.

The effects of different monoculture years on rhizosphere fungal communities (abundance, diversity, structure, and cooccurrence network) of cut chrysanthemum were determined. Three different monoculture years were (i) planting for only 1 year (Y1), (ii) continuous monoculture for 6 years (Y6), and (iii) continuous monoculture for 12 years (Y12). Compared to the Y1 treatment, the Y12 treatment significantly decreased the rhizosphere fungal gene copy numbers but increased the potential pathogen Fusarium oxysporum (P < 0.05). Both the Y6 and Y12 treatments significantly increased fungal diversity (Shannon and Simpson indices), but Y6 had great potential to enhance fungal richness (Chao1 index) relative to the Y12 treatment. Monoculture treatments decreased the relative abundance of Ascomycota but increased that of Mortierellomycota. Four ecological clusters (Modules 0, 3, 4, and 9) were observed in the fungal cooccurrence network across the Y1, Y6, and Y12 treatments, and only Module 0 was significantly enriched in the Y12 treatment and associated with soil properties (P < 0.05). RDA (redundancy analysis) and Mantel analysis showed that soil pH and soil nutrients (organic carbon, total nitrogen, and available phosphorus) were the key factors affecting fungal communities during monoculture of cut chrysanthemum. Overall, the changes in soil properties were responsible for shaping rhizospheric soil fungal communities in long-term rather than short-term monoculture systems. KEY POINTS: • Both short- and long-term monocultures reshaped the soil fungal community structure. • Long-term monoculture enhanced the network complexity of the fungal community. • Soil pH, C and N levels mainly drove modularization in the fungal community network.

Soil pqqC-harboring bacterial community response to increasing aridity in semi-arid grassland ecosystems: Diversity, co-occurrence network, and assembly process.

Aridity is increasing in several regions because of global climate change, which strongly affects the soil microbial community. The soil pqqC-harboring bacterial community plays a vital role in soil P cycling and P availability. However, the effect of shifts in aridity on the pqqC community is largely unknown. Here, based on high-throughput sequencing technology, we investigated the response patterns of the diversity, co-occurrence networks, and assembly mechanisms of the soil pqqC communities along a natural aridity gradient in adjacent pairs of natural and disturbed grasslands in Inner Mongolia, China. The results showed that the α-diversity of the pqqC community first increased and then decreased with increasing aridity in the natural grassland, while it linearly increased as aridity increased in the disturbed grassland. The pqqC community dissimilarity significantly increased with increased aridity, exhibiting a steeper change rate in the disturbed grassland than in the natural grassland. Increased aridity altered the pqqC community composition, leading to increases in the relative abundance of Actinobacteria but decreases in Proteobacteria. The composition and structure of the pqqC community showed significant differences between natural and disturbed grasslands. In addition, the network analysis revealed that aridity improved the interactions among pqqC taxa and promoted the interspecific competition of pqqC microorganisms. The pqqC community assembly was primarily governed by stochastic processes, and the relative contribution of stochastic processes increased with increasing aridity. Furthermore, disturbances could affect pqqC-harboring bacterial interactions and assembly processes. Overall, our findings fill an important knowledge gap in our understanding of the influence of aridity on the diversity and assembly mechanism of the soil pqqC community in grassland ecosystems, and this work is thus conducive to predicting the pqqC community and its ecological services in response to future climate change.

Tracing the Transformation and Allocation of the Newly Applied-P in Calcareous Soil Using an Enriched Oxygen Isotope Labeling Technique.

Different phosphorus (P) fertilizations significantly impact the transformation of the applied-P in soils. However, knowledge about how different P fertilization regimes influence the allocation of the amended-P in soil remains incomplete. Herein, we carried out a pot experiment to explore the fate of applied-P in calcareous soil using an oxygen isotope labeling technique (18O-P18O43-). Treatments included check (CK), single, and repeated applications. The phosphorus mass balance result showed that more than 48.5% of the applied-P was held in labile and moderately labile fractions with the repeated treatment, while approximately 27.4% of the added-P was recovered in nonlabile forms in the single application treatment. The isotopic tracer (18O-P18O43-) result demonstrated that the δ18OP values of NaHCO3-P and NaOH-P in the repeated P application were significantly higher than those in the single P application. Ultimately, better agronomic performances of the crops and higher PUE were achieved in the repeated treatment. Our findings highlighted that repeated P fertilization can improve P availability by reducing P fixation. These results pronounced that the enriched oxygen isotope technique can be considered an effective approach for tracing applied-P in soils.

Nitrapyrin Addition Mitigated CO2 Emission from a Calcareous Soil Was Closely Associated with Its Effect on Decreasing Cellulolytic Fungal Community Diversity.

Application of nitrification inhibitors (NIs) has been widely used to inhibit nitrification and reduce N2O emissions. However, the impacts of NI addition on soil carbon transformation and carbon-degrading microbial communities have not been well explored. Here, a microcosm experiment was carried out, and four treatments were designed: (i) unfertilized control, (ii) urea alone, (iii) urea plus cattle manure, and (iv) urea plus cattle manure with nitrapyrin. The influence of nitrapyrin on soil CO2 emissions, carbon-degrading extracellular enzyme activities, and the abundance and diversity of the cbhI community was investigated. Compared to the treatment of urea plus cattle manure, nitrapyrin significantly decreased cumulative CO2 emissions by 51.8%. Moreover, cbhI community gene copies and their α-diversities (P < 0.05) were also significantly reduced by nitrapyrin application. A partial least squares path model showed that CO2 emission was positively associated with cbhI community α-diversity but negatively associated with nitrapyrin addition. We conclude that the mitigation of soil CO2 emissions by nitrapyrin can be ascribed to its effects on decreasing of cellulose-degrading gene community diversity. Our findings provide new insights into the side-effects of nitrapyrin on abating CO2 emission.

Di-(2-ethylhexyl) phthalate (DEHP) exposure suppressed the community diversity and abundance of ammonia-oxidizers and mitigated N2O emissions in an alkaline soil.

Phthalic acid esters (PAEs) pollution has become an increasing issue worldwide, but little is known about its effects on ammonia-oxidizers and nitrous oxide (N2O) in the soil environment. Here, a 50-day soil microcosm experiment was conducted using low and high doses bis (2-Ethylhexyl) phthalate (DEHP) to estimate the effect of DEHP exposure on soil N2O emissions and the nitrifying community in calcareous soil. The results showed that DEHP exposure at 10 and 100 mg kg-1 doses significantly reduced N2O by 67.5% and 73.6%, respectively, relative to the DEHP absent treatment. The microbial biomass carbon and nitrogen (MBC and MBN) were consistently and significantly decreased with DEHP exposure at 5, 22, and 50 days after incubation, especially with high-dose. The bipartite association networks showed that DEHP exposure changed the compositions of both ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) communities. Moreover, the AOA and AOB amoA gene abundances were significantly decreased by DEHP addition to the soil (P < 0.05). Random forest modeling showed that the AOB Shannon index and pH were the most important biotic and abiotic factors affecting N2O emissions in the soil with DEHP exposure, respectively. Partial least squares path modeling (PLS-PM) demonstrated that the reduction of N2O emissions due to DEHP exposure was mainly ascribed to the changes of the AOB community. The results from this study highlight the toxicity of DEHP on the ammonia oxidizers, and its mitigating effect on N2O emissions in the soil where ammonia-oxidation is largely driven by AOB.

Optimization and Characterization of Polyphosphate Fertilizers by Two Different Manufacturing Processes.

To explore how different reaction parameters affect the major features of short-chain ammonium polyphosphate (APP) fertilizers, a batch of manufacturing experiments were conducted under two different manufacturing processes [phosphoric acid (PA)-urea and monoammonium phosphate (MAP)-urea]. The APP features including polymerization degree, polymerization rate, solubility, and N and P recovery rates were significantly varied and influenced by the molar ratio of raw materials (P:N), reaction temperature, time, and pressure under different manufacturing conditions. In the MAP-urea process, the optimized APP products were gained under the combination condition of molar ratio = 1.6:1, T = 130 °C, and t = 45 min, while this happened in molar ratio = 1:1.7, T = 180 °C, and t = 60 min in the PA-urea process. Comprehensively, the features of APP fertilizers produced by the MAP-urea process were better than those produced by the PA-urea process. Our results provide valuable references for manufacturing high-quality short-chain APP fertilizers.

Short-chain soluble polyphosphate fertilizers increased soil P availability and mobility by reducing P fixation in two contrasting calcareous soils.

Short-chain polyphosphate fertilizers have been increasingly applied in agriculture, but little is known about the chemical behaviors of polyphosphate in soils. Herein, a cylinder experiment was carried out to investigate the influences of different P types (i.e., mono-ammonium phosphate (MAP), phosphoric acid (PA) and ammonium polyphosphate (poly-P)) and their application methods (single vs split) on the mobility and availability of P in soil through a column millimeter-scale slice cutting method; meanwhile a soil microcosm experiment (560-day) was conducted to investigate the effects of different P types on phosphorus dynamic transformation. Polyphosphate addition significantly increased P mobility. The average distance of P downward movement (81.5 mm) in soil profile in the poly-P application treatment increased by 33.6% and 81.1%, respectively, compared to the MAP and PA treatments. Different P application methods also markedly influenced phosphorus mobility. For instance, the average distance of P vertical movement in the split P application treatment was 21.2% higher than in the single application treatment, indicating that split P addition significantly increased P downward movement. Moreover, polyphosphate application decreased soil P fixation by blocking the transformation of the applied-P from labile to recalcitrant forms (HCl-P and residual-P). Overall, our findings provide meaningful information to current phosphorus fertilization practice in increasing soil P mobility and bioavailability. We suggest that polyphosphate could be regarded as an alternative P source used in agriculture, and split polyphosphate application is recommended as an effective P fertilization strategy.

Mitigating N2O emission by synthetic inhibitors mixed with urea and cattle manure application via inhibiting ammonia-oxidizing bacteria, but not archaea, in a calcareous soil.

Synthetic inhibitors and organic amendment have been proposed for mitigating greenhouse gas N2O emissions. However, their combined effect on the N2O emissions and ammonia-oxidizer (ammonia-oxidizing bacteria and archaea, AOB and AOA) communities remains unclear in calcareous soils under climate warming. We conducted two incubation experiments (25 and 35 °C) to examine how N2O emissions and AOA and AOB communities responded to organic amendment (urea plus cattle manure, UCM), and in combination with urease (N-(n-butyl) thiophosphoric triamide, NBPT) and nitrification inhibitor (nitrapyrin). The treatments of UCM + nitrapyrin and UCM + nitrapyrin + NBPT significantly lowered total N2O emissions by average 64.5 and 71.05% at 25 and 35 °C, respectively, compared with UCM treatment. AOB gene abundance and α-diversity (Chao1 and Shannon indices) were significantly increased by the application of urea and manure (P < 0.05). However, relative to UCM treatment, nitrapyrin addition treatments decreased AOB gene abundance and Chao 1 index by average 115.4 and 30.4% at 25 and 35 °C, respectively. PCA analysis showed that UCM or UCM plus nitrapyrin notably shifted AOB structure at both temperatures. However, fertilization had little effects on AOA community (P > 0.05). Potential nitrification rate (PNR) was greatly decreased by nitrapyrin addition, and PNR significantly positively correlated with AOB gene abundance (P = 0.0179 at 25 °C and P = 0.0029 at 35 °C) rather than AOA (P > 0.05). Structural equation model analysis showed that temperature directly increased AOA abundance but decrease AOB abundance, while fertilization indirectly influenced AOB community by altering soil NH4+, pH and SOC. In conclusion, the combined application of organic amendment, NBPT and nitrapyrin significantly lowered N2O emissions via reducing AOB community in calcareous soil even at high temperature. Our findings provide a solid theoretical basis in mitigating N2O emissions from calcareous soil under climate warming.

A 2-year study of the impact of reduced nitrogen application combined with double inhibitors on soil nitrogen transformation and wheat productivity under drip irrigation.

BACKGROUND: Nitrification inhibitors (NIs) and urease inhibitors (UIs) can decrease the risk of nitrogen (N) loss and extend N uptake by plants. However, there are few case studies about reduced N application combined with double inhibitors (DIs, NI plus UI), especially under drip irrigation systems. A 2-year field experiment was therefore conducted to explore the effect of 80% N application rate combined with NI or DIs on soil N transformation, wheat productivity and N use efficiency (NUE) in a drip-irrigated field. The four treatments included a no-fertilizer control, 100% urea, 80% urea + NI (nitrapyrin) and 80% urea + DIs (nitrapyrin and N-(n-butyl) thiophosphorictriamide (NBPT)). RESULTS: Our results showed that the 80% urea + DIs treatment significantly increased the ratio of NH4 + to NO3 - and N content (urea-N, NH4 + -N and NO3 - -N) in soil at 0-20 cm depth (P < 0.05) at the heading stage and the filling stage of wheat in both 2013 and 2014, relative to the 100% urea treatment. A total of 80% urea + NI treatment decreased wheat N uptake and wheat productivity (plant biomass and yield) compared to 100% urea treatments (P < 0.05). However, application of 80% urea combined with DIs achieved equivalent wheat productivity with 100% urea treatment. Moreover, the greatest NUE (43.6%) was recorded with the application of DIs. CONCLUSIONS: Cutting the N application rate by 20% combined with NBPT and nitrapyrin could provide a sustainable fertilization strategy for wheat production under drip irrigation. © 2020 Society of Chemical Industry.

Reduction of N2O emission by biochar and/or 3,4-dimethylpyrazole phosphate (DMPP) is closely linked to soil ammonia oxidizing bacteria and nosZI-N2O reducer populations.

Biochar has been demonstrated to reduce nitrous oxide (N2O) emissions from soils, but its effect is highly soil-dependent. In particular, in soils with strong nitrification potential, biochar addition may increase N2O emissions. Thus, in soils with strong nitrification potential, the combination of biochar with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) may be more effective in reducing N2O emissions than biochar alone. However, the combined use of biochar and DMPP on soil N2O emissions is relatively unexplored, and underlying microbial mechanisms of how biochar and/or DMPP amendment affect N2O emissions is still largely unknown. Here, a 30-day incubation experiment was established with four treatments: CK (control), BC (biochar), DMPP, and BD (biochar and DMPP), all at agronomically recommended rates, and N cycling assessed following addition of urea. Treatment of soil with BC, DMPP and BD reduced N2O emissions (compared with urea alone) by 59.1%, 95.5% and 74.1%, respectively. Quantification of N cycling genes (amoA, nirS, nirK, and nosZ) indicated that biochar stimulated growth of ammonia oxidizing archaea (AOA) and bacteria (AOB), while DMPP alone inhibited the activity and growth of AOB. In the BD treatment, DMPP was absorbed onto biochar reducing its efficacy in inhibiting AOB growth. The response patterns of nirS/nirK nitrite-reducing denitrifiers to biochar and/or DMPP addition varied among clades. Notably, biochar and/or DMPP increased the abundance of nosZI and nosZII-N2O reducers, but nosZI-clade taxa were more closely associated with reducing N2O emission than nosZII taxa. Overall, our findings proved that the dynamics of AOB and nosZI-N2O reducers resulting from the addition of biochar and/or DMPP played a key role in governing soil N2O emissions.

Effects of urease and nitrification inhibitors on the soil mineral nitrogen dynamics and nitrous oxide (N2O) emissions on calcareous soil.

Urease inhibitors and nitrification inhibitors can reduce nitrogen (N) loss in agriculture soil. However, the effect of inhibitors on soil N2O emissions under the drip irrigation system remains unclear. A pot and a field experiment with two inhibitors were conducted to explore how inhibitors regulate soil nitrogen transformation and N2O emissions. In the pot experiment, three treatments included control, urea, and urea + N-(n-butyl)thiophosphoric triamide (NBPT, urease inhibitor). In the field experiment, three treatments included control, urea, and urea + NBPT + 2-chloro-6-(trichloromethyl)pyridine (nitrapyrin, nitrification inhibitor). The urease inhibition rate in the treatment of urea + NBPT was 27.5% at the 14th day of incubation (pot experiment), and NH4+-N was significantly decreased by 37-64% compared with urea alone treatment. In the field experiment, the nitrification inhibition rate in the treatment of urea + NBPT + nitrapyrin was 47.7 and 63.9% on the 3rd day after fertilization at the wheat heading and filling stages, respectively. Compared to urea treatment, NO3--N concentration in the double-inhibitor-added treatment was significantly decreased by 32 and 20% on the 5th day after fertilization at the heading and filling stages, respectively; N2O fluxes were also decreased by 30.9 and 33.3% at the two stages of wheat, respectively. In total, adding an inhibitor reduced N loss by 7.39 and 7.44% at the 14th and 35th day in the pot experiment and by 10.53 and 6.65% at the two growing stages of wheat in the field experiment, respectively. Path and correlation analysis showed that N2O emissions were significantly correlated with soil NO3- in both pot and field experiments.

Nitrous oxide emission and denitrifier communities in drip-irrigated calcareous soil as affected by chemical and organic fertilizers.

The effects of consecutive application of chemical fertilizer with or without organic fertilizer on soil N2O emissions and denitrifying community structure in a drip-irrigated field were determined. The four fertilizer treatments were (i) unfertilized, (ii) chemical fertilizer, (iii) 60% chemical fertilizer plus cattle manure, and (iv) 60% chemical fertilizer plus biofertilizer. The treatments with organic amendments (i.e. cattle manure and biofertilizer) reduced cumulative N2O emissions by 4.9-9.9%, reduced the N2O emission factor by 1.3-42%, and increased denitrifying enzyme activities by 14.3-56.2%. The nirK gene copy numbers were greatest in soil which received only chemical fertilizer. In contrast, nirS- and nosZ-copy numbers were greatest in soil amended with chemical fertilizer plus biofertilizer. Chemical fertilizer application with or without organic fertilizer significantly changed the community structure of nirK-type denitrifiers relative to the unfertilized soil. In comparison, the nirS- and nosZ-type denitrifier genotypes varied in treatments receiving organic fertilizer but not chemical fertilizer alone. The changes in the denitrifier communities were closely associated with soil organic carbon (SOC), NO3-, NH4+, water holding capacity, and soil pH. Modeling indicated that N2O emissions in this soil were primarily associated with the abundance of nirS type denitrifying bacteria, SOC, and NO3-. Overall, our findings indicate that (i) the organic fertilizers increased denitrifying enzyme activity, increased denitrifying-bacteria gene copy numbers, but reduced N2O emissions, and (ii) nirS- and nosZ-type denitrifiers were more sensitive than nirK-type denitrifiers to the organic fertilizers.

Nitrapyrin addition mitigates nitrous oxide emissions and raises nitrogen use efficiency in plastic-film-mulched drip-fertigated cotton field.

Nitrification inhibitors (NIs) have been used extensively to reduce nitrogen losses and increase crop nitrogen nutrition. However, information is still scant regarding the influence of NIs on nitrogen transformation, nitrous oxide (N2O) emission and nitrogen utilization in plastic-film-mulched calcareous soil under high frequency drip-fertigated condition. Therefore, a field trial was conducted to evaluate the effect of nitrapyrin (2-chloro-6-(trichloromethyl)-pyridine) on soil mineral nitrogen (N) transformation, N2O emission and nitrogen use efficiency (NUE) in a drip-fertigated cotton-growing calcareous field. Three treatments were established: control (no N fertilizer), urea (225 kg N ha-1) and urea+nitrapyrin (225 kg N ha-1+2.25 kg nitrapyrin ha-1). Compared with urea alone, urea plus nitrapyrin decreased the average N2O emission fluxes by 6.6-21.8% in June, July and August significantly in a drip-fertigation cycle. Urea application increased the seasonal cumulative N2O emission by 2.4 kg N ha-1 compared with control, and nitrapyrin addition significantly mitigated the seasonal N2O emission by 14.3% compared with urea only. During the main growing season, the average soil ammonium nitrogen (NH4+-N) concentration was 28.0% greater and soil nitrate nitrogen (NO3--N) concentration was 13.8% less in the urea+nitrapyrin treatment than in the urea treatment. Soil NO3--N and water-filled pore space (WFPS) were more closely correlated than soil NH4+-N with soil N2O fluxes under drip-fertigated condition (P<0.001). Compared with urea alone, urea plus nitrapyrin reduced the seasonal N2O emission factor (EF) by 32.4% while increasing nitrogen use efficiency by 10.7%. The results demonstrated that nitrapyrin addition significantly inhibited soil nitrification and maintained more NH4+-N in soil, mitigated N2O losses and improved nitrogen use efficiency in plastic-film-mulched calcareous soil under high frequency drip-fertigated condition.

[Effect of mineral N fertilizer reduction and organic fertilizer substitution on soil biological properties and aggregate characteristics in drip-irrigated cotton field.] / å‡æ°®é æ–½æœ‰æœºè‚¥å¯¹æ»´çŒæ£‰ç”°åœŸå£¤ç”Ÿç‰©å­¦æ€§çŠ¶ä¸Žå›¢èšä½“ç‰¹æ€§çš„å½±å“.

A four year field study was conducted to determine how soil biological properties and soil aggregate stability changed when organic fertilizer and biofertilizer were used to reduce chemical fertilizer application to a drip irrigated cotton field. The study consisted of six fertilization treatments: unfertilized (CK); chemical fertilizer (CF, 300 kg N·hm-2; 90 kg P2O5 · hm-2, 60 kg K2 O·hm-2); 80% CF plus 3000 kg·hm-2organic fertilizer (80%CF+OF); 60% CF plus 6000 kg·hm-2organic fertilizer (60%CF+OF); 80% CF plus 3000 kg·hm-2biofertilizer (80%CF+BF); and 60% CF plus 6000 kg·hm-2biofertilizer (60%CF+BF). The relationships among soil organic C, soil biological properties, and soil aggregate size distribution were determined. The results showed that organic fertilizer and biofertilizer both significantly increased soil enzyme activities. Compared with CF, the biofertilizer treatments increased urease activity by 55.6%-84.0%, alkaline phosphatise activity by 53.1%-74.0%, invertase activity by 15.1%-38.0%, ß-glucosidase activity by 38.2%-68.0%, polyphenoloxidase activity by 29.6%-52.0%, and arylsulfatase activity by 35.4%-58.9%. Soil enzyme activity increased as the amount of organic fertilizer and biofertilizer increased (i.e., 60%CF+OF > 80%CF+OF, 60%CF+BF > 80%CF+BF). Soil basal respiration decreased significantly in the order BF > OF > CF > CK. Soil microbial biomass C and N were 22.3% and 43.5% greater, respectively, in 60%CF+BF than in CF. The microbial biomass C:N was significantly lower in 60%CF+BF than in CF. The organic fertilizer and the biofertilizer both improved soil aggregate structure. Soil mass in the >0.25 mm fraction was 7.1% greater in 80%CF+OF and 8.0% greater in (60%CF+OF) than in CF. The geometric mean diameter was 9.2% greater in 80%CF+BF than in 80%CF+OF. Redundancy analysis and cluster analysis both demonstrated that soil aggregate structure and biological activities increased when organic fertilizer and biofertilizer were used to reduce chemical fertilizer application. In conclusion, the organic fertilizer and the biofertilizer significantly increased SOC, soil enzyme activity, and soil microbial biomass C and N. The organic fertilizers also improved soil aggregation. Therefore, soil quality could be improved by using these fertilizers to reduce chemical fertilizer application, especially under drip-irrigation.

[Effects of different cropping patterns on soil enzyme activities and soil microbial community diversity in oasis farmland].

Effects of long-term cropping patterns on the activities of peroxidase, invertase, arylsulfatase, dehydrogenase and protease were investigated in this paper. Four long-term cropping patterns included (1) 10 years continuous cropping of corn, (2) 8 years continuous cropping of wheat followed by 10 years continuous cropping of cotton, (3) 15 years continuous cropping of cotton, and (4) 6 years continuous cropping of cotton followed by 6 years of wheat/sunflower rotation. The responses of soil bacteria, fungi, ammonia oxidizing bacteria (AOB) , and the ammonia oxidizing archaea (AOA) to different copping patterns were analyzed. The results showed that cropping patterns significantly affected the activities of soil peroxidase, arylsulfatase, dehydrogenase and protease, while had no significant effect on soil invertase activity. The cropping patterns significantly influenced the diversity index of AOA, but had no significant influence on that of soil bacteria, fungi and AOB. The community structures of soil fungi and AOB were more sensitive to cropping patterns than soil bacteria and AOA. In conclusion, long-term continuous cropping of cotton decreased the activities of soil enzymes activities and soil microbial diversity in oasis farmland, while crop rotation could alleviate the negative influence.

[Effects of brackish water irrigation on soil enzyme activity, soil CO2 flux and organic matter decomposition].

Brackish water irrigation utilization is an important way to alleviate water resource shortage in arid region. A field-plot experiment was set up to study the impact of the salinity level (0.31, 3.0 or 5.0 g · L(-1) NaCl) of irrigated water on activities of soil catalase, invertase, ß-glucosidase, cellulase and polyphenoloxidase in drip irrigation condition, and the responses of soil CO2 flux and organic matter decomposition were also determined by soil carbon dioxide flux instrument (LI-8100) and nylon net bag method. The results showed that in contrast with fresh water irrigation treatment (CK), the activities of invertase, ß-glucosidase and cellulase in the brackish water (3.0 g · L(-1)) irrigation treatment declined by 31.7%-32.4%, 29.7%-31.6%, 20.8%-24.3%, respectively, while soil polyphenoloxidase activity was obviously enhanced with increasing the salinity level of irrigated water. Compared to CK, polyphenoloxidase activity increased by 2.4% and 20.5%, respectively, in the brackish water and saline water irrigation treatments. Both soil microbial biomass carbon and microbial quotient decreased with increasing the salinity level, whereas, microbial metabolic quotient showed an increasing tendency with increasing the salinity level. Soil CO2 fluxes in the different treatments were in the order of CK (0.31 g · L(-1)) > brackish water irrigation (3.0 g · L(-1)) ≥ saline water irrigation (5.0 g · L(-1)). Moreover, CO2 flux from plastic film mulched soil was always much higher than that from no plastic film mulched soil, regardless the salinity of irrigated water. Compared with CK, soil CO2 fluxes in the saline water and brackish water treatments decreased by 29.8% and 28.2% respectively in the boll opening period. The decomposition of either cotton straw or alfalfa straw in the different treatments was in the sequence of CK (0.31 g · L(-1)) > brackish water irrigation (3.0 g · L(-1)) > saline water treatment (5.0 g · L(-1)). The organic matter decomposition rate in the plastic film mulched soil was significantly higher than that in the no plastic film mulched soil. 125 days after incubation, the recovery rates of cotton straw and alfalfa straw were 39.7% and 46.5% with saline water irrigation, 36.3% and 36.5% with brackish water irrigation, and 30.5% and 35.4% with CK, respectively. In conclusion, brackish water drip irrigation had a significant adverse effect on soil enzyme activities, which decreased soil microbial biomass, soil CO2 flux and soil organic matter decomposition, and subsequently deteriorated the soil biological characteristics in oasis farmland.

[Response of water coupling with N supply on maize nitrogen uptake, water and N use effi- ciency, and yield in drip irrigation condition].

Water and nitrogen are two major limiting factors for upland crop growth and development in arid region. Optimizing regulation irrigation schedule, rates and coupling with N fertigation is an effective way for realizing crop production improvement as well as water and nutrient use efficiency enhancement. In the present study, a field trial was carried out to study the influence of water (4500, 6750, 9000 m³ · hm⁻²) coupling with N (0, 225, 330, 435, 540 kg · hm⁻²) supply on maize dry matter accumulation, N uptake, yield and nitrogen fertilizer use efficiency in drip irrigated high cultivated density (≥ 105000 plant · hm⁻²) condition. There was an obvious tendency that the amounts of corn dry matter accumulated and plant N absorbed increased with levels of water and N supply, however, those decreased gradually when the N applied rate beyond 435 kg · hm⁻² and irrigation level above 9000 m³ · hm⁻². For instance, the effect of irrigation level on corn dry matter accumulation order exhibited W6750 (36359 kg · hm⁻²) > W9000 (35077 kg · hm⁻²) > W45°° (33451 kg · hm⁻²), the sequence of amount of N absorbed showed N435 (462.0 kg · hm⁻²)> N540 (459.4 kg · hm⁻²) > N330 (423.4 kg · hm⁻²) > N225 (348.1 kg · hm⁻²), the amount of N absorbed in N435 treatment increased by 9.1% and 32.7%, respectively, in contrast with treatments of N330 and N220, whereas, the amount of N absorbed in N540 decreased by 0.6% than that in N435 treatment. The highest N absorption rate increased with N application rate increasing within N supply range of 0-435 kg · hm⁻², it reached peak value of 6.57 kg · hm⁻² · d⁻¹ at N application rate of 435 kg · hm⁻²,then had decline trend with increasing N rate. Both irrigation and N supply exerted a significant role on maize yield as well as yield component of kernel number per spike and kernel mass per spike. An obvious positive interaction was obtained between water and nitrogen, moreover, the effect of N on yield was substantially higher than that of irrigation. N fertilizer use efficiency increased with increasing N level within N supply range of 0-435 kg · hm⁻² and then dropped markedly when N rate above 435 kg · hm⁻² It was found that the water productivity of irrigation (WP i increased with increasing N level, while, that decreased with increasing irrigation rate. At the suitable irrigation range of 4500-6750 m³ · m⁻² the WP of 2.57-3.80 kg · m⁻³could be achieved. The maximum corn yield of 18072 kg · hm⁻² as reached at N rate of 567.0 kg · hm⁻² The best N rate of 427.9-467.7 kg N · hm⁻² btained the optimum yield of 17109-17138 kg · hm⁻² with the nitrogen partial factor productivity of 122 kg N · hm²and nitrogen use efficiency of 45.0% reached. In sum, optimizing water coupling with N supply was the effective strategy for realizing corn yield improvement as well as resources of water and N use efficiency in drip irrigation condition in arid region.