Nitrogen Mineralization Potentials of Upland Soils inCentral China

Nitrogen mineralization potentials of 15 soil samples were studied by the methods of soil asrobic incuba-tion, and the correlation between the potentials and the amounts of nitrogen taken up by rye grass (Lolium.multifiorum Lam.) in pot culture was calculated. The soils were collected from Hubei Province in Cen-tral China. Soil nitrogen mineralization potentials (N_O) were calculated and optimized by a quick-BASICprogram. N_O ranged from 60 mg kg￣(-1) to 340 mg kg￣(-1), which accounted for 9.1% to 34.6% of the totalnitrogen content. Among the examined soils, yellow-brown soil collected from Wuhan had the largest N_Oand brown-red soil from Xianning had the smallest one. The mineralization rate constants (k) ranged from0.00556 d￣(-1) to 0.01280 d￣(-1) , in average 0.00882 d￣(-1) . Chao soil from Wuhan had the greatest k while yellow-cinnamon soil from Zhaoyang had the smallest one. There were apparent differences between mineralizationparameters (N_O and k) optimized and non-optimized ones. Optimized N_O had a better correlation thannon-optimized N_O with the amount of nitrogen accumulated in the aerial parts of rye grass. N_O , N_O × k andN_t(accumulated mineralized nitrogen within time t) could be used as indexes of soil nitrogen supply. Amongthem N_t was the best, which was significantly correlated with the amounts of nitrogen accumulated in theaerial parts of rye grass harvested at three different times.

Composition of Sulphur Pool in Selected Upland Soils inNorth China

Soil sulfur fractions, including monocalcium phosphate-extractable S, slowly soluble inorganic S, C- O-S ,C-bonded S and unidentified organic S, were analyzed for 48 soils, as representatives of 6 major groups ofupland soils, fiuvisol, cinnamon soil, loessial soil, chestnut soil, black soil and brown soil, in North China.The contemns of total S and monocalcium phosphate-extractable S in the above 48 soils ranged from 234 to860 and 5.1 to 220.3 mg kg--1 , respectively, and each of 6 soil groups contained the samples with a low level ofphosph ate-extractable S. Great differences in the average contents of each fraction of S were observed amongthe above 6 soil groups. Expressed as average percentage of the total S in soils, fiuvisols, cinnamon soils,loessial soils, chestnut soils, black soils and brown soils contained 6.1%, 9.5%, 5.7%, 13.2%, 3.5% and 6.8%monocalcium phosphate-extractable S, 5. 7%, 3. 0%, 9. 3%, 1 0. 4%, 3. 2% and 3. 1 % slowly soluble inorganic S ,51.6%, 26.7%, 17.4%, 31.2%, 28.9% and 22.7% C-O-S, 11.0%, 9.1%, 6.6%, 6.8%, 9.7% and 9.4% in C-bondedS, and 25.6%, 51.7%, 60.8%, 38.4%, 54.7% and 53.0% unidentified organic S, respectively. For the above 6groups of soils, the mean C/N ratios were remarkably similar, ranging from 9.7 to 10.7, while the mean N/Sratios ranged from 1.16 to 3.12. The highest ratios of C/N, C/C-O-S and C/C-bonded S were found in blacksoils, averaging 30.4, 104.9 and 314.7, respectively, while the lowest ratios arose in chestnut soil, averaging12.4, 39.7 and 183.3, respectively.

Indices of Sulfur-Supplying Capacities of Upland Soils in North China

Fifteen upland soils collected from the major arable areas in North China were used to assess the availability of soil sulfur (S) to plants in a pot experiment. Soils were extracted with various reagents and the extractable S was determined using turbidimetric method or inductively coupled plasma atomic emission spectrometry (ICP-AES), respectively. In addition, mineralizable organic S, organic S, N/S ratio, sulfur availability index (SAI) and available sulfur correction value (ASC) in soils were also determined. The S amount extracted by 1.5 g L-1 CaCl2 was nearly equivalent to that by 0.25 mol L-1 KCl (40 ℃), and both of them were slightly smaller than that by 0.01 mol L-1 Ca(H2PO4)2 solution, as measured by turbidimetric method or ICP-AES. The extractable S measured by turbidimetric method was consistently smaller than that by ICP-AES. All methods tested except that for organic S and N/S ratio produced satisfactory results in the regression analyses of the relationships between the amounts of S extracted and plant dry matter weight and S uptake in the pot experiment. In general, 0.01 mol L-1 Ca (H2PO4) 2-extracted S determined by ICP-AES or turbidimetric method and 0.25 mol L-1 KCl(40℃)-extracted S determined by ICP-AES appeared to be the best indicators for evaluation of soil available S.

Nitrous oxide fluxes from upland soils in central Hokkaido,Japan

Nitrous oxide (N2O) fluxes from soils were measured using the closed chamber method during the snow-free seasons (middle April to early November),for three years,in a total of 11 upland crop fields in central Hokkaido,Japan.The annual mean N2O fluxes ranged from 2.95 to 164.17 μgN/(m2·h),with the lowest observed in a grassland and the highest in an onion field.The instantaneous N2O fluxes showed a large temporal variation with peak emissions generally occurring following fertilization and heavy rainfall eve...

Some Fertility Characteristics and Fertilizer Requirements of a Newly Reclaimed Upland Red Soil Derived from Quaternary Red Clay

A series of field experiments from 1990 to 1994 in Yingtan, Jiangxi Province, were conducted on an upland red soil derived from Quaternary red clay which had been reclaimed three years before the experiments, in order to study the fertility characteristics and fertilizer requirements of the newly reclaimed soil. The field experiments included that on nutrient characteristics and fertilizer effect, that on K-supplying potential and K-Mg relationship, that on fertilization rates of K and N, etc. The newly reclaimed upland soil was low in both N and P, and its responses to nitrogen and phosphate application were very significant. The K-supplying potential was also low, so the soil was highly responsive to K fertilizer. The effect of Ca and Mg fertilizers was not so great for the reason that certain amounts of Ca and Mg were incorporated into the soil through application of calcium magnesium phosphate during land leveling before the experiments. Among the four micronutrients, B, Mo, Zn and Cu, B had the greatest effect on the soil. The fertilizer requirements of the soil were in an order of P and N > K > lime and B > Mg > Mo, Zn and Cu. Eight crops tested had different fertilizer-requiring characteristics. Rapeseed was very sensitive to P and B fertilizers. Barely was especially sensitive to P and lime and it also responded to B, Mo, Zn and Cu. And sweet potato was especially sensitive to K.

Nitrogen cycling and environmental impacts in upland agricultural soils in North China： A review

The upland agricultural soils in North China are distributed north of a line between the Kunlun Mountains, the Qinling Mountains and the Huaihe River. They occur in arid, semi-arid and semi-humid regions and crop production often depends on rain-fed or irrigation to supplement rainfall. This paper summarizes the characteristics of gross nitrogen（N） transformation, the fate of N fertilizer and soil N as well as the N loss pathway, and makes suggestions for proper N management in the region. The soils of the region are characterized by strong N mineralization and nitrification, and weak immobilization and denitrification ability, which lead to the production and accumulation of nitrate in the soil profile. Large amounts of accumulated nitrate have been observed in the vadose-zone in soils due to excess N fertilization in the past three decades, and this nitrate is subject to occasional leaching which leads to groundwater nitrate contamination. Under farmer＇s conventional high N fertilization practice in the winter wheat-summer maize rotation system（N application rate was approximately 600 kg ha–1 yr–1）, crop N uptake, soil residual N, NH_3 volatilization, NO_3~– leaching, and denitrification loss accounted for around 27, 30, 23, 18 and 2% of the applied fertilizer N, respectively. NH_3 volatilization and NO_3~– leaching were the most important N loss pathways while soil residual N was an important fate of N fertilizer for replenishing soil N depletion from crop production. The upland agricultural soils in North China are a large source of N_2O and total emissions in this region make up a large proportion（approximately 54%） of Chinese cropland N_2O emissions. The “non-coupled strong ammonia oxidation” process is an important mechanism of N_2O production. Slowing down ammonia oxidation after ammonium-N fertilizer or urea application and avoiding transient high soil NH4＋ concentrations are key measures for reducing N_2O emissions in this region. Further N management should aim to minimize N losses from crop and livestock production, and increase the recycling of manure and straw back to cropland. We also recommend adoption of the 4 R（Right soure, Right rate, Right time, Right place） fertilization techniques to realize proper N fertilizer management, and improving application methods or modifying fertilizer types to reduce NH_3 volatilization, improving water management to reduce NO_3~– leaching, and controlling the strong ammonia oxidation process to abate N_2O emission. Future research should focus on the study of the trade-off effects among different N loss pathways under different N application methods or fertilizer products.

Effects of Long-term Fertilization on Soil M icrobial Com m unity Structure,Labile Organic Carbon and Nitrogen and Enzym e Activity in Paddy Field and Upland

To investigate the effects of long-term fertilization systems on soil microbial community structure,labile organic carbon and nitrogen and enzyme activity in yellow sand paddy field and upland,a field experiment was conducted at the experimental station of Dongyang Institute of Maize Research in Zhejiang Province,China in 2009.The experiment consisted of six treatments with three replicates,and they were arranged in a completely randomized design,including no fertilization in paddy field (PCK),conventional fertilization in paddy field (PCF),formulated fertilization by soil testing in paddy field (PSTF),formulated fertilization by soil testing with organic manure in paddy field (PSTF+OF),conventional fertilization on upland (DCF),and formulated fertilization by soil testing with organic manure on upland (DSTF+OF).Soil nutrients,enzyme activity,microbial biomass and community structure were determined in 2015.The results showed that compared with no fertilization in paddy field (PCK),fertilization increased soil phosphorus and potassium content,and decreased pH value.No fertilization in paddy field (PCK) had no significant effect on soil culturable microorganisms in paddy field and upland,but formulated fertilization by soil testing with organic manure on upland (DSTF+OF) significantly increased the number of fungi.Formula fertilization by soil testing with organic manure (PSTF+OF) also significantly increased soil microbial biomass carbon and nitrogen in paddy field and upland.Moreover,fertilization had no significant effect on soil cellulase activity,but formula fertilization by soil testing with organic manure (PSTF+OF) significantly increased soil dehydrogenase and catalase activity.Therefore,long-term application of chemical fertilizer with organic fertilizer can effectively improve soil fertility.

Soil Phosphorus Release to the Water Bodies in the Upland Fields of Yellow Soil Areas and Impacting Factor

Soil phosphorus release to the water bodies in the upland fields of yellow soil areas and impacting factor was studied in Guizhou province. The results showed that the content of dissolved active P of surface runoff from various upland fields of yellow-soil were significantly different, which the concentrations of dissolved active P of runoff correlated with the contents of available-P, amorphous oxides of A1, and organic matter in the soils. The amount of soil phosphorus release to the water bodies affected by the level of applying P fertilizer and the process of corn growth, which with fertilizing from 150 to 900 kg P205 ha^-1 in the soil with high P level, the average contents of dissolved active P in the permeability-water of the soil increased from 0.020 mg L^-1 to 0.137 mg L^-1. The amount of soil phosphorus release to the water bodies also affected by environmental factor, which the amount of soil phosphorus release significantly increased under the conditions that temperature is 30℃-35℃, water/soil ratios is 15：1-25：1, submergence-time by water is 12-18 h and pH value of acid rains is 3.82-3.73.

Deforestation effects on biological and other important soil properties in an upland watershed of Bangladesh

Deforestation occurs at an alarming rate in upland watersheds of Bangladesh and has many detrimental effects on the environment. This study reports the effects of deforestation on soil biological proper- ties along with some important physicochemical parameters of a southern upland watershed in.Bangladesh. Soils were sampled at 4 paired sites, each pair representing a deforested site and a forested site, and having similar topographical characteristics. Significantly fewer （p〈0.001） fungi and bacteria, and lower microbial respiration, active microbial biomass, metabolic and microbial quotients were found in soils of the deforested sites. Soil physical properties such as moisture content, water holding capacity, and chemical properties such as organic matter, total N, avail- able P and EC were also lower in deforested soils. Bulk density and pH were significantly higher in deforested soils. Available Ca and Mg were inconsistent between the two land uses at all the paired sites. Re- duced abundance and＇biomass of soil mesofauna were recorded in defor- ested soils. However, soil anecic species were more abundant in defor- ested soils than epigeic and endogeic species, which were more abundant in forested soils than on deforested sites.

Effects of Long-term K Fertilizer Application on the Crop Yield and K Distribution of Soil Aggregates in a Paddy-Upland Rotation System

[Objective]A long-term paddy-upland experiment was conducted to evaluate the effects of the recommended amount of potassium( K)fertilizer on crop yield,distribution of soil aggregate,and soil available K content. It was mainly to ascertain the distribution of K in the soil aggregate components in the paddy-upland rotation system,and then to provide theoretical basis for soil structure improvement,K pool management,and reasonable application of K fertilizer. [Method]There were 2 treatments selected,namely,NP(-K) treatment and NPK( + K) treatment in this study. Then the effects of K fertilizer application on the yield,available K content,and aggregate distribution in the middle rice-winter rape rotation system were analyzed. [Result]The results showed that the output of the crop rotation was affected by the year and fertilization. Compared with NP(-K),the average yield increases of rice and winter rape after application of K fertilizer were 0.51 and 0.33 t/hm2,with the increments of 7.5%and 14. 1% respectively. The long-term application of K fertilizer( 7 a) had no significant effects on the distribution of soil aggregates but could significantly increase the water-soluble K content and available K content at depths of 20-30 and 30-40 cm,and available K content of aggregates in each particle size. In addition,the balance of available K at the 10-20 and 30-40 cm of soil layers was the most significant through calculation of surplus-deficit value of available K in agglomerates of different soil layers. [Conclusion]Compared with the initial available K content in the farmland in 2011,the current K fertilizer application could lead to that farmland K content continues to decline. Therefore,we should pay attention to straw returned and supplement of organic K fertilizer,to maintain crop rotation system's productivity and soil K balance.

Fixed Ammonium Content and Maximum Capacity of Ammonium Fixation in Major Types of Tillage Soils in Hunan Province,China

In order to understand the status of fixed ammonium, fixed ammonium content, maximum capacity of ammonium fixation, and their influencing factors in major types of tillage soils of Hunan Province, China, were studied with sampling on fields, and laboratory incubation and determination. The main results are summarized as follows： （1） Content of fixed ammonium in the tested soils varies greatly with soil use pattern and the nature of parent material. For the paddy soils, it ranges from 135.4 ± 57.4 to 412.8±32,4 mg kg^-1, with 304.7±96.7 mg kg^-1 in average; while it ranges from 59.4 to 435.7 mg kg^-1, with 230.1 ± 89.2 mg kg^-1 in average for the upland soils. The soils developed from limnic material and slate had higher fixed ammonium content than the soils developed from granite. The percentage of fixed ammonium to total N in the upland soils is always higher than that in the paddy soils. It ranges from 6.1 ±3.6% to 16.6±4.6%, with 14.0% ±5.1% in average for the paddy soils and it amounted to 5.8±2.0% to 40.1 ± 17.8%, with 23.5 ± 14.2% in average for upland soils. （2） The maximum capacity of ammonium fixation has the same trend with the fixed ammonium content in the tested soils. For all the tested soils, the percentage of recently fixed ammonium to maximum capacity of ammonium fixation is always bellow 20% and it may be due to the fact that the soils have high fertility and high saturation of ammonium-fixing site. （3） The clay content and clay composition in the tested soils are the two important factors influencing their fixed ammonium content and maximum capacity of ammonium fixation. The results showed that hydrous mica is the main 2：1 type clay mineral in 〈 0.02 mm clay of the paddy soils, and its content in 0.02-0.002 mm clay is much higher than that in 〈 0.002 mm clay of the soils. The statistical analysis showed that both the fixed ammonium content and the maximum capacity of ammonium fixation of the paddy soils were positively correlated with the total 2：1 type clay mineral content and hydrous mica content in 〈 0.02 mm clay and 0,02-0.002 mm clay at the significant level of P0.01 or P0.05, respectively, but not correlated with the total 2：1 type clay mineral content and hydrous mica content in 〈0.002 mm clay significantly, It demonstrated that the ammonium-fixing matrix of the tested soils mainly exists in the 0.02-0.002 mm clay. The above-mentioned results showed that fixed ammonium is a major form of N in the tillage soils in Hunan Province, China. It would play an important role in N nutrition of crops, especially for upland crops, and deserve to be further researched.

N_2O emissions from a cultivated Andisol after application of nitrogen fertilizers with or without nitrification inhibitor under soil moisture regime

The aim of this work was to examine the emission of N 2O from soils following addition of nitrogen fertilizer with a nitrification inhibitor(+inh) or without the nitrification inhibitor(-inh) at different soil water regime. Higher soil moisture contents increased the total N 2O emissions in all treatments with total emissions being 7 times larger for the CK and >20 times larger for the fertilizer treatments at 85% WFPS(soil water filled pore space) than at 40% WFPS. The rates of N 2O emissions at 40% WFPS under all treatments were small. The maximum emission rate at 55% WFPS without the nitrification inhibitor(-inh) occurred later (day 11) than those of 70% WFPS (-inh) samples (day 8). The inhibition period was 4—22 d for 55% WFPS and 1—15 d for 70% WFPS comparing the rates of N 2O emissions treated (+inh) with (-inh). The maximum emission rates at 85% WFPS were higher than those at the other levels of soil water content for all treatments. The samples(+inh) released less N 2O than (-inh) samples at the early stage. Nevertheless, N 2O emissions from (+inh) samples lasted longer than in the (-inh) treatment. Changes in mineral N at 55%, 70% and 85% WFPS followed the same pattern. NH + 4-N concentrations decreased while NO - 3-N concentrations increased from the beginning of incubation. NH + 4-N concentrations from 40% WFPS treatment declined more slowly than those of the other three levels of soil water content. Nitrification was faster in the (-inh) samples with 100% NH + 4-N nitrified after 22 d(50% WFPS) and 15 d(70% and 85% WFPS). N 2O emissions increased with soil water content. Adding N-fertilizer increased emissions of N 2O. The application of the nitrification inhibitor significantly reduced total N 2O emissions from 30.5%(at 85%WFPS) to 43.6%(at 55% WFPS).

Effects of different levels of compost application on amounts and distribution of organic nitrogen forms in soil particle size fractions subjected mainly to double cropping

Effects of different levels of compost application on the amounts and percentage distribution of organic N forms in whole soils and particle size fractions were investigated. Soil samples were collected from three plots: (a) F, only chemical fertilizers;(b) F+LC, chemical fertilizers plus low level of compost;(c) F+HC, chemical fertilizers plus high level of compost. Each soil sample was divided into five fractions: coarse sand-sized aggregate (CSA), medium sand-sized aggregate (MSA), fine sand-sized aggregate (FSA), silt-sized aggregate (SIA) and clay-sized aggregate (CLA) fractions. The sand fractions were subdivided into decayed plants (DP) and mineral particles (MP). The amounts of total N and different organic N forms in the whole soils as well as size fractions generally increased with increasing the amount of compost. In the whole soils, percentage distribution of non-hydrolysable-N and amino sugar-N increased by compost application while the distribution values of the hydrolysable ammonium- N and unidentified-N decreased. The application did not affect the distribution degree of amino acid-N. In the size fractions, the distribution values of most organic N forms increased in the CSA-DP, MSA-DP and FSA-DP fractions by compost application. In the CLA fractions, the amounts and percentage distribution of organic N forms were the highest, although the application caused decreases in their distribution values. These findings indicate that the CLA fraction merit close attention as an important reservoir of various organic N.

土壤水分含量对旱稻根系和土壤呼吸速率的影响

在池栽条件下比较研究了不同土壤水分含量处理(65%WHC、75%WHC、85%WHC、95%WHC和100%WHC,WHC代表田间最大持水量)对旱稻277土壤呼吸速率及根条数的影响。结果表明,土壤水分含量对旱稻土壤呼吸速率和根条数有显著影响。随着土壤水分含量的提高,土壤呼吸速率显著下降;随着旱稻生育期的推进,除100%WHC处理的土壤呼吸速率减小外,其余水分含量处理的土壤呼吸速率都呈升高趋势;随着土壤水分含量的增加,旱稻根条数逐渐降低,在分蘖前期处理间差异达到显著水平,随着生育期的推进,处理间的差异逐渐减小,且根条数与土壤呼吸速率呈显著正相关关系。土壤呼吸速率日变化在65%WHC、75%WHC和85%WHC处理下表现为逐渐增加后保持稳定,在95%WHC处理下表现为达最大值后逐渐下降,在100%WHC处理下表现为达最大值后略有下降,并一直保持在较低水平。土壤温度日变化在不同土壤水分含量下均呈现先升高再趋于平稳的变化趋势,以75%WHC水分处理下的温度最高,95%WHC和100%WHC水分处理下土壤温度较低。相关分析表明,不同水分含量处理条件下(100%WHC处理除外),土壤呼吸速率与土壤温度呈显著或极显著的二次抛物线关系,根条数与土壤呼吸速率呈显著的正相关关系。

限制红壤旱地芝麻产量提高的关键土壤肥力因子探究

本研究在第四纪红黏土发育的红壤上,种植10个芝麻品种(赣芝5号、赣芝9号、青麻、金黄麻、武宁黑芝麻、玉山黑芝麻、豫芝11号、丰城白芝麻、中芝13号和樟树褐芝麻),研究不同生育期土壤化学性质和土壤酶活性的动态变化及其与芝麻产量的关系。结果表明,随着芝麻生育进程的推进,土壤pH、有效磷、有效锌、纤维素酶和脲酶活性呈升高趋势。与苗期相比,各指标花期分别升高4.1%、19.4%、15.4%、11.1%、21.4%,成熟期分别升高3.3%、12.9%、13.0%、70.4%、11.3%。有机质、全氮、速效氮含量和蛋白酶活性呈降低趋势,花期分别降低8.2%、1.7%、30.3%、17.1%,成熟期分别降低9.0%、5.8%、33.2%和30.3%。速效钾含量和酸性磷酸酶活性呈先升高后降低趋势,花期分别升高23.3%、10.7%,成熟期分别降低20.6%、3.5%。有效硼含量、蔗糖酶活性呈“V”型变化,花期有效硼含量降低41.4%,成熟期升高7.3%;花期蔗糖酶活性降低25.8%,而成熟期与苗期无差异。与苗期相比,β-葡萄糖苷酶活性在花期未产生显著差异,但成熟期却降低了33.5%。土壤有效锌、速效钾、有效硼、速效氮和有效磷含量、纤维素酶和蔗糖酶活性在芝麻生育期间和品种间变化较大,而土壤全氮、有机质、pH值、β-葡萄糖苷酶、蛋白酶、酸性磷酸酶和脲酶活性在芝麻生育期间和品种间则相对稳定。苗期土壤速效氮含量和蛋白酶活性,花期土壤有效硼含量和纤维素酶活性,以及成熟期土壤pH值与芝麻产量呈显著正相关关系。因此,注重芝麻基肥的氮肥投入,花期喷施硼肥,同时施用石灰等碱性物质或其他措施阻控土壤酸化是红壤旱地芝麻产量提高的关键。

Soil and Land Suitability Assessment for Rice Cultivation at Tono Irrigation Area in the Upper East Region, Ghana

Agriculture is one of the livelihood supports for the people of Upper East Region of Ghana. Soil evaluation research was conducted at Tono Irrigation Scheme to assess soil and land suitability for rice cultivation in the irrigable area of Tono Irrigation Scheme. A total of eleven (11) soil samples were collected and analysed for their chemical and physical properties. Based on field observation and criteria for soil suitability assessment, the different soil types that were identified were classified at the series level based on their position, parent material and the observed physical characteristics. The results indicated that the pH of the soils was within the acceptable range for crop production;however, the overall fertility level of the soils was very low. Physically, the upland soils were well to moderately well-drained, consisting of coarse-grained sandy loams topsoil overlying similar sandy loams and sandy clay loams at depth. They included Leptosols and Lixisols. The soils of the Scheme under lowlands and valley bottom sites, however, included Eutric Gleysol, Calsic Vertisol, Eutric Fluvisol and Eutric Plinthosol, which were heavily textured and relatively poor drained, or medium-textured and moderately to imperfectly well-drained. They showed a low to a very low rate of water percolation losses, which is good for the current farming system of cropping rice within the lowlands and valley bottom sites of the Scheme.

轮作模式和氮肥处理对稻田土壤有机碳储量及其结构的影响

【目的】探讨不同水旱轮作模式与水稻季施氮水平在稻田土壤固碳(有机碳储量及其官能团特征)中的作用。【方法】依托中国水稻研究所水-旱轮作长期定位试验(2003年至今),研究4种轮作模式[水稻-冬闲(RF)、水稻-紫云英(RC)、水稻-小麦(RW)和水稻-稻草覆盖种植马铃薯(RP)]与2个水稻季氮肥处理[不施氮(N0,0kg/hm^(2))和正常施氮(N1,135kg/hm^(2))]对稻田土壤有机碳储量(0-50cm)和有机碳官能团特征(0-20cm)的影响。【结果】1)在土壤浅耕层(0-20 cm)内,轮作能够在一定程度上提高有机碳含量,表现为RP>RC>RW或RF;但对于全耕层(0-50、0-40和0-30cm)土壤有机碳储量而言,冬作(RP,RC和RW)与冬闲(RF)无显著差异,而施氮更有利于土壤固碳。2)水稻季不施氮处理下:相较于RF,冬作模式显著增加包括烷基碳和芳香碳在内的难降解组分,而抑制以烷氧碳为主的易降解组分,明显提高了土壤腐殖化指数、芳香性和疏水性,助力浅层土壤(0-20 cm)总有机碳储备的增加。其中,腐殖化指数和疏水性与还田秸秆C/N比值关系密切,这在浅层土壤固碳上具有重要意义。【结论】相较于轮作,适度施氮对全层土壤有机碳储备更有意义;而周年水旱轮作中全量秸秆还田对土壤有机质积累的效应仅停留在浅耕层,对全土层土壤有机碳储备的作用则被高估。秸秆碳在稻田的去向还有待进一步探索。

长期施钾红壤中铁铝氧化物调控有机无机复合体钾素分布

【目的】探究长期施用钾肥如何调控有机无机复合体中速效钾的分布及作用机制,为红壤钾库健康培育提供理论依据。【方法】旱地红壤长期定位试验始于1986年,2022年玉米收获后采集不施肥(CK)、化学氮磷肥配施(NP)、化学氮磷钾肥配施(NPK)3个处理的土样,通过干筛法获得各处理大团聚体(>2 mm)、小团聚体(0.25~2 mm)和微团聚体(<0.25 mm)土样,结合虹吸法进一步分离得到各级团聚体下的有机无机复合体(<2、2~10、10~50和>50μm)样品,分析各粒级有机无机复合体颗粒组成、速效钾和铁铝氧化物含量与分布,探究铁铝氧化物与速效钾之间的相互关系。【结果】1)与CK和NP处理相比,NPK处理大团聚体中<2μm粒级复合体含量占比分别提高20.5%和149.0%,10~50μm粒级复合体含量占比分别提高18.6%和降低31.0%。2)在0~50μm粒级复合体范围内,大、小和微团聚体中10~50μm粒级复合体速效钾含量均为最低水平。土壤速效钾主要存在于<2μm粒级复合体中,占比为54.6%~85.9%。与CK和NP处理相比,NPK处理大团聚体中<2μm粒级复合体速效钾含量占比分别提高44.6%和23.0%。3)与NP处理相比,NPK处理大团聚体<2μm粒级复合体游离铁、铝氧化物含量分别提高30.0%、467.0%,无定形态铁、铝氧化物含量分别降低79.7%、59.3%。与NP处理相比,NPK处理大团聚体<2μm粒级复合体有机络合态铝氧化物含量提高9.8%;10~50μm粒级复合体有机络合态铝氧化物含量降低33.2%。4)在<2μm粒级复合体中,游离态铁铝氧化物、无定形态铝氧化物和有机络合态铝氧化物与速效钾之间存在极显著的正相关关系。无定形态和有机络合态铝氧化物对速效钾含量分布解释度较高,分别为11.2%和11.0%。【结论】长期施用钾肥显著提高红壤旱地土壤大团聚体<2μm粒级复合体速效钾含量占比和游离态铁铝氧化物含量,降低无定形态铝氧化物含量。且无定形态、有机络合态铝氧化物对<2μm粒级复合体速效钾具有正向调控作用,有助于增加土壤钾库。

江西省信丰县山稻基地硒及相关元素分布特征

为了寻找绿色富硒农产品,对江西省信丰县山稻基地表层土壤、山稻、根系土及土壤垂向剖面样品开展硒及相关元素的测试分析和质量评价,并利用环境水化学软件Visual MINTEQ 3.1开展硒形态模拟。结果表明,本区表层土壤为强酸性,硒平均含量等级为适量,土壤环境地球化学等级为清洁;山稻根系土为强酸性,硒平均含量等级为富硒,土壤环境地球化学等级为清洁。土壤垂向剖面显示Cd、Hg、Cr、有机质(SOM)在地表富集趋势明显,且Se含量与Cd、As、Hg、Cr、SOM含量呈正相关,与Ni、Cu、Zn、Pb含量及pH呈负相关,表明山稻有重金属污染风险。本区土壤中硒形态主要为HSeO_(3)^(-)和SeO_(4)^(2-),其中HSeO_(3)^(-)生物有效性低于SeO_(4)^(2-),但对重金属拮抗效果好。因此,可通过喷洒SeO_(4)^(2-)和HSeO_(3)^(-)溶液改善农作物品质。本区种植的山稻绿色富硒,对Hg和Cd表现出良好的富集能力,可作为修复Hg和Cd污染土壤的优选植物。

高原湿地公路工程边坡不同恢复措施对土壤理化性质及酶活性的影响

[目的]研究高寒湿地高速公路工程干扰后不同恢复措施下边坡土壤理化性质及酶活性变化,为高寒湿地植被恢复模式的筛选,水土流失治理,改善生态环境提供理论依据。[方法]以自然演替、喷播植草、草皮回覆3种处理边坡模式为研究对象,并以原始未扰动植被作为对照,测定土壤理化指标和土壤酶活性,分析其相互关系及影响因素。[结果](1)3种恢复措施与对照相比均导致土壤pH值、全钾显著升高(p<0.05),土壤有机质、全氮、细根生物量、速效钾显著降低(p<0.05),在自然演替处理下都最小,分别为15.16±0.15,0.75±0.01,0.60±0.27,65.00±4.50;喷播植草、草皮回覆处理下土壤颗粒中黏粉粒比例显著降低(p<0.05);喷播植草、自然演替与对照相比丰富度指数显著降低(p<0.05),在自然演替下最小,为1.29±0.02,草皮回覆与喷播植草2种恢复措施的土壤pH值、有机质、全氮、速效钾、细根生物量及其丰富度指数高于自然演替。(2)与自然演替相比,喷播植草与草皮回覆能更好地恢复蔗糖酶、脲酶、碱性磷酸酶、过氧化氢酶活性,甚至过氧化氢酶活性能恢复至接近对照,酶活性在自然演替条件下都最小,分别为12.65±10.87,0.24±0.03,0.23±0.05,1.73±0.48。(3)4种酶活性与土壤理化性质之间相关性显著,脲酶活性对土壤理化性质最为敏感,能够很好评价高原湿地边坡土壤质量。[结论]采取喷播植草、草皮回覆相对于自然演替可有效改善土壤理化性质和提高土壤酶活性,土壤酶活性能作为评价高原湿地边坡土壤质量的敏感性指标。