污泥农用对土壤和作物重金属累积及作物产量的影响

以3 a定位试验为基础,比较3种不同处理的污泥肥料（消化污泥、污泥堆肥及污泥复混肥）农田施用下土壤养分、土壤和作物籽粒中Mn、Cu、Zn、Pb、Cd 5种重金属的积累以及作物产量的变化情况,以阐明污泥农用对土壤及作物的影响。研究表明,3种污泥肥料提高了土壤中氮素和有机质的含量;与空白和普通化肥处理相比,3种污泥肥料增加了土壤中Mn和Cu的含量,而对土壤交换态重金属含量没有显著影响;3种污泥处理均增加了小麦籽粒中Zn的含量;相对普通化肥处理,3种污泥肥料处理对小麦和玉米产量均无显著影响。合理施用污泥肥料可以有效地提高作物产量;污泥肥料施用对土壤重金属有一定累积效应,但短期施用对土壤比较安全。     

Discrepancy in Fertilizer Nitrogen Equivalency Estimates of Dry Sewage Sludge Application in Soil

Fertilizer nitrogen (N) equivalency estimates of sewage sludge are essential to assess benefits from its use in agricultural fields and minimize agronomic failure and environmental risks. Using an outdoor pot experiment, where sludge was applied to the upper layer of the soil in pots, this study aimed to estimate the rate of dried sewage sludge application needed to replace a given amount of inorganic fertilizer and to investigate eventual variations of this estimate depending on whether N replacement value referred to grain yield of barley, biomass production, or overall plant N uptake. Equivalencies were obtained from the response curves of these crop characteristics in relation to the rate of sludge application. It was shown that the patterns of carbon (C) and N allocation to grain and straw were different between the inorganic fertilizer and the sewage sludge treatment, presumably due to the timing of mineral N provision. When the same grain yield was obtained at these two treatments, straw yield and grain N content were greater at the sludge fertilized crop. It was concluded that fertilizer N equivalency value of sewage sludge should inevitably refer to a single crop yield component determined by a producer.     

Potential of Gamma Irradiated Sewage Sludge as Fertilizer in Radish: Evaluating Heavy-Metal Accumulation in Sandy Loam Soil

Soil application of sewage sludge as an amendment in crop plants has became a popular method of municipal sewage-sludge disposal in many countries. However, the presence of heavy metals in untreated sewage sludge has raised concerns of adverse effects on crop growth, quality of product, and environmental health. Gamma irradiation is one of the treatments for hygienization of sewage sludge before use as fertilizer. To evaluate the potential of gamma-irradiated sewage sludge as fertilizer in vegetable crops, the field investigation was conducted in a root crop, radish (Raphanus sativus L.), during the 2005–06 and 2006–07 growing seasons in a sandy loam soil. Treatments consisted of three source of fertilizers [farmyard manure (FYM), gamma-irradiated sewage sludge (GISS), and nonirradiated sewage sludge (NISS)]; each were compared at six application levels (1, 3, 6, 7, 9, and 11 t ha^?1). The physicochemical properties of all the three fertilizers used in this study were compared. Growth parameters and yields of radish were not significantly influenced by source of fertilizers or their application levels, except plant stand, which was influenced by type of fertilizers used. There was no significant difference observed between source of fertilizer treatments with respect to any of the measured soil properties, including major nutrients [nitrogen (N), phosphorus (P), and potassium (K)], metallic micronutrients [copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn)], and heavy metals [nickel (Ni), lead (Pb), cadmium (Cd), and cobalt (Co)]. Soil P and Zn were influenced by the various level of fertilizers. However, the interaction effect of source and level of fertilizer was absent for all the measured parameters. The maximum pollutant limits in sewage sludge and soil for agricultural use in different countries were compared. The concentration of metallic micronutrients and heavy metals in soil were less than the prescribed limit of the United States Environmental Protection Agency (USEPA), and no significant accumulation was noted after 2 years of application of GISS and NISS even at higher application rates.     

施用辐照处理的污水污泥对作物产量和土壤氮的影响

A field experiment was conducted to study the feasibility of irradiated and non-irradiated sewage sludge as a fertilizer for the growth of wheat and rice. The irradiated and non-irradiated sewage sludge were applied at rates of 0 (CK), 75, 150, 225 and 300 kg N ha^-1 for wheat, and 0 (CK), 112.5, 225, 337.5 and 450 kg N ha^-1 for rice, respectively. (NH₄)₂SO₄ at a rate of 150 kg N ha^-1 for wheat, and 225 kg N ha^-1 for rice were added to the control treatments. Additionally, 20 kg ¹⁵N ha^-1 in the form of (NH₄)₂SO₄ was added to each treatment for wheat to study the effect of sewage sludge on chemical nitrogen fertilizer recovery. The results showed that the irradiation of sewage sludge by gamma ray at a dosage of 5 kGy increased crop yield by 11%~27% as compared to the non-irradiated treatments. Irradiation stimulated mineralization of organic nitrogen in the sludge and improved seedling growth. It was found that addition of irradiated sludge could reduce the leaching loss of chemical nitrogen fertilizer. Both irradiated and non-irradiated sewage sludge could increase the content of soil total nitrogen. Based on the preliminary results, it was concluded that irradiated sewage sludge could partly substitute for chemical nitrogen fertilizer in crop production.     

Growth and Heavy-Metal Uptake by Lettuce Grown in Soils Applied with Sewage Sludge Compost

A pot experiment was conducted to investigate the effect of sewage sludge compost (SSC) alone and applied with chemical fertilizer on growth and heavy-metal accumulations in lettuce grown on two soils, a Xanthi-Udic Ferralosol and a Typic Purpli-Udic Cambosol. The treatments included control; nitrogen–phosphorus–potassium (NPK) fertilizer; sewage sludge compost applied at the rates of 27.54 (SSC), 82.62 (3SSC), 165.24 (6SSC) t hm^–2; and coapplication treatment (1/2 SSC + 1/2 NPK), where the N, P, and K inputs from NPK fertilizer, SSC, and coapplication treatments were normalized to the local recommend rates. The SSC application increased the biomass; copper, zinc, and lead contents in lettuce; and soil total and diethylenetriaminepentaacetic acid (DTPA)–extractable metals. However, SSC alone at the recommended rate caused less plant biomass than NPK fertilizer alone. Coapplication treatment obtained greater or similar biomass to NPK fertilizer alone and did not increase heavy-metal accumulation in soils and plants. The results demonstrated that SSC should be applied to soils with chemical fertilizers.     

Recycling gamma irradiated sewage sludge as fertilizer: A case study using onion (Alium cepa)

Recycling sewage sludge into fertilizer for agricultural purposes may improve soil fertility by influencing the physical, chemical, and biological properties of the land. However, there is concern regarding elevated levels of heavy metals and pathogenic microorganisms, which may result from the use of untreated sewage sludge. Gamma radiation is found to be an efficient tool in the hygienization of municipal sewage sludge. In order to evaluate the agricultural potential of gamma irradiated sewage sludge and to assess the safety of this fertilizer, field experiments were performed in a root crop, onion (Alium cepa), during the 2003–2004 and 2004–2005 winter months. The influence over major nutrients, metallic micronutrients, and heavy metals in soil and crop plant were key factors to be analyzed. Treatments consisted of three source of fertilizers {S₁: farmyard manure (FYM); S₂: gamma irradiated sewage sludge (GISS); and S₃: non-irradiated sewage sludge (NISS)}, each at three separate levels (L₁: 5 t ha^?1; L₂: 10 t ha^?1; and L₃: 15 t ha^?1), which were evaluated and compared. The growth parameters and onion yield were not significantly influenced by the different sources of fertilizer, or the different application levels. Values of pH, organic carbon, organic N, available P and K, metallic micronutrients (Zn, Mn, Fe, Cu) and heavy metals (Ni, Cd, Pb, Co) indicate no negative effects on either soil or plant properties. Concentrations of heavy metals in soil and plant were slightly higher in NISS treatment in compare to GISS; however, the concentrations did remain within the prescribed limit, and no significant increase was consistently noted. The results prove that the gamma irradiated sludge material was of equal quality compared to the conventional FYM.     

EFFECTS OF ORGANIC AMENDMENTS APPLICATION ON GRAIN YIELD,LEAF CHLOROPHYLL CONTENT AND SOME MORPHOLOGICAL CHARACTERISTICS IN SOYBEAN CULTIVARS

A field experiment was conducted to evaluate the effect of organic amendments on grain yield, leaf chlorophyll content, and some morphological characteristics of three soybean cultivars in Mazandaran province located at north of Iran in 2006. Chemical fertilizer (75 kg ha^?1 potassium sulfate and triple superphosphate), two levels of municipal solid waste, vermicompost and sewage sludge biosolid (20 and 40 Mg ha^?1) enriched with%50 chemical fertilizers needed by soil were applied to soybean cultivars (‘032’ and ‘033’ promising lines and ‘JK’ cultivar). The experiment was carried out in split plot based on randomized complete block design with three replications. Some important plant characters such as grain yield, leaf chlorophyll content, number of branches, number of nodes on the main stem, length of internodes, stem diameter, first pod height and plant height were determined. Results showed that application of 40 Mg ha^?1 sewage sludge enriched with chemical fertilizers increased plant grain yield and stem diameter and application of 40 Mg ha^?1 vermicompost enriched with half chemical fertilizer increased the number of nodes on the main stem, significantly. The maximum length of internodes, first pod height and plant height were obtained when the 40 Mg ha^?1 sewage sludge and vermicompost enriched with half chemical fertilizer in ‘032’ line was used. Biomass, number of branches, stem diameter, number of nodes on the main stem of soybean cultivars had a positive and significant correlation with grain yield.     

Availability of Heavy Metals for Brassica Chinensis Grown in an Acidic Loamy Soil Amended with a Domestic and an Industrial Sewage Sludge

The use of sewage sludge on agriculture provides an alternativefor sewage sludge disposal. Therefore, it was the aim of thepresent study to evaluate the feasibility of using a domestic(Tai Po sludge) and an industrial (Yuen Long sludge) sewagesludge produced in Hong Kong for the growth of vegetable crops.The acidic loamy soil with or without lime treatment was amendedseparately with each sludge at application rates of 0, 5, 10, 25and 50% (v/v) for the growth of a common local vegetable crop,Brassica chinensis. The plant available metal contents, asindicated by the DTPA extraction, increased with an increase insludge amendment, but decreased with lime amendment at eachsludge application rate due to the reduced metal availabilityat a higher pH. Sludge amendment enhanced the dry weight yieldof B. chinensis and the increase was more obvious for thesoil with lime treatment. The industrial sludge caused a loweryield than that of the domestic sludge amendment and asignificant reduction in yield at high application rates of YuenLong sludge was also noted. Tissue heavy metal contents, exceptfor Fe, increased as the sludge amendment rate increased whileplant grown in Yuen Long sludge amended soil contained higher Crand Zn contents at each sludge application rate. Liming the soilreduced the heavy metal contents in the plant tissues, exceptfor Fe, which were all below the allowable levels for vegetablecrops. The present experiment demonstrates that liming wasimportant in facilitating the growth of B. chinensis in sludge amended soil. The optimal sludge amendment rate for thesoil with lime amendment was 25% Tai Po sludge and 10% YuenLong sludge, while for the soil without lime amendment was 10% and5%, respectively.     

污泥农用对土壤理化性质及作物产量的影响

为了研究污泥农用的有效性,通过田间试验,开展了污泥农用前后土壤理化性质及作物产量变化研究.结果表明,随着污泥施用量的增加,土壤容重最大降低了14.8%;水稳性团粒总量达31.5%;速效氮、磷的含量和土壤中的有机质含量明显增多;小麦和玉米都增产,其中污泥施用量为56.25 t/hm~2时,小麦增产达极显著水平;玉米的产量都比对照要高,而且产量随施肥量的增加而增大.     

Vermicompost from municipal sewage sludge affects growth and mineral nutrition of winter rye (Secale cereale) plants

The aim of the study was to investigate sewage sludge vermicompost application effects on growth and mineral nutrition of winter rye (Secale cereale L.) plants as compared to two initial levels of mineral nutrient availability, pure sand and sand enriched with inorganic nutrients at the optimal level. Addition of sewage sludge vermicompost significantly inhibited rye seed germination at 20 to 50% sand substitution independently on mineral nutrient supplement. Growth inhibition was evident at early stages of plant development. However, at the later stages, sewage sludge vermicompost acted both as mineral fertilizer and plant growth-promoting agent. Significant stimulation of mineral uptake was seen only at high rates of vermicompost substitution (40 and 50%) already causing decrease in shoot dry matter accumulation. Vermicompost substitution resulted in a significant increase of leaf chlorophyll content. Beneficial effect of sewage sludge vermicompost in conditions of optimal mineral supply can result mainly from plant growth-promoting activity.     

不同施肥处理对连续三季作物氮肥利用率及其分配与去向的影响

采用室外盆栽试验系统研究了不同施肥处理对连续3个生长季作物生长状况、标记^15N利用率及其分配与去向的影响。结果表明,高量氮肥的施用能显著提高作物的生长和产量,而化肥配施玉米秸秆在第1生长季表现为抑制,第2、第3生长季则相反。作物体内来自标记氮肥的含量和比例随生长季的增加显著下降,高量氮肥和玉米秸秆的施用能显著提高其含量和比例（P〈0.05）。标记氮肥在土壤中的残留率随作物生长季的增加而降低,而标记氮肥的累积作物利用率和总损失率随着生长季的增加而增加,经过连续3季作物的吸收利用,标记氮肥在土壤中的残留率、累积作物利用率和总损失率分别平均为15．82％、61．11％和23．07％。标记氮肥的作物利用率和损失率主要发生在第1生长季内,高量氮肥的施用降低了标记肥料氮在土壤中的残留率,增加了氮素损失率;与单施化肥处理相比,化肥配施玉米秸秆能明显增加标记肥料氮在土壤和作物中的回收率,降低氮素损失率,提高比例为21．74％,从而说明在施肥当季,通过施入高C/N比有机物料玉米秸秆合理调节土壤中C源和N素营养的施用比例,可以达到增加氮肥在土壤中的残留率,提高氮肥利用率的目的。     

Zinc and copper availability in herbage and soil of a Pinus radiata silvopastoral system in Northwest Spain after sewage‐sludge and lime application

Silvopastoral systems are ancient farming systems in the world, consisting of the combination of a woody component (trees or shrubs) and crops and/or animals within the same land‐management unit. In various European Union (EU) countries, the possibility of using sewage sludge as a fertilizer is under consideration as a viable method of disposal, considering the increase in sewage‐sludge production in recent years and the restrictions imposed by European policy on the usual methods of disposal. The concern is the concentration of heavy metals, which can reach humans through the food chain. In Spain, R.D. 1310/1990, as well as European Directive 86/278, limit the total in‐soil heavy‐metal concentration, but not the solubility changes, which directly affect plant absorption and leaching of heavy metals throughout the soil profile. The objective of this experiment was to compare, in a silvopastoral system over a period of 3 years, the effect of applying three doses of sewage sludge combined with and without liming, on total and available soil Zn and Cu and their concentration in plants. Liming did not affectct Zn and Cu availability; however, sewage sludge increased Zn and Cu availability, though total in‐soil Zn was increased only in November 2000. In‐plant Zn concentration was increased by sewage sludge in the last 2 years of the study. In all cases, the quality of forage obtained and measured with regard to the concentrations of Zn and Cu was adequate for animal consumption. With respect to sewage‐sludge application as a fertilizer, the management of heavy‐metal availability must be included in the policy, because environmental risk could then be adequately evaluated.     

污泥加石灰后作为肥料用于玉米生长中施肥研究

The use of sewage sludge on agricultural land provides an alternative for its disposal. Therefore, the aim of the present study was to evaluate the feasibility of using industrial sewage sludge produced in Pakistan, as an agricultural fertilizer. The agricultural soil amended with 250 g kg^-1 sewage sludge with or without lime treatment was used for the growth of the common local grain crop, maize （Zea maize）. The mobility of the trace and toxic metals in the sludge samples was assessed by applying a modified BCR sequential extraction procedure. The single extraction procedure was comprised of the application of a mild extractant （CaCl2） and water, for the estimation of the proportion of easily soluble metal fractions. To check the precision of the analytical results, the concentrations of trace and toxic metals in every step of the sequential extraction procedure were summed up and compared with total metal concentrations. The plant-available metal contents, as indicated by the deionized water and 0.01 mol L^-1 CaCl2 solution extraction fractions and the exchangeable fraction of the sequential extraction, decreased significantly （P 〈 0.05） with lime application because of the reduced metal availability at a higher pH, except in the cases of Cd and Cu, whose mobility was slightly increased. Sludge amendment enhanced the dry weight yield of maize and the increase was more obvious for the soil with lime treatment. Liming the sewage sludge reduced the trace and toxic metal contents in the grain tissues, except Cu and Cd, which were below the permissible limits of these metals. The present experiment demonstrates that liming was an important factor in facilitating the growth of maize in sludge-amended soil.     

Effects of Linear Alkylbenzene Sulfonates (LASs) in Sewage Sludge–Amended Soils on Nutrient Contents of Broccoli Plants

Abstract

Sewage sludge is used in agriculture as a fertilizer and an organic amendment to improve physical and chemical soil properties. However, sludge contains organic compounds, such as surfactants, which may be toxic in the soil–plant system. The effects on plants of linear alkylbenzene sulfonates (LAS), a group of anionic surfactants that are widely used in detergent products, have not been well defined. In this experiment, the effect of differently treated sewage sludge containing LAS on the macronutrient and sodium contents of different parts of broccoli plants (Brassica oleracea L. var. botrytis subvar. cymosa Lam.) was studied in a field experiment. Fertilizer treatments were un‐composted sewage sludge (UCSS), composted sewage sludge (CSS), and a control without fertilization (NF). The LAS levels were established across all fertilizer treatments by addition of 0, 15, or 30 g LAS m^?2 (LAS0, LAS15, and LAS30, respectively). In general, the macronutrient contents in shoots, leaves, and edible parts of broccoli were higher in plants cultivated without fertilization but with LAS. In most cases, the LAS application increased the nitrogen, phosphorus, and sodium contents of the different plant parts, whereas calcium and magnesium concentrations were reduced.     

Content and chemical form of mercury and selenium in soil,sludge, and fertilizer materials

The content and chemical from of Hg and Se were determined for several samples of municipal sewage sludge and sludge ash, garden soil having a history of sludge and residential compost application, and selected fertilizer materials (peat moss, cow manure, residential compost, composted municipal refuse and sewage sludge, Miloganite). Municipal sewage sludge had the highest levels of total Hg (averaging 1240 ppb), while sludge ash had the lowest levels (averaging 5.6 ppb). Total Se levels were lowest in compost (averaging 255 ppb), while being highest in sludge ash (averaging 11550 ppb). The methylmercury percentage was fairly constant for all samples, averaging 6.0% of the total Hg content. Hexavalent Se averaged 24.3 of the total Se content, and was notably higher in sludge and fertilizer samples. Successive annual application of sludge and compost to garden soil resulted in a gradual increase of total Hg and Se in the soil, but had no significant influence on chemical form distribution for both elements.     

Recycling of sewage sludge and household compost to arable land: fate and effects of organic contaminants, and impact on soil fertility

Effective use of organic wastes for agricultural production requires that risks and benefits be documented. Two types of sewage sludge, household compost and solid pig manure were studied under field and greenhouse conditions to describe their fertilizer value and effects on soil properties and soil biota, the fate of selected organic contaminants, and their potential for plant uptake. A 3-year field trial on two soil types showed no adverse effects of waste amendment on crop growth, and a significant fertilizer value of one sludge type. Accumulation of N and P_i was indicated, as well as some stimulation of biological activity and micro-arthropod populations, but these effects differed between soil types. There was no detectable accumulation of polycyclic aromatic hydrocarbons (PAH), di(2-ethylhexyl)phthalate (DEHP), nonylphenol and ethoxylates (NP+NPE) or linear alkylbenzene sulfonates (LAS) after three repeated waste applications, and no plant uptake was suggested by analysis of the third crop. A plot experiment with banded sludge was conducted to examine sludge turnover and toxicity in detail. Less than 5% of NP or LAS applied in organic wastes was recovered after 6 months, and less than 6% of DEHP applied was recovered after 12 months. Potential ammonium oxidation (PAO) at 0–1 cm distance from the banded sludge was stimulated despite toxic concentrations in the sludge, which suggested that contaminants were degraded inside sludge particles. Phospholipid fatty acid (PLFA) profiles suggested a gradual shift in the composition of the microbial community within sludge, partly due to a depletion of degradable substrates. A pot experiment with sludge-amended soil and soil spiked with contaminants showed no plant uptake of NP, DEHP or LAS. Degradation of LAS and NP added in sludge was delayed and the degradation of DEHP was faster than when the contaminants were added directly to the soil. In conclusion, adverse effects of organic waste application on soil or crop were not found in this study, and for some waste products positive effects were observed.     

污泥肥和生活垃圾肥对小麦-玉米重金属累积及产量的影响

以肥料定位试验为基础,比较了污泥肥、生活垃圾肥和常见农用肥料(化肥、鸡粪肥)农田施用下土壤和作物籽粒、秸秆中Cd、Cr、Pb、Hg、As、Cu、Zn、和Ni八种重金属的积累以及作物产量的变化情况,用来阐明污泥肥和生活垃圾肥施用对土壤和作物籽粒以及产量的动态影响规律。研究表明,与化肥和鸡粪肥分别比较,施用生活垃圾肥可以显著带来作物的增产,而污泥肥处理作物增产效果不明显;根据国家粮食卫生标准(GB 2715-2005)、MPCC以及《食品卫生标准》(GB2762-2005)的规定,施用污泥肥和生活垃圾肥处理的作物籽粒重金属含量均在其标准限量值范围之内,完全符合安全标准;污泥肥和生活垃圾肥比化肥、鸡粪显著增加了土壤Cr和Hg含量。所有处理的土壤重金属含量均在土壤环境质量一级标准(GB15618-1995)的重金属限量值(pH>7.5)范围内。     

Reactions of chrome tannery sludge with organic and mineral soils

Chrome tannery sludge applied to agricultural land may have benefits in terms of added N for crop growth. An experiment was designed to compare tannery waste with commercial N fertilizer and investigate the potential of the waste as an alternative or supplement to commercial fertilizer. Soils with 38% and 7% organic C and N content of 1.3% and 0.2%, respectively, were amended with lime, commercial N fertilizer, or tannery sludge containing 1.6% Cr. A portion of the tannery waste was supplemented with additional Cr 3⁺ salt before adding to the soils. The amended soils were analyzed for total Cr, ammonium acetate extractable Cr, selected nutrient and trace element concentrations. The tannery sludge increased soil pH, total Cr and N, S, Ca, P, Mg, and Na concentrations. DTPA extractable Cr increased only when Cr³⁺ salt was added, but soil pH decreased markedly. Electroconductivity of the soils increased with the waste application rate and, at the highest rate of Cr³⁺ salt addition, far exceeded values recommended for successful crop production. The acidic, high salt conditions complicated interpretation of the Cr³⁺ salt addition results. Tannery sludge may be applied to agricultural land as a fertilizer amendment without adversely affecting soil chemical properties. The amount and frequency of application should be determined by (1) total and available N, (2) total salt content, (3) total and available Cr, and (4) soil organic matter.     

Effect of Application of Different Types of Organic Composts on Rice Growth under Laboratory Conditions

In the present study, pot experiments were conducted to evaluate the effects of the application of two different kinds of composts: pea-rice hull compost (PRC) and cattle dung-tea compost (CTC) on rice growth. These composts differed in their nitrogen composition, as well as in their effect on plant height, number of tillers, dry matter yield and nutrient uptake (nitrogen (N), phosphorus (P), potassium (K)) of rice plants. Plants were cultivated in 1/5,000 Wagner pots, which contained 3 kg of soil, completely mixed with the composts (PRC 404 g; CTC 380 g) and chemical fertilizer (CHEM), respectively in the first crop. The residual effect of the composts was studied after the plants of the first crop were harvested. All the treatments were replicated four times, with a randomized complete block design. The nutrient concentrations in the roots, leaf sheaths, leaf blades, stalks, and grain were analyzed at different growth stages. At the most active tillering and heading stages of the plants of the first crop, the number of tillers, dry matter yield and the amount of nutrients absorbed from the CHEM treatment were found to be higher than those in the other treatments. The values of the plant height, straw growth and nutrient uptake of the rice plants with the PRC treatment were the highest among all the treatments at the maturity stage. In the plants of the second crop, the values of the plant height, number of tillers, straw and whole plant yield and the N and K uptake from the PRC treatment were the highest among all the treatments at the heading and maturity stages. The chemical fertilizer was a fast-release fertilizer used to supply nutrients at the early stage of rice growth in the first crop. The beneficial effect of the composts on rice growth and nutrient uptake was conspicuous in the second crop, compared with that of routine treatment of chemical fertilizer.     

Impact of organic residues and mineral fertilizer application on soil–crop systems I: yield and nutrients content

A five-season experiment was initiated to study the effects of the recycling of some organic residues on a soil–crop system of a guar–wheat rotation in a sandy clay loam soil located in the semi-arid tropics of Sudan. Treatments included: incorporation of crop residues alone after harvest (Cr⁺), with (FCr⁺) or without (FCr^?) inorganic fertilizer, sewage sludge (SS) and humentos (H). Grain yield of wheat in FCr⁺ and Cr⁺ treatments was significantly higher than that obtained in FCr^? and control plots by ～22?62% and 116?119%, respectively. When crop residues were incorporated with inorganic fertilizer, the priming effect of crop residues on straw yield (106%) was almost double that of the priming effect of inorganic fertilizer (56%). The sustainable yield index of wheat straw dry matter for the control, crop residue, humentos, inorganic fertilizer, combined fertilizer and crop residue and sewage sludge was 28, 27, 8, 35, 21 and 38%, respectively. In general, N, P and K of straw dry matter (SDM) was in the order of FCr⁺ > FCr^? > SS > Cr⁺> H > C. The findings suggest that repeated incorporation of crop residues with inorganic fertilizer and applications of SS could both sustain wheat performance in the dryland ecosystems.