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Pausch J.,University of Gottingen | Pausch J.,University of Bayreuth | Tian J.,University of Gottingen | Tian J.,Key Laboratory of Plant Soil Interactions | And 2 more authors.
Plant and Soil | Year: 2013

Background and aims: Rhizodeposition of plants is the most uncertain component of the carbon (C) cycle. By existing approaches the amount of rhizodeposition can only roughly be estimated since its persistence in soil is very short compared to other organic C pools. We suggest an approach to quantify rhizodeposition at the field scale by assuming a constant ratio between rhizodeposited-C to root-C. Methods: Maize plants were pulse-labeled with 14CO2 under controlled conditions and the soil 14CO2 efflux was separated into root and rhizomicrobial respiration. The latter and the 14C activity remaining in the soil corresponded to total rhizodeposition. By relating rhizodeposited-14C to root-14C a rhizodeposition-to-root ratio of 0. 56 was calculated. This ratio was applied to the root biomass C measured in the field to estimate rhizodeposition under field conditions. Results: Maize allocated 298 kg C ha-1 as root-C and 166 kg C ha-1 as rhizodeposited-C belowground, 50 % of which were recovered in the upper 10 cm. The fate of rhizodeposits was estimated based on the 14C data, which showed that 62 % of total rhizodeposition was mineralized within 16 days, 7 % and 0. 3 % was incorporated into microbial biomass and DOC, respectively, and 31 % was recovered in the soil. Conclusions: We conclude that the present approach allows for an improved estimation of total rhizodeposition, since it accounts not only for the fraction of rhizodeposits remaining in soil, but also for that decomposed by microorganisms and released from the soil as CO2. © 2012 The Author(s). Source

Tian J.,Key Laboratory of Plant Soil Interactions | Fan M.,Key Laboratory of Plant Soil Interactions | Guo J.,Key Laboratory of Plant Soil Interactions | Marschner P.,University of Adelaide | And 2 more authors.
European Journal of Soil Biology | Year: 2012

In the last three decades there has been a major shift in China's agriculture with the conversion from cereal fields to vegetable production, however little is known about the impact of this land use change on labile soil carbon and microbial community structure. We conducted a study to characterize dissolved organic carbon (DOC) and soil microbial community by comparing greenhouse vegetable fields with contrasting management intensity and adjacent cereal fields (wheat-maize rotation) in Shouguang and Quzhou in North China. Compared with cereal fields, greenhouse vegetable cultivation increased soil organic carbon (SOC) and total nitrogen (TN), while it decreased the soil pH, particularly at the high-intensity site. The DOC concentration was significantly higher in greenhouse vegetable fields than in cereal fields, whereas DOC composition differed between greenhouse vegetable fields and cereal fields only at high management intensity. Chemical fractionation indicated that DOC from greenhouse vegetable fields with high management intensity was less decomposed than DOC from cereal fields, because the percentage of hydrophobic acid (HOA) as DOC was higher in vegetable fields. Vegetable production significantly changed the microbial community structure in comparison to cereal fields: high-intensity management increased total bacteria, G (+) bacteria and fungi, while low-intensity decreased fungi and increased bacteria-to-fungi ratio. The main factor affecting microbial community structure was soil pH in this study, accounting for 24% of the differences. © 2012 Elsevier Masson SAS. Source

Tian J.,Key Laboratory of Plant Soil Interactions | Lu S.,Sichuan Academy of Agricultural science | Fan M.,Key Laboratory of Plant Soil Interactions | Li X.,Key Laboratory of Plant Soil Interactions | Kuzyakov Y.,University of Gottingen
Plant and Soil | Year: 2013

Aims: Understanding the effects of long-term crop management on soil organic matter (SOM) is necessary to improve the soil quality and sustainability of agroecosystems. Method: The present 7-year long-term field experiment was conducted to evaluate the effect of integrated management systems and N fertilization on SOM fractions and carbon management index (CMI). Two integrated soil-crop system management (ISSM-1 and ISSM-2, combined with improved cultivation pattern, water management and no-tillage) were compared with a traditional farming system at three nitrogen (N) fertilization rates (0, 150 and 225 kg N ha-1). Results: Management systems had greater effects on SOM and its fractions than did N fertilization. Compared with traditional farming practice, the integrated management systems increased soil organic carbon (SOC) by 13 % and total nitrogen (TN) by 10 % (averaged over N levels) after 7 years. Integrated management systems were more effective in increasing labile SOM fractions and CMI as compared to traditional farming practice. SOC, TN and dissolved organic matter in nitrogen increased with N fertilization rates. Nonetheless, N addition decreased other labile fractions: particulate organic matter, dissolved organic matter in carbon, microbial biomass nitrogen and potassium permanganate-oxidizable carbon. Conclusions: We conclude that integrated management systems increased total SOM, labile fractions and CMI, effectively improved soil quality in rice-rapeseed rotations. Appropriate N fertilization (N150) resulted in higher SOC and TN. Though N application increased dissolved organic matter in nitrogen, it was prone to decrease most of the other labile SOM fractions, especially under higher N rate (N250), implying the decline of SOM quality. © 2013 Springer Science+Business Media Dordrecht. Source

Zhang Q.,China Agricultural University | Zhang Q.,Key Laboratory of Plant Soil Interactions | Ren L.,China Agricultural University | Ren L.,Key Laboratory of Plant Soil Interactions
Shuili Xuebao/Journal of Hydraulic Engineering | Year: 2012

Based on the sensitivity analysis and calibration of the Root Zone Water Quality Model (RZ-WQM) at the Yucheng Experimental Station, the simulated crop yield, water and nitrogen dynamics in winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) double cropping systems from 1960 to 2005 are compared with the data obtained from the statistical yearbooks of Yucheng county and the Weis-han irrigation district. It is found that the mean relative error (MRE) for the simulated yields of winter wheat and summer maize from 1985-2005 were -54.2% and 13.3%, respectively. Then the results of scenario analysis show that the best choice for the purpose of achieving the highest yields and WUE might be the combination between the optimal irrigation schedule and the optimal fertilizer management. The yield, WUE and partial factor productivity (PFP) of the crop in this scenario were 10302 kg/hm 2, 1.40 kg/m 3 and 23.2 kg/kg, respectively. Source

Shi J.,China Agricultural University | Shi J.,Key Laboratory of Plant Soil Interactions | Shi J.,Key Laboratory of Arable Land Conservation North China | Ben-Gal A.,Israel Agricultural Research Organization | And 5 more authors.
Plant and Soil | Year: 2013

Background and aims: Michaelis-Menten (MM) kinetics and a physical-mathematical (PM) model are the popular approaches to describe root N uptake (RNU). This study aimed to examine RNU and compare the two model approaches. Methods: A hydroponic experiment (Exp. 1) investigated the effects of root length, root N mass, transpiration, plant age and solution N concentration on RNU of wheat (Triticum aestivum L. cv. Jingdong 8). The two models were applied to simulate the RNU and soil N dynamics in a soil-wheat system (Exp. 2), and the results were compared to the measured data. Results: Under the hydroponic conditions, RNU was better correlated with root N mass and transpiration than root length. The influences of solution N concentration on RNU rate per root length (MM1) and RNU rate per root N mass (MM2) were described well with MM kinetics. The kinetic parameters for MM1 changed with plant age but the parameters for MM2 were not age dependant. The description of RNU with the PM model was also independent of plant age, and was more reliable when the RNU factor decreased as a power function with the solution N concentration (PM2) than an assumed constant (PM1). In Exp. 2, the root mean squared errors between the simulated and measured soil solution N concentration and the relative errors between the simulated and measured N uptake mass for MM kinetics were much larger than those for the PM model. Conclusions: Both the MM and PM models successfully described RNU under the hydroponic conditions, but the PM model (especially PM2) was more reliable than the MM model in the soil-wheat system. © 2012 Springer Science+Business Media B.V. Source

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