Trends In Soil Organic Carbon Research Articles

Using the CENTURY model to assess the impact of land reclamation and management practices in oasis agriculture on the dynamics of soil organic carbon in the arid region of North-western China

Large-scale reclamation of arid land in North-western China over the past 50 years has converted the natural desert landscape into anthropogenic oasis, particularly in the lower part of watersheds. Drastic human activities may have caused the change of soil organic carbon (SOC) in anthropogenic oasis. This study employs the CENTURY model (Version 4.0) to investigate the effects of land reclamation and management practices in oasis agriculture on the dynamic of SOC at the lower part of Sangong river watershed, a typical anthropogenic oasis reclaimed at 50 years ago. Based on field investigation, history of crop rotations, and past farm practices in study area, land management practices were divided into five categories, corresponding five periods, 0–1958, 1959–1984, 1985–1992, 1993–1998 and 1999–2008. The model successfully simulated the SOC dynamics of the top layer soil (0–20 cm) in the different periods. The state of equilibrium of total SOC and the active, slow, and passive carbon pools were built by CENTURY model in 0–1959. Over the 50 years’ cultivation (1959–2008), the mean change in total SOC exhibited complex ways. SOC increased rapidly in the first 2 years (1959–1960) after shrubland reclamation, and declined slowly during the period 1961–1984 and then decreased rapidly from 1985 to 1992. Between 1993 and 1998, it remained relatively stable, and climbed rapidly again during 1999–2008. The trend in total SOC showed “N” shape, i.e., increase, decrease, then increase. Finally, total SOC is greater (8.2%) in 2008 than the original level of SOC under the natural desert shrub. The improvements of land management practices such as ploughing being replaced with no tillage, straw being crushed before returning it to soil, and reasonable application of fertilizers, played a key role in the change in total SOC. Especially, soil carbon sequestration was obviously increased since protective management practices were implemented in 1993, such as no tillage, straw returning to soil, and the balanced fertilization technique. The results were different from the conclusions that loss of soil organic carbon would happen due to reclamation and continuous farming in tropical forests, semiarid grasslands of northern China and Nigerian semiarid Savannah.

The impact of agroforestry combined with water harvesting on soil carbon and nitrogen stocks in central Chile evaluated using the ICBM/N model

Soil organic carbon (SOC) and total nitrogen (N) stocks in an agroforestry system with water harvesting were analysed in a field experiment and the results compared with those of other crop management systems in the Mediterranean zone of central Chile. Agroforestry with water harvesting showed higher positive effects on N stocks, mainly in the upper soil layer, than the other crop management systems. However, soil analysis revealed a lack of differences between treatments, a fact that might be related mainly to the short study time (12 years) and the high spatial variability in these soil properties at the experimental site. In addition, the Introductory Carbon Balance Model that simulates N processes (ICBM/N) was evaluated for simulating trends in SOC and N stocks in the field experiment. Soil data collected between 1996 and 2008 in the field experiment and primarily literature data sets were used to test ICBM/N and its performance was evaluated by considering uncertainty in model inputs using Generalised Likelihood Uncertainty Estimation (GLUE) methodology. The GLUE estimates (5% and 95%) and measured SOC and N stocks were in satisfactory agreement. The observed SOC and N stocks were bracketed by the uncertainty bands in 70% and 80% of the simulations, respectively. Sensitivity analysis showed the model to be most sensitive to C parameters, such as the humification coefficient (h). The results of this study show that ICBM/N can be an effective tool for estimating SOC and N stocks from agroforestry combined with water harvesting systems in the Mediterranean zone of central Chile over the medium term. However, they also indicate that additional data sets are needed to redefine the parameter distributions in the model and thus to predict trends in SOC and N stocks in the future.

Spatial analysis of soil organic carbon evolution in Belgian croplands and grasslands, 1960-2006

Given the importance of soil organic carbon (SOC) as a pool in the global carbon cycle and an indicator for soil quality, there exits an urgent need to monitor this dynamic soil property. Here, we present a modelling approach to analyze the spatial patterns and temporal evolution of organic carbon in mineral soils under agricultural land use in Belgium. An empirical model, predicting the SOC concentration in the top 0.3 m, as a function of precipitation, land use, soil type and management has been constructed and applied within a spatial context using data from different time slices. The results show that SOC content is strongly correlated with precipitation and temperature under cropland and with texture and drainage under grassland. Total SOC stock increased with 1.3% from 6.18 ± 0.03 kg C m−2 in 1960 to 6.26 ± 0.07 kg C m−2 in 2006. Although this increase was not significant (P>0.05), a significant discrepancy between cropland (−8%) and grassland (+10%) was observed. Foremost, the grasslands in the hilly southern part of the country, under relatively wet climate conditions, acted as important sinks of CO2. Under cropland, all soil types were characterized by a decrease in SOC, except for the clay soils in the north-west. Currently, croplands in the central loam region have SOC concentrations close to 10 g C kg−1 indicating that these soils are at risk of a decline in aggregate stability. An overall strong SOC decline in poorly drained soils is probably caused by artificial drainage. Further research is needed to gain more insight into the processes driving the observed SOC trends. Moreover, the use of updated drainage class information and land management history would improve the empirical models.

An evaluation of the century model to predict soil organic carbon: examples from Costa Rica and Canada

Greater organic matter inputs in agroforestry systems contribute to the long-term storage of carbon (C) in the soil, and the use of simulation models provides an opportunity to evaluate the dynamics of the long-term trends of soil organic carbon (SOC) stocks in these systems. The objective of this study was to apply the Century model to evaluate the long-term effect of agroforestry alley crop and sole crop land management practices on SOC stocks and soil C fractions. This study also evaluated the accuracy between measured field data obtained from a 19-year old tropical (TROP) and 13-year old temperate (TMPRT) alley crop and their respective sole cropping systems and simulated values of SOC. Results showed that upon initiation of the TROP and TMPRT alley cropping systems, levels of SOC increased steadily over a ~100 year period. However, the sole cropping systems in both tropical and temperate biomes showed a decline in SOC. The active and passive C fractions increased in the TROP agroforestry system, however, in the TMPRT agroforestry system the active and slow fractions increased. The input of organic matter in the TROP and TMPRT agroforestry systems were 83 and 34% greater, respectively, compared to the sole crops, which likely contributed to the increased SOC stock and the C fractions in the alley crops over the 100 year period. Century accurately evaluated levels of SOC in the TROP (r2 = 0.94; RMSE = 226 g m−2) and TMPRT (r2 = 0.94; RMSE = 261 g m−2) alley crops, and in the TROP (r2 = 0.82; RMSE = 101 g m−2) and TMPRT (r2 = 0.83; RMSE = 64 g m−2) sole crops. Century underestimated simulated values in the alley cropping systems compared to measured values due to the inability of the model to account for changes in soil bulk density with increasing organic matter inputs with tree age from prunings or litterfall.

Soil organic carbon dynamics under long-term fertilizations in arable land of northern China

Abstract. Soil carbon sequestration is a complex process influenced by agricultural practices, climate and soil conditions. This paper reports a study of long-term fertilization impacts on soil organic carbon (SOC) dynamic from six long-term experiments. The experiment sites are located from warm-temperate zone with a double-cropping system of corn (Zea mays L.) – wheat (Triticum Aestivium L.) rotation, to mild-temperate zones with mono-cropping systems of continuous corn, or a three-year rotation of corn-wheat-wheat. Mineral fertilizer applications result in an increasing trend in SOC except in the arid and semi-arid areas with the mono-cropping systems. Additional manure application is important to maintain SOC level in the arid and semi-arid areas. Carbon conversion rate is significant lower in the warm-temperate zone with double cropping system (6.8%–7.7%) than that in the mild-temperate areas with mono-cropping systems (15.8%–31.0%). The conversion rate is significantly correlated with annual precipitation and active accumulative temperature, i.e., higher conversion rate under lower precipitation and/or temperature conditions. Moreover, soil high in clay content has higher conversion rate than soils low in clay content. Soil carbon sequestration rate ranges from 0.07 to 1.461 t ha−1 year−1 in the upland of northern China. There is significantly linear correlation between soil carbon sequestration and carbon input at most sites, indicating that these soils are not carbon-saturated thus have potential to migrate more CO2 from atmosphere.

Spatially explicit simulations of soil C dynamics in Southern Brazil: Integrating century and GIS with i_Century

Soil organic carbon (SOC) sequestration in agricultural soils requires appropriate cropping systems and conservation practices that increase crop biomass production. No tillage agriculture provides several advantages to establish “carbon friendly” production systems. Conservation agriculture has greatly expanded over the past three decades in the North Central region of Rio Grande de Sul, the southernmost state of Brazil, with about 6 million ha of land under dryland grain crop agriculture. A shift from intensive conventional tillage to mulch tillage and then no tillage has resulted in increased SOC levels across much of the region as verified in field measurements. In this study a modeling system was constructed by coupling the interactive Century (i_Century) software running Century 4.0 and ArcGIS data layers to simulate the long-term SOC trends in the Ibirubá region, which occupies a land area of 83,500 ha. This system was capable of accounting for cropping system and management practices trends from 1900 to the present times, as well as simulating projections out to the year 2050, capturing periods of decreasing or increasing SOC trends. Simulations performed with the modeling system show that SOC stocks in Ibirubá, estimated at 5.05 Tg C before human activity, decreased to 3.71 Tg C (31%) by 1985. An estimated recovery to 3.97 Tg C by 2005 in response to adoption of SOC-enhancing practices such as conservation tillage and no tillage was observed. Simulations to 2050 with maintenance of these cropping systems and soil management showed that total C stocks could reach 4.21 Tg C, which would still be 21% less than originally present in those soils. The integration of Century with GIS was greatly expedited with the use of the i_Century interface and its readily-accessible database format. Data transfer between the modeling and geoprocessing environment was facilitated for quick visualization and further processing. This approach can be applied for carbon monitoring and accounting schemes at several scales, from the field to the national level.

Using 137Cs to quantify the redistribution of soil organic carbon and total N affected by intensive soil erosion in the headwaters of the Yangtze River, China

Characteristics of soil organic carbon (SOC) and total nitrogen (total N) are important for determining the overall quality of soils. Studies on spatial and temporal variation in SOC and total N are of great importance because of global environmental concerns. Soil erosion is one of the major processes affecting the redistribution of SOC and total N in the test fields. To characterize the distribution and dynamics of SOC and N in the intensively eroded soil of the headwaters of the Yangtze River, China, we measured profiles of soil organic C, total N stocks, and 137Cs in a control plot and a treatment plot. The amounts of SOC, 137Cs of sampling soil profiles increased in the following order, lower>middle>upper portions on the control plot, and the amounts of total N of sampling soil profile increase in the following order: upper>middle>lower on the control plot. Intensive soil erosion resulted in a significant decrease of SOC amounts by 34.9%, 28.3% and 52.6% for 0–30 cm soil layer at upper, middle and lower portions and 137Cs inventory decreased by 68%, 11% and 85% at upper, middle and lower portions, respectively. On the treatment plot total N decreased by 50.2% and 14.6% at the upper and middle portions and increased by 48.9% at the lower portion. Coefficients of variation (CVs) of SOC decreased by 31%, 37% and 30% in the upper, middle and lower slope portions, respectively. Similar to the variational trend of SOC, CVs of 137Cs decreased by 19.2%, 0.5% and 36.5%; and total N decreased by 45.7%, 65.1% and 19% in the upper, middle and lower slope portions, respectively. The results showed that 137Cs, SOC and total N moved on the sloping land almost in the same physical mechanism during the soil erosion procedure, indicating that fallout of 137Cs could be used directly for quantifying dynamic SOC and total N redistribution as the soil was affected by intensive soil erosion.

Validation of the CANDY model with Russian long-term experiments

The CANDY model has been qualitatively as- sessed for simulating long-term dynamics of soil organic carbon and tested against different long-term experiments representing various land uses and geographical sites, but never before against conditions of the Former Soviet Union (FSU). Our goal was to simulate long-term trends in soil organic carbon for the long-term experiments of Barybino (Moscow region, Russia), Grakov (Kharkow region, Uk- raine) and Yachenka (Minsk region, Belarus) representing the predominant arable soil types, climate conditions and typical management strategies for the investigated arable areas. The fit of modelled results to the observed data was evaluated to assess the suitability of the model for further applications in the FSU. The crop parameters of the CANDY model had to be adapted to the low yields ob- served under the Russian site conditions resulting in a higher sensitivity to crop-derived carbon input as a func- tion of yield. The results show that the approach of treating the organic carbon situated in micro pores as inert, is an applicable solution for simulating soil carbon dynamics under Russian conditions. This evaluation of CANDY, against long-term experiments from Russia, gives confi- dence for its wider application in this region.

Application of the RothC model to the results of long‐term experiments on typical upland soils in northern China

AbstractArable land can be either a source or a sink for atmospheric carbon dioxide depending on its management. It is important to assess changes in soil organic carbon (SOC) under future climate change scenarios using models at regional or global scales. This paper aims to calibrate the RothC model on non‐waterlogged soils in northern China to obtain the necessary model input parameters for later use in large‐scale studies. Data sets from three long‐term experiments in northern China were used to evaluate the performance of the RothC soil carbon turnover model. The plant carbon input rate, an important model input parameter, was calibrated using experimental data under typical rotation systems with different fertilization. The results showed that RothC accurately simulated the changes in SOC across a wide area of northern China (northeast, north, and northwest China. The modelling error expressed as root mean square error for four treatments (nil, manure, fertilizer, fertilizer + manure) at three sites were less than 20.2%, and less than 7.8% if occasional extreme measured values were omitted. The simulation biases expressed as M (i.e. relative error) for all treatments at the three sites were non‐significant. Observed trends in SOC included a decrease for the nil (no fertilizer or manure) treatment and an increase for the treatments which received both manure and fertilizers. The experiments also indicated that manures applied at an appropriate rate were more effective in increasing or maintaining SOC than fertilizers which were more effective in increasing crop yields.

Simulation of fluxes of greenhouse gases from European grasslands using the DNDC model

Agricultural management of grasslands results in sequestration and emission of greenhouse gases (GHGs, particularly CO 2, N 2O and CH 4). Here, we used a process-based model (DNDC) to estimate the fluxes of the major GHGs from grasslands at 0.5° resolution across Europe, and combined these to produce a spatially explicit estimate of the total global warming potential (GWP, expressed in CO 2 equivalents). The DNDC model [Li, C., Frolking, S., Crocker, G.J., Grace, P.R., Klir, J., Korchens, M., Poulton, P.R., 1997. Simulating trends in soil organic carbon in long-term experiments using the DNDC model. Geoderma 81, 45–60] simulates carbon and nitrogen cycling in agro-ecosystems at a sub-daily time step and consists of four interacting submodels: soil and climate (including water flow and leaching), plant growth, decomposition, and denitrification. Input data sets for grassland area, climate, nitrogen deposition, and soil properties were collated. The typical current grassland management regime was established for ten biogeographical regions on the basis of questionnaires sent to national experts, and used to derive model input data. A 20-year simulation was carried out using DNDC for each site. Simple estimates of methane emissions from grazing livestock were made according to the IPCC Tier 1 method. Most grassland areas are net sources for GHGs in terms of total global warming potential—the beneficial effect of sequestering carbon in soil is outweighed by the emissions of N 2O from soil and (predominantly) CH 4 emissions from livestock. The net effect of European grasslands on GWP (emission of 23 Tg C year −1) corresponds to a 2.5% increase on the EU-15 fossil fuel CO 2 emissions (907 Tg C year −1).

Quantifying carbon sequestration in a conventionally tilled crop rotation study in southwestern Saskatchewan

In this study we used results from 10 cropping systems in a 37-yr field experiment being conducted on a medium-textured Orthic Brown Chernozem in semiarid southwestern Saskatchewan, in which soil organic carbon (SOC) had been sampled in 7 different years, to quantify trends and changes in SOC in the 0- to 15-cm depth. We tested the effectiveness of three models: Century, the Introductory Carbon Balance Model (ICBM), and the Campbell model to predict the measured values. The 10 cropping systems allowed us to assess the influence of cropping frequency, fertilization and crop type on SOC and, because growing season weather was distinctly more humid in the final 12 yr of the study, we were able to assess the impact of weather. In this soil on which a fallow-wheat (Triticum aestivum L.) (F-W) rotation was maintained for the previous 60 yr, SOC remained fairly constant under normal weather for the first 20 yr of the study for the systems that were frequently fallowed, except for fallow-fall rye (Secale cereale L.)- wheat (F-Rye-W). In contrast, in the final 12 yr, SOC increased in all systems in response to increased C inputs from crop residues associated with improved precipitation. SOC gains were greater for well-fertilized extended crop rotations such as continuous wheat (Cont W) and wheat-lentil (Lens culinaris Medikus) (W-Lent) and the F-Rye-W systems receiving N and P than for the F-W, F-W-W, F-Flax (Linum usitatissimum L.)-W (F-Flx-W) receiving N and P, and Cont W receiving only P. SOC was also greater for well- fertilized than for poorly fertilized systems. The ICBM and Campbell models performed well in simulating SOC trends, partly because they used measured grain yields to estimate C inputs. However, the Century model was less effective in its simulation of SOC especially for the fallow-containing systems due to its difficulty in estimating spring soil water and crop yields. We showed how grain yields can be used, together with coefficients of conversion of C inputs from crop residues to SOC, to estimate SOC changes. Using these relationships, and assuming the coefficient of conversion of C inputs to SOC sequestered is 15% for well-fertilized extended rotations, or 10% for well-fertilized frequently fallowed spring-seeded systems, one can make reasonable first estimates of the impact of management on C sequestration in degraded soils of the semiarid prairies. Key words: ICBM model, Century model, Campbell model, soil organic C, N and P fertilizer, cropping frequency

Current trends of soil organic carbon in English arable soils

. A model of the impact of land management changes upon soil organic carbon (SOC) was constructed, and the total amount of topsoil organic carbon was estimated for the arable area of England from 1940 to 2000. The largest influence on the overall mean SOC in arable topsoils proved to be a decline in the area of both permanent and temporary grassland. SOC declined over a prolonged period (60 years), but has now reached a plateau. Modelling changes in mean values enabled a statistical evaluation to be made between a measured decline in the number of sites with ‘high’ SOC levels between 1980 and 1995, and the decline predicted by the model. The SOC content of arable soils in England was measured at National Soil Inventory sites twice in recent decades: in 1980 and 1995. The proportion of fine textured soils in the lowest SOC class (<2.3%) rose from just over 40% to about 50% over the same period. There was a significant difference between the observed values of 1995 and those expected from modelling the decline from 1980 values, in the category of ‘low SOC’ fine textured soils. The variation in the fine textured soils represents a significant and widespread decline in topsoil organic carbon concentrations, which was greater than the underlying long-term trend.

EFFECTS OF MANURE AND FERTILIZER ON GRAIN YIELD, SOIL CARBON AND PHOSPHORUS IN A 13-YEAR FIELD TRIAL IN SEMI-ARID KENYA

Long-term indicators of soil fertility were assessed by measuring grain yield, soil organic carbon (SOC) and soil Olsen phosphorous for a P-deficient soil. In one set of treatments, goat manure was applied annually for 13 years at 0, 5 and 10 t ha−1, and intercrops of sorghum/cowpea, millet/green gram and maize/pigeonpea were grown. Yield depended on rainfall and trends with time were not identifiable. Manure caused an upward trend in SOC, but 10 t ha−1 manure did not give significantly more SOC than 5 t ha−1. Only 10 t ha−1 manure increased Olsen P. Measurements of both SOC and Olsen P are recommended. In another set of treatments, manure was applied for four years; the residual effect lasted another seven to eight years when assessed by yield, SOC and Olsen P. Treatment with mineral fertilizers provided the same rates of N and P as 5 t ha−1 manure and yields from manure and fertilizer were similar. Fertilizer increased Olsen P but not SOC. Management systems with occasional manure application and intermediate fertilizer applications should be assessed. Inputs and offtakes of C, N and P were measured for three years. Approximately 16, 25 and 11% of C, N and P respectively were stabilized into soil organic matter from 5 t ha−1 a−1 manure. The majority of organic P was fixed as soil inorganic P.

InfoCrop: A dynamic simulation model for the assessment of crop yields, losses due to pests, and environmental impact of agro-ecosystems in tropical environments. II. Performance of the model

InfoCrop, a generic crop model, simulates the effects of weather, soils, agronomic management (planting, nitrogen, residues and irrigation) and major pests on crop growth, yield, soil carbon, nitrogen and water, and greenhouse gas emissions. This paper presents results of its evaluation in terms of its validation for rice and wheat crops in contrasting agro-environments of tropics, sensitivity to the key inputs, and also illustrates two typical applications of the model. Eleven diverse field experiments, having treatments of location, seasons, varieties, nitrogen management, organic matter, irrigation, and multiple pest incidences were used for validation. Grain yields in these experiments varied from 2.8 to 7.2 ton ha −1 in rice and from 3.6 to 5.5 ton ha −1 in wheat. The results indicated that the model was generally able to explain the differences in biomass, grain yield, emissions of carbon dioxide, methane and nitrous oxides, and long-term trends in soil organic carbon, in diverse agro-environments. The losses in dry matter and grain yield due to different pests and their populations were also explained satisfactorily. There were some discrepancies in the simulated emission of these gases during first few days after sowing/transplanting possibly because of the absence of tillage effects in the model. The sensitivity of the model to change in ambient temperature, crop duration and pest incidence was similar to the available field knowledge. The application of the model to quantify multiple pests damage through iso-loss curves is demonstrated. Another application illustrated is the use of InfoCrop for analyzing the trade-offs between increasing crop production, agronomic management strategies, and their global warming potential.

Current trends of soil organic carbon in English arable soils

Current trends of soil organic carbon in English arable soils

Long-term effects of crop rotation and different fertilization systems on soil fertility and productivity

The effects of crop rotation and fertilization systems on yield and soil fertility parameters have been investigated in a long-term field trial established in southeast Norway in 1953. The results indicate the small differences between crop rotations and different fertilization systems in yield and soil fertility parameters; the decreasing trend in soil organic carbon (SOC) (from 3.8 to 3.7%) and increasing trend of N with time (from 0.32 to 0.36%) and, as a result, the decreasing trend in C/N ratio (from 12 to 10).

Simulating trends in soil organic carbon of an Acrisol under no-tillage and disc-plow systems using the Century model

Soil organic matter (SOM) and its different pools have key importance in nutrient availability, soil structure, in the flux of trace gases between land surface and the atmosphere, and thus improving soil health. This is particularly critical for tropical soils. The rates of accumulation and decomposition of carbon in SOM are influenced by several factors that are best embodied by simulation models. However, little is known about the performance of SOM simulation model in an acid tropical soil under different tillage systems including no-tillage (NT). Our objective was to simulate soil organic matter dynamics on an Acrisol under no-tillage and different plowed systems using Century model. Tillage systems consisted of no-tillage, disc plow, heavy disc harrow followed by disc plow, and heavy disc harrow. Soil C stocks simulated by Century model showed tendency to recovery only under no-tillage. Also, simulated amounts of C stocks of slow and active pools were more sensitive to management impacts than total organic C. The values estimated by Century of soil C stocks and organic carbon in the slow and passive pools fitted satisfactorily with the measured data. Thus fitted, except for the active pool, Century showed acceptable performance in the prediction of SOM dynamics in an acid tropical soil.

Carbon sequestration in a long-term conventional versus conservation tillage experiment

The impact of conservation tillage practices on carbon sequestration has been of great interest in recent years. Changes in the soil organic carbon (SOC) as influenced by tillage, is more noticeable under long-term rather than short-term tillage practices. This experiment analyzed the organic carbon status of soils sampled at depth increments from 0 to 60 cm after 25 years of five tillage treatments in a silt loam soil. Zero tillage (ZT) treatment was compared to conventional tillage practices of mouldboard and chisel plow operations conducted either during the fall or spring season in a randomized complete block design with four replications. The SOC was calculated on depth and equivalent soil mass bases. Contrast analysis showed a significantly (5%) higher soil bulk density for zero versus fall and zero versus chisel tillage operations at 5–10 cm soil depth. The SOC concentration was dependent on the depth of tillage operation and followed the trend of higher SOC for zero, chisel, and mouldboard tillage at 0–5, 5–10, and 20–40 cm depth, respectively. There were more significant differences in the SOC storage when expressed on depth compared to an equivalent soil mass basis. SOC storage was significantly higher for ZT at the 0–5 cm soil depth compared to conventional tillage practices. Contrast analysis on an equivalent mass basis showed that SOC storage was significantly higher for spring tillage compared to fall tillage at 0–60 cm depth. In conclusion, ZT practices increased SOC concentration and storage compared to conventional tillage operations only for the surface layer but not for the entire soil profile.

Influence of manuring and irrigation scheduling on system productivity, resource use efficiency, nutrient uptake and incidence of early shoot-borer (Chilo infuscatellus) in sugarcane (Saccharum spp. hybrid complex) and garlic (Allium sativum) intercropping system

A field experiment was conducted during the autumn seasons of 201013 at Pusa, Bihar, to identify suitable fertilizer and irrigation requirement in sugarcane (Saccharum spp. hybrid complex) + garlic (Allium sativum L.) in- tercropping system for system productivity, resource-use efficiency, nutrient utilization and early shoot borer (Chilo infuscatellus Snellen) incidence in sugarcane. Sugarcane + garlic (1: 2) with 100% recommended dose of fertilizer (RDF) to sugarcane (150, 37.1, 49.8 kg N, P, K/ha) and garlic (100, 34.9, 66.4 kg N, P, K/ha) showed sig- nificantly higher dry weight of garlic bulb (1.14 t/ha), bulb yield of garlic (3.5 t/ha), cane-equivalent yield (130.3 t/ ha), land-equivalent ratio (1.30), area-time equivalent ratio (1.08), net returns ( 1,96,300/ha) and benefit: cost ra- tio (2.96) than rest of the fertilizer treatments. The total N, P and K uptake by sugarcane and garlic were also found the maximum in this treatment. Fertility levels did not affect available N and K status after harvesting of sug- arcane and garlic but significantly increased organic carbon and available P when analyzed after harvesting of sugarcane and garlic. Intercropping system exhibited significantly lowest incidence of early shoot borer (6.7%) than sole sugarcane (11.4%). Different irrigation schedules significantly influenced growth and yield attributes. Ap- plication of 4 irrigations at 30, 60, 90 and 120 days after sowing (DAS), being at par with 3 irrigations, resulted in higher cane yield (92.4 t/ha), bulb yield of garlic (3.6 t/ha) and land-equivalent ratio (1.36) than the remaining irri- gation levels. With the increase in irrigation from 1 to 4 resulted increase in cane-equivalent yield, area-time equivalent ratio and net returns, maximum being recorded with 4 irrigations at 30, 60, 90 and 120 DAS. However, benefit: cost ratio (3.05) and N, P and K uptake by sugarcane were significantly improved up to 3 irrigations (30, 60 and 90 DAS). There was increasing trend of soil organic carbon and available N, P and K in post-harvest soil with increasing irrigation levels, whereas increasing level of irrigation reduced the incidence of early shoot borer in sugarcane. Sugarcane + garlic with 100% RDF to both the crops in combination with 4 irrigations (30, 60, 90 and 120 DAS) resulted in the highest N (29.1 kg/ha), P (12.5 kg/ha) and K (27.6 kg/ha) uptake by garlic. The interac- tion effects showed that sugarcane + garlic (1: 2) with 100% RDF to both the crops in combination with 3 irriga- tions at 30, 60 and 90 DAS gave at par net returns with that of sugarcane + garlic with 100% RDF to both the crops along with 4 irrigations at 30, 60, 90 and 120 DAS in sugarcane + garlic intercropping system.

Soil stripping and replacement for the rehabilitation of bauxite-mined land at Weipa. III. Simulated long-term soil organic matter development

Long-term trends in soil organic carbon (C) and nitrogen (N) under current and alternative rehabilitation practices at Weipa were simulated using the CENTURY model. After 100 years, predicted organic C in the surface soils (0–20 cm) of each treatment had risen to new dynamic equiliPbria. Since the ‘passive’ pool of recalcitrant organic C, which occupied 47% of organic C, changed little over the simulation period, the new equilibria differed according to initial organic C content. Most organic matter recovery occurred in the ‘slow’ fraction, although the greatest rate of change occurred in the ‘active’ C pool, which stabilised within 50 years at levels similar to the native forest. Similarly, ‘slow’ C accumulated in all treatments to new equilibria which were similar to that in undisturbed forest soil. The main difference between treatments was in the predicted time until a stable equilibrium in the ‘slow’ pool was reached: between 90 and 160 years depending on the soil stripping and replacement operation used. Successful development of new equilibria was highly sensitive to the amount of legume N2 fixation in the system and also to the severity of C and N losses during fire events. Reasonable agreement was found between simulated organic C accumulation and that observed in surveyed rehabilitation of up to 15 years of age (r2 = 0.67 for freshly replaced soils, r2 = 0.72 for soils stockpiled before respreading).