Changes to soil quality indicators following conversion to organic vegetable production (OF0401)

This is the final report of Defra project OF0401. The attached report document starts with an Executive Summary, from which this text is extracted. The aim of this 1 year study was to examine how key functional indicators of soil quality are affected by contrasting organic and conventional management regimes. In particular, the project investigated the impact of contrasting fertility building regimes on soil quality, focussing on the initial 5-year period following conversion from conventional to organic production. Five 0.8 ha areas at HRI-Wellesbourne were selected for study. These were: two organic vegetable rotations supporting contrasting fertility building regimes, an organic arable rotation, a grass-clover ley, and a conventionally managed cereal rotation. The organic areas had been converted from conventional cereal production 5 years prior to the start of the study. The conventional area was adjacent. A range of chemical, biological and physical attributes were determined. There were differences between the organic and conventional management regimes in most chemical, biological and physical soil quality parameters. Contrasting organic management regimes had different effects on soil quality. Relative to organic vegetable and conventional arable management, the organic arable management rotation enhanced amounts of light fraction organic matter and labile N, with beneficial implications for long term nutrient retention and soil organic matter development. There was little difference in chemical quality between the organic vegetable and the conventional arable areas. There was evidence that organic management promoted a microbial community that was distinct in composition and functional attributes to that in conventional soil. Relative to conventional management, areas under organic management had greatly increased inoculum of arbuscular mycorrhizal fungi, a larger proportion of 'active' relative to 'resting' biomass within the microbiota, increased metabolic diversity and a distinct microbial community metabolism. However, there was evidence that the productivity of newly converted organic systems could be limited by low inoculum and diversity of arbuscular mycorrhizal fungi inherited following conventional management. The clearest effect on soil structure was with regard to the detrimental effects of vegetable production rather than to any benefit associated with organic management. Wheeling lines caused compaction that resulted in poor growth of subsequent cereal crops. However, it is likely that increased levels of organic matter may result in a soil better able to cope with damaging operations. There were differences in the susceptibility of the chemical and biological quality parameters to change. These differences provide possibilities to use selected parameters as early indicators of the effects of management on soil quality. Furthermore, the results highlight the need, when investigating soil quality, to consider a wide variety of 'quality' analyses. Limited data sets, focussing on traditional measures of soil quality (e.g. total SOM and biomass-N), could lead to unsound conclusions regarding the effects of management on other functional aspects of soil quality. There are opportunities to conduct further statistical analysis of our comprehensive data set in order to develop an index suitable for quantifying soil quality in organic systems. Such an index would be of generic value to rate soil quality in diverse agricultural systems. Further work is needed to determine the applicability and conclusions of our study to other soil types and organic management regimes. The work has highlighted fundamental shifts in microbial community structure and functioning following conversion from conventional to organic management. There is a need to characterise and quantify these changes. This will provide new groups of 'indicator' organisms which could be suitable for assessing changes to soil quality, and could also provide opportunities to manage soil microbial communities to improve the sustainability of organic and conventional farming

The impact of rain water on soil pore networks following irrigation with saline-sodic water

The soil pore network is an important factor affecting soil hydraulic conductivity (Ksat). In this study we examine the effect on the soil pore network of a Red Ferrosol caused by irrigation with good quality irrigation water (GQW), as well as saline-sodic water with varying sodium absorption ratios (SAR; 10, 50 and 120) and constant electrical conductivity (EC; 2 dS m-1), followed by application of distilled water (simulating rain water). The Ksat was measured for the different waters before and after applying the rain water to the soil. Soil samples were taken from different depths (1, 4 and 8 cm) for exchangeable cations measurement and the changes in ESP of the soil. Soil horizontal cross-sections were taken from the first 2 cm of the soil cores after drying with acetone and impregnation with polyester resin mixed with green fluorescent dye catalyst and hardener. These sections were polished and visualized under a microscope to investigate the changes in the soil pore network. By increasing the SAR of the water applied from 0.11 (GQW) to SAR 50 and 120, a significant reduction in Ksat was found, alongside a significant increase in the ESP of the soil from 3 to 10 and 11, respectively; this was most evident near the soil surface. After applying rain water, the Ksat reduced significantly approaching 0 mm h-1 where soil was treated with water of SAR 120. Visualisation of the soil pore network of the treated soils following the application of deionised water clearly showed a reduction in soil macroporosity where water quality of SAR ≥10 was applied, even where soils were non-sodic. Where irrigation occurred with good quality, low SAR water, this reduction was not evident

Tillage Manure Managemen and Water Quality, April 2005

Tillage and manure application practices significantly impact surface and ground water quality in Iowa and other Midwestern states. Tillage and manure application that incorporates residue and disturbs soil result in higher levels of soil erosion and surface runoff. Phosphorus and sediment loading are closely linked to the increase in soil erosion and surface water runoff. Manure application (i.e., injection or incorporation) reduces surface residue cover, which can worsen soil erosion regardless of the tillage management system being used. An integrated system approach to manure and tillage management is critical to ensure effi cient nutrient use and improvement of soil and water quality. This approach, however, requires changes in manure application technology and tillage system management to ensure the success of an integrate

Monitoring of Finnish arable land: changes in soil quality between 1987 and 1998

This study is part of the long-term monitoring of Finnish arable land and it is based on soil analyses of 705 monitoring sites sampled in 1998. The same sites were sampled twice previously,in 1974 and 1987. We describe here the state of the Finnish cultivated soils in 1998 and changes in soil quality since 1987. The samples were analysed for organic C, volume weight, pH, P, K, Ca, S, Mg, Al, B, Cd, Co, Cr, Cu, Fe, Mn, Mo, Se and Zn.Macronutrients were extracted with 0.5 M ammonium acetate + 0.5 M acetic acid (pH 4.65) and most micronutrients, Al and heavy metals with the same solution + 0.02 M Na 2 EDTA. Hot water was used to extract B and Se. From 1987 to 1998, soil P, Ca, Mg, S, Cr, Cu, Zn, volume weight and electrical conductivity increased and soil K, B, pH and organic C decreased. There was no change in soil Al, Cd, Mn and Ni. Between 1987 and 1998,the use of P,K,B and Cu in mineral fertilisers declined whereas that of Ca in liming agents and Zn in mineral fertilisers increased. With the exception of P and Cu,these changes affected the concentrations of easily soluble macro- and micronutrients in the soil accordingly. The slight decrease in soil pH might be due to the increase in the use of fertliser N. The finding that soil Cd and Ni ceased to increase and that soil Cr increased only slightly was attributed to the dramatic reduction in national emissions and bulk depositions of heavy metals

Plant species effects on soil organic matter turnover and nutrient release in forests and grasslands

1996 Fall.Includes bibliographic references (pages 23-27).Although feedbacks between plant species and ecosystem dynamics have been demonstrated in a variety of terrestrial ecosystems, little research has examined the mechanistic relationship between plant species characteristics, the formation and turnover of soil carbon and nitrogen pools, and ecosystem processes such as net N mineralization. My objective was to examine two possible effects of species on soil C and N dynamics; changes in organic matter quality and changes in soil aggregation. For several forest ecosystems, litter lignin:N ratio correlated negatively (non-linear) with net N mineralization, but the relationship did not apply to grass species. Climatic factors (temperature, precipitation) explained little of the variation in net N mineralization. The relationship between litter lignin:N ratio and net N mineralization from mineral soil and the forest floor was similar, suggesting that plant litter quality affects both forest floor and mineral soil organic matter quality. For tree species monocultures in Wisconsin, net N mineralization during 387 day laboratory incubations indicated that species alter the quality of readily decomposable pools of soil N, and have little effect on more recalcitrant soil N. Changes in the quality of soil N correlated positively with in situ net N mineralization. Grass species did not influence N mineralization. Neither grass nor tree species influenced soil C dynamics, but differences in soil characteristics between sites influenced soil C dynamics. Soil microbes appear to act as a “decay filter”, converting heterogeneous plant material into relatively homogeneous soil humus. Changes in soil aggregate size distribution should alter whole-soil C and N quality because different size aggregates contain organic matter of different quality. Although tree species slightly altered aggregate size distribution, aggregate size distribution related poorly to whole-soil C and net N mineralization. Tree species had no effect on the physical protection of organic matter in soil aggregates or on organic matter quality of different size aggregates. Species characteristics had little effect on soil C mineralization, but species-related changes in the quality of readily decomposable soil N pools (not the pool size) influenced net N mineralization. This suggests that the feedbacks between plant species and soil N cycling occur rapidly, ensuring an adequate nutrient supply when plant community structure changes

Links between soil microbial communities and plant traits in a species-rich grassland under long-term climate change

Climate change can influence soil microorganisms directly by altering their growth and activity but also indirectly via effects on the vegetation, which modifies the availability of resources. Direct impacts of climate change on soil microorganisms can occur rapidly, whereas indirect effects mediated by shifts in plant community composition are not immediately apparent and likely to increase over time. We used molecular fingerprinting of bacterial and fungal communities in the soil to investigate the effects of 17 years of temperature and rainfall manipulations in a species‐rich grassland near Buxton, UK. We compared shifts in microbial community structure to changes in plant species composition and key plant traits across 78 microsites within plots subjected to winter heating, rainfall supplementation, or summer drought. We observed marked shifts in soil fungal and bacterial community structure in response to chronic summer drought. Importantly, although dominant microbial taxa were largely unaffected by drought, there were substantial changes in the abundances of subordinate fungal and bacterial taxa. In contrast to short‐term studies that report high resistance of soil fungi to drought, we observed substantial losses of fungal taxa in the summer drought treatments. There was moderate concordance between soil microbial communities and plant species composition within microsites. Vector fitting of community‐weighted mean plant traits to ordinations of soil bacterial and fungal communities showed that shifts in soil microbial community structure were related to plant traits representing the quality of resources available to soil microorganisms: the construction cost of leaf material, foliar carbon‐to‐nitrogen ratios, and leaf dry matter content. Thus, our study provides evidence that climate change could affect soil microbial communities indirectly via changes in plant inputs and highlights the importance of considering long‐term climate change effects, especially in nutrient‐poor systems with slow‐growing vegetation

Extractable nitrogen and microbial community structure respond to grassland restoration regardless of historical context and soil composition.

Grasslands have a long history of invasion by exotic annuals, which may alter microbial communities and nutrient cycling through changes in litter quality and biomass turnover rates. We compared plant community composition, soil chemical and microbial community composition, potential soil respiration and nitrogen (N) turnover rates between invaded and restored plots in inland and coastal grasslands. Restoration increased microbial biomass and fungal : bacterial (F : B) ratios, but sampling season had a greater influence on the F : B ratio than did restoration. Microbial community composition assessed by phospholipid fatty acid was altered by restoration, but also varied by season and by site. Total soil carbon (C) and N and potential soil respiration did not differ between treatments, but N mineralization decreased while extractable nitrate and nitrification and N immobilization rate increased in restored compared with unrestored sites. The differences in soil chemistry and microbial community composition between unrestored and restored sites indicate that these soils are responsive, and therefore not resistant to feedbacks caused by changes in vegetation type. The resilience, or recovery, of these soils is difficult to assess in the absence of uninvaded control grasslands. However, the rapid changes in microbial and N cycling characteristics following removal of invasives in both grassland sites suggest that the soils are resilient to invasion. The lack of change in total C and N pools may provide a buffer that promotes resilience of labile pools and microbial community structure

Soil Quality of the Land Under Coffee-Based Farming System (Case Study at Sumberjaya, West Lampung)

Forest conversion to coffee-based farming systems has raised concern among many stakeholders since it may create serious impact to the deterioration of forest functions, declining soil productivity in particular and land degradation in general. Study on the impact of forest conversion on changes of soil quality, and the role of coffee for soil quality recovery has been conducted at Bodong and Laksana Sub Village of Sumberjaya Village, West Lampung. In Laksana, the observed landuse consisted of young (< 3 years) coffee plantation, mature (> 10 years) coffee, mix farming (multistrata), caliandra and forest, while in Bodong are young and mature coffee plantations and forest. The soil quality parameters used in this experiment were soil organic matter status and soil physical properties. Changes of soil quality as affected by forest conversion to coffee farming depends on soil resistance (resilience to structural break down). Soils with low resistance are easier to degrade than those with high soil resistance. The mix (multistarata) system shows better impact on soil quality than monoculture system does

Jena Soil Model (JSM v1.0; revision 1934): a microbial soil organic carbon model integrated with nitrogen and phosphorus processes

Plant–soil interactions, such as the coupling of plants' below-ground biomass allocation with soil organic matter (SOM) decomposition, nutrient release and plant uptake, are essential to understand the response of carbon (C) cycling to global changes. However, these processes are poorly represented in the current terrestrial biosphere models owing to the simple first-order approach of SOM cycling and the ignorance of variations within a soil profile. While the emerging microbially explicit soil organic C models can better describe C formation and turnover, at present, they lack a full coupling to the nitrogen (N) and phosphorus (P) cycles with the soil profile. Here we present a new SOM model – the Jena Soil Model (JSM) – which is microbially explicit, vertically resolved and integrated with the N and P cycles. To account for the effects of nutrient availability and litter quality on decomposition, JSM includes the representation of enzyme allocation to different depolymerisation sources based on the microbial adaptation approach as well as of nutrient acquisition competition based on the equilibrium chemistry approximation approach. Herein, we present the model structure and basic features of model performance in a beech forest in Germany. The model reproduced the main SOM stocks and microbial biomass as well as their vertical patterns in the soil profile. We further tested the sensitivity of the model to parameterisation and showed that JSM is generally sensitive to changes in microbial stoichiometry and processes

Combination of Imaging Infrared Spectroscopy and X-ray Computed Microtomography for the Investigation of Bio-and Physicochemical processes in Structured Soils

Soil is a heterogeneous mixture of various organic and inorganic parent materials. Major soil functions are driven by their quality, quantity and spatial arrangement, resulting in soil structure. Physical protection of organic matter (OM) in this soil structure is considered as a vital mechanism for stabilizing organic carbon turnover, an important soil function in times of climate change. Herein, we present a technique for the correlative analysis of 2D imaging visible light near-infrared spectroscopy and 3D X-ray computed microtomography (mCT) to investigate the interplay of biogeochemical properties and soil structure in undisturbed soil samples. Samples from the same substrate but different soil management and depth (no-tilled topsoil, tilled topsoil and subsoil) were compared in order to evaluate this method in a diversely structured soil. Imaging spectroscopy is generally used to qualitatively and quantitatively identify OM with high spatial resolution, whereas 3D X-ray mCT provides high resolution information on pore characteristics. The unique combination of these techniques revealed that, in undisturbed samples, OM can be found mainly at greater distances from macropores and close to biopores. However, alterations were observed because of disturbances by tillage. The correlative application of imaging infrared spectroscopic and X-ray mCT analysis provided new insights into the biochemical processes affected by soil structural changes