John W. Doran

Soil health and sustainability: managing the biotic component of soil quality

Soil health is the capacity of soil to function as a vital living system, within ecosystem and land-use boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health. Anthropogenic reductions in soil health, and of individual components of soil quality, are a pressing ecological concern. A conference entitled ‘Soil Health: Managing the Biological Component of Soil Quality’ was held was held in the USA in November 1998 to help increase awareness of the importance and utility of soil organisms as indicators of soil quality and determinants of soil health. To evaluate sustainability of agricultural practices, assessment of soil health using various indicators of soil quality is needed. Soil organism and biotic parameters (e.g. abundance, diversity, food web structure, or community stability) meet most of the five criteria for useful indicators of soil quality. Soil organisms respond sensitively to land management practices and climate. They are well correlated with beneficial soil and ecosystem functions including water storage, decomposition and nutrient cycling, detoxification of toxicants, and suppression of noxious and pathogenic organisms. Soil organisms also illustrate the chain of cause and effect that links land management decisions to ultimate productivity and health of plants and animals. Indicators must be comprehensible and useful to land managers, who are the ultimate stewards of soil quality and soil health. Visible organisms such as earthworms, insects, and molds have historically met this criterion. Finally, indicators must be easy and inexpensive to measure, but the need for knowledge of taxonomy complicates the measurement of soil organisms. Several farmer-participatory programs for managing soil quality and health have incorporated abiotic and simple biotic indicators. The challenge for the future is to develop sustainable management systems which are the vanguard of soil health; soil quality indicators are merely a means towards this end. Published by Elsevier Science B.V.

Soil health and global sustainability: translating science into practice

Interest in the quality and health of soil has been stimulated by recent awareness that soil is vital to both production of food and fiber and global ecosystems function. Soil health, or quality, can be broadly defined as the capacity of a living soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health. Soil quality and health change over time due to natural events or human impacts. They are enhanced by management and land-use decisions that weigh the multiple functions of soil and are impaired by decisions which focus only on single functions, such as crop productivity. Criteria for indicators of soil quality and health relate mainly to their utility in defining ecosystem processes and in integrating physical, chemical, and biological properties; their sensitivity to management and climatic variations; and their accessibility and utility to agricultural specialists, producers, conservationists, and policy makers. Although soils have an inherent quality as related to their physical, chemical, and biological properties within the constraints set by climate and ecosystems, the ultimate determinant of soil quality and health is the land manager. As such, the assessment of soil quality or health, and direction of change with time, is the primary indicator of sustainable management. Scientists can make a significant contribution to sustainable land management by translating scientific knowledge and information on soil function into practical tools and approaches by which land managers can assess the sustainability of their management practices. The first steps, however, in our communal journey towards sustainable land management must be the identification of our final destination (sustainability goals), the strategies or course by which we will get there, and the indicators (benchmarks) that we are proceeding in the right direction. We too often rush to raise the sails of our ‘technological’ ship to catch the wind, before knowing from where it comes or in properly defining our destination, charting our course, and setting the rudder of our ship. Examples are given of approaches for assessing soil quality and health to define the sustainability of land management practices and to ‘translate our science into practice’.

Microbial biomass and mineralizable nitrogen distributions in no-tillage and plowed soils

SummaryDistribution of soil microbial biomass and potentially mineralizable nitrogen (PMN) in long-term tillage comparisons at seven sites in the United States varied with tillage management and depth in soil. Microbial biomass and PMN levels of no-tillage soils averaged 54% and 37% higher, respectively, than those in the surface layer of plowed soil. Biomass and PMN levels were greatest in the surface 0 to 7.5-cm layer of no-tillage soil and decreased with depth in soil to 30 cm. Biomass and PMN levels of plowed soil, however, were generally greatest at the 7.5 –15 cm depth. Microbial biomass levels were closely associated with soil distributions of total C and N, water content, and water-soluble C as influenced by tillage management. Potentially mineralizable N levels in soil were primarily associated with distributions of microbial biomass and total N. Absolute levels of PMN and microbial biomass and the relative differences with tillage management were dependent on climatic, cropping, and soil conditions across locations. The additional N contained in soil biomass and PMN in the surface 0–7.5 cm of no-tillage compared with plowed soils ranged from 13 to 45 and 12 to 122 kg N/ha, respectively, for 6 of 7 locations. Fertilizer placement below the biologically rich surface soil layer and/or rotational tillage may improve short-term nitrogen use efficiency and crop growth on reduced-tillage soils.

Soil quality: Current concepts and applications

Soil quality has evolved as an educational and assessment tool for evaluating relative sustainability of soil resource management practices and guiding land-use decisions.This review discusses the rapid development of the soil quality concept throughout the decade of the 1990s,addresses misconceptions regarding soil quality efforts,and presents examples to illustrate how soil quality research,education,and technology-transfer activities are being used to help solve various soil resource and agroecosystemproblems.This review stresses that soil quality assessment re .ects biological,chemical,and physical properties,processes,and their interactions within each soil resource unit.By using examples from throughout the United States and around the world,we demonstrate the importance of using soil quality concepts to integrate both inherent and dynamic properties and processes occurring within a living,dynamic medium.We also emphasize that there is no ideal or magic soil quality index value by illustrating a framework for indexing that can be adapted to local conditions.The framework requires identifying critical soil functions,selecting meaningful indicators for those functions,developing appropriate scoring functions to interpret the indicators for various soil resources, and combining the information into values that can be tracked over time to determine if the soil resources are being sustained,degraded,or aggraded.This review is intended to provide a reference and background for land managers,resource conservationists,ecologists,soil scientists,and others seeking tools to help ensure that land-use decisions and practices are sustainable

Changes in soil microbial community structure with tillage under long-term wheat-fallow management

Fatty acid methyl esters (FAMEs) were used to ‘fingerprint’ soil microbial communities that evolved during 25 years of wheat-fallow cropping following native mixed prairie sod at Sidney, Nebraska, USA. Total ester-linked FAMEs (EL-FAMEs) and phospholipid-linked FAMEs (PL-FAMEs) were compared for their ability to discriminate between plots remaining in sod and those cropped to wheat or left fallow under no-till, sub-till or plow management. Cropped plots were higher in microbial biomass than their fallowed counterparts, and did not diAer significantly with tillage for the 0‐15 cm depth. Under fallow, microbial biomass was greatest in no-till and least in plow. Both cluster and discriminant analysis of PL- and EL-FAMEs clearly separated the remaining native sod plots from the existing wheat-fallow plots. This separation was particularly pronounced for the EL-FAMEs and was largely driven by high amounts in sod of a single FAME, C16:1(cis11), which has been cited as a biomarker for arbuscular mycorrhizal (AM) fungi. Within wheat-fallow, C16:1(cis11) declined significantly from no-till to plow, which supports the origin of C16:1(cis11) from extraradical mycelium and spores of AM fungi known to be sensitive to soil disturbance. Although discriminant analysis of PL- and EL-FAMEs diAerentiated wheat and fallow systems by tillage, discrimination among tillage treatments was expressed most strongly during fallow. FAME profiles from fallow plow were most dissimilar from cropped soils which suggests a relationship between tillage management and the long-term resiliency of the microbial community developed under the wheat crop. 7 2000 Elsevier Science Ltd. All rights reserved.

Soil microbial activity, nitrogen cycling, and long-term changes in organic carbon pools as related to fallow tillage management

Two experiments were established in 1969 and 1970 near Sidney, NE, to determine the effect of moldboard plow (plow), sub-tillage (sub-till), and no-tillage (no-till) fallow management on soil properties, biological activities, and carbon and nitrogen cycling. One experiment was on land which had been broken from sod in 1920, seeded to crested wheatgrass [Agropyron cristatum (L.) Gaertn.] from 1957 to 1967, and cultivated for wheat again in 1967 (Previously Cultivated site). The second experiment was established on land that was in native mixed prairie sod until 1969 (Native Sod site), and compared the three tillage management practices listed above in a winter wheat-fallow system as well as replicated plots remaining in sod. Soil sampling done 10–12 years after these experiments were initiated, indicated that the biological environment near the soil surface (0–30 cm) with no-till was often cooler and wetter than that with conventional tillage management practices, especially moldboard plowing. Biological activity and organic C and N reserves were concentrated nearer the soil surface (0–7.6 cm) with no-tillage, resulting in greater potential for tie-up of plant available N in organic forms. However, regardless of tillage practice with wheat-fallow management at either site, long-term (22–27 years) losses of soil organic C from surface soil (0–30 cm) ranged from 12 to 32% (320–530 kg C ha−1 year−1), respectively, for no-till and plowing. These soil C losses were closely approximated by losses measured to a depth of 122 cm, indicating that under the cropping, tillage, and climatic conditions of this study, soil C changes were adequately monitored by sampling to a depth of 30 cm within which most C loss occurs. No-till management maintains a protective surface cover of residue and partially decomposed materials near the soil surface. However, the decline in soil organic matter, and associated degradation in soil quality, will likely only be slowed by increasing C inputs to soil through use of a more intensive cropping system which increases the time of cropping and reduces the time in fallow.

Microorganisms and the Biological Cycling of Selenium

Most studies on the microbial transformations of elements have emphasized nutrient cycling within the biosphere or the economics of agricultural or industrial processes. Cyclic transformations within the biosphere between soluble, insoluble, and gaseous forms of carbon, nitrogen, hydrogen, oxygen, and sulfur are well known. Recently, attention has been focused on the role of microorganisms in the production and degradation of chemicals containing toxic elements (Alexander, 1973; Wood, 1974). Measures to increase animal and food crop production or disposal of waste materials can result in the introduction of elements in amounts harmful to terrestrial and aquatic ecosystems. Many elements and their compounds vary widely in both toxicity and mobility. Consequently, their safe disposal or effective recycling requires an understanding of their potential toxicities and possible transformations in the environment.

Maize plant contributions to root zone available carbon and microbial transformations of nitrogen

Root-derived C influences soil microbial activities that regulate N transformations and cycling in soil. The change in 13C abundance of soil microbial biomass was used to quantify contributions from maize (Zea mays L.), a C4 plant, to root zone-available C during growth in soil with a long history of C3 vegetation. Effects of root-derived available C on microbial transformations of N were also evaluated using a 15NH415NO3 fertilizer tracer. Root-released C (microbial respired C4C + soil residue C4C) accounted for 12% (210 kg C ha−1) of measured C fixed by maize at 4 wk and 5% at maturity when root-released C totaled 1135 kg C ha−1. Of the C4C remaining in soil, only 18–23% was found in microbial biomass, indicating either a rapid turnover rate of biomass or a lower availability of C4 substrates. Average daily production of root-derived available C was greatest during 4–8 wk maize growth (7 kg C ha−1 d−1) when 4–11% of the soil microbial biomass came from this C source. At maize maturity, 15% of the microbial biomass (161 kg C ha−1) came from root-derived available C, which totaled 402 kg ha−1. Of the 15N remaining in bare and cropped soils, averages of 23 and 16% (10 and 2 kg N ha−1) were found in microbial biomass, and 64 and 2% (28 and 0.2 kg N ha−1) were in inorganic 15N form, leaving 13 and 82% (6 and 10 kg N ha−1) as non-biomass organic N, respectively; this suggests that N cycling through microbial biomass was enhanced by root-derived C. Denitrification and N2O losses from planted soils were low (1–136 g N ha−1 d−1) when soil water-filled pore space (WFPS) was 2–3 mg kg−1) was present in the soil. The presence of maize plants increased denitrification losses from soil by 19 to 57% (average of 29%) during early growth stages when the release of root-derived C was greatest.

Chapter 4 Biological attributes of soil quality

Publisher Summary The biological attributes of soil include living organisms and material derived from living organisms. Living organisms (the biotic component of soil) include plants, animals, and microbes, ranging in size and function. After these organisms die, their residues remain in the soil in various stages of decomposition. Both living organisms and their residues interface with the abiotic component of the soil, which is nonliving and chemically derived and includes minerals, clays, water, and chemical ions and compounds. These components are tightly linked, shaping and affecting each other. The biological attributes of soil quality include the many soil components and processes related to organic matter cycling, such as total organic carbon and nitrogen, microbial biomass, mineralizable carbon and nitrogen, light fraction enzyme activities, and soil fauna and flora. Soil organic matter, composed of various fractions, is a key attribute of soil quality. It is the primary source of, and a temporary sink for, plant nutrients. It is important for soil quality, because it helps to maintain soil tilth, aids the infiltration of air and water, promotes water retention, reduces erosion, and controls the efficacy and fate of pesticides.

Influence of alternative and conventional agricultural management on soil microbial processes and nitrogen availability

Microbial activities important to effects on crop productivity and nutrient cycling can be altered by agricultural management practices. This study was conducted to determine whether soil microbial populations and their N cycling activities differ between conventional and alternative management practices. Physical, chemical, and microbial soil properties were measured at soil depth intervals of 0 to 7.5, 7.5 to 15, and 15 to 30 cm at a site in southeastern Pennsylvania during the second and fifth years after conversion from a conventional, chemically intensive system to alternative systems utilizing legumes and animal manure as N sources. In the second year after conversion, populations of fungi and bacteria, dehydrogenase activity, and soil respiration in the surface soil layer were greatest with alternative systems planted to red clover (Trifolium pratense L.). Differences in soil biological factors between management systems were related primarily to crop characteristics and, to a lesser extent, to soil physical properties. Levels of microbial populations and activities with conventional management were the same as with alternative management systems when similar crops such as corn (Zea mays L.) or soybean [Glycine max (L.) Merrill] were grown. Soil NO 3 -N contents, at most sampling depths, were markedly increased by application of fertilizer N or recent plow-down of red clover or hairy vetch (Vicia villosa Roth). The growth of red clover in the second year or hairy vetch in the fifth year was accompanied by significantly increased microbial biomass and potentially mineralizable N (PMN) reserves in the top 30-cm soil layer-these changes being most pronounced in the surface 0- to 7.5-cm layer. Nitrogen deficiency symptoms and lower corn grain yields in a legume/cash grain rotation as compared with conventional management in the second year were associated with lower soil NO 3 , levels and a greater proportion of N present as weed biomass and belowground microbial biomass. In 1985, management systems comparisons were limited to corn as the main crop; soil NO 3 levels during the growing season were inversely related to soil microbial biomass and PMN levels where hairy vetch was overseeded and incorporated as green manure by plowing before corn planting. Under the conditions of this study, the use of chemicals had little effect on microbial populations, their activity, or the cycling of nitrogen. Cropping systems-in particular, the growth of red clover or hairy vetch—profoundly influenced soil microbial biomass levels and soil pools of organic and available NO 3 -N during the growing season. Competitiveness of alternative management systems employing legumes as? sources for grain crops may depend largely on the growers ability to synchronize supplies of available soil N with periods of maximum uptake by grain crops.