The problem of land degradation is not new, but never before has it been so widespread or affected the lives of so many people. The need for a global assessment of land degradation was highlighted by the United Nations Conference on the Human Environment in 1972. Since then, several attempts have been made to develop methodologies that will allow for systematic assessment and monitoring of global land degradation. Systematic work started in 1975, when FAO and United Nations Environment Programme (UNEP) collaborated in a study to develop a provisional method for soil degradation. This method was tested, and maps on a scale of 1:5,000,000 were produced for North Africa and the Near East. However, the method proved difficult to apply accurately, so this project was followed by another where the method was revised and refined in an effort to assess and map desertification. Again, problems were encountered because of the complexity of the subject and the lack of usable reliable data. More recently, ISRIC, using a simplified methodology and the assistance of some 250 scientists from around the world, has produced a world map of human induced soil degradation at a scale of approximately 1:10,000,000. Meanwhile, interest has been growing in the problem of nutrient depletion in developing countries and a study has been completed of N, P and K balances in the soils of 38 African countries. Although we still do not have an accurate assessment of global land degradation and no systematic monitoring is yet in place, these innovative studies have provided us with a sound basis for future work and have identified many of the practical problems of measuring land degradation, data collection and analysis that will have to be overcome before more accurate assessment and monitoring can be achieved.

Panels of 40 to 60 “non-expert” consumers attempted to distinguish between the taste of organically and conventionally grown fruits and vegetables. Wherever possible, samples of the two types of produce were obtained by picking them in the growing orchards/fields to avoid any question of authenticity, and cold-stored without treatment under the same conditions, for periods reflecting their shipping time to markets. Some physical, chemical, and instrumental analytical tests were also performed. No consistent preference pattern emerged. For grapefruit, grapes, carrots, spinach, sweet corn and tomatoes, the differences in hedonic ratings and scores between the two types of produce were not significant. For mangoes and orange juice, the conventional type was preferred, while the reverse was true for bananas; in each of these three instances the result could be ascribed to fruit being tasted closer to its optimum maturity.

Screening tests were performed to detect any traces, at the parts-per-billion level, of chlorinated hydrocarbons and organophosphorus compounds used as pesticides, or their degradation products. No traces were detected in any of the samples examined (bananas, grapes, carrots, spinach, sweet corn or tomatoes), whether organically or conventionally grown. In those samples examined (bananas, grapes, carrots, spinach, sweet corn and tomatoes) by quantitative tests for the three major fertilizer elements used conventionally (NPK), nitrogen and phosphorus concentrations were not consistently greater, while potassium concentrations were either equal or greater, than in the organically grown samples. Among the anion analyses performed on orange juice, grapefruit juice, carrots, spinach and tomatoes, nitrates and particularly nitrites either were not detected, or occurred at negligible concentrations in all samples. Phosphates were found at higher concentrations, but not significantly so, in four of the five organic products tested; no phosphates were detected in either type of tomatoes.

Crops grown in narrow rows (NR, 0.25 to 0.38 m) shade weed seedlings more than do those grown in traditional wide rows (WR, 0.76 m). NR crops may require less herbicide and interrow cultivation than WR crops for equally effective weed control. This hypothesis was tested by comparing weed control and crop yield in NR and WR crops when the following percentages of recommended application rates (RAR) of standard herbicides were applied: soybean, 0, 50 and 100%; sunflower, 0, 25, 50, and 100%; and corn, 0, 33, and 100% in three separate sets of experiments conducted over 2, 3, and 4 years, respectively. In all treatments with 100% RAR, excellent weed control prevented reductions in crop yield. When only 25 to 50% RAR was applied, weed control was consistently high in NR (82 to 99% control), but variable in WR (42 to 99% control). Weed control and crop yields typically were lowest in NR without herbicides. Interrow cultivation controlled 0 to 81% of weeds in WR crops. In reduced herbicide treatments (25 to 50% RAR), yields of NR soybean and sunflower typically were about equal to those in WR with 100% RAR, but NR corn yields were about 10% less. Considering the reduced herbicide use and lower weed control costs, planting corn, soybean, and sunflower in narrow rows may represent a practical form of low-input production of these important crops.

The impact of soil degradation on human welfare and the global environment presents a major challenge. A significant decline in soil quality has occurred worldwide through adverse changes in its physical, chemical and biological attributes and contamination by inorganic and organic chemicals. There is a need to develop criteria to evaluate soil quality so that the progress of any corrective action required by the international community can be monitored.

There currently are no generally accepted criteria to evaluate changes in soil quality. This lack impedes the design and evaluation of meaningful soil management programs. This paper examines the principal physical and chemical attributes that can serve as indicators of a change in soil quality under particular agroclimatic conditions. Proposed indicators include soil depth to a root restricting layer, available water-holding capacity, bulk density/penetration resistance, hydraulic conductivity, aggregate stability, organic matter, nutrient availability/retention capacity, pH, and where appropriate, electrical conductivity and exchangeable sodium. We also discuss the justification for selecting these key attributes, their measurement, critical limits for monitoring changes in soil productivity, and future research needs in soil quality.

Genetic improvements in crop tolerance to diseases, insects, and other stresses have reduced or eliminated applications of pesticides and other inputs for many crops. However, little work has been done to examine the potential for increasing levels of tolerance to weeds, even though herbicides account for 69% of the pesticides used in the United States eachyear. This paper documents thatfor all 21 crops examined, varieties differ in their tolerance of non-parasitic weeds. Characteristics influencing varietal tolerance to weeds are summarized.

Recognition of the environmental costs of fossil fuels coupled with concern over their depletion within the next few decades has broadened the search for alternative energy resources, including biomass energy. Ethanol produced from corn (Zea mays L.) grain currently is the primary form of biomass energy produced in the Midwest, but its net energy balance commonly is negative when corn grain is produced under conventional practices. Reducing fossil fuel inputs, particularly for nitrogen fertilizer, will improve the energy balance, but more substantial improvements involve increased efficiency of ethanol production. An alternate source involves fermentation of crops such as sweet sorghum (Sorghum bicolor [L.]Moench).

Other potential biomass energy resources for the Midwest include oils extracted from seed crops, methane from waste digestion, and combustion, gasification or fermentation of woody and herbaceous crops and crop residues. These resources may serve as an energy supplement or a useful energy source for individual farms, households or rural communities. Biomass energy systems in Midwest agriculture must be evaluated regarding their long term environmental impacts and their sustainability. Externalities that must be considered include surface and ground water pollution, soil erosion, and economic and social benefits to the rural community.

Diverse soil microbiological studies have attempted to assess deterioration or improvement in soil quality. These studies have been done on three levels: population level studies of the dynamics of species that are presumed to be important or sensitive; community level studies of microbial community structure, such as species diversity and frequency of occurence of species; and ecosystem level studies of a range of soil processes. We suggest that ecosystem level approaches offer the best possibilities for rapidly assessing changes in soil quality. Data from such studies will allow researchers to decide whether to proceed with population or community level studies.

Agricultural research conducted in the United States since establishment of the U.S. Dept. of Agriculture and Land-Grant University System in 1862 has shown that regular and proper additions of organic materials are very important for maintaining the tilth, fertility, and productivity of agricultural soils, protecting them from wind and water erosion, and preventing nutrient losses by runoff and leaching. Several millennia earlier, Roman agriculturists were advocating crop rotations, green manuring, composts, legumes, farmyard manures, crop residues, wood ashes, seaweed, and sewage wastes for supplying humus and nutrients to restore or enhance soil productivity. Even earlier, Asian farmers also used these practices to maintain healthy and productive soils. Today the most serious problem in U.S. agriculture and agriculture worldwide is the widespread degradation of agricultural soils through erosion and the consequential decline in productivity. In view of how much information is available on the benefits of organic recycling on agricultural lands, one wonders why we aren't doing a better job of protecting and conserving our land resource base. We discuss strategies for using organic resources more effectively to achieve a more sustainable agriculture for the future.

The increased effort by Congress to reduce agriculture's adverse consequences on the environment has been focused almost entirely on changing agricultural production practices at the farm level Because the agricultural sector is highly integrated, attempts to change a specific industry within the sector, such as production, input supply, or processing, may have undesirable effects. Programs designed to achieve society's environmental objectives by forcing change in agricultural production practices will lead to increased frustration, new programs and regulations, and further conflict between society and farmers. To guarantee sustainability of U.S. agriculture into the next century, efforts to incorporate new social needs into production agriculture should include changes in the research agendas of public and private institutions, marketing grades and standards, and the institutions that support the agricultural producer.

Invertebrates are an integral part of soils and are important in determining the suitability of soils for the sustainable production of healthy crops or trees. We discuss the importance of the soil invertebrate fauna in relation to terrestrial habitats and global biodiversity as we understand it. We describe the role of the main invertebrate groups in soils, including earthworms, termites, springtails, and nematodes, and how they determine soil quality. Practical problems in dealing with the invertebrate fauna include sampling, taxonomy and availability of biological information on species. Various measures are available that use invertebrates to assess soil quality, each with its advantages and disadvantages. They include abundance, biomass, density, species richness, trophic/guild structure, food web structure, keystone species and ecosystem engineers. We propose the three most useful and practical of these as suitable to be combined with other biological (microbial) and non-biological (hydrological, physical, chemical) criteria into a single index of soil quality that might be used on a regional, if not international basis.

People are becoming more aware that our soil resources are as vulnerable to degradation as air or water, but criteria are needed to learn how soil quality is changing. Our objectives in this review are: (1) to illustrate that interactions between human and natural factors determine soil quality; (2) to identify indicators that can be used to evaluate human-induced effects on soil quality; and (3) to suggest soil and crop management strategies that will sustain or improve soil quality. The physical, chemical, and biological processes and interactions within the soil are critical factors affecting all indicators of soil quality. The biological processes are especially important because they provide much of the resiliency or buffering capacity to ameliorate stress. Presumably, no single soil or crop management practice will guarantee improved soil quality, but conservation tillage, cover crops, and crop rotations are practices that may be effective. Alley or narrow-strip cropping may facilitate adoption of several of those agronomic practices and increase temporal and spatial diversity across the landscape. To maintain or possibly improve soil quality and simultaneously address a growing waste disposal problem, we suggest that urban lawn and newspaper waste be evaluated as carbon sources. We conclude that the most critical factor, regardless of the soil and crop management strategy, is to recognize that carbon is an essential element for improving soil quality in the U.S. and around the world.

The formation of crusts or seals at the soil surface is exceedingly important in determining how much rainfall infiltrates into the soil and how much runs off, causing soil erosion. This paper explores the processes involved in the formation of crusts, such as raindrop impact and clay dispersion, to formulate a picture of the mechanisms involved. We discuss the major consequences of crusting, namely, runoff, erosion, and impaired seedling emergence, and present strategies to reduce soil degradation. Examples are offered from many parts of the world.