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Abstract. The mining of sand and graver deposits and excavation of topsoil in urban areas have left extensive tracts of exposed subsoils that do not support plant growth because of adverse soil chemical and physical properties Such degraded and marginal soils, or spoils, are infertile, low in organic master, often acidic, and subject to severe erosion and surface runoff. Many of these lands are owned by small and part-lime farmers who wish to restore their aesthetic value and agricultural productivity. Research has shown that with liming and the proper use of organic amendments such as animal manures and sewage sludge compost, these lands can be restored to a high lever of productivity in as little as three years The methods and techniques for improving the productivity of marginal soils described in this paper can be of considerable benefit to some farmers in developed and developing countries where there is no other choice but to farm marginal soils because of the lack of highly productive agricultural lands. With increased efforts to restore the productivity of degraded and marginal soils through the use of organic amendments, conservation tillage, and crop rotations, future research should address the effect of best management practices on crop yields, the nutritional quality of crops, and the bioavailability of plant nutrients to both animals and humans.
Regular additions of organic materials such as animal manures and crop residues are of utmost importance in maintaining the tilth, fertility and productivity of agricultural soils, protecting them from wind and water erosion, and preventing nutrient losses through runoff and leaching. These materials have predictable beneficial effects on soil physical properties such as increased water-holding capacity, soil aggregation, soil aeration and permeability, and decreased soil crusting and bulk density (USDA, 1957; 1978).
Failure to recycle organic wastes and residues, intensive row crop production, and lack of sod-based crop rotations can result in extensive soil degradation and a decline in productivity due to excessive soil erosion and loss of fertility. The continuing desertification of Sub-Saharan Africa and the dustbowl of the central U.S. Great Plains in the 1930's can be attributed largely to improper farming methods that neglected the importance of soil organic master in crop production.
When organic materials, such as compost, animal manures, crop residues and sewage sludges are used as the primary sources of plant nutrients, the management system has often been referred to as "organic farming" (USDA, 1980). More recently, the terms alternative, regenerative. low-input, and sustainable have been used to describe farming systems that recycle available on-farm organic resources and sometimes off-farm materials such as municipal wastes, to maintain or improve soil productivity.
In addition, organic materials can be used effectively for land reclamation purposes. For example, the mining of topsoil and sand and graver deposits in urban areas has left extensive tracts of exposed, highly erodible subsoils which are not conducive to the support of plant growth because of their adverse chemical and physical properties. Such areas detract from the aesthetic value of an urban environment and are major contributors to environmental pollution through surface runoff, eutrophication (i.e., nutrient enrichment) of lakes and streams and sedimentation from soil erosion. Thus, there is a need to develop sound practices for restoring the productivity and value of these lands in the most economic and expedient way.
A wide variety of different organic wastes and residues can be used as soil conditioners and sources of plant nutrients on agricultural soils, with little or no adverse effects on public health and the environment. The purpose of this paper is to discuss how some organic amendments can provide an effective means of restoring the productivity of marginal, degraded, and infertile soils and how changes in cultural practices may affect crop quality.
Some of the areas mined for sand and gravel in the northeast corridor of the United States are owned by small farmers who, after mining operations are completed, want to revegetate the barren areas to minimize erosion and improve the aesthetic value of the land. Som~ want to put the land back into agricultural production so as to gain a more favorable (i.e., lower) tax assessment.
Research was conducted by the USDA Agricultural Research Service beginning in the late 1970's to determine the feasibility and practicability of re vegetating these spoiled lands. After mining, the residual spoil materials were generally acidic (pH 4.5), of sandy texture and lacking sufficient organic matter and nutrients to maintain plan growth. For two years, 0, 40, 80 and 16 mt/ha of feedlot manure and sewage sludge compost produced by the Beltsville Aerated Pile Method (Willson et al., 1980) were applied to spoil area plots and incorporated by rototilling. All treatments were replicated three times. Table 1 shows that after two cropping years with sweet corn and two repeated applications of each waste, both the soil organic master and gravimetric water content increased significantly. Additions of 160 metric tons per hectare of either compost or manure increased the organic master content from an initial lever of 0.8 percent to 4.2 percent and 8.5 percent, respectively. Gravimetric water content was similarly affected, increasing from 7 percent for the control soil, which received only the recommended rate of commercial inorganic fertilizer for sweet corn, to 15 percent and 32 percent for the 160 mt/ha rate of compost and manure, respectively. Initially the manure contained twice as much water (80 percent by weight) as did the compost (40 percent by weight), but the larger increase in the soil water content for the manure-treated plots versus the compost-treated plots was attributed to the fact that the manure had a higher water-holding capacity than did the compost.
These changes in soil physical properties are important, because the increased lever of organic master increased the soil's capacity to retain more plant nutrients, including water, resulting in increased crop growth and yield. During drought conditions, sweet corn grown on the manure-treated plots showed fewer signs of moisture stress (wilting and rolling of leaves) than did the compost-treated plots, again indicating the higher water-holding capacity of the manure over compost.
With sandy soils, high afternoon temperatures can dry out newly planted seeds and, therefore, reduce cotyledon emergence and seedling survival. Soil temperatures taken at a 4-inch depth on plots receiving either 160 mt/ha of compost or manure were consistently 5 to 10 degrees Fahrenheit longer than on the unamended control soils (Hornick, 1982a). The magnitude of temperature lowering was directly related to application rate of the organic material. Such a reduction in temperature may not be desirable in heavy soils in cool regions because of possible adverse effects on seed germination. There was considerably less erosion on those plots treated with manure or compost because of an improvement in soil physical properties, particularly soil structure . This was evidenced by visible gullying in the control plots.
Significant increases in corn stalk yields were noted for plots treated with compost and manure (Table 2). However, sweet corn ear yields were not always improved by additions of organic materials (Hornick, 1982a). Sahs and Lesoing (1985) also noted similar results when corn was grown with synthetic fertilizer versus feedlot manure. For corn grown on manure-treated plots they found significantly higher yields in a drought year, but significantly longer than normal yields in years of average temperature and adequate rainfall. Similar results and observations were also cited by the USDA study team on organic farming (USDA, 1980).
The most dramatic increase in crop yield occurred when green snap bush beans were grown on plots receiving 0, 40 and 80 mt/ha of sewage sludge compost (Table 2). The yields of green beans receiving 40 and 80 mt/ha of compost were 34 percent and 49 percent higher, respectively, than the yields on the control plots (Hornick, 1982a, 1982b). In these studies, as well as those discussed earlier for sweet corn, the productivity of the sand and graver spoils was restored. to a relatively high lever in two to three years.
An important concept that is often overlooked is that for most agricultural soils, degradative processes such as soil erosion, nutrient runoff losses, and organic master depletion are going on simultaneously with conservation practices such as residue management, crop rotations, and conservation tillage. The potential productivity of a particular soil then depends on the interaction of degradative processes and conservation practices (Figure 1; Parr and Meyer, 1987). On our best agricultural soils, e.g., gently-sloping, medium-textured, well-structured, and deep-profile, a high level of productivity can be maintained by a relatively few, but essential, conservation practices that can readily offset most degradative processes. However, on marginal soils, e.g., steeply-sloping, coarse-textured, poorly-structured, shallow-depth, and low fertility, soil conservation practices must be maximized to offset further degradation. The vital component in this dynamic equilibrium is organic matter.
Organic matter can be supplied to marginal soils from a number of sources including (1) on-farm wastes such as animal manures and crop residues, as well as green manure crops or (2) off-farm wastes such as sewage sludge and composted refuse. Off-farm wastes can be important sources of organic matter to farmers who do not have sufficient animals or cropping area to produce the amount of manure and crop residues needed to maintain soil productivity.
The plant nutrient contents of most organic materials are generally much lower than those supplied by commercially available chemical fertilizers. For example, the macronutrient content of crop residues can range from 0.7 to 2.5 percent for nitrogen, 0.07 to 0.2 percent for phosphorus and 0.9 to 1.9 percent for potassium; animal manures can range from 1.7 to 4 percent for nitrogen, 0.5 to 2.3 percent for phosphorus, and 1.5 to 2.9 percent for potassium (USDA, 1978); while sewage sludges range from 3 to 7 percent for nitrogen, 1 to 3 percent for phosphorus and 0.2 to 3 percent for potassium (Hornick et al., 1984).
Organic materials can differ widely in their properties and characteristics. Some materials, such as uncomposted animal manures, green manures, and sewage sludges, are subject to rapid microbial decomposition (i.e., mineralization) in soils and tend to release their plant nutrients rapidly. This is desirable for soils that are already at a relatively high lever of fertility and productivity. On the other hand, some other materials, such as cereal straws, wood bark, and composted animal manures and sewage sludges, would be more resistant to microbial attack and release their nutrients at a relatively slower rate. This higher lever of organic stability provides a distinct advantage in the initial reclamation of marginal soils because it imparts a beneficial and long-term residual improvement of soil physical properties. Unless the physical nature of these soils is improved first, the plant Use efficiency of nutrients, whether from organic amendments or chemical fertilizers, will be unacceptably low (Parr et al., 1986).
In many developing countries there is a scarcity of suitable organic materials for composting or direct recycling on agricultural lands because of competitive uses. Thus, treating the entire soil-root zone with an organic amendment is often not feasible because of limited amounts of material. Consequently, the farmer must seek colt-effective methods of utilizing these materials to enhance soil productivity and crop yields. It is noteworthy that the productivity of marginal lands can be improved substantially with relatively small amounts of materials. This can be accomplished through localized placement techniques such as side-dressing, banding, bed and furrow systems, vertical mulching (Parr, 1959) and slot-mulching (Saxton et al., 1981).
Composting or co-composting an organic waste results in a more stable product that is easier to store and use. Co-composting of wastes that vary widely in their carbon to nitrogen ratios or solids content may produce a higher quality product and allows recycling of some wastes that could not be utilized as the only source of organic master due to some inherent chemical or physical property (Parr et al., 1986). Possible wastes that could be co-composted are municipal refuse or garbage, pit latrine wastes, sewage sludges, animal manures and crop residues.
Fertilizer use efficiency can be very low in strictly monoculture systems or where organic recycling is not practiced. This inefficiency allows for the movement of nutrients through the soil profile and into the "round water. Due to heavy use of pesticides and nitrogen fertilizer, contamination of "round water is evident in our major agricultural areas (Hallberg, 1986; 1987). The possibility of Federal and State regulatory agencies enacting legislation to control these chemical inputs is also a major concern to the agricultural community.
Many farmers have already pulled back from their long-held goal of achieving maximum yields because of the costly production inputs and low market prices which have steadily decreased their profitability. The recycling of organic wastes can longer production inputs by decreasing the amount of chemical fertilizer required for crop growth with minimal adverse environmental impact. As this change in cultural practice occurs, the effect of various longer fertilizer levers on crop quality could become very important.
Although there are many factors that can affect crop quality, the cultivar and post-harvest handling are considered to have the greatest effect on the nutrient composition of crops (Harris, 1975; Kader, 1987). One is reminded, however, that cultivars are often selected for their response to production inputs, especially chemical fertilizers, and with maximum crop yields as the primary consideration. As farmers attempt to reduce their dependency on chemical fertilizers and pesticides, they will undoubtedly adopt various cultural practices to fulfill the plant nutrient requirement and to control weeds and insects. Thus, cultural practices could have considerable impact on crop quality both now and in the future.
There has been much speculation on the benefits of consuming crops grown conventionally with chemical fertilizers compared with those grown on soils amended with organic materials as the primary source of plant nutrients. For example, researchers have shown conflicting results with respect to the ascorbic acid (vitamin C) content of crops. Kansal et al. (1981) showed that as the lever of farmyard manure increased, the ascorbic acid content of spinach decreased. On the other hand, Schuphan (1974) reported higher ascorbic acid values for spinach grown on manure treated soil compared with chemical fertilizer. Similarly, Harwood (1984), using Pak Choi, and Ahrens et al. (1983), using spinach, also showed higher levers of ascorbic acid with increasing rates of composted manure versus chemical fertilizer.
The results of an NPK factorial experiment conducted to determine whether the results observed for ascorbic acid were due mainly to an organic amendment, or simply a fertilizer effect based on the nitrogen content of each amendment showed a significant decline in ascorbic acid content of kale as the rate of inorganic nitrogen increased (Hornick and Lloyd, 1986). These results indicate that increased nitrogen rates do tend to depress ascorbic acid levels. While this may be attributed in part to a dilution effect from increased yields, other biochemical interactions appear to be involved.
Most of the conflicting results that have been reported on crop response to chemical and organic fertilizers are most likely due to the fact that the organic materials were mineralizing at different rates, thus, providing different levers of inorganic nitrogen to the crop. More-over, it is possible that results were influenced by the predominance of a particular form of inorganic nitrogen i.e., nitrate (NO3 ) or ammonium (NH4 ), that was taken up by the plant. In a review of possible fertilizer effects on crop quality, Grunes and Allaway (1985) noted that the addition of boron to boron deficient soils increased the carotene (a vitamin A precursor) content in carrots and speculated that fertilizers that correct chlorosis in plants may increase the carotene content of the plant. This concept is especially interesting in light of the fact that after basic needs for protein and calories are satisfied, the lack of a suitable source of vitamin A is one of the biggest health problems in developing countries. Perhaps with the addition of boron or through some other management factor we may also increase the lever of carotene or some other nutrient that is presently deficient in native diets.
Recently we have become increasingly concerned about "round water quality and the increased levers of nitrates and pesticides that have been reported in our major agricultural areas (Hallberg, 1987). Some states have already developed strategies for reducing the recommended rates of fertilizer nitrogen to minimize the risk of "round water pollution. It would indeed be ironic if it was shown that longer rates of fertilizer N were related to crops of a higher nutritional value.
The concept of producing better quality crops, however, is a complex issue because bioavailability of crop nutrients depends on many factors. Bioavailability refers to the amount of a particular nutrient that is absorbed from a food after consumption that is utilized by an animal or human It is not the total amount of a nutrient in the food that is consumed. Measurements of nutrient bioavailability are difficult because of the many interactions that occur between minerals, vitamins and food components such as fiber. For example, iron bioavailability is determined by the iron status of the individual and the source of - iron being consumed. It is enhanced by the presence of ascorbic acid (vitamin , C) in the meal. In addition, iron bioavailability may decrease when a meal high in dietary fiber is consumed by an individual who does not normally consume a large amount of dietary fiber. Therefore, each of these nutrients, iron, ascorbic acid, and fiber is important in the diet for optimum health and normal bodily function, but the presence of one might enhance or impair the function of the other.
In addition to these types of interactions, little is known about the bioavailability of nutrients in crops grown under different management conditions. At the 1st International Symposium on Horticulture and Human Health held in 1987 in Virginia, it was very apparent how little the horticulturalists and nutritionists knew about the practices and needs of one another. It is clear that research on cultural practices and bioavailability of nutrients in foods and feeds consumed by humans and animals is needed, and should be conducted by multidisciplinary teams including soil scientists, agronomists, horticulturalists, crop breeders, physiologists, and nutritionists.
Marginal, infertile farm soils exist throughout the world. Many of the soils in developing countries are similar to those of sand and graver spoil areas in that they are low in organic master content and nutrients and occur in aria, harsh environments. These soils can be made productive if the soil degradation processes are offset by appropriate soil conservation/reclamation practices.
Many of the farms are very small and have limited available resources. Even so, composted animal manures and wastes can be utilized effectively by using selective placement techniques such as side-dressing of plants or seeding directly into a compost-treated zone. This type of localized placement will provide maximum benefit of the material as a soil conditioner and as a source of plant nutrients and ultimate utilization of the limited amount of available resources.
After restoration of marginal soils, it is very important that small amounts of organic materials are available each year to maintain soil productivity. As a rule, wherever people live there is a source of waste materials that could be utilized advantageously as organic amendments for agricultural soils. Even people in remote areas, on small farms, on farms without animals, and in the aria regions of developing countries can utilize the idea of cg-composting to recycle their human wastes and refuse. Because composting is a thermophilic process, it inactivates certain pathogens and a reduction in the incidence of parasitic infestation and enteric diseases may also be accomplished. In addition, composting provides a stabilized form of organic master that has a longer residence time in soil compared with raw wastes which can decompose very rapidly, especially under the extreme climatic conditions of the aria regions.
Regular additions of organic materials to soils can reduce erosion and nutrient runoff losses, improve soil structure, increase water-holding capacity, longer soil temperatures, provide a source of plant nutrients, and increase the crop use efficiency of chemical fertilizer. Further research is needed to characterize the interaction of organic amendments, soil type, climate, and the crop to improve our estimates and predictions of soil tilth, fertility, and productivity. In so doing, we can achieve a practical and workable balance between degradation processes and conservation practices to maintain a productive soil with minimal environmental pollution.
In our efforts to increase a farmer's net returns, we have emphasized the use of heavy and costly off-farm production inputs such as fertilizers and pesticides to produce maximum yields of unflawed fruits and vegetables for American consumers. In some cases, "round water pollution has resulted and in others, the heavy production inputs are no longer profitable. Initial research indicates that longer nitrogen rates can produce higher quality crops with respect to ascorbic acid content. Because of environmental concerns, we may need to change our soil management practices, even though longer yields may result.
Further research by multidisciplinary groups could elucidate the effect of fertilizer rates and sources on crop quality and resulting nutrient bioavailability, and the feasibility of utilizing this new information for production of crops of greater nutritional value in both developed and developing countries. In addition, such information would be particularly attractive to farmers producing fruits and vegetables for urban consumers, who would be willing to pay a premium for produce grown with limited chemical input. For low input farmers with limited capital, this may be a particularly viable option.
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Citation : Hornick Sharon B., Parr James F., 1987, "Restoring the productivity of marginal soils with organic amendments", Vol. 2, No. 2, 1987, pp. 64-68
Copyright © 1987 Reprinted with permission.
Reprinted with permission.
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