A erosão hídrica é a principal causa de degradação do solo em ambientes tropicais e subtropicais úmidos e a perda da camada superficial do solo é o maior desafio para sustentabilidade da agricultura no mundo. Ela afeta a qualidade e o volume dos corpos d\'água e diminuí a qualidade dos solos. Apesar disso, o mercado não é capaz de corrigir estes problemas em razão da sua característica de bens públicos (não-exclusividade e não-rivalidade). Assim, o controle da erosão agrícola gera um serviço benéfico para toda a sociedade, mas os seus custos são exclusivamente dos agricultores. Pagamentos por Serviços Ambientais - PSA são mecanismos de compensações em que os beneficiados pelos serviços pagam os seus provedores. PSA são mecanismos promissores para o financiamento da proteção ambiental e podem complementar as atuais regulações. Entretanto, a literatura atual ainda é limitada em termos de quantificação dos serviços gerados, da sua demanda e sua viabilidade econômica. Este estudo analisa a viabilidade econômica de esquemas de PSA para o controle da poluição hídrica advinda da agricultura no Brasil. O objetivo específico do estudo é estimar ofertas de Serviços Ambientais - SA de conservação do solo. As ofertas de SA foram estimadas para áreas de cana-de-açúcar (na Bacia do Rio Corumbataí) e horticultura (na Sub-Bacia Cabeceiras do Tietê) utilizando uma metodologia de dados mínimos. As ofertas foram estimadas para diferentes práticas agrícolas, permitindo a comparação da eficiência das diferentes práticas na produção do SA. No caso da cana, a implantação e manutenção de florestas nas APPs mostrou-se a prática mais eficiente. Gastos de R$150,00/ha/ano com esta prática conservam cerca de 140.000 Mg de solo, enquanto o mesmo gasto aplicado na prática de não utilização das APPs conserva 70.000 Mg. Os resultados indicam que existe potencial para aplicação do modelo como forma de integrar as políticas públicas agrícolas com as ambientais. O estudo mostra que a adoção de práticas com maior produção de SA depende de incentivos. Nas condições atuais elas não são atrativas na medida em que geram menores retornos aos agricultores. Os incentivos podem ser através de subsídios das práticas adequadas, estímulo à demanda de produtos ambientalmente amigáveis ou pagamentos diretos pelos SA produzidos. / Water erosion is the main cause of soil degradation in tropical and sub-tropical environments and top soil loss is the biggest challenge for sustainable agriculture in the world. It affects water quality and quantity, and decreases soil quality. Despite this, the market is not able to solve these problems because of their public good characteristics (non-rivalness and non-excludability). Agricultural pollution control by farmers is a service society free rides because only farmers pay its costs. Payments for Environmental Services - PES schemes are flexible mechanisms in which providers of these services get paid by their users. PES schemes are considered to be promising mechanisms for financing environmental protection and restoration as well as for complementing and enforcing regulations. However, most of the on-going schemes don\'t use studies to quantify the services produced, to analyze the demand for them, or to check the schemes\' economic viability. This study analyses the economic viability of PES schemes in order to control the agricultural pollution of water resources in Brazil. The specific objective is to estimate the Environmental Services - ES of conservation soil supplies. These supplies were estimated for sugar cane (Corumbataí Watershed) and horticulture areas (Tietê Cabeceiras Subwatershed), using a minimum-data model. The supplies were calculated for different practices, so it is possible to compare the different practices\' efficiency to produce ES. For the sugar cane area it is more efficient to plant trees in the riparian buffer zones. Paying 150 reais per ha per year produces 140.000 Mg of conserved soil through tree planting, while with the same amount, the exclusion of the riparian zones from cultivation produces approximately 70.000 Mg. The results show this model can be applied as a way of integrating agricultural and environmental public policies. It was concluded that incentives are necessary to make the farmers adopt the practices that produce ES, because they are not economically feasible under current market conditions. The incentives could be either subsidies for these practices, fostering the demand for environmental friendly products, or direct payments for the ES produced.

Nitrate pollution of ground and surface water can stem from the mismanagement and over-application of both inorganic and organic fertilizers. This results in the occurrence of non-point externalities, which infringe on the overall level of social welfare. Market based environmental policies, known as economic instruments, can be developed to curb the level of this non-point externality. Such policies directly affect the management decisions of agricultural producers, providing them with incentives to change their management practices. The overall objective of this study is to analyze an array of economic instruments which could feasibly curb water quality degradation resulting from the over-application and misuse of manure and inorganic fertilizers in agricultural production. The economic instruments are compared in terms of their relative effectiveness in decreasing nitrate water pollution and social damage. This thesis develops a three agent manure market model, wherein a vegetable producer and composter can purchase manure from a dairy producer or inorganic fertilizer from an exogenous fertilizer market. The production activities of each agent are modelled using real world production data. A non-linear programming technique is used. The imposition of a percentage manure tax was found to alter the vegetable producer’s derived demand for manure, and resulted in less manure being exchanged between the dairy and vegetable producers. The provisions of a percentage manure composting subsidy increased the quantity of manure demanded by the composter and decreased the amount of manure consumed by the vegetable and dairy producers. The imposition of an inorganic fertilizer tax increased the demands for manure fertilizer, as did the manure application limit. The effects on social damage are dependent on the leaching and surface run-off susceptibilities of each operation’s associated land base. The composting subsidy appeared to be the most efficient instrument for decreasing the overall level of social damage, when qualitatively analyzed. It induced decreases in the demand for manure by both the dairy and vegetable producers, while increasing the demand for manure of the composter. This results in an overall social benefit. There must be, however, financial justification for the implementation of such an instrument. / Land and Food Systems, Faculty of / Graduate

Nonpoint source pollution from cropland has been identified as the primary source of nitrogen and sediment, and a significant source of phosphorus in the Chesapeake Bay. These pollutants, whether from point or nonpoint sources, have been found to be the primary cause of declining water quality in the Bay. Numerous studies have indicated that, for many watersheds, a few critical areas are responsible for a disproportionate amount of the nutrient and sediment yield. Consequently, if pollution control activities are concentrated in these critical areas, then a far greater improvement in downstream water quality can be expected with limited funds. In this research a phosphorus transport model is incorporated into ANSWERS, a distributed parameter watershed model. The version of ANSWERS used has an extended sediment transport model which is capable of simulating the transport of individual particle classes in a sediment mixture during the overland flow process. The phosphorus model uses a nonequilibrium desorption equation to account for the desorption of phosphorus from the soil surface into surface runoff. The sediment-bound phosphorus is modeled as a function of the specific surface area of the soil and transported sediment. The equilibrium between the soluble and sediment-bound phosphorus is modeled using a Langmuir isotherm. The extended ANSWERS model was verified using water quality data collected from rainfall simulator plot studies conducted on the Prices Fork Research Farm in Blacksburg, Virginia. The plots consisted of four 5.5 m wide by 18.3 m long strips with average slopes ranging from 6.2 to 11 percent. Two of the plots were tilled conventionally, and the remaining two were no-till. Simulated rainfall at an intensity of 5 cm/h was applied to the plots and runoff samples were analysed for sediment and phosphorus. The model was then verified by comparing the simulated responce with the observed data. The results of the verification runs ranged from satisfactory to excellent. Also developed is a technique for selecting a design storm for ANSWERS. The technique creates an n-year recurrence interval storm with a duration equal to the time of concentration of the watershed. The intensity pattern is simulated on a ten-minute interval using a first-order Markov model with a lognormal distribution. Using a two-year recurrence interval design storm, the use of the model is demonstrated for evaluating the application of conservation practices to critical areas on a Virginia watershed. Application of BMP's to critical areas is shown to be substantially more cost effective in terms of pollutant reduction than nonselective placement of BMP's if cost sharing funds are involved. / M.S.

Although agricultural pesticide use is suspected of being a major contributor to the risk of toxic contamination of the Chesapeake Bay, little information concerning the nature and extent of that risk is available. Such information is essential, however, for setting pesticide risk management priorities and for designing policies to reduce the risk of toxic pollution from agricultural sources. To help meet the information needs of Bay region water quality Management, a model of agricultural pesticide risk is developed and used to assess pesticide risk in Virginia’s Chesapeake Bay Region. The information generated by the model includes: an inventory of which chemicals are used; where they are used; estimates of aggregate chemical use for counties and crops; and an evaluation of the potential adverse environmental effects of that use. This information is provided for both current (1990) and future (2000) pesticide risk. An econometric model of land use in the Bay region is used to predict acreage in various crops to which pesticides will be applied in 1990 and 2000. Next, acreage estimates are combined with pesticide application rates to yield estimates of aggregate use of each pesticide. Finally, environmentally relevant characteristics of the pesticides (toxicity, persistence, mobility, etc.) are used to evaluate the potential environmental risk associated with that use. The policy implications of this modeling are then explored. Particular attention is paid to the potential for targeting of pesticide risk management programs at chemicals, sub-regions, or production systems (i.e. crops) that represent the greatest risk of toxic contamination of the Chesapeake Bay. Results indicate that while urbanization in the Chesapeake Bay region will reduce the amount of land devoted to crop production, the reduction in the acreage to which pesticides may be applied will not greatly reduce pesticide risk in the near future. The risk evaluation effort reveals that pesticide risk is highly concentrated in small subsets of the crops grown in the Bay region, of the pesticides used on those crops, and of the counties located in the region. / Master of Science

Research was conducted in soils of the Chesapeake Bay area primarily to determine the combined effects of tillage practice and N fertilizer application rates on N leaching and denitrification losses from corn fields. Three well known models - the NTRM, CERES- Maize, and VT-MAIZE - were also tested to determine their predictive ability of N distribution in soil and crop, the various components of the N cycle, and corn yields. To accomplish the above objectives, two field sites were located (in 1986) for a 3 year study on agronomically important and representative soils that are used for corn production in the Chesapeake Bay drainage basin. The main plot treatment was tillage and consisted of no-till and conventional-till. The subplot treatments were N application rates which consisted of 6 levels with 4 inorganic and 2 organic (sewage sludge) N fertilizers. Denitrification experiments were also conducted on the Groseclose silt loam soil to estimate and compare N loss through denitrification from both till and no-till practices. C₂H₂ was used to inhibit N₂ production and N₂O was collected in closed chambers located on the soil surface. Tensiometers and neutron moisture meter access tubes were also installed to monitor soil moisture and energy levels. Nitrogen leaching losses were determined by applying the principle of N mass balance. Denitrification N loss during the corn growing season was less than 2% of the applied N fertilizer. The N losses from the two tillage systems were not significant at p > 0.10. If Fick’s law is to be applied for predicting N loss from the soil subsequent to C₂H₂ application, sampling must occur after a minimum preset critical time. In the Groseclose soil, there was an increase in both total yield and total N uptake when sewage sludge was applied compared to the split and preplant inorganic fertilizers applied at the same rate. There was no difference in yield or N uptake due to applying N as either preplant or a split application. Where no-till management was used, there was an increase in both yield and N uptake as compared with conventional tillage. In the Suffolk soil, tillage management did not influence yield or N uptake where time and source of N application were studied. The relationship between yield and N application rates for both soil types could be described with quadratic equations. The total N recovery could also be described with quadratic equations. However, these relationships do not hold every year for every season or tillage management practice. The no-till plots retained higher moisture content than conventional tillage plots in the upper 0-100 cm depth. Below 100 cm depth, however, no-till retained less than conventional till. The gain and loss of N in soil was dependent on the tillage type and seasons of the year. During the growing season, generally the conventional tillage gained more N than the no-till. During winter, however, the N losses due to leaching were proportional to the amount of N retained at the end of the growing season. Thus, conventional tillage lost more N by leaching during the winter months. Mineralization of N was higher in conventional till, while denitrification was higher in no-till. Split application has shown less N loss due to leaching than the preplant. Mineralization, denitrification, and leaching took place from both the upper and lower zones of the soil profile. The model performances varied from year to year and from one tillage practice to another. Since they were generally written for average (normal) soil and climatic conditions, they did not make satisfactory predictions under the severe moisture conditions experienced during this study. Thus, they require a great deal of readjustment. Considering all aspects, however, the NTRM is the best model. The unmodified VT-MAIZE is the next best. / Ph. D.