The performance of a subsurface irrigation system in a clay soil was investigated under field conditions from 1989 to 1991. It was found that subsurface irrigation could be practised successfully in some clay soils of Quebec. The 10 m drain spacing was found to be better than the 20 m drain spacing in terms of keeping a uniform water table between the drains. The water table distribution between the drains was found to be a factor of the applied hydraulic head. The relationship between the applied hydraulic head and the midspan water table elevation could not be determined due to unfavourable weather conditions during the study period. The soil moisture content was found to follow the same behavior as the water table elevation, however, the relationship between these two parameters could not be properly established. It was also found that under the same applied hydraulic head, the drain spacing did not affect the soil moisture distribution. Subsurface irrigated plots were found to make better use of rain water than drained only plots since they did not permit the formation of well-defined pathways (macropores) allowing rainfall to move below the root zone without wetting it. It was also found that subsurface irrigation did not alter the soil structure appreciably and that autumn drainability was not affected in 1990 and 1991.

Three systems for filtering polluted river water for use in subsurface irrigation have been designed, operated and evaluated. One system consisted of filtering the water through filter basins covered with grass. The second system used geotextiles in filter basins. The third system consisted of flooding a section of a field. In this system, the water was filtered as it moved through the soil towards the subsurface drainage/irrigation drain pipes. / It was found that grass filter basins are very efficient in removing sediment from river water. Grass filter basins having drain pipes placed in trenches 30 cm wide backfilled with sand gave the best results. More than 90% of sediments were removed from the river water. From the outflow measurements, it was found that less than 0.2% of the field to be irrigated needs to be devoted to the filtration system. / Important filter design parameters, namely filtration rates per unit area of filter basin and per unit length of filter trench and drain pipe, were determined. / Due to the fast clogging of the geotextile, filtration of river water through basins covered with geotextile was found to be impractical and expensive, as compared to filtration using water tolerant grasses as a basin cover. / Flooding a section of the crop land combined with controlled drainage was found to be an efficient way of irrigating maize crop. The yields obtained with this system were comparable with those obtained with conventional subsurface irrigation. Flood irrigation combined with controlled drainage would be particularly commendable on relatively flat fields which have subsurface drains.

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A cultura da soja (Glycine max (L.) Merrill) é uma das principais “commodities” do agronegócio mundial. O Brasil tem se configurado neste cenário como um dos maiores produtores desta oleaginosa, destacando-se com obtenções de produtividades elevadas. A várzea irrigada é uma área de extrema importância econômica e social para o estado do Tocantins, gerando renda e empregos durante todo o ano. A fertilização foliar é utilizada com a finalidade de suplementar os níveis de nutrientes na planta, para que a mesma consiga realizar normalmente todos os seus processos metabólicos. O boro é um elemento essencial em todas as fases do ciclo da cultura da soja, participando de vários processos fisiológicos. Objetivou-se com este trabalho verificar a influência da adubação boratada foliar, aplicado em três estádios fenológicos da cultura da soja no período reprodutivo, com crescentes doses de fontes de boro, sobre os componentes de rendimento, produtividade e germinação das sementes de soja. O trabalho foi conduzido em condições de várzea irrigada, no município de Formoso do Araguaia - TO, na entressafra do ano agrícola de 2016. O delineamento experimental adotado foi o de blocos casualizados em esquema fatorial triplo 2x3x5 (produtos x épocas x doses) com quatro repetições. As características avaliadas foram: número de vagens por planta (NVP), número de sementes por planta (NSP), massa de cem sementes (MCS), produtividade (PROD), porcentagem de germinação (G%) e índice de velocidade de emergência (IVE). Verificou-se que os tratamentos em que houve aplicação da fonte de boro, composto por ácido bórico e octaborato, obtiveram as melhores respostas para todas as características avaliadas. Nas condições edafoclimáticas de entressafra na várzea irrigada, aplicações de B em R2 e R4 obtiveram a melhor resposta. Maiores médias foram obtidas com a aplicação de 1,5 a 2 kg.ha-1 de boro. / Soybean cultivation (Glycine max (L.) Merrill) is one of the main commodities of world agribusiness. Brazil has been configured in this scenario as one of the largest producers of this oilseed, standing out with high yields. The irrigated várzea is an area of extreme economic and social importance for the southern state of Tocantins, generating income and jobs throughout the year. Foliar fertilization is used to supplement or complement nutrient levels in the plant, so that it can perform all its metabolic processes normally. Boron is an essential element in all phases of the soybean cycle, participating in several physiological processes. The objective of this work was to verify the influence of foliar fertilization, applied at three stages of soybean cultivation in the reproductive period, with increasing doses of boron sources, about the components of yield, yield and germination of soybean seeds. The work was carried out under lowland conditions, in the municipality of Formoso do Araguaia - TO, between the harvest of the agricultural year of 2016. The experimental design was a randomized complete block design in 2x3x5 triple factorial (products x seasons x doses) with four replications. The characteristics evaluated were: number of pods per plant (NVP), number of seeds per plant (NSP), mass hundred seeds (MCS), productivity (PROD), Percentage of germination (G%) and emergence speed index (EVI). It was verified that the treatments in which there was application of the source of boron, composed of boric acid and octaborate, obtained the best answers for all characteristics evaluated. In the soil and climatic conditions of irrigated lowland harvest, applications of B in R2 and R4 obtained the best response. Higher averages were obtained with the application of 1,5 to 2 kg. ha-1 of boron.

The purposes of this thesis are to examine experimental results obtained with subsurface irrigation of maize in 1988, and to provide preliminary plans and an economic analysis for the subsurface irrigation of maize in Richelieu County, Quebec. A mean increase in maize yield of 3.7 % was observed in 1988 on experimental plots with subsurface irrigation at the Charbonneau farm. However, a review of results obtained at the same experimental site from 1982 to 1988 indicated that the mean increase in maize yield with subsurface irrigation was 29 %. / Plans for two possible water supply systems designed to provide 180 mm a year of irrigation water for the subsurface irrigation of 1,250 ha in Richelieu County were considered. An economic analysis indicates that subsurface irrigation using groundwater has the greatest net benefits with an internal rate of return of 22.92 % and benefit to cost ratios of 1.90, 1.72 and 1.56 for discount rates of 8 %, 10 % and 12 % respectively. However, much of the groundwater in this region is saline and its use for irrigation may need to be restricted. Subsurface Irrigation using surface water from the Yamaska River was also profitable with an internal rate of return of 17.31 % and benefit to cost ratios of 1.66, 1.46 and 1.30 for the same discount rates.

This thesis tested the hypothesis that nitrogen use efficiency of subirrigated potted chrysanthemum (Chrysanthemum morifolium Ramat.) can be improved by managing the NO3- status of the plant. Replacement of NO3- with water one week prior to flower development was the most effective method of reducing tissue NO3- content and improving the nitrogen usage index, as compared to various combinations of NO3- and Cl-. Shoot or flower dry mass and N content were unaffected and the medium electrical conductivity was reduced. Supplying N in the NH4+ form in combination with NO3- did not affect nitrogen use indices. Reducing N supply improved various indices of nitrogen use efficiency, with a slight loss of quality. Elimination of NO3- prior to flower development and reduction in N supplied are effective strategies for improving nitrogen use efficiency in subirrigated potted chrysanthemums without sacrificing quality. / Cecil Delworth Foundation