Freshwater is a finite resource that is rapidly becoming more scrutinized in agricultural consumption. Specialty crop producers, especially ornamental crop producers, must continually improve production sustainability, with regards to water resource management, in order to continue to stay economically viable. Soilless substrates were initially developed to have increased porosity and relatively low water holding capacity to ensure container crops would not remain overhydrated after irrigations or rain events. As a result, substrates were selected that are now considered to be in efficient in regards to water resource management. Therefore, to provide growers with additional means to improve production sustainability, soilless substrate hydrology needs be innovated to provide increased water availability while continuing to provide ample air filled porosity to ensure productive and efficient water interactions. Historically, soilless substrates have been characterized using "static" physical properties (i.e. maximum water holding capacity and minimum air-filled porosity). The research herein involves integrating dynamic soilless substrate hydraulic properties to understand how substrate hydrology can be manipulated to design sustainable substrates. This task involved adapting new technologies to analyze hydrological properties of peat and pine bark substrates by employing evaporative moisture characteristic measurements, which were originally designed for mineral soils, for soilless substrate analyses. Utilizing these evaporative measurements provide more accurate measures of substrate water potentials between -10 and -800 hPa than traditional pressure plate measurements. Soilless substrates were engineered, utilizing only three common substrate components [stabilized pine bark (Pinus taedea L.), Sphagnum peatmoss, and coconut coir fiber], via particle fractionation and fibrous additions. The engineering process yielded substrates with increased unsaturated hydraulic conductivity, pore connectivity, and more uniform pore size distributions. These substrates were tested in a greenhouse with irrigation systems designed to hold substrates at (-100 to -300 hPa) or approaching (-50 to -100 hPa) water potentials associated with drought stress. Substrate-water dynamics were monitored, as were plant morphology and drought stress indicators. It was determined that increased substrate unsaturated hydraulic conductivity within the production water potentials, allowed for increased crop growth, reduction in drought stress indicators, while producing marketable plants. Furthermore, individual plants were produced using as low as 5.3 L per plant. Increased production range substrate hydraulic conductivity was able to maintain necessary levels of air-filled porosity due to reduced irrigation volumes, while providing water for plants when needed. The substrates were able to conduct water from throughout the container volume to the plant roots for uptake when roots reduced substrate water potential. Furthermore, increased substrate hydraulic conductivity allowed plants within the substrate to continue absorbing water at much lower water potentials than those in unaltered (control) pine bark. Finally, HYDRUS models were utilized to simulate water flux through containerized substrates. These models allowed for better understanding of how individual hydraulic properties influence substrate water flux, and provided insight towards proportions of inaccessible pores, which do not maintain sufficient levels of available water. With the models, researchers will be able to simulate new substrates, and utilize model predictions to provide insight toward new substrates prior to implementing production tests. It has been determined, that increasing substrate hydraulic conductivity, which can be done with just commonly used components, water requirements for production can be reduced, to produce crops with minimal wasted water resources. Concluding, that re-engineering substrate hydrology can ameliorate production sustainability and decrease environmental impact. / Ph. D.

Foi desenvolvido um estudo com o objetivo de avaliar o efeito de diferentes sistemas de pastejo e manejo da pastagem sobre o Intervalo Hídrico Ótimo (IHO). A amostragem foi realizada na área experimental do Centro Nacional de Pesquisa de Gado de Corte, unidade da Empresa Brasileira de Pesquisa Agropecuária (Embrapa Gado de Corte). O solo estudado foi um Latossolo Vermelho Distrófico argiloso. Foram avaliados quatro piquetes, sendo dois no sistema de pastejo contínuo e dois no sistema de pastejo rotacionado, e uma área de cerrado (CN). No sistema de pastejo contínuo, implementado com a espécie Brachiaria decumbens cv. Basilisk, foram retiradas 30 amostras por piquete, obedecendo a uma malha regular de 10 x 10 m, sendo que um dos piquetes não havia recebido adubação de manutenção (Cs) enquanto o outro havia recebido adubação bianual de manutenção (Cc). No sistema de pastejo rotacionado, implementado com a espécie Panicum maximum cv. Tanzânia, foram retiradas 60 amostras por piquete, sendo 30 na posição espacial touceira (t) e 30 na posição espacial entre touceiras (e), obedecendo a uma malha regular de 5 x 10 m. O diferencial entre os piquetes no sistema de pastejo rotacionado foi o resíduo pós pastejo. Em um dos piquetes o resíduo era de 2,0-2,5 Mg matéria seca total (MST) ha -1 (R1), enquanto no outro era de 3,0-3,5 Mg MST ha -1 (R2). No CN foram retiradas 30 amostras obedecendo a uma malha regular de 10 x 10 m. As amostras foram submetidas a um gradiente de tensão de água sendo posteriormente utilizadas nas determinações da densidade do solo (Ds), resistência à penetração de raízes (RP) e umidade volumétrica (qV). Em seguida, os resultados foram utilizados para o ajuste por regressão das curvas de resistência à penetração (CRP) e retenção de água do solo (CRA). Através da CRP e da CRA foi possível quantificar o IHO e a densidade crítica (Dsc), definida como o valor de Ds onde o IHO é igual a zero. O CN apresentou a melhor condição física do solo para o crescimento de plantas, sendo o IHO igual à água disponível. No sistema de pastejo contínuo estudado, a realização de adubação de manutenção não influenciou o IHO, o que foi atribuído às taxas de lotação animal equivalentes nos dois piquetes. O sistema de pastejo rotacionado apresentou as piores condições físicas do solo para o crescimento vegetal, avaliadas pelo critério do IHO. Os maiores valores de Ds e menor IHO foram observados no R1e, o que foi atribuído às taxas de lotação elevadas aplicadas neste piquete. A posição espacial de amostragem (touceira e entre touceiras) não exerceu influência sobre o IHO no R2 enquanto no R1 o IHO foi muito menor entre as touceiras, o que pode ser atribuído ao hábito de crescimento cespitoso da espécie Panicum maximum cv. Tanzânia, deixando parte do solo descoberto e, portanto, sujeito à ação direta do pisoteio dos animais. / A study was developed for evaluating the effect of different grazing systems and pasture management strategies on the Least Limiting Water Range (LLWR). The experimental site was located at the National Beef Cattle Research Center of Brazilian Agricultural Research Corporation (Embrapa Beef Cattle). The soil studied was a clay Oxisol (Typic Acrudox). Five sampling sites were selected: two under continuous grazing system, two under intensive short-duration grazing system, and one under native vegetation "cerrado" (CN). Thirty soil cores were collected in each site under continuous grazing system, established with Brachiaria decumbens cv. Basilisk species. Sampling at continuous grazing sites was performed in a 10 x 10 m regular grid. One of the continuos grazing sites had received biannual fertilization (Cc) while the other was not fertilized (Cs). Sixty soil cores were collected in each site under intensive short-duration grazing system, established with Panicum maximum cv. Tanzânia species, with thirty cores in the spatial position under the plants (up) and thirty cores in the spatial position between the plants (bp). Sampling at intensive short-duration grazing sites was performed in a 5 x 10 m regular grid. The difference between sites in intensive short-duration grazing system was the post-graze stubble. The post-graze stubble was 2,0-2,5 Mg total dry matter (TDM) ha -1 in one site (R1), and 3,0-3,5 Mg TDM ha -1 in the other (R2). Thirty soil cores were collected in CN, in a 10 x 10 m regular grid. The cores were subjected to a soil water suction gradient, and then used for soil bulk density (Db), soil penetration resistance (PR) and volumetric water content (qV) determinations. The data was used for developing soil resistance to penetration curve (SRP) and soil water retention curve (SWR) models doing regression fitting procedures. From SRP and SWR was possible to quantify the LLWR and the critical bulk density value (Dbc) identified as the Db value where LLWR is null. The CN site had the best soil physical condition for plant growth with the LLWR equal to available water. The fertilization did not influenced the LLWR in the continuos grazing system under evaluation, as a consequence of the similar stocking rates at both sites. The intensive short-duration grazing system had the worst soil physical condition for plant growth, as evaluated by the LLWR. The highest Db values and the lowest LLWR were found in R1bp, which may be a consequence of the high stocking rates observed at this site. The spatial sampling position (under the plants and between the plants) did not influenced the LLWR in the R2 site while in R1 the LLWR was much lower between plants. This result is a consequence of the cespitose growth habit of the Panicum maximum cv. Tanzânia species, which leaves part of the soil surface uncovered and subjected to a direct action of animal trampling.

Foi desenvolvido um estudo com o objetivo de avaliar o efeito de diferentes sistemas de pastejo e manejo da pastagem sobre o Intervalo Hídrico Ótimo (IHO). A amostragem foi realizada na área experimental do Centro Nacional de Pesquisa de Gado de Corte, unidade da Empresa Brasileira de Pesquisa Agropecuária (Embrapa Gado de Corte). O solo estudado foi um Latossolo Vermelho Distrófico argiloso. Foram avaliados quatro piquetes, sendo dois no sistema de pastejo contínuo e dois no sistema de pastejo rotacionado, e uma área de cerrado (CN). No sistema de pastejo contínuo, implementado com a espécie Brachiaria decumbens cv. Basilisk, foram retiradas 30 amostras por piquete, obedecendo a uma malha regular de 10 x 10 m, sendo que um dos piquetes não havia recebido adubação de manutenção (Cs) enquanto o outro havia recebido adubação bianual de manutenção (Cc). No sistema de pastejo rotacionado, implementado com a espécie Panicum maximum cv. Tanzânia, foram retiradas 60 amostras por piquete, sendo 30 na posição espacial touceira (t) e 30 na posição espacial entre touceiras (e), obedecendo a uma malha regular de 5 x 10 m. O diferencial entre os piquetes no sistema de pastejo rotacionado foi o resíduo pós pastejo. Em um dos piquetes o resíduo era de 2,0-2,5 Mg matéria seca total (MST) ha -1 (R1), enquanto no outro era de 3,0-3,5 Mg MST ha -1 (R2). No CN foram retiradas 30 amostras obedecendo a uma malha regular de 10 x 10 m. As amostras foram submetidas a um gradiente de tensão de água sendo posteriormente utilizadas nas determinações da densidade do solo (Ds), resistência à penetração de raízes (RP) e umidade volumétrica (qV). Em seguida, os resultados foram utilizados para o ajuste por regressão das curvas de resistência à penetração (CRP) e retenção de água do solo (CRA). Através da CRP e da CRA foi possível quantificar o IHO e a densidade crítica (Dsc), definida como o valor de Ds onde o IHO é igual a zero. O CN apresentou a melhor condição física do solo para o crescimento de plantas, sendo o IHO igual à água disponível. No sistema de pastejo contínuo estudado, a realização de adubação de manutenção não influenciou o IHO, o que foi atribuído às taxas de lotação animal equivalentes nos dois piquetes. O sistema de pastejo rotacionado apresentou as piores condições físicas do solo para o crescimento vegetal, avaliadas pelo critério do IHO. Os maiores valores de Ds e menor IHO foram observados no R1e, o que foi atribuído às taxas de lotação elevadas aplicadas neste piquete. A posição espacial de amostragem (touceira e entre touceiras) não exerceu influência sobre o IHO no R2 enquanto no R1 o IHO foi muito menor entre as touceiras, o que pode ser atribuído ao hábito de crescimento cespitoso da espécie Panicum maximum cv. Tanzânia, deixando parte do solo descoberto e, portanto, sujeito à ação direta do pisoteio dos animais. / A study was developed for evaluating the effect of different grazing systems and pasture management strategies on the Least Limiting Water Range (LLWR). The experimental site was located at the National Beef Cattle Research Center of Brazilian Agricultural Research Corporation (Embrapa Beef Cattle). The soil studied was a clay Oxisol (Typic Acrudox). Five sampling sites were selected: two under continuous grazing system, two under intensive short-duration grazing system, and one under native vegetation "cerrado" (CN). Thirty soil cores were collected in each site under continuous grazing system, established with Brachiaria decumbens cv. Basilisk species. Sampling at continuous grazing sites was performed in a 10 x 10 m regular grid. One of the continuos grazing sites had received biannual fertilization (Cc) while the other was not fertilized (Cs). Sixty soil cores were collected in each site under intensive short-duration grazing system, established with Panicum maximum cv. Tanzânia species, with thirty cores in the spatial position under the plants (up) and thirty cores in the spatial position between the plants (bp). Sampling at intensive short-duration grazing sites was performed in a 5 x 10 m regular grid. The difference between sites in intensive short-duration grazing system was the post-graze stubble. The post-graze stubble was 2,0-2,5 Mg total dry matter (TDM) ha -1 in one site (R1), and 3,0-3,5 Mg TDM ha -1 in the other (R2). Thirty soil cores were collected in CN, in a 10 x 10 m regular grid. The cores were subjected to a soil water suction gradient, and then used for soil bulk density (Db), soil penetration resistance (PR) and volumetric water content (qV) determinations. The data was used for developing soil resistance to penetration curve (SRP) and soil water retention curve (SWR) models doing regression fitting procedures. From SRP and SWR was possible to quantify the LLWR and the critical bulk density value (Dbc) identified as the Db value where LLWR is null. The CN site had the best soil physical condition for plant growth with the LLWR equal to available water. The fertilization did not influenced the LLWR in the continuos grazing system under evaluation, as a consequence of the similar stocking rates at both sites. The intensive short-duration grazing system had the worst soil physical condition for plant growth, as evaluated by the LLWR. The highest Db values and the lowest LLWR were found in R1bp, which may be a consequence of the high stocking rates observed at this site. The spatial sampling position (under the plants and between the plants) did not influenced the LLWR in the R2 site while in R1 the LLWR was much lower between plants. This result is a consequence of the cespitose growth habit of the Panicum maximum cv. Tanzânia species, which leaves part of the soil surface uncovered and subjected to a direct action of animal trampling.