Abstract. Declining soil-saturated hydraulic conductivity (Ks) as a result of saline and sodic irrigation water is a major cause of soil degradation. While it is understood that the mechanisms that lead to degradation can cause irreversible changes in Ks, existing models do not account for hysteresis between the degradation and rehabilitation processes. We develop the first model for the effect of saline and sodic water on Ks that explicitly includes hysteresis. As such, the idea that a soil's history of degradation and rehabilitation determines its future Ks lies at the center of this model. By means of a “weight” function, the model accounts for soil-specific differences, such as clay content. The weight function also determines the form of the hysteresis curves, which are not restricted to a single shape, as in some existing models for irreversible soil processes. The concept of the weight function is used to develop a reversibility index, which allows for the quantitative comparison of different soils and their susceptibility to irreversible degradation. We discuss the experimental setup required to find a soil's weight function and show how the weight function determines the degree to which Ks is reversible for a given soil. We demonstrate the feasibility of this procedure by presenting experimental results showcasing the presence of hysteresis in soil Ks and using these results to calculate a weight function. Past experiments and models on the decline of Ks due to salinity and sodicity focus on degradation alone, ignoring any characterization of the degree to which declines in Ks are reversible. Our model and experimental results emphasize the need to measure “reversal curves”, which are obtained from rehabilitation measurements following mild declines in Ks. The developed model has the potential to significantly improve our ability to assess the risk of soil degradation by allowing for the consideration of how the accumulation of small degradation events can cause significant land degradation.
The need to improve the knowledge of vegetative propagation and create a paradigm shift in the attention of farmers and researchers through the introduction of the use of alternative hormones which will help to bypass the juvenile stages of certain species for better field establishment and to improve reforestation of certain threatened or extinct species. This study was conducted to determine the best alternative hormone on the semihardwood stem cutting of Parkia biglobosa. The alternative hormones used were Pure Honey, Coconut Water, Moringa Leaf Extract and Control. Five (5) semi-hardwoods stem cuttings of Parkia biglobosa with three (3) replicates giving 60 experimental units and were place in a propagating chamber for rooting. Moringa Leaf Extract was significantly higher than other treatments in terms of total number of roots, total length of roots and length of longest root. Coconut water was significantly higher in terms of percentage of rooted cuttings and number of cuttings with callus due to the presence of auxins and cytokinins. However, there was no significant difference between Moringa leaf extract and coconut water treatment in number of rooted cuttings, formation of callus, rooting success.
Abstract. Declines in soil saturated hydraulic conductivity (Ks) as a result of saline and sodic irrigation water are a major cause of soil degradation. While it is understood that the mechanisms that lead to degradation can cause irreversible changes in Ks, existing models do not account for hysteresis between the degradation and rehabilitation processes. We develop the first model for the effect of saline and sodic water on Ks that explicitly includes hysteresis. As such, the idea that a soil's history of degradation and rehabilitation determines its future Ks lies at the center of our model. By means of a weight function, the model accounts for soil specific differences, such as clay content. The weight function also determines the form of the hysteresis curves, which are not restricted to a single shape, as in some existing models for irreversible soil processes. The concept of the weight function is used to develop a reversibility index, which allows for the quantitative comparison of different soils and their susceptibility to irreversible degradation. We discuss the experimental setup required to find a soil's weight function and show how the weight function determines the degree to which Ks is reversible, for a given soil. We demonstrate the feasibility of this procedure by presenting novel experimental results showcasing the presence of hysteresis in soil Ks, and using these results to calculate a weight function. Past experiments and models on the decline of Ks due to salinity and sodicity focus on degradation alone, ignoring any characterization of the degree to which declines in Ks are reversible. Our model and experimental results emphasize the need to measure reversal curves, obtained from rehabilitation measurements following mild declines in Ks. The developed model has the potential to significantly improve our ability to assess the risk of soil degradation, by allowing for the consideration of how the accumulation of small degradation events can cause significant land degradation.
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