Dummy regression to predict dry fiber in Agave lechuguilla Torr. in two large-scale bioclimatic regions in Mexico.

Agave lechuguilla Torr., of the family Agavaceae, is distributed from southwestern United States to southern Mexico and is one of the most representative species of arid and semiarid regions. Its fiber is extracted for multiple purposes. The objective of this study was to generate a robust model to predict dry fiber yield (Dfw) rapidly, simply, and inexpensively. We used a power model in its linear form and bioclimatic areas as dummy variables. Training, generation (80%) and validation (20%) of the model was performed using machine learning with the package 'caret' of R. Using canonical correlation analysis (CCA), we evaluated the relationship of Dwf to bioclimatic variables. The principal components analysis (PCA) generated two bioclimatic zones, each with different A. lechuguilla productivities. We evaluated 499 individuals in four states of Mexico. The crown diameter (Cd) of this species adequately predicts its fiber dry weight (R2 = 0.6327; p < 0.05). The intercept (ß0), slope [lnCd (ß1)], zone [(ß2)] and interaction [lnCd:Zona (ß3)] of the dummy model was statistically significant (p < 0.05), giving origin to an equation for each bioclimatic zone. The CCA indicates a positive correlation between minimum temperature of the coldest month (Bio 6) and Dwf (r = 0.84 and p < 0.05). In conclusion, because of the decrease in Bio 6 of more than 0.5°C by 2050, the species could be vulnerable to climate change, and A. lechuguilla fiber production could be affected gradually in the coming years.

Number of residual thermotolerant coliforms on plants and in soil when using reclaimed domestic wastewater for irrigation.

The reclamation of domestic wastewater for irrigation is one alternative approach to solve the water scarcity crisis, but it is essential to control the microbiological quality of wastewater used for irrigation. The removal of thermotolerant coliforms, also known as faecal coliforms (FC), from treated domestic wastewater by intermittent media infiltration (IMI) in column was studied. The columns were filled with natural filter media (soil, soil/charcoal and zinc-modified zeolite, Zeo-Zn), and wastewater, IMI-treated wastewater and disinfected wastewater were compared. The numbers of residual FC on Swiss chard (Beta vulgaris) and in agricultural soil were determined over a 4-month period. The column using Zeo-Zn had a higher FC removal efficiency (2.98 log) than columns with other filter media and disinfection (1.87-2.57 log) due to the bactericidal properties of Zn(2+). The treatment of wastewater using Zeo-Zn and disinfection both decreased the accumulation of FC on plants and in soil to approximately 1-20 MPN/g dry matter. IMI-treated wastewater using the column with Zeo-Zn was suitable for unrestricted agricultural use, complied with Mexican regulations (as did disinfected wastewater) and had a low risk of FC contamination of plants and soil.