Irrigation & Drainage Systems Engineering

An equation that expresses lateral pressure as an explicit function of distance from the lateral inlet is derived for linear-move sprinkler irrigation systems. The equation takes into account the effects of both field slope and span geometry on lateral pressure. The proposed equation is not intended for predictive use. Instead, it is used here in an additional evaluation of the validity of the unique pressure profile variability patterns, of linear-move laterals, produced in an earlier study through numerical simulations. Accordingly, the pressure profiles computed with the equation are compared with those obtained through simulations. Six data-sets, covering a range of field slopes and lateral parameters, are used in the evaluation. The results show that pressure profiles computed with the equation closely match those obtained through simulations. Overall, the spatial patterns of the pressure profiles computed here, with the equation, confirm observations made in an earlier study that the variability attributes of the pressure profiles of linear-move laterals exhibit dual characteristics, consisting of local span-scale variability patterns and inter-span/ lateral-wide trends. Analysis of the pressure head equation shows that pressure head profile of a lateral is a stepwise linear function of distance from the inlet with discontinuities at computational nodes. The practical significance of this observation in the computation and description of lateral pressure head profile is highlighted. The pressure head equation derived here is also used to define a pressure slope function that can potentially be used to characterize the full range of variation of the pressure profile patterns of linear-move laterals.

Low availability of surface water has exacerbated the use of groundwater for irrigation in New Mexico. About 75% of the groundwater in NM is brackish and prolonged application without treatment could increase soil salinity. Reverse Osmosis (RO) treats brackish groundwater but disposal or reuse of RO concentrate is a problem. The objective of this study was to test germination and emergence of six halophyte species under a water salinity gradient. Four irrigation water treatments were tap water (EC 0.8 dS/m), brackish groundwater (EC 5.0 dS/m), RO1 concentrate water (EC 8.0 dS/m), and RO1 concentrate mixed with NaCl (RO2; EC 10 dS/m). Experiments with six halophytes species (Atriplex canescens, Hordeum vulgare, Lepidium alyssoides, Distichlis stricta, Panicum virgatum, xTriticosecale) were carried out for 30 days in a greenhouse. H. vulgare and xTriticosecale had no significant difference in percent germination with higher germinations under salinity treatments, and other species showed similar germinations under higher salinity treatments. On the other hand, D. stricta seeds displayed lower germinations under higher salinity treatments. Results of the emergence percentage showed that H. vulgare and xTriticosecale had no significant difference with higher emergence under higher salinity treatments, while other species showed similar emergence percentage under higher salinity treatments. In contrast, L. alyssoides and A. canescens seeds showed lower emergence percentage under higher salinity treatments. Increasing irrigation water salinity increased mean germination time for all species except L. alyssoides, but did not affect the percentage germination significantly except for A. canescens. Increasing irrigation water salinity increased mean emergence time for all species except L. alyssoides, but did not affect the percent emergence for H. Vulgare, xTriticosecale, and P. virtagum species significantly. Results showed that H. vulgare (barley), xTriticosecale (triticale), and P. virtagum (switchgrass) are candidate species for irrigation with brackish groundwater and RO1 concentrate in water scarce areas. However, their survival and growth should be further tested in different soils.

Agricultural water is scarce in many parts of the world and becoming a global agenda. It is the largest among sectors which are consuming huge fresh water. This experiment was carried out for three years to investigate the yield and water productivity of onion under different deficit irrigation levels. The method used was field experiment contains combination of five treatments (100% ETc throughout the season, 85% of ETc throughout the season, 70% of ETc throughout the season, 50% of ETc throughout the season and farmers practice laid out in randomized complete block design (RCBD) with three replications. The combined yield results showed that maximum yield was obtained from 100% ETc (26.44 t/ha) and minimum yield was obtained from 50% of ETc (18.5 t/ha). Among treatments 100% ETc, 85% of ETc, 70% of ETc and farmers practice, there was insignificant yield difference with minimum yield reduction. But the treatment 50% of ETc had the significant yield difference with 100% ETc and 85% ETc. Maximum and minimum water productivity was obtained from 50% of ETc (7.8 kg/m3) and farmers practice (3.877.8 kg/m3), respectively. Water productivity of 85% of ETc (6.24 kg/m3) was greater than 100% ETc (5.56 kg/m3). The result of economic analysis indicated that Irrigating 85% of ETc earns best marginal rate of return next to 70% of ETc. From these result it can be concluded that in water scarce area using 85% of ETc provides a better yield, Water productivity and earns better income.