Steven J. Guldan

Hydrologic, Riparian, and Agroecosystem Functions of Traditional Acequia Irrigation Systems

ABSTRACT Traditional cultures in arid landscapes of the southwestern United States and northern Mexico developed irrigation systems to irrigate floodplain valleys along streams and rivers. Many of these traditional irrigation systems, referred to as acequias, continue to be used today. Population growth in the region is creating pressures to convert agricultural land and irrigation water to urban and other uses. Unique hydrologic features of the acequia systems suggest that, beyond providing crop irrigation, they may provide additional valuable hydrologic, riparian, and agroecosystem functions worth maintaining. We investigated in detail the seepage and the groundwater response to seepage from a traditional acequia irrigation ditch along the Rio Grande in north-central New Mexico. We found that 16% of ditch flow seeps into the ditch bed and banks. Groundwater levels near the ditch and midway between the ditch and the river rise 1 m or more within three to four weeks following the start of the irrigation season. The elevated groundwater table produced by ditch and field seepage is sustained until late summer when groundwater levels again drop. The seepage that provides this annual groundwater recharge also sustains riparian vegetation along the main ditch and side ditches. In light of our hydrologic analysis, we considered seepage-supported riparian areas and their ecological functions including aquatic habitat, terrestrial habitat, and water quality effects. Acequia hydrology plays an important role in contributing to an ecologically healthy, agriculturally productive, and community-sustaining floodplain agroecosystem.

Surface Water–Groundwater Interactions Between Irrigation Ditches, Alluvial Aquifers, and Streams

Improved descriptions of surface water–groundwater interactions are required for enhanced water resource management in irrigated areas of the western U.S. We are conducting a research project to determine surface water–groundwater interaction effects on hydrologic budgets and water quality along the upper Rio Grande in New Mexico. This article reports on the initial phase of the project to ascertain the effects of unlined irrigation ditch seepage on shallow groundwater at the Alcalde Science Center in north-central New Mexico. Results from two seepage tests in which 60- and 80 m-long impoundments were established in the Alcalde Ditch indicate that under normal ditch flow depths about 11 cm/day seeps out of the Alcalde Ditch. Based on flow estimates over the 9 km length of the Alcalde Ditch, at least 5% of the total ditch flow seeps out of the ditch bed and banks during the irrigation season. Water level measurements from monitoring wells showed that within 1 month of the beginning of ditch flow, irrigation seepage caused a raised water table and orientation of flow paths towards the river. Specific conductance measurements of surface and shallow groundwater indicated that surface water was the origin of shallow groundwater. Seepage from earthen ditches such as the one in this study could possibly have multiple benefits: diluting agricultural chemicals or septic tank leachate in shallow groundwater, providing groundwater recharge to shallow wells, and providing delayed return flow to the stream thus maintaining in-stream flow after peak runoff periods.

River Hydrograph Retransmission Functions of Irrigated Valley Surface Water–Groundwater Interactions

Storage and release functions of western U.S. traditional river valley irrigation systems may counteract early and rapid spring river runoff associated with climate variation. Along the Rio Grande in northern New Mexico, we instrumented a 20-km-long irrigated valley to measure water balance components from 2005 to 2007. Hydrologic processes of the system were incorporated into a system dynamics model to test scenarios of changed water use. Of river water diverted into an earthen irrigation canal system, some was consumed by crop evapotranspiration (7.4%), the rest returned to the river as surface return flow (59.3%) and shallow groundwater return flow that originated as seepage from canals (12.1%) and fields (21.2%). The modeled simulations showed that the coupled surface water irrigation system and shallow aquifer act together to store water underground and then release it to the river, effectively retransmitting river flow until later in the year. Water use conversion to nonirrigation purposes and reduced seepage from canals and fields will likely result in higher spring runoff and lower fall and winter river flow.

Nitrogen Recovery from 15N-Labeled Green Manures: I. Recovery by Forage Sorghum and Soil One Season After Green Manure Incorporation

ABSTRACT This investigation was part of a project to evaluate green manure forage legumes as relay intercrops for sweet corn (Zea mays L.) and chile (Capsicum annuum L.) in north-central New Mexico. The study was carried out under irrigated conditions in 1994 on a Fruitland sandy loam (coarse-loamy, mixed, calcareous, mesic Typic Torriorthent) to evaluate the 15N recovery by forage sorghum (Sorghum bicolor [L.] Moench) and soil after the incorporation of 15N-labeled alfalfa (Medicago sativa L. ‘Nitro’) or hairy vetch (Vicia villosa Roth. ‘Madison’). Two application rates of alfalfa (2.7 or 4.0 Mg dry matter ha□1) or hairy vetch herbage (3.2 or 6.4 Mg dry matter ha□1), were incorporated into soil microplots. Additional treatments consisting of 56, 112, and 168 kg N ha□1 (as urea) were used to compare soil inorganic N concentrations with those released from the legumes. Nitrogen-15 recovery by sorghum tops was 16% of the 15N applied, in two harvests. Of this, 80% was recovered at the first harvest. In soil, 15N recoveries were 50 and 3% of the input at the 0–0.3 and 0.3–0.6 m depths, respectively. Maximum inorganic N concentrations were found 14 d after amendment application. At the end of the growing season, inorganic N concentrations in all treatments were essentially the same as the background (8 mg N kg□1). The low 15N recoveries by crop plus soil and inorganic N concentrations in soil at the end of the season suggest that about 12% and 35–58% of the N applied as green manure was lost from the system for alfalfa and hairy vetch, respectively.

Shallow Aquifer Recharge from Irrigation in a Semiarid Agricultural Valley in New Mexico

AbstractIrrigation percolation can be an important source of shallow aquifer replenishment in arid regions of the southwestern United States. Aquifer recharge derived from irrigation percolation can be more significant in fluvial valleys overlying shallow aquifers, where highly permeable soils allow rapid water infiltration and aquifer replenishment. This study used data from various irrigation experiments and data at the piezometric level to assess the irrigation percolation effects on the recharge of a shallow aquifer in an agricultural valley of northern New Mexico. The water balance method (WBM) and the water table fluctuation method (WTFM) were used to estimate aquifer recharge at the field scale (<1  ha) and the WTFM was used to determine recharge at the entire valley scale (40  km2). Also, the temporal and spatial distribution of aquifer response to irrigation percolation and canal seepage inputs was characterized. The results showed that for separate irrigation events at the field scale, aquifer r...

Nitrogen Recovery from 15N-Labeled Green Manures: II. Recovery by Oat and Soil Two Seasons After Green Manure Incorporation

ABSTRACT Forage legumes in crop rotations are often used to supply N for succeeding crops. However, the residual effect of forage legume green manures for second crops has not been thoroughly investigated in high desert regions of the Southwestern United States. The objective of this study was to evaluate the 15N recovery by a second subsequent crop (oat [Avena sativa L.]) and soil from microplots amended with 15N-labeled alfalfa (Medicago sativa L. ‘Nitro’) and hairy vetch (Vicia villosa Roth ‘Madison’). In 1994, two application rates of each legume were incorporated into 1 m2 microplots and forage sorghum (Sorghum bicolor [L.] Moench) was used to evaluate the 15N recovery. Above-ground residues were removed from microplots immediately after each of the two sorghum harvests. In 1995, the 15N recovery by the oat crop and soil was determined. Nitrogen-15 recovery by oat averaged 3% of the 15N applied as green manure. Of this, 95% was found in tops and 5% in roots. Averaged across application rates, oat recovery of 15N was 63% greater in treatments amended with alfalfa than with hairy vetch. Green manures did not affect the total N concentration of oat parts. Most of the residual 15N was found in soil at the 0–0.3 m depth at the end of the oat season. The percent of 15N recovery by soil in plots amended with alfalfa was 238% higher than with hairy vetch. Green manures applied in 1994 had little residual effect on the N nutrition of oat.

An Economic Analysis of Transplanting versus Direct Seeding of Selected Medicinal Herbs in New Mexico

ABSTRACT Transplanted and direct-seeded Nepeta cataria L., Urtica dioica L., Calendula officinalis L., Melissa officinalis L., and Sphaeralcea incana Torr. ex Gray were evaluated at two sites in New Mexico. In Las Cruces, the Nepeta cataria, Melissa officinalis, and Sphaeralcea incana earned a positive return to land and risk from transplanting and direct seeding, although in each case transplants resulted in a higher return to land and risk. Transplanted Urtica dioica and Calendula officinalis at the Las Cruces site resulted in a negative return to land and risk, but at the Alcalde site the Nepeta cataria earned a positive return from transplanting and direct seeding. Transplanted Melissa officinalis and direct seeded Calendula officinalis in Alcalde generated a positive return. Direct seeded Urtica dioica and Sphaeralcea incana did not survive in Alcalde.

Documenting Hydrological Benefits of Traditional Acequia Irrigation Systems: Collaborative Research in New Mexico, USA

In New Mexico, USA, acequia-based agriculture is under threat as pressures rise to transfer water and land out of agriculture. The amount and cash value of agricultural production coming out of acequia-irrigated valleys is not great when compared to many production areas – yet, the overall value of acequia agricultural systems may go beyond food and fiber production in ways not apparent to the general public. Research on the hydrology of acequias has been carried out in collaboration with acequia associations, irrigators, and other community residents in north-central New Mexico. This research indicates these acequia irrigation systems provide important hydrologic benefits including aquifer recharge and groundwater return flow. In our water budget study, of water diverted into the Acequia de Alcalde, on average only 7% was consumed by crop evapotranspiration, 59% returned to the river as surface return flow, and 33% returned to the river as shallow groundwater return flow. In effect, the acequia irrigation system stores spring snowmelt runoff in the valley alluvial aquifer and releases it to the river later when river flows are normally low. If acequia agriculture decreases significantly, these key hydrologic functions could be lost and fall and winter river flows could diminish, particularly during drought, causing negative effects on downstream water users as well as river ecology.