ArkValley Irrigation Grant Final Report

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I I I I I I I I I I I I I I I I I I I INTRODUCTION The site selected for this demonstration, partially funded by the Colorado Water Conservation Board (Fig. I), was the Stonewall Springs (Fann) located in Pueblo County east of the City of Pueblo and divided by Highway 50 (Fig.2). The property is located immediately north of the Arkansas River and has a shallow water table varying from 8 to 22 feet as seen in static well levels. "Perched" water table areas have been created by over-irrigation in some areas of the property causing excessive salting of the soils. Nine full-circle and two half-circle center pivot systems are located on the property. Two full circle pivots were that represented different soil types or salinity conditions. The pumps being used to supply these pivots were tested to determine pumping capacity and pump efficiency and the pivots were "customized" to fit the specifications of these pumps. Crops and/or grass and legume mixtures planted on these soils were determined by the soil type and salinity levels shown by the soils and salinity mapping. Also, the quality of the water being pumped to each of the demonstration sites was tested for irrigation suitability and different methods of water application used by LEPA system were observed to determine the effect of water quality on crops. Drag hoses and low drift nozzles (LON) were used to apply the water. Where possible, higher quality water was applied to the alfalfa and the lower quality water was applied to the more salt-tolerant grass-legume and/or grass mixtures. The demonstration area was re-mapped for soil type in the summer of 1993 by the NRCS, (Fig. 3). Soil types and shallow water table conditions found on the demonstration site property are similar to those found in river bottom areas in Colorado and New Mexico. Management problems of irrigated soils of this type are greater due to the high clay content. Clayey soil is difficult to cultivate as it is cloddy and cracks when dry (Fig. 4) and sticky and plastic when wet These soils also have a low water-infiltration rate and the available water holding capacity is high. Also, these soils are moderately to strongly affected by salts, partially due to the shallow water tables. Salts tend to accumulate in soils that are not well drained. Salinity problems start when previously non-saline soils become saline as a result of irrigation. Salts begin to accumulate within the soil profile because all waters contain some dissolved salts. The accumulation occurs when salts are left behind as crops take up water. With continued salt accumulation, water becomes less available for plant growth, causing lower crop yields. Salinity problems in fields are often difficult to spot before significant crop damage occurs. Typically, saline soils are recognized by the presence of white crusting on the soil surface, spotty crop stands or by irregular plant growth. Historically, field salinity problems have been assessed by taking soil samples and sending them to a laboratory for analysis. There are several limitations to assessing salinity using this conventional technique. To effectively sample a field, several hundred soil samples may be required, particularly for large fields. At 10 minutes per sample, time investment in the field is substantial. Second, it is not uncommon for the cost of analysis to exceed $25 per sample. Third, it is common for laboratory resuhs to take weeks before information is received. Fourth, conventional methods aren't conducive to returning to a field to check and monitor the effectiveness of any management or structural practice on the salinity problem. 5