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 through most of the soil profile), Special care would be required to avoid local accumulations of salinity in the vicinity of the seedling in order to obtain a good stand. The SAR is also sufficiently high to cause degradation of soil tilth-crusting, reduced permeability, hard/compact clods, etc.-- especially after rains or irrigations with dilute waters. Parts of the field have considerably higher levels of salinity and SAR than the mean values (see Tables 2 & 6 and Figure 7). Hence, the salt- related problems in these "higher" areas would be even greater than for the average area. This field is subject to the additive effects of two other problems because it is irrigated by sprinklers, One is the foliar uptake of salts and the resulting toxicity and "burning" that occurs when the water applied is as high ( 2500-6000 ppm) as it is in the well waters used on this field. This will especially be a problem if these saline waters are applied to the plants in their very early growth stage (emerging seedlings) when they are very susceptable in this regard. The young plants can be literally killed under such conditions, especially when the soil is so saline, as well as the irrigation- water. A second is the enhanced loss of tilth caused by the impact of water falling upon the topsoil. This extra physical-energy adds to that caused by the chemical-energy forces (those associated with high SAR and low salinity) which cause aggregate failure, soil crsting, etc. Thus, I would expect substantial problems of stand establishment in this field caused by the combination of high soil salinity, high water salinity and high soil sodicity. Obviously, without stand, crop production can not be achieved. Average soil salinity levels (about 4.5-6,0) in field #3 are low enough to be able to grow wheat and other crops of moderate or greater salt-tolerance, provided stand can be established. The SAR, especially in the topsoil, is sufficiently low (4) to not expect substantial tilth problems in the field, iffalling-water impact and excessive & too-wet tillage are avoided. Of the four fields that we examined during the trip, this field has the lowest levels of salinity and sodicity, Apparently, the water used to irrigate this field is of better quality. Results are given in Tables 4 & 7. Average soil salinity and sodicity levels (about 7-12 in EC, and about 14-23 in SAR) are higher, more variable and more limiting to crop production in field #4 than in the other three fields(see Tables 4 & 7 and Figures 8 & 9). For example, a value of -15 mmho/cm was measured in one ofthe 0-30 cm. soil samples and as high as 22 mmho/cm in one of the 60-90 cm. soil samples. An SAR of35,7 was measured in one of the 0-30 em. soil samples. Thus, one can expect some areas of this field to be essentially incapable of conventional crop production. These areas are shown in Figures 8 & 9 (Figure 9 was created from the mobile, four-electrode tractor measurements). I suspect the source of the problem here is related to the uneven microrelief and differences in soil texture, but possibly also to a shallow water table. We didn't collect data in this regard. You will see in Table 4 and in Figure 4 that there is a fair correlation between EC, and SP in this field. Since the salinity increases with depth in essentially all of the soil profiles sampled in the field, including those with high salinity levels, I conclude that the net flux of water is downward everywhere in the field--thus, the high levels of salinity are not likely caused directly by the upflux of water and salts from the water table. Rather the areas of high salinity seem to be resulting from inadequate leaching in these areas, which may be because the soil is less permeable in these areas--either because of higher clay content or poorer drainage conditions--or because the farmer is underirrigating or the uniformity of the irrigation-system is very poor. The analyses of the three well water samples the farmer of this field gave me are shown at the bottom of page 6 of the analytical results table. These waters are saline enough to have produced the higWy salt- affected conditions found in parts of this field only if the leaching fraction in these areas is very low (about 5% Of less, see the enclosed WATSUIT printouts).