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 All grasses and grass/legume mixtures were planted at the NRCS prescribed rates based on Pure Live Seed per acre. These grasses germinated and died. The second four spans were planted to sorghum-sudangrass that came to a good stand (Fig. 8) but, once the roots grew past the first foot of soil, the plants became stunted and were overgrown with weeds even though the weeds were sprayed with herbicides. Again as in 1996, different grass mixtures and/or grass-legume mixtures were planted in Pivot #7 as were two different types of sorghumlsudangrass. The different grasses and grass-legume mixes were planted in early spring and irrigated with water from Well #1 I, which has better water quality than previously applied using Well #13. The Total Dissolved Solids (TDS) in Well #11 was down to 1,200 ppm as compared to the 4,000 ppm when using Well #13. Seedling sprouts were found throughout the field, however; very few of these sprouts emerged above the soil surface. The grasses and grass-legume mixtures were sprinkle irrigated to germinate the seed and part of this area was irrigated using drag lines extending down from the sprinkler heads to the ground. Applying irrigation water in this manner eliminated saline water being applied to the leaf surface, thus, reducing the possibility of increased salinity due to crystalizing of this water on the leaf. Grasses planted in 1997 were the same mixtures and same locations as used in 1996. The area not planted to grasses was again planted to sorghum-sudangrass. The crop came up to a excellent stand but, once the roots reached the second foot, the plants became stunted and the crop was overtaken by weeds The high salts in the water and in the lower root zone was considered to be the reason for the continuing crop failure These mixtures included NewHy Wheatgrass and different mixtures of Orchard grass, Smooth Bromegrass and Intermediate Wheatgrass as well as Birdsfoot Trefoil and Cicer Milkvetch. The two different types ofsorghwnlsudangrass planted under Pivot #7 were a standard type and a Brown Mid Rib type. The Brown Mid Rib type has been show to be more palatable because of the reduction in lignin. The Brown Mid Rib appeared to be more susceptible to salinity as the early growth was not as vigorous as the standard, however; excessive amounts of weeds masked any results that would have shown this effect. Early growth of the sorghum/sudangrasses was encouraging but stunting ofthe plants started to occur just as the weeds were emerging. The weeds were sprayed aerially as the crop could not be cultivated because of the close row spacing. Unfortunately, the spraying did not give the kill that was anticipated and resulted in weeds continuing to be competitive with the crop. The sorghum-sudangrass was harvested twice during the growing season, but, again, untimely rains severely reduced the quality of the hay. In consulting with Dr. Rhoades, he felt the combination of high salt levels in the soil and the high salt levels in the water being applied was a "double blow" to the very sensitive seeding plants. "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 susceptible 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 caused aggregate failure, soil crusting, etc. Thus, I would 16