by U.S. Salinity Laboratory, Agricultural Research Service, U.S. Dept. of Agriculture in Riverside, Calif .
Written in English
|Statement||C. Dirksen ... [et al.].|
|Series||Research report / U.S. Salinity Laboratory -- no. 135, Research report (Salinity Laboratory (U.S.)) -- no. 135.|
|Contributions||Salinity Laboratory (U.S.)|
|The Physical Object|
|Pagination||xviii, 127 p. :|
|Number of Pages||127|
As soils rest in an untilled condition, they actually change in their ability to transport water and exchange gases. The movement of water through the soil causes silt particles to relocate in the plow layer and form a layer which blocks macropores to reduce the rate at which water moves through the root zone. take to build plant carbohydrates and biomass. Excessive salinity in the crop rootzone creates osmotic stress that reduces root uptake of water and crop transpiration. The added stress then reduces forage yield. At the same time, Class 1 water and land costs have doubled in the last 3 to 4 years; forcing hay growers to more marginal ground. Water tables in the area are typically within meters of the soil surface, and the ground water quality is near the threshold water quality tolerance for alfalfa (EC sw) of dS/m. At an EC e of dS/m and an EC sw of dS/m, the leaching requirement necessary to maintain alfalfa yields is calculated to be 15% of the total applied water. Salt Tolerance/Ability to Utilize Degraded Water—Recent data has shown that alfalfa has a high degree of salt tolerance. A recent trial in Fresno County, where EC water was used for irrigation over 3 years, yields were normal ( tons/acre).
Bresler E () Simultaneous transport of solute and water under transient unsaturated flow conditions. Relationship between root uptake-weighted mean soil water salinity and total leaf water potentials of alfalfa. Irrig Sci 6: 39–50 Google Scholar. Dirksen C () Water and salt transport in daily irrigated root zone. Neth J Agric Sci. Interaction of alfalfa with transient water and salt transport in the root zone, Research report no. US Salinity Laboratory, Riverside, CA, pp. Google Scholar. Dirksen C, Huber MJ, Raats PAC, Rawlins SL, Van Schilfgaarde J, Shalhevet J, Van Genuchten MTh () Interaction of alfalfa with transient water and salt transport in the root zone. Research report No. , US Salinity Lab, Riverside, CA, USA, p. 4 Alfalfa Management Guide Surviving plants will be stunted and continue to yield less in subsequent years (Figure 2). A waiting period after destroying the old stand is necessary to allow the toxic compounds to degrade or move out of the root zone of the new seedlings. Weather conditions influ-ence the speed with which the toxins are removed.
In the case of alfalfa, for each point above an EC=2, alfalfa yield is reduced by percent. Production fields with EC values of more than 2 have a potential salinity problem and will benefit from the planting of a salt-tolerant alfalfa variety. Alfalfa production losses due to salinity may occur in several forms in the field. Diffusion and dispersion of salt will, of course, counteract this steepening. DISCUSSION The theory presented in this paper provides a concise, quantitative descrip- tion of the interaction of several variables influencing the distribution of salts in the root zone. Equations 6 . Results from our field trials also indicated a higher degree of salt tolerance for alfalfa than current guidelines suggest. In one study, a three-year variety trial on clay loam soil near Five Points, Calif., using irrigation water of 5 to 7 dS per m ECw and final soil salinities near 9 dS per m ECe, indicated normal yields and excellent stand survivability. The advent of salt-tolerant alfalfa varieties provides producers with another crop option for these salt-affected cropping systems. The advantages of salt-tolerant alfalfa varieties is twofold: They have the genetic flexibility to produce top yields in non-saline soils as well as improved performance on marginally saline soils.