Use of saline drainage water in irrigated agriculture, as a means of its disposal, was evaluated on a 60 ha site on the west side of the San Joaquin Valley. In the drip irrigation treatments, 50 to 59 % of the irrigation water applied during the six-year rotation was saline with an ECw ranging from 7 to 8 dS/m, and containing 5 to 7 mg/L boron and 220 to 310 gg/L total selenium. Low salinity water with an ECw of 0.4 to 0.5 dS/m and B ~ 0.4 mg/1 was used to irrigate the furrow plots from 1982 to 1985 after which a blend of good quality water and saline drainage water was used. A six-year rotation of cotton, cotton, cotton, wheat, sugar beet and cotton was used. While the cotton and sugar beet yields were not affected during the initial six years, the levels of boron (B) in the soil became quite high and were accumulated in plant tissue to near toxic levels. During the six year period, for treatments surface irrigated with saline drainage water or a blend of saline and low salinity water, the B concentration in the soil increased throughout the 1.5 m soil profile while the electrical conductivity (ECe) increased primarily in the upper 1 m of the profile. Increases in soil ECe during the entire rotation occurred on plots where minimal leaching was practiced. Potential problems with germination and seedling establishment associated with increased surface soil salinity were avoided by leaching with rainfall and low-salinity pre-plant irrigations of 150 mm or more. Accumulation of boron and selenium poses a major threat to the sustainability of agriculture if drainage volumes are to be reduced by using drainage water for irrigation. This is particularly true in areas where toxic materials (salt, boron, other toxic minor elements) cannot be removed from the irrigated area. Continual storage within the root zone of the cropped soil is not sustainable.

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A procedure is described for optimizing plant tissue digestion conditions for accurate selenium (Se) analysis. Optimal concentrations of nitric acid, ceric ammonium nitrate, hydroxylamine HCl and the use of vapor trapping funnel were evaluated for total recovery of Se in NIST wheat flour reference material using atomic absorption spectrophotometry with continuous Se hydride generation. During sample digestion, excessive or insufficient amounts of nitric acid (<0.45 M or >1.02 M), ceric ammonium nitrate (<6.7 x 10 -5 M or >6.6 x 10 -4 M), or hydroxylamine HCl (<0.016 M or >0.398 M) caused a 15-20% reduction in the total Se recovered. Additional losses up to 15% were observed in the same samples without the use of the vapor trapping funnel. These results demonstrated how digestion conditions must be optimized for precise and accurate Se analysis in plant tissue.

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Abstract-Static flux chambers are often used to determine emission flux of gases such as greenhouse gas nitrous oxide (N 2 O). However, the sampling process is laborious especially when many treatments/plots are included for measurements to compare treatment effects in the effort to develop mitigation strategies. To solve this problem, we constructed an automatic sampler (autosampler) at low cost, simple to operate, and easy maintenance and used it with static chambers to sample N 2 O emissions. The construction involves mechanical work including mainly woodworking for building a chassis (mounting board), syringe mounting block, and servo mounting block, and electronics for the controller involving hardware assembly, soldering, and programming to control the operation of the sampler. This paper provides the detailed information and instructions as well as price of materials for the construction of the sampler with the flexibility for modification to meet various research needs. The samplers were used to measure N 2 O emissions in a pomegranate field demonstrating improved sampling efficiency. The results illustrated treatment differences with much higher flux from surface drip irrigation than that from subsurface drip irrigation.Index Terms-Greenhouse gas, emission flux, nitrogen fertilizer, drip irrigation.