Water boron in irrigation

The sensitivity to excessive boron varies among plant species (Nable et al. 1997). The range in variation is such that the most tolerant species are unaffected by boron exposure that kills the most sensitive species. An example of the variation in sensitivity to boron is that safe concentrations of boron in irrigation water range from 0.3 mgL for sensitive plants such as avo-... 

The first observation of boron toxicity caused by irrigation water was made in 1925 by Kelley and Brown (37). They associated specific injury symptoms with abnormally high concentrations of boron in leaves of walnut and citrus orchards in southern California. They noted that orchards irrigated with water containing 1.0 /xgram of B/ml or more frequently exhibited injury symptoms. In 1931, Scofield and Wilcox (38) concluded from additional studies of water supplies in southern California that the critical (injurious) concentration of boron in irrigation waters... 

In addition to the general osmotic effects summarized in Table 11.2, many plants ate sensitive to specific ions in irrigation waters or soil solutions. Boron toxicity is probably the most common. Table 11.3 lists some plants according to their sensitivity to the B concentration of irrigation water. Boron is more difficult to control than is salinity in general because it leaches more slowly than more soluble salts. 

Boron does not represent any health hazard if present at the concentrations occurring in clean surface and fresh groundwaters. However, its presence is not suitable in irrigation waters as it inhibits the growth of plants. Therefore, the concentration of boron in these waters should be limited to values ranging from 0.5-2.0 mg 1 ... 

Adsorbed Boron. Boron precipitated and adsorbed on surfaces of soil particles is probably of greater importance to plant growth because of equilibria existing between adsorbed and soluble boron. A substantial proportion of the boron added to soil either as a component of fertilizers or in irrigation water is adsorbed by certain soil materials, the balance remaining in the soil solution. This soil solution concentration is especially important to plant nutrition because of its immediate availability to plants. Plants respond primarily to the soil solution boron, independently of the amount of boron adsorbed by soil (ii). Consequently, conditions affecting equilibria between adsorbed and soluble boron are highly rele-... 

The fact that boron is essential to plants is firmly established. However, when boron concentrations in irrigation waters exceed 2.0 mg/L, extensive plant toxicity should be... 

If the retort water is considered for domestic or irrigation uses, it would have to be treated to remove a number of contaminants. Of the major constituents in retort water, the NH4, HCOa", and organic compounds in the water clearly make it unsuitable for other uses (18). Of the trace constituents, the arsenic and selenium concentrations listed in Table IV are above the maximum permissible concentrations for drinking water (36). The boron concentration may make water unsuitable for irrigation (22). Other studies have found silver and lead concentrations in retort waters have exceeded the maximum permissible concentrations for drinking water (1,2,36). Numerous studies for the treatment of the retort water have been initiated (37). The objectives of these studies are usually to find a method to recover the ammonia and organic material from the water so that treatment costs will be lowered through by-product recovery. 

In each group the plants named first arc considered to be more tolerant. Those named last are more sensitive. The figures at the top and bottom of each column represent limiting boron concentrations of the irrigation water. 

A review paper covering forms of boron in soils, interactions between soil solution boron and adsorbed boron, adsorption-desorption processes, and relationships to plant nutrition is presented. Diagnostic criteria are given for chemical analysis of soils and irrigation waters in terms of boron status, i.e., deficient, adequate, or excessive, and specified according to crop species group. The potential boron hazard of municipal sewage effluents to water supplies is discussed. 

Perhaps the most widely accepted irrigation water criteria are those published in 1954 by the staff of the U. S. Salinity Laboratory (33). Criteria for boron include possible limits for four classes of irrigation waters according to sensitive-, semitolerant-, and tolerant-crop species. More recently, Wilcox (39) published a modified set of critical concentrations which are somewhat more fiexible in that fewer categories are involved. He proposed the following for irrigation waters ... 

A serious limitation of such boron criteria is the lack of provision for difference in soils, irrigation management, and climate. Soils differ in their capacity for adsorbing boron, and irrigation and rainfall characteristics likewise exert an effect on the distribution of available boron in soils. Additional details are presented in discussions of criteria for irrigation water quality by Bernstein (41) and Rhoades (42). 

Recent laboratory studies and field operations have demonstrated the excellent performance of a macroreticular boron-specific ion-exchange resin, Amberlite XE-243, for deborat-ing several process streams, sea water, and irrigation water. One large plant is now operating successfully on sea water. Further studies on this product are currently in progress in several areas throughout the world. 

Because of the current widespread presence of boron in most waterways and the need to remove it from many irrigation waters and industrial... 

High concentrations of boron have been found in the San Joaquin Valley of California in irrigation drainwater and in aquatic plants consumed by waterfowl. Measured boron concentrations in that locale exceeded 20.0 mg/L in subsurface agricultural drainage waters. 

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