Phosphorus is an essential element in both plant and animal nutrition. However, in some alkaline soils alfalfa (Medicago sativa L.) does not always respond to P fertilization despite deficient or low P concentrations in the tissues. Objectives of this study were to determine the feasibility of selection for increased P concentration in alfalfa grown in alkaline soils and effects on nontarget forage yield and quality characteristics. Ten diverse unselected alfalfa populations, and first and second cycle selected populations were evaluated for P and Ca concentration, Ca:P ratio, and forage yield. selected populations were also evaluated for forage yield, nontarget minerals, and forage quality characteristics. Unselected populations differed in P concentration, but variability among individual plants was considerably greater than among populations. Selection on the basis of P concentration of individual plants was effective with 7 to 12% increases over the check in Cycle 1 and an additional gain of 6% with a second cycle of selection. Realized heritabilities with individual plant phenotypic selection were 0.17 and 0.36 in the first and second cycles of selection, respectively. Selection for increased P concentration did not affect Ca concentration, but reduced the Ca:P ratio and increased Zn concentration. No detrimental effects of selection for increased P concentration were found for nontarget minerals, components of forage quality, or yield. Selected populations did not differ from the check population in response to P fertilization. Selection among individual alfalfa plants from any genetic source based on P concentration in forage from the first harvest would be the most efficient breeding procedure to increase P concentration.
We surveyed 15 commercial irrigated orchards of ‘Western’ pecan [Carya illinoinensis (Wangenh.) K. Koch] along a 120‐km stretch of the middle Rio Grande basin in southern New Mexico. Our intent was to determine if high salinity and boron (B) broadly threaten pecan cultivation in this region. Ten of the fifteen sites were found to be on soils considered too saline for pecan trees (>2–3 dS m−1 in the soil saturation extract of the upper 0–60 cm of soil depth). Of these 10 sites, 4 had saturation extract Na concentration exceeding 20 mM, which is at or about the concentration corresponding to pecan seedling rootstock growth suppression. A laboratory study showed that cell membranes of excised, subapical seedling root segments from ‘Riverside’ pecan were damaged by about twice the salinity of the saturation extract at the highest salinity sites (9 dS m−1). At all sites, midsummer leaflet B concentration surpassed the published accepted range for pecan of about 50 to 100 mg B kg−1 dry weight, especially at the sites with higher soil salinity. Evaluation of two nearby sites (low salinity and B and high salinity and B orchards) showed that the higher salinity and B were associated with 25% lower yield efficiency, 3% lower percentage kernel, 13% lower mass per nut, and a 9 to 16% reduction in the tree's capacity to recycle N and P into perennial storage organs. The findings bring attention to the sustainability of current irrigation and soil management practices in much of this concentrated pecan producing region.
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