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Can salt be used beneficially on asparagus?

Wade H. Elmer

The Connecticut Agricultural Experiment Station
123 Huntington St.
P. O. Box 1106
New Haven, CT 06504 USA

History of salt use on asparagus

It was noted long ago that asparagus (Asparagus officinalis L) could grow without injury in brackish soils. Even though asparagus is not classified as a halophyte (salt loving plant), it ranks as one of the most salt tolerant plants cropped by man. Since asparagus favored the seacoast, gardeners in the 1800’s believed that asparagus had a nutritional requirement for NaCl. As plantings were established inland, the practice of dressing fields with rock salt (NaCl) was initiated. One source in the 1890’s suggested the exorbitant rate of "two quarts to the square yard". Many growers probably adopted the salting practice to control weeds, but research conducted in the early 1900’s found that applications of rock salt also increased vigor and yield, especially in older fields. However, in the 1940’s synthetic herbicides were developed and the salting practice was gradually discontinued.

Appearance of root and crown rot

Coincident with the discontinuation of the salting practice was an increase in the number of reports of a destructive crown and root rot disease (Figure 1 Mid-season foliar symptoms of Fusarium crown and root rot) and (Figure 2 Asparagus crown and roots showing symptoms of Fusarium crown and root rot. The rotted crown has vascular discoloration, collapsed storage roots, and a complete destruction of feeder roots). The pathogens which cause the disease are soilborne fungi called Fusarium. By the 1960’s, this disease had caused major reductions in asparagus yields in many US states.

Effect of salt on asparagus yield and crown and root rot

We decided to test whether or not applications of NaCl could be effective in fighting this disease. Experimental field plots were established in 1989 with healthy asparagus crowns. In 1991, half of the plots were treated with NaCl at 500 pounds/A and the other half of the plots were left untreated. These treatments were applied every spring thereafter. During the summers, the fern growth from treated plots was more vigorous and had denser canopies than untreated plots (Figure 3 Midseason response of asparagus to NaCl. The five asparagus plants to the left of red bag were treated with NaCl (500 pound/A). The five asparagus plants to right of the red bag were left untreated). Spears were cut in the spring for only two weeks in 1992 and then for 6 weeks in years thereafter. Yields of asparagus plots that were dressed with NaCl were greater than control plots in 6 out of 8 years (Figure 4 The effect of NaCl concentration in the initial irrigation on the percentage of greenhouse grown asparagus roots with rot).

To understand if the NaCl was directly affecting the disease, greenhouse studies were conducted. Young asparagus transplants were grown in soil infested with the fungal pathogens. Plants were irrigated at the beginning of the experiment once with solutions of NaCl ranging from 0 to 1 % and then irrigated with water for the rest of the time. We found that all rates of the NaCl were equal in their ability to suppress the root rot (Figure 5 The effect of NaCl on the marketable yield of asparagus from 1991-1999). The NaCl also reduced the number of colonies of the fungal pathogen that grew from the roots.

Conclusions

It was clear from our studies that asparagus benefits from salt applications. One mechanism may be its ability to suppress the disease. The use of salt has since been adopted by commercial growers in many different areas to increase yields and increase the longevity of their fields. The gradual discontinuation of the salting practice during the 1940’s in the United States may have increased the importance of the crown rotting disease.

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