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Irrigation-Nitrogen Studies in Asparagus and Measurement of Soil Moisture Changes by the Neutron Method¹

ABSTRACT

Three irrigation levels controlled at 0.4, 0.8, and 2 to 5 bar soil suction were combined factorially with two N levels and two varieties of asparagus (Asparagus officinalis) in a 4-year study. The two N treatments consisted of 112 kg N/ha and 560 kg N/ha obtained from (NH₄)₂SO₄ and the two varieties were ‘309’ and ‘500W’. Significantly higher spear yields were obtained in the 0.8 and 2 to 5 bar irrigation treatments as compared to the 0.4 bar level. The decreased spear yields in the relatively wet treatment were attributed to the effects of lower soil temperatures in that treatment prior to and during the cutting season. Fern yields were highest in the 0.4-bar suction treatment and decreased progressively with drier irrigation treatments. High N significantly increased both spear and fern yields and was significantly superior in efficient use of water in spear production as compared to a lower N level.

Soil moisture changes with irrigation treatments were measured with neutron equipment and the data used to determine depth of root activity, depth of wetting, and the volume of water in the soil following each irrigation. The water measured in the soil was compared to that applied. The differences ranged from ± 1.2% to 1.6% which is within the range of counting error for the neutron equipment.

Efficiency in production was calculated from water applied because this included all plots rather than only those with access tubes used for neutron measurements.

¹ Contribution from Department of Vegetable Crops, University of California, Riverside.

² Soil Physicist and Specialist, respectively, Department of Vegetable Crops.

Received for publication December 1, 1969. Accepted for publication January 9, 1970.