Nine row‐crop sites, where data for nitrogen fertilizer use, crop yields, and amounts of irrigation water used were available for a number of years, were studied to estimate the N balance as related to NO3− in water in the unsaturated zone from below the zone of root influence to the water table or to the 15‐m depth.The system of predicting NO3− concentrations in drainage waters based on the difference between N inputs and N removal in harvested crop sand the drainage volume in which the excess N, converted to NO3−, is dissolved, was valid in open‐porous soils containing no layers that restrict water movement within the soil profile (0‐ to 2‐m depth). A combination of losses plus net immobilization of up to 56% had to be assumed in some soils to account for all the N loss. In two soils that had been used for disposal of feedlot manure, net mineralization of N from the organic N pool had to be assumed to explain the data obtained.The current fertilization and irrigation practices used for some row crops in southern California leave varying amounts of NO3− in the drainage water. The amounts depend on the total N added, crop removal, drainage volume, net mineralization, and losses.

Soil samples to the 15‐m depth beneath asparagus (Asparagus officinalis L.) and celery (Apium graveolens L.) were taken to determine the NO3− concentration in the solution of the unsaturated zone and to estimate the soil N balance. Transit time for water to move to the 15‐m depth was calculated from drainage volumes and volumetric water contents. Nitrogen balance was calculated from data for N input, N removal in harvested crops, and water records for the calculated transit time.The NO3− concentration in the unsaturated zone increased with increase in N rate but was inversely related to the leaching volume. Denitrification was assumed to be the cause of high N losses with high irrigation levels. However, the rather high loss of 67.7% in the celery experiment, which received large amounts of chicken manure, was assumed to be a result of both net immobilization and denitrification. A combination of high losses of N, which ranged from 18.3 to 67.7%, and large amounts of excess N, in the NO3− form in the soil could have been one cause of the low efficiency of recycling N by these crops. The data suggest that high rates of N combined with high levels of water use are conducive to denitrification in relatively permeable soils.

In propagating Asparagus officinalis L. through the method of shoot apex culture, apices of terminal buds of spears produced in vitro were found to be equally satisfactory as explants as those of lateral buds of spears obtained from the field. A maximum number of plants was obtained when the cultures were illuminated 4-20 hr daily with white fluorescent or Gro-Lux lamps at an intensity of 1000 lux. A constant 27°C temp was also optimum for plant formation in vitro. Histological examination revealed that roots arose adventitiously from callus which formed at the base of the explant, whereas spears originated from axillary buds. Successful transfer of plants from laboratory to soil required a prior reculture in a medium lacking NAA and with the light intensity increased to 3000 or 10,000 lux. Examination of the chromosome numbers of plants propagated through shoot apex culture showed that the original diploid status had been retained in every plant.

Asparagus, a cross-pollinated dioecious crop, is generally propagated through seeds, and extreme variation in yielding ability of individuals in a variety is common. Consequently, the use of small plot technique for field investigations has been virtually inapplicable.