Ammoni losses does not appear to be a very significant pathway for loss. Soil pH decreased markedly a few centimeters from the emitter .An experiment was conducted to evaluate celery response, N uptake and N leaching as related to form, amount, and method of N-fertilizer application under drip irrigation . Fertilizer forms included ammonium sulfate and a slow release fertilizer applied to the soil before planting and urea ammonium nitrate applied with the irrigation water during the growing season. AS and SR were applied at 314 kg Nlha and UAN was applied at 168-, 336-, and 504 kg N/ha. Two irrigation variables were 400 and 500 rom of water application. The experiment was conducted on San Ernigdio sandy loam soil at the University of California South Coast Field Station near Santa Ana. Celery seedlings were-obtained from a commercial nursery and planted in two rows per bed. The distance between centers of each bed was 1 m. Three row spacings were used for each treatment. Bi-wall drip irrigation tubing was placed on the soil surface down the center of each bed equidistant from each celery row. The soil-applied fertilizer was placed approximately 5 em below the soil surface,fodder system for sale immediately below the drip line. All of the AS and SR fertilizer was applied prior to transplanting. Ten per cent of the N to be applied with the drip irrigation water was applied through the drip lines prior to planting.
Thereafter, UAN was applied during each irrigation to the appropriate rows until approximately one month before harvest after which fertilizer injection was stopped. Irrigation was usually done three times a week and occasionally a fourth irrigation was applied during hot, dry, windy periods. There was no marketable yield on the plot which did not receive N fertilizer. Treatments receiving UAN with the irrigation water had higher yields with 500 as compared to 400 rom water application. On the other hand, higher yields were obtained under the 400 as compared to the 500 rom irrigation treatment for the AS and SR fertilizer treatments. Furthermore, at comparable N application rates, the soil applied N resulted in significantly lower yields than application of N with the irrigation water. With the higher water application, more N leached below the root system than at lower irrigation rates, based on the pattern of N distribution in the profile at the end of the experiment. Application of N.with the irrigation water is superior to application of the N to the soil in a preplant operation. Split applications to the soil are mechanically impractical with drip irrigation. Celery requires continuously high soil water content which results in which leaching 105ses of soil-applied fertilizer. Applying the N with the irrigation water made it available to the plant continuously over the growing season and apparently much of the N was extracted by the root system as the water flowed past the roots; there was very little difference in the amount of N leached beyond the root zone for the different water application treatments. Nevertheless, there was some deep N movement with the drip system even under low N application.
The SR fertilizer produced a higher yield than AS. Nitrogen was retained within the granules and slowly released during the growing period, and was thus partially protected from leaching. In fact,observation at the end of the experiment indicated that not all of the N had been released from the capsules by harvest. The N left in the soil after cropping is a potential source for groundwater pollution. Whether the N does in fact get carried to the groundwater depends upon a number of subsequent factors such as precipitation and/or irrigation which will carry the N downward. A barley crop was grown on the experimental area after the celery crop was removed without further N application to measure residual N in the profile which could be removed by barley. For the plots receiving UAN, there was an increase in N uptake from plots receiving increasing amounts of UAN during the celery crop. For comparable amounts of N application, much more N was taken up in the barley on the plots receiving the SR as compared to the AS and UAN treatments. This is partially a result of the N retained in the capsules and also the N in the profile which had moved beyond the celery roots but remained accessible to the deeper rooted barley crop. For both AS and SR there was more N uptake from the 400 mm irrigation treatment as compared to the 500 rom irrigation treatment, suggesting that the higher water treatment moved some N beyond the depth of recovery by the barley plant. Two experiments were conducted at the University of California South Coast Field Station on celery using a sprinkler irrigation system . This system was chosen to experimentally apply a continuous water amount variable across the plot to determine the interaction between fertilizer N and water application on celery gro~h. This was accomplished by using “line source” irrigation where water application is highest next to the sprinkler line and decreases at increasing distances from the sprinkler line.
A standard sprinkler system applied water uniformly over the entire plot with fertilizer. Then irrigation was applied through a single line which provided high water application near the line which decreased with distance away from the line. In one experiment, different fertilizer N treatments were applied to the soil in rows perpendicular to the line source. This provided an opportunity to determine the growth under the different fertilizer treatments at different rates of water application. In the second experiment, some of the N was applied with the irrigation water under the standard irrigation and again these plots were perpendicular to the line source which allowed a comparison of celery growth in response to differential water application. In experiment 1, a comparison is made between preplant and no preplant fertilizer treatment and different amounts of N applied with the irrigation water. The preplant fertilizer was AS whereas the injected fertilizer was DAN. In experiment 2, all of the N was applied to the soil in bands with none being applied with the irrigation water.There are apparently counterbalancing factors in the effect of quantity of water application to celery. The celery prefers high soil water availability to maintain high turgor, rapid growth, and succulence. On the other hand, large applications of water could leach N from the root zone and decrease its availability to the plant. Since N was applied with the irrigation water throughout the growing season,fodder growing system it could partially compensate for N that might be leached. This was observed to be the case under the drip irrigation system. However, on the AS150 UAN150 treatment, the added leaching of preplant N under the highest water application may not have been sufficiently compensated for by the N applied in the irrigation water. For the soil-applied fertilizer treatments the results from the control and AS300 treatments clearly illustrate the interaction between water and N availability as dual determinants of crop yield. The highest yields under these two treatments were observed at the intermediate water application and decreased yields were found under the lower and higher water application. Presumably the reduced yields at lower water application was because of less than optimum water content and the decreased yield at high water application was due to low N availability, much of the N having leached from the root zone. Since all N in both of these treatments was in the soil at the beginning, this N was exposed to the greatest potential for leaching loss. A small experiment was conducted on celery using furrow irrigation , In this experiment, four rates of N fertilizer were applied. All treatments received 100 kg N/hapreplant as ammonium phosphate. The remainder of the N was applied as side dressed N split in two equal increments of urea applied 29 and 49 days after celery transplanting. At harvest time, there was no significant difference in yield for the three highest N application rates but the lowest had significantly lower yield. Even though the final yield was not significantly different for the three higher application rates, there was increasing rate of growth with increasing N application during the early stages, with the growth rate reaching a peak and then diminishing thereafter.
The lowest N treatment had not yet reached its peak grow~h rate at harvest time. These data illustrate that celery growth can be stimulated by high N but that with sufficient time the effects of N application rate on yield tend to diminish. Two experiments were conducted using furrow irrigation with broccoli as the test crop . The first experiment was conducted on a San Emigdio sandy loam soil very low in inherent fertility. The experimental variables consisted of three fertilizer N application rates , two irrigation treatments , and two N application procedures . One-third of the fertilizer was applied to the soil in a band adjacent to the plants prior to planting on all plots including those which were to receive N with the irrigation water. Thereafter the soi1- applied fertilizer was applied in two side dressings of 16-20-0 fertilizer or injected into the irrigation water in equal proportions during each irrigation. Hereafter the treatments will be referred to “inject” where fertilizer was applied with the irrigation water and “soil-applied” when fertilizer was applied as the two side dressings. Irrigation frequency was the same for both irrigation treatments but 30% more water was applied at each irrigation for the ET +30 treatment than for the ET treatment. Fertilizer was injected into the irrigation water continuously by a proportioning unit except at the end of each irrigation when the lines were flushed with water. The furrows were dammed at the end to avoid runoff. Under the lower irrigation treatment there were no differences in yield due to method of applying the N. Under the higher irrigation there was consistently higher yield when the N was applied with the irrigation water as compared to side dressing. Furthermore, there was lower yield under each fertilizer rate for the higher irrigation treatment. Irrigation to replenish water loss through ET provided for both high yields and higher N use efficiency as compared to excessive irrigation. Potential advantages of injecting N with the irrigation water include savings of labor and energy for the two side dress operations and avoiding plant damage during the side dress operations. In this experiment, efficient energy, N, and water use were consistent with high crop production. A second experiment was conducted with broccoli and furrow irrigation on the Sorrento loam. The furrows were 90 ill long. Yields were higher under the higher N application as compared to the lower application and for a given N application the average yields were always higher for the side dressing as compared to applying the N with the irrigation water. More N was removed in the crop than applied as fertilizer for the lower application rate and a very high percentage of the N applied under the higher rate was removed in the crop. Tensiometers installed indicated there was very little water movement deep into the profile, thus minimizing leaching losses. Under these conditions, N is used efficiently and growth appears to be related to the rate of application. In the second experiment, there was higher average yield when the fertilizer was applied as side dressing rather than injected with the irrigation water whereas there was no difference in the first experiment. The more uniform application throughout the row with continuous injection in the first experiment may have been a factor as compared to injection during part of the irrigation cycle during the second experiment. No harvestable yield resulted from unfertilized plants. There was a trend toward decreased plant growth with increased water application for the treatment which did not receive N, due to leaching of the small amount of N in the profile. The lower fertilizer treatment resulted in fairly uniform growth at different water contents except at the very dry end where there was relatively less growth, while the plots receiving the higher fertilizer treatments had a trend toward higher production with higher water content.