Study of Soil Pollution Risk by Nitrates in Orchard Irrigation

1. Study of the risk of soil pollution by nitrates in the irrigation of orchards on light soilsVladia Subkova, Evlogy MarkovInstitute for Land Reclamation and MechanizationSofia, BULGARIA Introduction Taking into account the specific requirements of the culture and type of soil, leading to higher yields and better quality production, the following topics are fixed: The annual fertilizer rate determined on the basis of chemical analysis of soil samples from the active root zone; The single fertilizer rate and periods for its application; Conditions for applying of the fertilizers, including the frequency and manner of their submission so to prevent infiltration into the lower soil layers and ground water.

2. Needs of fruit crops by nitric fertilizationEffect of the fertilization with nitric fertilizers and rules for achieving it Necessary elements of plants usually suffer a shortage of nitrogen, phosphorus and potassium. From previous experiments with fertilization of fruit-growing it can be considered the following: All the fruit trees strongly respond to nitric fertilizers, especially the peaches. Although in many cases the fruit trees do not respond to phosphorous and potassium, but to nitric fertilization only, there are indications that long-term nitric fertilization leads to serious physiological disturbances.

3. Nitric fertilizers Need for fertilization with nitrogen is determined on the basis of the soil reserves with mineral nitrogen by analysis of soil samples in accordance with the fruit needs.It is a salt of ammonia with nitric acid, white or slightly yellow in a color with a crystalline substance containing 34.5% nitrogen, of which half of the nitrogen in nitrate form and half in ammonium. The two forms are combined very successfully, which makes it suitable for almost all soil types and crops.Both the high water solubility and weak retention of ammonium nitrate from the soil to water leads to leaching and its removal in the groundwater. Excessive fertilization leads to environmental problems and to increased levels of nitrates in fruit.

4. Methods and deadlines for the fertilizer application in orchards • High yields are achieved when large quantities of fertilizer were applied by the following conditions: • Soil to be treated carefully and have shown good buffering capacity to absorb imported fertilizers and attach them gradually; • Fertilization is carried out not only mineral but with organic fertilizers; - To practice the profound apply of fertilizers; • To maintain a favorable water regime. Annual nitrogen fertilizer rate (0.4- 2.0 kg active substance/hae of nitrogen) should be allocated to two or three parts.

5. Fertilizer rates in the orchards The balance between imported and exported nutrients in the soil is the base of the concept of sustainable agriculture and is an integral part of "good agricultural practices” in EU. Approximately for each year of age of trees it should be applied 20-40 g of nitrogen (an active ingredient) per year. In this way, five-year tree should be enriched with an annual fertilizer nitric rate 100-200 g.

6. Nitric fertilizer rate The required quantity of fertilizer for the test plot, which must be applied in the spring, is determined by supplementing the reserves of the soil with nitric fertilizer to the needs of crop, in accordance with the data given in Table № 1. The annual fertilizer rate for maintenance fertilization of perennial crops in kg/ha, better security in the soil and optimal value of analysis for apples is 0.6 – 0.8 kg/ha nitrogen in the active substance which is equal to 1.76 – 2.35 kg/ha ammonium nitrate, because it contains 34.5% nitrogen. In the experimental section of the plot it has been applied nitric fertilizer rate in two parts -1/2 of the estimated nitrogen rate at the end of June, and after about 1 month - the second 1/2 fertilizer rate.

7. Results and discussionDetermination of reserves of the soil with nitric fertilizer The reserves of soil nutrients and humus content were determined by chemical analysis of soil samples taken before fertilization. It has adopted the following schedule of soil sampling – experimental plot was divided into three zones along the lateral line - I, II and III, in which the soil samples were taken from three depth zones - 30, 60 and 90 cm in near the trees. As a comparison, the control samples were taken from the middle of the main plot in order of the same depth. The data are presented in table 2.

8. Determination of reserves of the soil with nitric fertilizer - Table № 2

9. Reserves into the soil after application of the first doze of the fertilization–Table № 3

10. In the main plot, after applying the whole annual fertilizer dose, the mean value is 8.7 mg/kg as it can be seen in table 3. In the test area, where half of the filed annual fertilizer rate was applied, the amount of NH4 + NO2 is almost equal and it s respectively 8.30 mg/kg. • This indicates that in the main plot only part of the applied mineral nitrogen is absorbed by plants. So, about half of it was washed in lower soil layers. This is due to the fact that providing a greater quantity of fertilizer at once requires more water for reconstitution and thus more time for its application. • In the experimental section of the plot the mean value of the mineral sum indicate that almost all the submitted nitrogen was utilized by the plants and still have enough stocks in the soil before application of the second dose. In this section the last doze was filed in the late July, which will ensure the needs of culture in subsequent periods - after harvesting and setting of fruit buds for next year.

11. Leaf analysisTable № 4 • There were taken approximately 30 leaves from each tree at the site of sampling. The result shown in table 4 confirm the result describe above.

12. Conclusions Annual nitrogen fertilizer rate of 4 to 2.0 kg active substance of nitrogen per hectare must be allocated to two or three parts especially in the orchard on the light soils. Thank you very much!