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V. SUMMARY AND CONCLUSIONTwo field experiments were carried out at EL-Khattara Experimental Farm, Fac. Agric., Zagazig University during two successive winter seasons of 2000 - 2001 and 2001 - 2002.First Experiment: Effect of application methods and different levels of nitrogen and potassium fertilizers on onion plants.This experiment was conducted to investigate the effect of fertilizer application method , i.e. fertigation and soil application and N + K2O rate; i.e., 60 kg N + 75 kg K2O , 80kg N + 100 kg K2O and 100 kg N + 125kg K2O / fed. via using drip irrigation system on growth , plant chemical composition, yield and its components as well as storability of onion under sandy soil conditions.The obtained results could be summarized as follows :1. Application of fertilizers via fertigation method significantly increased plant height , number of leaves per plant, diamater of both bulb and neck as well as bulbing ratio and dry weight of different plant parts, i.e. leaves, bulb and roots compared to soil application method.2. Increasing the rate of N + K2O fertilizer up to the highest used level, i.e. 100 kg N + 125 kg K2O /feddan significantly increased all the above mentioned characters with no significant differences with the medium rate, i.e. 80 kg N + 100 kg K2O /feddan.3. The best interaction treatment for all studied growth character of onion plants was application of 100 kg N +125 kg K2O / fed. via fertigation compared to the other interaction treatments.4. The highest values of photosynthetic pigments in onion levels, i.e. chlorophyll a, b, total and carotenoids were recorded by using fertigation methods in comparison with traditional application method (soil application).5. The maximum concentrations of chlorophyll a, b, total and carotenoids in onion leaves were recorded with the highest N + K2O application rates 80 kg N + 100 kg K2O and 100 kg N + 125 kg K2O per feddan at different sampling dates.6. Application of 100 kg N + 125 kg K2O /fed. Through fertigation method was the best interaction treatment for increasing all studied photosynthetic pigments in onion leaves.7. Nitrogen, phosphorus and potassium total uptake by onion plant were recorded at its maximum values when plants fertilized via fertigation methods compared to traditional method of fertilizer application.8. Increasing N + K2O fertilizer rate up to the highest rate ( 100 kg N + 125 kg K2O /fed.) increased N, P and K total uptake by onion plants when compared to the lowest N + K2O rate.9. Total minerals uptake (N, P and K) by onion plant was at its maximum value in the case of using the interaction between application of 100 kg N + 125 kg K2O / fed. via using fertigation method.10. Fertigation method of fertilizer application was the best treatment for increasing yield of grade 1, 2 , total yield, exportable yield , and marketable yield as well as average bulb weight of onion compared to soil application method under sandy soil conditions via using drip irrigation system .11. Application of 100 kg N + 125 kg K2O was the best fertilizer rate for maximizing yield and its components with no significant differences with 80 kg N + 100 kg K2O/ feddan in this respect.12.The highest increments of yield and its components were obtained by using fertigation method and application of 100 kg N + 125 K2O / feddan when compared with the other interaction treatments.13. The lowest weight loss, sprouting and decay percentage in onion bulbs were recorded by using traditional fertilizer application compared to fertigation method which recorded the highest values in this respect.14. Application of lowest N + K2O fertilizer rate (60 kg N + 75 kg K2O/fed.) significantly decreased weight loss, sprouting and decay percentage in onion bulbs and it was the best fertilizer rate in this respect .15. Application of the low fertilizer rate (60 kg N 75 kg K2O /fed.) via soil application method was the best interaction treatment for reducing weight loss, sprouting and decay percentage in onion bulb compared to the other interaction treatment.Second Experiment: Effect of the water supply and different levels of nitrogen and potassium fertilizers on onion plants.This experiment was conducted to investigate the effect of irrigation water quantities, i.e. 1500, 2500 and 3500m3/ feddan and N + K2O fertilizers rates; i.e., 60 kg N + 75kg K2O, 80 kg N + 100 kg K2O and 100 kg N + 125 kg K2O / feddan on growth , plant nutritional statues, yield and its components , bulb quality, as well as bulb storability.The obtained results could be summarized as follows:1. Application of 2500 or 3500 m3 water/ feddan produced the highest values of plant height, number of leaves/ plant, bulb diameter, neck diamater and bulbing ratio compared to 1500m3 /feddan.2. Increasing the rate of N + K2O fertilizer up to the highest used level, i.e. 100 kg N + 125 kg K2O / feddan significantly increased all the above mentioned characters with no significant differences with the medium rate, i.e. 80 kg N + 100 kg K2O /feddan.3. The interaction between water quantity (3500 m3 /fed. and 100 kg N + 125 kg K2O/fed.) was the best interaction treatment for increasing the above mentioned studied growth parameters of onion plants.4. Chlorophyll a , b, total (a +b) as well as carotenoids content were significantly increased with decreasing irrigation water quantity up to 1500m3/ feddan , while 2500 and 3500 m3 /feddan recorded the lowest values in this respect.5. The maximum concentrations of chlorophyll a, b, total and carotenoids in onion leaves were recorded with the highest N + K2O application rates up to the two highest rate 80 kg N + 100 kg K2O and 100 kg N + 125 kg K2O per feddan at different sampling dates.6.Application of 1500 m3/water/feddan and fertilization of onion plants with 60 kg N + 75 kg K2O / feddan gave the highest values of chlorophyll a, b, total (a+ b) and carotenoids in leaves tissues of onion plant and this treatment was the best interaction treatment in this respect.7.Irrigation onion plants with moderate or high levels of water quantities (2500 or 3500m3 water / feddan) recorded the higher values of minerals total uptake ( N ,P and K) by onion plants compared to the low water quantity (1500 m3 /feddan) which recorded the lowest values of N , P and K total uptake.8. Increasing N + K2O fertilizer rate up to the highest rate ( 100 kg N + 125 kg K2O /fed.) increased N, P and K total uptake by onion plants when compared to the lowest N + K2O rate.9. The best interaction treatment for increasing N, P and K total uptake was irrigation onion plants with 2500 or 3500 m3/feddan and fertilizer with 100 kg N + 125 kg K2O / feddan.10. Irrigation water quantity at 2500 or 3500 m3 / feddan gave the highest yield of grade 1, 2, exportable and marketable yield as well as average bulb weight with no significant differences between them. On the other hand, application of 1500 m3 /feddan recorded the lowest values in this respect and recorded maximum values of water use efficiency.11. Application of 100 kg N + 125 kg K2O was the best fertilizer rate for maximizing yield and its components and water use efficiency with no significant differences with 80 kg N + 100 kg K2O/ feddan in this respect.12.Irrigation onion plants with 2500 or 3500 m3/feddan and fertilization it with 100 kg N + 125 kg K2O was the best interaction treatment for increasing yield and its components as well as average bulb weight. The best interaction treatment for water use efficiency was water quantity at 1500m3/fed and 80kg N+ 100 kg K2O or 100 kg N + 125 Kg K2O.13.The lowest weight loss, sprouting and decay percentage during storage periods were recorded from irrigation onion plants with 1500 m3 water/ feddan.14.Application of lowest N + K2O fertilizer rate (60 kg N + 75 kg K2O/fed.) significantly decreased weight loss, sprouting and decay percentage in onion bulbs and was the best fertilizer rate in this respect .15. The best interaction treatment for reducing weight loss , sprouting and decay percentage in onion bulbs., during storage periods were irrigation quantity 1500m3/ feddan and fertilization with 60 kg N + 75 kg K2O / feddan.General ConclusionFrom the aforementioned results, it could be concluded that fertilization of onion with the highest rate of NK fertilizers (100 kg N + 125 kg K2O/feddan) through irrigation water at 2500m3 /feddan under drip irrigation system in sandy soil were enough for enhancing onion growth, minerals uptake and maximizing onion bulbs yield with good bulbe quality. But, it was not beneficial and favorable for the storability of onion bulbs, for this reason, it is nessesary to make more works to find the suitable and favorable fertilization through fertigation with other treatment such as micro elements, organic fertilizer, date of applying fertilizer, ect., which give the maximum onion yield with good storability.
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