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Abstract Nitrogen application to soils has greatly increased in the past 10 years. Millions of tons of N fertilizers have been added to soils at each year, often disregarding the possible decrease in the efficiency use when losses of N occurred. Ammonium N is oxidized to NO-3- N in mo~t soils during all seasons except when environmental conditions are prohibitive. If N could be kept in the NH+. form until plant utili~ation. less N loSS would occur. The n$t result would be greater Nuse efficiency. The ideal fertiliz~r m~y be considered as orie that (1) needs only a single application to ’supply the amounts of nutrients required for optimum plant growth during the entire growing season, (2) has:high maximum percentage recovery in order to achieve higher return to production input. and (3) has minimum detrimental effects on soil. water and atmospheric environments. In recent years considerable interest has been evident in controlled- release N fertilizers to regulate the supply of nitrogen of the plant through -out the growing Beason, thus minimizing N losses and maximizing the efficiency of the applied N in terms of uptake and yield. The purpo8~ of this study was to evaluate the efficiency of some N- slow- release fertilizers applied alone or in combination· with phosphatic fertilizers. The research work embodied in this investigation included four experiments: 1- First green-house experiment: The first green~ house experiment was carried out in the summer season of 1992 at the Giza Farm, Soils and Water Research Institute, to evaluate both direct and residual effect of N source, i.e. ammonium nitrate, ammonium sulphate, urea, seu, UF and Kpp- UF combined with calcium superphosphate for corn grown on an alluvial caly loam soil. The obtained results could’be.8WD11larized as follows 1- Regardless P appli~ation, most of the N sources, except urea and seu showed almost similar irowth response pattern where’ dry matter, ’cyieJd ins isniff cant;lyincreased : , -,’,.1 with N application a8comp;a~e:(Ito original treat.m’entsafAS and AN, which were equally eftictive. 2- The slow- release fertilizer KPP- UF (alone) and seD combined with 15 kg P205/ fed. were the most effictive .. treatments in respect to corn growth followed by UFo 3- Corn plants increased gradually .Ln their content of N, P and K by increasing the rate of applied Buperphosphate. On the other hand KPP- UF showed the highest stimulative effect on P and Kcontent of corn plants. 4- KPP- UP and seu produced the highest values of N uptake by corn plants when they were added in combination with superphosphate. 2- Nitrogen and potassium losses from clay 100m soil treated with sol~ble and slow- release fertilizers under corn and fallow: ]- Values of total leached soluble N (NH4+ + No”::’3) during 9 weeks were maximized under fallow conditions. In respect to NH3 loss, the highest figures were observed under fallow condition. while. the rate of loss was decrease with N fertilization according to the order AS > AN > Urea > seu ’) KPP- UF . 2- Leaching 10s8 of Nij+4- N is negligible either under fallow conditions or with corn cropping during the experimental periods. Only with AN and seu, the N loss was not appreciable under fallow till the 6th week. but AN was very low only under cropping at the same period. 3- Appreciable NO-3-N could not be detected •i. n leachates of soil treated with either seu Or ~pp- UF under fallow or under corn cropping. AI_ost similar trends were also obtained with the total amount~ of N leached. 4- It is very much interesting to observe that the loss of soil K through leaching was minimized. in case of KPP -UF fertilization. 5- The amounts of Nand K leached at from the treatments of AN, AS. urea. SCU and’KPP-UF explain the dry matter yield of corn results. KPP- UF and SCU produced higher dry weight of corn plants and N. P arid K uptake than the other N- sources. 11- Field experiment: A field experiment was established at Bahteem Agricultural Research Station on a clay loamy soil for three successive growing season duririg 1989 and 1990. Sunflower plant (”elianthus annuus L.) cv. Giza 1 was grown on the experimental site in 1989. A wheat (L..aestivuIQ L.) crop. cv. Sakha was grown in October season. 1989. followed by corn plant (Zea mays L.)cv. ,Giza 2. In the first trial ur~a was applied at 45 kiN/fed. in two equal doses. i.e. just before sowing and before the 3rd irrigation. The slow release fertilizers KPP- UF and UF were added at the same rate in one dose. just before sowing. Superphosphate was applied in two doses. i.e. 15 a..nd 30 kg P20!/ fed.. however. potassium sulphate was added at 24 kg K20/ fed. as a basal dress to all experimental plots before planting. Thus. there were 3 N- treatments having Nfertilizers + 15 kg P20S and another 3 N- treatments having 30 kg P20S/ fed~ besideth.e control treatlnebnt in a COllplete randomized block desigp with four replicates. The obtained results are su•••a•rlzed as follows; 1,- Fertilization with”,readily soluble or slow-release N-fertiJizers in sunflowerp!ant enhanced plant, height stem diameter. head diameter and~husk percent compared with the untreated one. 2- There was no signi!icant difference in t~e vegetative characteristics: ~eed,weight per plant, yield of seeds and weight of 100 seed (seed index) of sunflower plant. Oil concentration in the seeds was increased as P20S addition was increased from 15 to 30 kg P20S/ feddan. 3- Slow- release fert£lizers have the disadvantage that they are not suitable for crops that require considerable supplementals of nitrogen through a short growth period. In such case a supporting dose of readily soluble N may over -come this disadvantage. 4- The application of slow- release tertil’izers combined with 15 or 30 kg P20~/ fad., resulted in higher dry weight of wheat plants as compared with the soluble release ones, or with the control. 5~ The dry weight of wheat plants obtained from the untreated plots ammounted to about 50 ’I. of that produced from plots treated with the recommended treatment. With KPPUF fertilization. the reduction was decreased by 10 ’I. only comprising about 90 ~ of the yield in case of recommended dose fertilizer. 6- There is a positive significant influence in nutrients uptake by wheat plants with slow- release fertilization. The order of increase in nutrients uptake was as follows UF 45 kg N/ fed. + 30’kg P20!5 / fed. > KPP- UP 45 kg N/ fed. + 30 kgP:iOe/:,fed. ) KPP- UF 45 kg N/ f~d. + 15 7- A stimulation effect on plant height. ..number of ’ tillers and number of spikes ~er plant was gradually dbserved comparing ~he slow- rel~ase fertilizer.withthe solubl~ one. The residual effects of KPP- UF treatments was observed to give the highest values either by the application of 45 kg N + 30 kg P20S / fedd~n or by 45 kg N + 15 kg P20!5/ fed. as compared to the application of urea. 8- Considering the residual effect due to N f e r t il ization on grain yield of wheat plants; the obtained response decreased in the following order : 45 kg N as KPP- UF + 30 kg P203/ fed. ; 45 kg N as UF + 30 kg P20!l / fed. ; 45 kg N as KPP- UFo 45 kg N as urea + 30 kg P20!l / fed. ; 45 kg N as urea + 15 kg P20~ / fed. and the controlled plants. 9- With respect to straw yield of wheat planted after sunflower, the residual effect due to slow- release fertili- ~er seems to be adequate either it was added alone or combined with 15 or 30 kg P20lS/ feddan. 10- The residual.effectfromKPP- UP and UP either alone or associated with S5 kg/ fed. ure~- N, aignificantly enhanced the length of ear~the number 6f ears per plant, the diameter of ear and the shelling percent of corn as compared to unfertilized plots, but there were no significant differences between them and the values obtained under the recommended treatment. 11- Regardless of the effect of residual treatments combined with superphosphate, a compensation rate w~s generrally adequate to corn yield. the preference of the slowrelease fertilizers i. eminent. Ammonia loss byvolatilization: 1- In calcareous soil, ~he obtained results revealed that NH3 loss generally followed this descending. order of : AS > urea > AN > KPP- Of > UF > SCU, within 4 weeks period. The rate of volatilization from AS and urea was much greater than from AN. 2- The risk of NH310ss increases in sandy soil, and the treatments had the following descending order: AS > Urea > AN> KPP- UF > UF > seu. 3- The greatest values of NH3 loss were observed in clay loam soil treated with urea and AS. While NH3 loss from KPP- UF, seu and UF occurred to 8 less extent. |