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Abstract The objectives of this study were to evaluate the impact of organic residues, time of incorporation of residue before sowing wheat vis-a-vis residues burning and removal on soil chemical properties, soil fertility status and crop production in rice–wheat system. This study aimed also to investigate rice straw decomposition, then nutrients release as a function length of incorporation period of rice straw. The study was also carried out to evaluate the bioavailability status of the studied nutrients in soil in a trial to control the environmental pollution. To achieve these objectives, four sets of studies were performed. The first study investigated the effect of incorporation period of rice straw on organic matter decomposition and on soil chemical properties under controlled conditions of the column experiment. The second experiment investigated the role of starter dose of N combined with rice residues together, or with either pig manure or the leguminous green manure of Sesbania sesban to enhance the decomposition of rice straw under field conditions (field experiment). In addition, the same study investigated the effect of incorporation period of rice residues on soil fertility parameters and on the yield of both wheat and rice. The third experiment was designed to estimate rice straw residues decomposition under field conditions using litterbag technique during the pre wheat fallow period and during wheat and rice growth. The obtained results of the three experiments could be summarized as follows: 1. Column experiment: 1. The alluvial soil exhibited higher EC and pH values, and N and K contents, as well, compared with the calcareous soil, in all treatments. 2. On contrast, the calcareous soil showed a higher P content when compared with the alluvial soil as a result of the applied all treatments.3. The treatment pig manure + rice straw residues incorporated at 105 days incubation gave the lowest pH and EC values of the calcareous and alluvial soils, while the control treatment gave the highest pH and EC values 4. The treatment pig manure + rice straw residues incorporated gave the highest values of N, P and K soil content, while the control gave the lowest values. 5. Incensing NPK fertilizer dose decreased pH values of the calcareous and alluvial soils but it increased EC, N, P and K values. 6. The treatment pig manure + rice straw residues incorporated + 100% NPK gave the lowest PH values followed by rice straw residues incorporated alone + 100% NPK. 7. The treatment pig manure + rice straw residues incorporated increased values of soil N, P and K were noticed with followed by rice straw residues incorporated alone 8. The treatment pig manure + rice straw residues incorporated +100% NPK gave the highest soil N, P and K, while the lowest values were obtained by control treatment. 2. The field experiment: 2.1. Soil N, P and K contents, Humic acid, fulvic acid, nutrients contents of humic acid & fulvic acid and organic matter after wheat harvesting: 1. Rice straw compost gave the highest soil N, P and K content, while, rice straw burning and rice straw removal gave the lowest values. 2. Increasing fertilizer dose increased soil N, P and K content 3. Rice straw compost + 100% NPK gave the highest values of soil N, P and K content while, the lowest values were obtained by 50% NPK with rice straw burning or rice straw removal 4. Rice straw incorporated at 45 days +pig manure+ 100% NPK andrice straw compost + 100% NPK enhanced humic acid, fulvic acid and organic matter, followed by rice straw incorporated at 45 days +green manure+ 100% NPK. 5. Rice straw incorporated at 45 days +pig manure+ 100% NPK and rice straw compost + 100% NPK enhanced the values of available nutrients of humic acid and fulvic acid at 15 and 30 cm depth after wheat harvesting comparing with rice straw burning + 100% NPK. 2.2. Soil EC, pH and SAR after wheat harvesting: 1. Rice straw incorporated at 45 days +green manure gave the lowest EC value (1.71ds/m) followed by rice straw compost and rice straw incorporated at 45 days+ pig manure(1.72 and 1.73 d S/m) respectively, 2. Rice straw incorporated at 45 days +green manure+ 50% NPK gave the lowest EC value followed by rice straw compost + 50% NPK and rice straw incorporated at 45 days+ pig manure+ 50% NPK 3. Rice straw incorporated at 45 days+ pig manure showed the lowest p H value followed by rice straw compost 4. Rice straw incorporated at 45 days+ pig manure+ 50% NPK produced the lowest pH value followed by rice straw incorporated at 45 days+ pig manure+ 100% NPK and rice straw compost + 50% NPK ( 7.72, 7.79 and 7.81)respectively. 5. Rice straw incorporated at 45 days +green manure+ 50% NPK and rice straw compost + 50% NPK showed the lowest SAR followed by rice straw incorporated at 45 days+ pig manure+ 50% NPK (8.29, 8.29, and 8.42) respectively. 6. Increasing fertilizer rate decreased EC, p H value and SAR 7. Rice straw burning + 100% NPK, rice straw burning + 50% NPK and rice straw removal + 100% NPK gave the highest EC, p H and SAR values.2.3. Wheat leaf, grain and straw N, P and K contents: 1. Rice straw incorporated at 45 days +green manure gave the highest values of leaf N, grain N and straw P contents followed by rice straw incorporated at 45 days +pig manure and rice straw compost. Leaf P, grain P and K and straw K contents were enhanced by rice straw compost, rice straw incorporated at 45 days +green manure or rice straw incorporated at 45 days +pig manure. Rice straw compost and rice straw incorporated at 45 days +pig manure increased Leaf K and straw N contents, respectively. On contrast, rice straw burning gave the lowest values. 2. Increasing NPK fertilizer dose increased wheat leaf, grain and straw N, P and k contents. Rice straw incorporated at 45 days +pig manure+ 100% NPK and rice straw compost + 100% NPK enhanced leaf K, grain N, increased P and K and straw P contents. 3. Rice straw incorporated at 45 days +green manure+ 100% NPK increased leaf N and P and straw K contents. While, the lowest values were obtained by rice straw burning or rice straw removal with 50% NPK. 2.4. Recovery efficiency, physiological efficiency and agronomic efficiency of wheat: 1. Rice straw incorporated at 45 days +green manure gave the highest values of N recovery efficiency (21.63%) and N agronomic efficiency (4.92 kg grain/kg N uptake) of wheat followed by rice straw compost and rice straw incorporated at 45 days +pig manure, respectively and the lowest values were produced by rice straw burning. 2. Rice straw incorporated at 30 days showed the highest value of physiological efficiency, while rice straw removal gave the lowest value. 3. Increasing NPK dose decreased physiological efficiency and agronomic efficiency of wheat but it increased recovery efficiency of N. 4. Rice straw incorporated at 45 days +green manure+ 100% NPK, rice straw incorporated at 30 days+ 50% NPK and rice straw incorporated at 45 days +green manure+ 50% NPK gave the highest values of N recovery efficiency, physiological efficiency and agronomic efficiency of wheat . 2.5. Wheat grain yield, straw yield, biological yield dry weights, harvest index and crop index: 1. Rice straw incorporated at 45 days +green manure gave the highest wheat grain yield, biological yield dry weights, harvest index and crop index (3.090 t/fed, 6.758 t/fed, 45.71% and 84.24%, respectively) followed by rice straw compost. While, the lowest values were obtained by rice straw burning. 2. Increasing fertilizer rate recorded the highest values of grain yield, straw yield, biological yield dry weights, harvest index and crop index 3. Rice straw incorporated at 45 days +green manure or rice straw compost with 100% NPK gave the highest values of grain yield dry weight (3.364 and 3.349 t/fed, respectively). in addition, rice straw incorporated at 45 days +green manure+ 100% NPK gave the highest biological yield dry weight (7.280 t/fed). on contrast, the lowest values of grain yield, straw yield and biological yield dry weights (2.531, 3.147 and 5.678 t/fed, respectively) were produced by rice straw burning + 50% NPK. 4. Rice straw compost + 100% NPK gave the highest values of harvest index and crop index (46.63 and 87.38%, respectively, followed by rice straw incorporated at 45 days +green manure+ 100% NPK. While, rice straw burning + 50% NPK gave the lowest values.2.6. Soil N, P and K contents, humic acid, fulvic acid, nutrients contents, humic acid & fulvic acid and organic matter after rice harvesting: 1. Rice straw incorporated +pig manure+ 100% NPK and rice straw compost + 100% NPK gave the highest values of soil humic acid, fulvic acid, humic acid and fulvic acid of nutrients contents and organic matter after rice harvesting. 2. Rice straw incorporated at 45 days +pig manure+ 100% NPK and rice straw compost + 100% NPK gave the highest values of soil N, P and K contents, humic acid, fulvic acid, humic acid and fulvic acid of nutrients contents and organic matter after rice harvesting followed by rice straw incorporated +green manure+ 100% NPK. 2. 7. Soil EC, pH and SAR after rice harvesting: 1. Rice straw compost gave the lowest EC value followed by rice straw incorporated at 45 days +green manure and rice straw incorporated at 45 days+ pig manure 2. Rice straw compost + 50% NPK gave the lowest EC value followed by rice straw incorporated at 45 days +green manure+ 50% NPK and Rice straw incorporated at 45 days+ pig manure+ 50% NPK. 3. Rice straw incorporated at 45 days+ pig manure gave the lowest p H value followed by rice straw compost 4. Rice straw incorporated at 45 days+ pig manure+ 50% NPK gave the lowest value of p H followed by rice straw compost + 50% NPK and rice straw incorporated at 45 days+ pig manure+ 100% NPK. 5. Rice straw compost + 50% NPK gave the lowest SAR followed by rice straw incorporated at 45 days+ pig manure+ 50% NPK and rice straw incorporated at 45 days +green manure+ 50% NPK 6. Rice straw burning + 100% NPK, rice straw burning + 50% NPK and rice straw removal + 100% NPK gave the highest EC ,p H and SAR value. 7. Increasing fertilizer rate decreased EC, p H and SAR value. 2.8. Rice leaf, grain and straw N, P and K contents: 1. Rice straw incorporated at 45 days +pig manure gave the highest rice leaf N, P and K, grain N, P and K and straw N and K contents values followed by rice straw compost and rice straw incorporated at 45 days +green manure. The highest K straw content was obtained by rice straw compost. While, rice straw burning gave the lowest values. 2. Increasing NPK dose enhanced rice leaf, grain and straw N, P and K contents values. 3. Rice straw at 45days +pig manure or rice straw incorporated at 45 days +green manure with 100% NPK improved rice leaf N and P and grain N. Also, Rice straw incorporated at 45 days +pig manure+ 100% NPK enhanced leaf K, grain P and K and straw N and P contents. While, rice straw burning + 50% NPK gave the lowest values. 2.9. Recovery efficiency, physiological efficiency and agronomic efficiency of rice: 1. Rice straw incorporated at 45 days +pig manure gave the highest values of N recovery efficiency (56.93%), rice straw incorporated at 45 days gave the highest values of N physiological efficiency (28.59 kg grain/kg N uptake) and rice straw compost gave the highest values of N agronomic efficiency (9.92 kg grain/kg N uptake) of rice were obtained. 2. Rice straw burning and rice straw removal gave the Lowest values in this respect 3. Increasing NPK dose decreased N physiological efficiency and agronomic efficiency of rice but it increased recovery efficiency. 4. Rice straw incorporated at 45 days +pig manure+ 100% NPK gave The highest values of N recovery efficiency (58.63%), rice straw incorporated at 45 days +green manure+ 50% NPK gave The highest values N physiological efficiency (35.54 kg grain/kg N uptake) and rice straw compost + 50% NPK gave The highest values of N agronomic efficiency (15.44 kg grain/kg N uptake) of rice. 2.10. Rice grain yield, straw yield, biological yield dry weights, harvest index and crop index: 1. Rice straw compost, rice straw incorporated at 45 days +green manure or rice straw incorporated at 45 days +pig manure gave the highest grain yield dry weight (2.875, 2.863 and 2.818 t/fed, respectively). Also, rice straw incorporated at 45 days +pig manure produced the highest straw yield and biological yield dry weights (4.247 and 7.065 t/fed, respectively). While, the lowest values were obtained by rice straw burning. 2. Increasing NPK dose increased Rice grain yield, straw yield and biological yield dry weights. 3. Rice straw incorporated at 45 days +green manure+ 100% NPK produced the highest grain yield dry weight value and the highest straw yield was noticed with rice straw incorporated at 45 days +pig manure+ 100% NPK. Also, rice straw incorporated at 45 days +green manure+ 100% NPK or rice straw incorporated at 45 days +pig manure+ 100% NPK gave the highest biological yield dry weight (7.740 t/fed). On contrary, rice straw burning + 50% NPK gave the lowest values. 4. Rice straw burning + 50% NPK and rice straw incorporated at 15 days+ 100% NPK produced the highest harvest index values produced by (46.69 and 46.63%, respectively). Also, rice straw burning + 50% NPK gave highest crop index (87.96%). While, rice straw incorporated at 45 days +pig manure+ 100% NPK gave the lowest values.3. The third experiment: 1. Rice straw incorporated at 15 days gave the highest values of rice straw residues remaining weight%, C% and C: N ratio were noticed with litterbags buried in plots received followed by Rice straw incorporated at 30 days, Rice straw incorporated at 45 days and rice straw incorporated at 45 days +green manure. While, rice straw incorporated at 45 days +pig manure gave the lowest values. 2. Litterbags buried in plots received rice straw incorporated at 45 days +pig manure produced the highest values of residues N, P and K contents followed by straw incorporated at 45 days +green manure. On contrast, rice straw incorporated at 15 days gave the lowest values. 3. Increasing NPK does decreased remaining weight%, C% and C: N ratio of rice straw residues, but it increased rice straw residues N%. 4. Rice straw residues buried at 15 cm in plots had higher values of N, P and K contents but it had lower values of remaining weight%, C% and C: N ratio compared with burying at 30 cm. 5. Litterbags of rice straw residues buried at 15 cm in plots received rice straw incorporated at 45 days +pig manure+ 100% NPK gave the highest values of N%, P and K contents and the lowest values of remaining weight%, C% and C:N ratio. 4. Evaluation of the bioavailability status of the studied nutrients in soil and water: 4.1. Bioavailability of Nitrogen in soil as a new recent approach to N management in soil or use of organic waste in agriculture in order to control N environmental pollution: A trial was made to apply an approach to N management in soil or use of organic waste in agriculture. The approach aims to calculate the amount of supplemental mineral N fertilizer needed by a desired crop yield from a simple equation gained from N –balance studies.If the mineral N added is lower than the amount should be added, it means that mineral N added is lower than crop N requirement of the desired yield needing more supplemental mineral N by the amount calculated. If the mineral N added is higher than the amount of N should be added, it means that mineral N added is higher than the crop N requirement of the desired yield. This excess of mineral N will be lost from the rooting zone, and mainly by leaching to the ground water in the form of NO3- . This approach was checked up for all yields of wheat field experiment for all the studied treatments. The values of excess mineral N may be either positive or negative. Negative values indicate the lake of N added, this appeared only with treatment of rice straw removal and 50%NPK(T1+F1), which means that mineral N added is deficient to balance N outputs in order to verify the wheat yield of this treatment (T1+F1). Positive values point to a tendency towards excess N from all inputs that represent a potential for N losses. The rest of the studied treatment exhibited positive excess of N added. The organic wastes; compost , green manure and pig manure, as well as incorporating rice straw proliferated an excess N as a result of the application of such wastes especially when receiving 100%of NPK of the recommended dose by the Ministry of Agriculture. 50% NPK (F1) treatments appeared an excess ranged from (-2.3 to +13.1 kg/fed.) while treatments of 100%NPK (F2) exhibited an excess ranged from (23.8 to 30.1 kg/fed.). The highest values were obtained with pig manure or rice straw compost. 4.2. Bioavailability of phosphorus in soil: Total fertilizer P inputs should balance the output to avoid hazards due to both excess and deficient P. Organic wastes addition proliferated an excess P as a result of the application of such wastes especially when receiving 100% NPK of the recommended dose by the Ministry of Agriculture. The excess of P for F1 (50% NPK) ranged from +6.8 to 11.8 kg P/fed., and F2 (100%NPK) ranged from 16.9 to 22.6 kg P/fed.However, the same trend of N was observed for phosphorus. Finally: it could be concluded that the proposed approach, although it needs more investigation, it seems to be valid either for N & P management in soil or for use of organic wastes in agriculture, without sacrificing crop yields but significantly reducing environmental pollution. 4.3. The status of nitrate and some micronutrients in the water sources: 1. NO3- concentration in the irrigation water of EL- Nasser canal is good for irrigation and can be used without any restrictions for different soils and various plants. 2. NO3- concentration in water of EL- Salam canal as well as the drainage water of both canals can be used for irrigation with slight to moderate restrictions. 3. NO3- concentration in the drainage water was higher than the irrigation water. 4. The chance of nitrate pollution is higher in EL- Salam canal area as compared with EL- Nasser one. 5. The concentration of micronutrients (Fe, Mn, Cu, and Zn) in all sources of water are lower than the maximum permissible limits in irrigation water. Conclusion: Farmers practicing rice-wheat system under similar conditions are recommended to incorporate rice straw with either green manure or organic manure instead of burning or wasting otherwise. Also, rice straw compost can reduce the environmental pollution. Hence, higher yield with more income is expected for the farming community in this system of farming. The overall fertility and productivity of the land can be improved on sustainable basis. If the mineral N added is higher than the amount of N should be added, it means that mineral N added is higher than the crop N requirement of the desired yield. This excess of mineral N will be lost from the rooting zone, and mainly by leaching to the ground water in the form of NO3- , where over application of N in cereal crops led to low N recovery efficiency and risk of NO3 pollution to ground water. Finally: it could be concluded that the proposed approach, although it needs more investigation, it seems to be valid either for N & P management in soil or for use of organic wastes in agriculture. It is possible by this approach to calculate that amount of mineral fertilizers should be added to soil to verify the optimum realistic yield. This will lead to reduce the amounts of mineral fertilizers added to soils, and consequently control environment pollution. |