الفهرس 
INTRODUCTION
Cropping sequenceOnly 14 pages are availabe for public view
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Abstract
Two field experiments were conducted at the Agronomy Department Farm, Faculty of Agriculture, Assiut University, Assuit Governorate, Egypt; during 2015/2016 and 2016/2017 seasons to study the impact of clover c.v. Fahl as a preceding crop and nitrogen fertilization on wheat. Two separate field experiments represented in wheat species (Triticum aestivum vulgare and Triticum durum). The cultivars studied were Sids-12 & Bany Suef-5 in which belongs to Triticum aestivum vulgare and Triticum durum, respectively. Each experiment was carried out in a randomized complete block design (RCBD) using a split-split plot arrangement with three replications. The cropping system (corn-clover-wheat and corn-fallow-wheat) were assigned in the main-plot, while the nitrogen rates (56.25, 75.00 and 93.75 kg N fed-1: application of 75, 100 and 125% of the recommended N fertilizer rate fed-1, respectively) were allotted in the sub-plot and different nitrogen split doses (two, three and four equal doses) were allotted in the sub-sub plots. The experimental unit area was 10.5 m2 (3×3.5) in each season.The first variable was cropping system. The intensification systems were as fallows.
3. Corn followed by temporary clover (Fahl) variety Giza 1 followed by wheat.4.Corn followed by fallow (without cultivation) followed by wheat.
The clover (Fahl berseem) was planted on September 22nd in the both seasons. After cutting the clover crop on December 6th in the both seasons then, wheat was sown on December 18th and 19th in 2015/2016 and 2016/2017 seasons, respectively using broadcasting (conventional tilled flat method).
The second variable was the nitrogen rates. Three rates of N were studied as follows: 4.75% of the recommended nitrogen fertilization (N56.25), (56.25 kg N fed-1).5.100% of the recommended nitrogen fertilization (N75.00), (75.00 kg N fed-1).6.125% of the recommended nitrogen fertilization (N93.75), (93.75 kg N fed-1).The nitrogen fertilization rates were applied in the form of urea (46.5% N) as a source of nitrogen.The third variable was the splitting of nitrogen fertilization doses. The treatments in this respect were as follows:4. Splitting of nitrogen fertilization doses into two equal parts before the second and third irrigations (Sp2).5. Splitting of nitrogen fertilization doses into three equal parts before the second, the third and the fourth irrigation (Sp3).6. Splitting of nitrogen fertilization doses into four equal parts before the second, third, fourth and fifth irrigations (Sp4).The results obtained for each experiment in this study could be summarized as follows: Chapter I Bread wheat 1.Weed traits:1. a. Weeds fresh weight (kg fed-1):The all studied factors had a significant effect in this respect through the two growing seasons. Moreover, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of weeds fresh weight (420.00 and 506.67 kg fed-1 in the first and second seasons, respectively) were obtained from the sequence of corn-fallow-wheat with high N rate (93.75 kg N fed-1) when it applied at two equal doses.1. b. Weeds dry weight (kg fed-1):
Weeds dry weight was significantly affected by all studied factors during the both seasons. Also, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of this trait (130.06 and 137.21 kg fed-1 in the two respective seasons) were recorded from the sequence of corn-fallow-wheat with high N rate (93.75 kg N fed-1) when it applied at two equal doses.2. Days number to 50% heading (day): The all studied factors turned to be significant in this respect through the both seasons. Here too, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of this trait (92.00 and 92.00 d in the two successive seasons, respectively) were obtained from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.3. Yield attributes:
3. a. Plant height (cm):The effect of all studied factors on plant height was significant in the two growing seasons. In addition, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of plant height (107.80 and 117.57 cm in the both seasons, respectively) were produced from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.3. b.Spike length (cm):The all studied factors proved to be significant in this respect through the two growing seasons. Also, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of spike length (12.73 and 14.23 cm) were noted from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses in the first and second seasons, respectively.3.c.Spikelets number spike-1:Spikelets number spike-1 was affected significantly by all studied factors in the two growing seasons. Furthermore, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of spikelets number spike-1 (21.47) was observed from the sequence of corn-clover-wheat with 75.00 kg N fed-1 when it applied at four equal doses in the first season, while the highest mean values of spikelets number spike-1 (22.07) was noticed from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses in the second season.3. d. Spikes number m-2:
The effect of all studied factors on spikes number m-2 was significant in the two growing seasons. Here too, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of spikes number m-2 (530.67 and 521.33 in the 1st and 2nd seasons, respectively) were noted from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.3. e. Grains number spike-1:Grains number spike-1 was affected significantly by all studied factors in the both seasons. In addition, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of grains number spike-1 (87.73 and 78.17 in the two respective seasons) were found from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.3. f. Seed index (g):The all studied factors caused a significant effect on seed index in the two growing seasons. Moreover, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of seed index (52.87 and 50.05 g in the two successive seasons, respectively) were produced from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.3. g. Grains weight spike-1 (g):
Grains weight spike-1 tended to be reacted significantly to all studied factors in the two growing seasons. Furthermore, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of grains weight spike-1 (3.86 and 3.61 g in the both seasons, respectively) were recorded from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.4- Yield traits and harvest index:
4. a. Grain yield (ardab fed-1):
The effect of all studied factors exerted significant influence on grain yield in the both seasons. Also, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of grain yield (27.47 and 28.22 ard fed-1 in the first and second seasons, respectively) were noticed from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.
4. b. Straw yield (ton fed-1):
The all studied factors had a significant effect on straw yield in the two growing seasons. Here too, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of straw yield (5.63 and 6.67 t fed-1 in the two respective seasons) were noted from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.4.c. Biological yield (ton fed-1)
The all studied factors proved to be significant on biological yield in the both seasons. In addition, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of biological yield (9.75 and 10.90 t fed-1 in the two successive seasons, respectively) were recorded from the sequence of corn-clover-wheat when with high N rate (93.75 kg N fed-1) when it applied at four equal doses.
4. d. Harvest index (%):The split nitrogen fertilizer factor had a significant effect in this respect in the both seasons, but the effect of studied cropping sequence did not reached a significant at 5% level of probability in the first season only, however the differences in the second season were significant. Also, harvest index was significantly affected by studied nitrogen fertilizer rates in the first season only, however the differences in the second season were not significant. In addition, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of harvest index (45.82%) was noticed from the sequence of corn-fallow-wheat with 93.75 kg N fed-1 when it applied at three equal doses in the first season, while in the second season the highest mean value of this trait (42.07%) was obtained from the sequence of corn-clover-wheat with 75.00 kg N fed-1 when it applied at four equal doses.5.Nitrogen Use Efficiency (NUE) (kg grains/kg nitrogen):The all studied factors had a significant effect in this respect through the two growing seasons except cropping sequence in the first season. Moreover, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of NUE (60.92 and 69.81 kg grains/kg N applied in the first and second seasons, respectively) were observed from the sequence of corn-clover-wheat with low N rate (56.25 kg N fed-1) when it applied at four equal doses.6.Quality traits:6. a. Flour percentage (%):The effect of all studied factors exerted significant influence on flour percentage in the two growing seasons. Also, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of this trait (92.57 and 92.75% in the two respective seasons) were obtained from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.6. b. Coarse bran percentage (%):The all studied factors caused a significant effect on coarse bran percentage in the both seasons. Here too, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of this trait (12.43 and 15.17% in the two successive seasons, respectively) were produced from the sequence of corn-fallow-wheat with low N rate (56.25 kg N fed-1) when it applied at two equal doses.6. c. Fine bran percentage (%):The all studied factors had a significant effect in this respect through the two growing seasons except cropping sequence in the second season. Moreover, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of this trait (3.60 and 3.81% in the two respective seasons) were obtained from the sequence of corn-fallow-wheat with low N rate (56.25 kg N fed-1) when it applied at two equal doses.
6. d. Wet gluten percentage (%):
The effect of all studied factors on wet gluten percentage was significant in the two growing seasons. In addition, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of wet gluten percentage (32.37 and 34.65% in the first and second seasons, respectively) were recorded from the sequence of corn-clover-wheat with 93.75 kg N fed-1 when it applied at four equal doses.6. e. Dry gluten percentage (%):The all studied factors turned to be significant in this respect through the both seasons. Also, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of dry gluten percentage (14.33 and 13.40% in the two successive seasons, respectively) were obtained from the sequence of corn-clover-wheat with 93.75 kg N fed-1 when it applied at four equal doses.6. f. Fermentation time (minute):The all studied factors proved to be significant on fermentation time in the both seasons. Here too, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of fermentation time (59.67 and 63.33 min in the two respective seasons) were recorded from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.
• Forage yield of clover (Fahl berseem) (ton fed-1):
The recorded averages of clover yield were 23.07 and 25.10 t fed-1 in the 1st and 2nd seasons, respectively.
• Economic Evaluation of wheat under different adopted treatments:
a. Total Cost:
The highest total cost e.g. 12315.00 and 13137.00 LE in the first and second seasons, respectively were attained with cropping sequence of temporary clover before wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses as against the lowest cost estimated 6967.00 and 7479.00 LE in the first and second seasons, respectively with cropping sequence of fallow before wheat with low N rate (56.25kg N fed-1) when it applied at two equal doses. b.Net return:
Based on the price of wheat outputs e.g. 430 LE ardeb-1 and 680 LE ton-1 of grain and straw yields in the first season, respectively being 575 LE ardeb-1 and 1200 LE ton-1 in the second season in the same order. Also, the price of clover forage yield e.g. 450 and 500 LE ton-1 in the first and second seasons, respectively. The highest net return (13707.00 and 23643.50 LE in the first and second seasons, respectively) was achieved due to cropping sequence of temporary clover before wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses. Meanwhile, cropping sequence of fallow before wheat with low N rate (56.25kg N fed-1) when it applied at two equal doses resulted in the lowest net return (2981.10 and 6960.50 LE in the first and second seasons, respectively).Chapter I- Durum wheat.1.Weed traits:1. a. Weeds fresh weight (kg fed-1):The all studied factors turned to be significant in this respect through the both seasons. Also, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of this trait (1286.67 and 846.67 kg fed-1 in the two successive seasons, respectively) were recorded from the sequence of corn-fallow-wheat with high N rate (93.75 kg N fed-1) when it applied at two equal doses.1. b. Weeds dry weight (kg fed-1):
The all studied factors caused a significant effect on weeds dry weight in the two growing seasons. Here too, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of this trait (286.64 and 230.83 kg fed-1 in the first and second seasons, respectively) were found from the sequence of corn-fallow-wheat with high N rate (93.75 kg N fed-1) when it applied at two equal doses.2.Days number to 50% heading (day):Days number to 50% heading was significantly affected by all studied factors during the both seasons. Moreover, the second order interaction was significant in this respect through the both seasons. In general, the highest values of this trait (88.67 and 89.67 d in the both seasons, respectively) were observed from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.3. Yield attributes:3. a. Plant height (cm):
The all studied factors had a significant effect in this respect through the two growing seasons. In addition, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of plant height (104.50 and 111.77 cm in the two respective seasons) were recorded from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.3. b. Spike length (cm):The effect of all studied factors on spike length was significant in the both seasons. Furthermore, the second order interaction was significant in this respect through the both seasons. The highest mean value of spike length (9.13 cm) was observed from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses in first season, while in second season the highest mean value of this trait (9.33 cm) was obtained from the sequence of corn-clover-wheat with 75.00 kg N fed-1 when it applied at four equal doses.3. c. Spikelets number spike-1:
The all studied factors proved to be significant in this respect through the two growing seasons. Also, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of spikelets number spike-1 (21.67 and 21.20 in the first and second seasons, respectively) were observed from the sequence of corn-clover-wheat with 93.75 kg N fed-1 when it applied at four equal doses.3. d. Spikes number m-2:
The all studied factors had a significant effect on spikes number m-2 in the both seasons. Here too, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of spikes number m-2 (386.67 and 514.67 in the both seasons, respectively) were obtained from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.3. e. Grains number spike-1:
Grains number spike-1 tended to be reacted significantly to all studied factors in the both seasons. In addition, the second order interaction was significant in this respect through the both seasons. The highest mean values of grains number spike-1 (79.40 and 78.07 in the first and second seasons, respectively) were recorded from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.
3. f. Seed index (g):
The all studied factors proved to be significant in this respect through the two growing seasons. Moreover, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of seed index (57.77 and 61.48 g in the two respective seasons) were noted from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.
3. g. Grains weight spike-1 (g):
Grains weight spike-1 was affected significantly by all studied factors in the both seasons. Furthermore, the second order interaction was significant in this respect through the both seasons. The highest mean values of grains weight spike-1 (3.82 and 4.27 g in the first and second seasons, respectively) were recorded from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.4.Yield traits and harvest index:
4. a. Grain yield (ardab fed-1):The all studied factors significantly influenced grain yield. Also, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of grain yield (27.29 and 28.93 ard fed-1 in the two successive seasons, respectively) were found from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.4. b. Straw yield (ton fed-1):Straw yield tended to be reacted significantly to all studied factors in the two growing seasons. Here too, the second order interaction was significant in this respect through the both seasons. In general, the highest mean values of straw yield (5.01 and 5.90 t fed-1 in the both seasons, respectively) were produced from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.4. c. Biological yield (ton fed-1):
The all studied factors exerted significant influence on biological yield in the both seasons. Moreover, the second order interaction was significant in this respect through the two growing seasons. In general, the highest mean values of biological yield (9.11 and 10.24 t fed-1 in the two respective seasons) were recorded from the sequence of corn-clover-wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses.4. d. Harvest index (%):The effect of cropping sequence did not reached a significant at 5% level of probability on harvest index in the both seasons. Here to, harvest index was significantly affected by studied nitrogen fertilizer rates in the first season only, however the differences in the second season were not significant. In addition, the effect of split nitrogen fertilizer on harvest index was significant in the both seasons. Moreover, the second order interaction was significant in this respect through the both seasons. The highest mean values of harvest index (45.76%) was noticed from the sequence of corn-clover-wheat with 93.75 kg N fed-1 when it applied at three equal doses in the first season, while in the second season the highest mean value of this trait (45.09%) was observed from the sequence of corn-fallow-wheat with 56.25 kg N fed-1 when it applied at four equal doses.5. Nitrogen Use Efficiency (NUE) (kg grains/kg nitrogen):
The effect of all studied factors on NUE was significant in the two growing seasons. Also, the second order interaction was significant in this respect through the both seasons. The highest mean values of NUE (66.96 and 67.79 kg grains/kg N applied in the first and second seasons, respectively) were noticed from the sequence of corn-clover-wheat with low N rate (56.25 kg N fed-1) when it applied at four equal doses.• Forage yield of clover (Fahl berseem) (ton fed-1):
The recorded averages of clover yield were 23.07 and 25.10 t fed-1 in the 1st and 2nd seasons, respectively.• Economic Evaluation of wheat under different adopted treatments:a. Total Cost:
The highest total cost e.g. 12315.00 and 13137.00 LE in the first and second seasons, respectively were attained with cropping sequence of temporary clover before wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses as against the lowest cost estimated 6967.00 and 7479.00 LE in the first and second seasons, respectively with cropping sequence of fallow before wheat with low N rate (56.25kg N fed-1) when it applied at two equal doses.b.Net return:Based on the price of wheat outputs e.g. 430 LE ardeb-1 and 680 LE ton-1 of grain and straw yields in the first season, respectively being 575 LE ardeb-1 and 1200 LE ton-1 in the second season in the same order. Also, the price of clover forage yield e.g. 450 and 500 LE ton-1 in the first and second seasons, respectively. The highest net return (13208.00 and 23127.75 LE in the first and second seasons, respectively) was achieved due to cropping sequence of temporary clover before wheat with high N rate (93.75 kg N fed-1) when it applied at four equal doses. Meanwhile, cropping sequence of fallow before wheat with low N rate (56.25kg N fed-1) when it applied at two equal doses resulted in the lowest net return (3059.40 and 7464.25 LE in the first and second seasons, respectively).