الفهرس 
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Abstract
Comparative studies on two and three - year crop sequences in newly reclaimed soils
The present research was concerned with studying the comparative difference between the two and three - year crop sequences and effect of intercropping cowpea with maize on yield and its components in order to increase the cropping area and the cropping index in the newly reclaimed soils. This study was carried out at the Arab El-Awammer Research station - Assiut Governorate, during the two growing seasons of 2013/2014 and 2014/2015. Each experiment included four crop sequences, in addition to three nitrogen fertilizer rates. This means that 12 different treatments combinations between two factor levels in each block distributed randomly.
The crop sequences were as follows:
1- Cowpea followed by clover (Fahl) followed by wheat (S1).
2- Cowpea with maize followed by clover (Fahl) followed by wheat (S2).
3- Maize followed clover (Fahl) followed by wheat (S3).
4- Maize followed by fallow (without cultivation) followed by wheat (S4).
Nitrogen Fertilizer rates were as follows:
1- 60 Kg/fed) F1).
2- 90 Kg/fed (F2).
3- 120 Kg/fed (F3). The recommended rates
The variables studied were distributed in a factorial experiment 3×4
in a randomized complete blocks design (RCBD) with four replications. Revised Least Significant Differences (LSD’) at 5% level of probability was used for comparing means. The results obtained in this study could be summarized as follows:
A. Effect of intercropping cowpea (Vigna sinensis L.) with maize (Zea mays L.) on yield and its components.
I. Effect of intercropping cowpea with maize on maize characters.
1- Plant height and Prolificacy of maize were reacted significantly to intercropping cowpea with maize in both seasons and the combined analysis in favour of it.
2- Number of rows/ear and 100-grain weight responded significantly to intercropping cowpea with maize in the 2nd season and the combined analysis only. However, number of rows/ear and 100-grain weight tended to be increased in intercropping cowpea with maize in both seasons and combined analysis.
3- Ear height, ear length, number of grains/row, ear weight, grain weight/ear and shelling% did not respond significantly to intercropping cowpea with maize in both seasons and the combined analysis. However, those characters tended to be increased in intercropping cowpea with maize in both seasons and the combined analysis.
4- Ear diameter of maize was significantly affected to intercropping cowpea with maize in the combined analysis only. However, intercropping cowpea with maize increased the values of this trait when compared with sole maize.
5- Maize grain yield (kg/fed) did not respond significantly to intercropping cowpea with maize in both seasons and the combined analysis. However, this character tended to be increased in intercropping cowpea with maize in both seasons and the combined analysis. Here, too the maximum values of grain yield (kg/fed) were recorded by the intercropping cowpea /maize, i.e. 2340, 2550 and 2445 kg/fed in the 1st, 2nd and combined analysis, respectively, while the minimum ones were recorded by the sole maize, i.e. 2245, 2413 and 2329 kg/fed in both seasons and its combined, respectively.
5- Straw and biological yields (kg/fed) of maize were significantly affected by intercropping cowpea with maize in the combined analysis only. However, intercropping cowpea with maize increased the values of those traits when compared with sole maize.
II. Effect of intercropping cowpea with maize on cowpea characters:
1- Data showed that intercropping of cowpea with maize affected significantly plant height of cowpea in the first cut and second cut in both seasons in favour of intercropping of cowpea with maize.
2- Data cleared that intercropping of cowpea with maize affected significantly number of branches/plant of cowpea in the first cut and second cut in both seasons in favour of sole cowpea. Number of branches/plant of cowpea was decreased when intercropped with maize in the first cut and the second cut in the both seasons.
3- The data indicated that intercropping of cowpea with maize had significant effects on fresh forage yield of cowpea in the first cut and the second cut in both seasons in favour of sole cowpea. Sole cowpea had the highest values of fresh forage.
4- Data indicated that intercropping cowpea with maize had significant effects on dry forage yield of cowpea in the first and the second cut in both seasons in favour of sole cowpea.
III. Effect of intercropping cowpea with maize on competitive relationships and yield advantages:
1- Land equivalent ratio (LER) values were greater than one, i.e. 1.59, 1.71 and 1.65, relative yield for maize (RYm) were increased, i.e. 1.04, 1.06 and 1.05 of the sole and relative yield for cowpea (RYc) were decreased, i.e. 0.55, 0.65 and 0.60 of sole in the both seasons and combined analysis, respectively.
2- Aggressivity (A) values of maize were positive, i.e. 0.49, 0.41 and 0.45 of the sole while cowpea values were negative, i.e. -0.49, -0.41 and -0.45 of the sole in both seasons and the combined analysis, respectively. It means that maize was the dominant crop and cowpea was the dominated crop in the both seasons and the combined analysis.
3- Competitive ratio (CR) values of maize were greater than one, i.e. 1.89, 1.63 and 1.75 in the both seasons and the combined analysis, respectively. Cowpea values which were less than one, i.e. 0.53, 0.61 and 0.57 in the both seasons and the combined analysis, respectively. This indicated that the maize was dominant crop and more competitive than cowpea.
4- Actual yield loss (AYL) values of maize were positive, i.e. +0.04, +0.06 and +0.05 indicating increases in yields were 4.0, 6.0 and 5.0% when intercropping with cowpea in both seasons and the combined analysis, respectively. (AYL) values of cowpea were negative, i.e. -0.45, -0.35 and -0.40 indicating decreases in yields, which were 45, 35 and 40% of sole in the same order.
5- The MAI are considered an indicator of the economic feasibility of intercropping system. These values of MAI were 2097.28, 2630.24 and 2361.27 in both seasons and the combined analysis, respectively. These values were positive due to LER and CR which were greater than one.
B. Effect of crop sequences and fertilization on wheat.
1- Agronomic characters, such as plant height and total chlorophyll were affected significantly to the crop sequences studied in the two growing seasons. The crop sequence of cowpea / clover / wheat (S1) & cowpea + maize / clover / wheat (S2) produced the maximum value of plant height and total chlorophyll. The lowest value in this respect was obtained from the sequence of maize / fallow / wheat (S4). The results indicated a significant increase in these traits as nitrogen level was increased up to the recommended rate (120 kg N/fed) in the two growing seasons. The interaction involved in this study was insignificant with regard to plant height. However, the interaction of crop sequence × fertilization was significant on total chlorophyll in the two growing seasons.
2- Earliness traits such as days to 50% heading and days to 50% maturity were responded significantly to crop sequences studied in the two growing seasons. The crop sequence of cowpea / clover / wheat (S1) tended to delay the appearance of 50% heading and 50% maturity as compared with the crop sequence of maize / fallow / wheat (S4). Nitrogen affected significantly these traits in the two growing seasons. Number of days to 50% heading and days to 50% maturity tended to be increased as nitrogen rates were increased up to the recommended rate (120 kg N/fed). The interaction of crop sequence × fertilization was not-significant in the two growing seasons.
3- Yield components such as spike length, number of spikelets/spike, number of spikes/m2, number of grains/spike, grains weight/spike and 1000-grain weight were reacted significantly to crop sequences studied in favour of the sequence of cowpea / clover / wheat (S1) as compared with the sequence of maize / fallow / wheat (S4) in the two growing seasons. Consistent increases in all yield components as nitrogen rate was increased up to the recommended rate (120 kg N/fed.). The interaction of crop sequence × fertilization was significant in the two growing seasons. Here, the interaction showed that the response of wheat to the nitrogen applied was differed from sequence to another.
4- Grain yield kg/fed was affected significantly to crop sequences studied in the two growing seasons in favour of the sequences of cowpea / clover / wheat (S1) and cowpea + maize / clover / wheat (S2). The lowest grain yield was produced from the sequence of maize / fallow / wheat (S4). The effects of nitrogen on the grain yield kg/fed in the two growing seasons were significant. Consistent increase in grain yield was observed as nitrogen rate was increased in the two growing seasons. The interaction of crop sequence × nitrogen fertilization was significant in the two growing seasons. This means that the response of grain yield to nitrogen applied differed among the crop sequences. Here, the maximum grain yield of wheat was produced from the sequence of cowpea / clover / wheat (S1) when fertilized with 120 kg N/fed. The lowest grain yield was produced from the sequence of maize / fallow / wheat (S4) when fertilized with 60 kg N/fed.
5- Straw and biological yields kg/fed were influenced significantly by the crop sequences studied in the two growing seasons in favour of the sequences of cowpea / clover / wheat (S1) as compared with the sequence of maize / fallow / wheat (S4). The effects of nitrogen on the straw and biological yields in the two growing seasons were significant. Consistent increases in the straw and biological yields were observed as nitrogen rate was increased up to the recommended rate (120 kg N/fed) in the two growing seasons. The interaction of crop sequence × nitrogen fertilization was significant in the two growing seasons. This means that the response of straw and biological yields to nitrogen applied differed among the crop sequences. Here, the maximum straw and biological yields of wheat were produced from the sequence of cowpea / clover / wheat (S1) when fertilized with 120 kg N/fed. The lowest straw and biological yields of wheat were produced from the sequence of maize / fallow / wheat (S4) when fertilized with kg N/fed.
6- Harvest index was affected significantly to crop sequences studied in the two growing seasons. The crop sequence of maize / fallow / wheat (S4) produced the highest values in this respect as compared with the crop sequence of cowpea / clover / wheat (S1). Negative trend was detected in harvest index as nitrogen rate was increased. This relation proved to be significant in the two growing seasons. The interaction of crop sequence × nitrogen fertilization was significant in the two growing seasons. This means that the response of harvest index to nitrogen applied differed among the crop sequences. Here, the maximum harvest index of wheat was produced from the sequence of maize / fallow / wheat (S4) when fertilized with 60 kg N/fed. The lowest harvest index was produced from the sequence of cowpea / clover / wheat (S1) when fertilized with 120 kg N/fed.
Naturally Occurring Biological Control Agents (NOBCA)
The maximum number of agents was existed in the sequences of cowpea / clover / wheat (S1) and cowpea + maize / clover / wheat (S2). The lowest number was existed in the sequence of maize / fallow / wheat (S4). The number of Naturally Occurring Biological Control Agents (NOBCA) was contained chrysopyrla vulgaris, Coccinella undecimpunctata, Coccinella setempunctata, Paederus alfierii and Syrphus corolla.
Yield of clover (fahl)
The maximum yield of clover (Fahl) was obtained from the sequence of cowpea / clover / wheat (S1). The lowest one was obtained from the sequence of maize / clover / wheat (S3). This trend is expected since the clover in the sequence of cowpea / clover / wheat (S1) was planted after legume crop, i. e. cowpea. The present response could be attributed to the poverty of the soil under study in minerals content.
Farmers benefit:
1. Cropping index
Here it should be noted that the two promising sequences contributed so much in increasing the cropping area. Therefore the cropping index was increased to be 2.87 or 3.39 in the year for the two sequences of cowpea / clover / wheat and cowpea + maize / clover / wheat, respectively. These values are considered to be more than the traditional index of Egypt which is 1.73.
2. Economic evaluation
The net return from the sequence of cowpea + maize / clover / wheat (S2) was the highest when compared with the other sequences. Thus increasing the cropping area which increased the cropping index caused an increase in the net return.