بررسی اثر کاربرد سطوح نیتروژن و نسبت‌های کشت مخلوط نخودفرنگی (Pisum sativum) و کاهو (Lactuca sativa)

Introduction   
The practice of growing two or more crops simultaneously in the same field is called intercropping and it is a common feature in traditional farming of small landholders. It provides farmers with a variety of returns from land and labour, often increases the efficiency with which scarce resources are used and reduces the failure risk of a single crop that is susceptible to environmental and economic fluctuation. This approach is increasing agricultural production per unit area by growing more than one crop in a year. Intercropping will be successful when competition for sources is less than competition within a species. Plants in the mixture can be chosen in a way that a species benefits from environmental changes caused by other species in mixed cultures directly. Intercropping inhibits the growth and development of weeds and leads to increased production. Since the system will reduce the pesticide use, environmental pollution will be also less proportionally. According to studying the intercropping of peas and lettuce in Gonbad Kavous despite the lack of need for the plant to irrigate and harvest earlier and unloading earlier land for cultivation next, objectives of the present study were to study the effect of nitrogen fertilizer and planting ratios mixture two plants on the performance of the plant, LER and some qualitative and quantitative characteristics of the pea.
 
Materials & Methods
In order to study the effect of nitrogen rates and planting patterns of pea and lettuce on quality and quantity of green pea seeds, a factorial layout based on a Randomized Complete Block Design was conducted with three replications at Gonbad Kavous University during 2014-2015 growing season. The treatments of planting pattern were included 9 levels of sole pea, 67% pea + 33% lettuce, 50% pea + 50% lettuce, 33% pea + 67% lettuce, 100% pea + 33% lettuce, 100% pea + 50 % lettuce, 100% pea + 67% lettuce, 100% pea + 100% lettuce and sole lettuce and nitrogen factor was included three levels of non-application and application of 25 and 50 kg N/ha. Row spacing was 30cm. Density of pea was 33.3 plants/m2 and lettuce was 16.7/m2. For analysis variance of data software of SAS Ver.9.1.3 were used and treatment mean differences were separated by the least significant difference (LSD) test at the 0.05 probability level.
 
Results & Discussion
The results showed that planting patterns and nitrogen rates had significant effect on plant eight, number of pods per plant, number of seeds per pod, number of seeds per plant, 100-seed weight, seed weight per plant, pods weight per plant, protein percent, solution carbohydrate percent and total yield. Plant eight in additive intercropping was more than replacement intercropping but number of pods per plant, number of seeds per pod, number of seeds per plant, 100-seed weight, seed weight per plant and pods weight per plant in replacement treatments and sole cropping of pea was more than additive treatments. Protein percent in sole cropping of pea and replacement intercropping of 67% lettuce instead of pea was greater than other treatments. At least percent of protein obtained from additive intercropping and replacement intercropping of 50 and 67% lettuce instead of pea. Solution carbohydrate percent in replacement intercropping of 67% lettuce instead of pea and additive intercropping of 100% pea + 67% lettuce and additive intercropping of 100% pea + 100% lettuce was more than other treatments. However, plant yield of pea in treatment of 67% lettuce and 33% pea and 50% lettuce and 50% pea with 30.25 and 27.44 respectively, was greater than other treatments. Land equivalent ratio in intercropping treatments was greater than sole cropping. The maximum land equivalent ratio with 1.48 belonged to additive intercropping of 100% pea + 100% lettuce. Therefore, intercropping of pea and lettuce especially in additive series was appropriate.
 
Conclusion
Of the two plants of pea and lettuce, lettuce plant produced more yield than pea plant in all treatments. Additive treatment of 100% lettuce to pea and lettuce sole crop with 61565 and 61473 kg/ha produced the maximum yield and pea sole crop with 11759 kg/ha produced the minimum total yield. With increasing of nitrogen fertilizer consumption, yield was increased. Protein percent in sole cropping of pea and replacement intercropping of 67% lettuce instead of pea was greater than other treatments.