Evaluation of Tillage Systems on Agronomic Aspect of Soybean (Glycine max L.) and Roselle (Hibiscus subdariffa L.) Relay Intercropping

With the ever-increasing world population, over-exploitation of natural resources and the limited availability of arable land, followed by the urgent need to increase food production, which is one of the world's challenges, it is essential to increase crop yield to meet demand and find a solution to more sustainable agricultural ecosystems. Sustainable agriculture is a kind of agriculture that increases the efficiency of resource use that is in balance with the environment. The components of sustainable agriculture are conservation tillage and intercropping. Intercropping is one of the common methods of multi-systems that it is widely used to diversify cultivation in spatial and temporal. One of the most important benefits of crop cultivation is the increase in production per unit of area relative to sole crop due to better use of environmental factors such as water, light, and nutrients in the soil. Soil conservation tillage has been researchers' interest by reducing energy consumption and soil fertility, as well as increasing soil and water production potential. The aim of this research was to study the soil tillage systems on the ecological aspects of crop mixing of soybean and Roselle.

This research was conducted in the research farm of Agriculture and Natural resources of Jiroft, in southern Kerman, Iran during 2016. The experiment was conducted as a split-plot in a randomized complete block design with three replications. The main factor included three levels: no-tillage, reduced tillage, conventional tillage and the sub-factor of different ratios and replacement of mixed soybean and Roselle in eight levels of: sole Roselle, sole soybean culture, 50% Roselle+ 50% Soybean, 75% Roselle+25% soybean, 25% Roselle+ 75% soybean, 100% Roselle+ 50% soybean, 100% soybean+50% Roselle, 100% Roselle+ 100% soybean. Each experimental unit has a length of 4 meters and a width of 3 meters and spaced two rows of one meter. Each plot consisted of 4 rows of planting (all treatments were a row of Roselle and a row of soybeans). The measured traits were the number of boll per plant, 1000-seed weight, biological yield, sepal yield, chlorophyll index of Roselle and soybean, and the amount of anthocyanin of Roselle and protein content in 100% Roselle+ 50% soybean, the soil ratio of land parity (LER). Data analysis was performed with SAS software version 1.9 and comparison of means was made using Duncan test at a 5% probability level.

The effect of tillage systems and different ratios of planting on the number of boll per plant, thousand seed weight, biological yield, sepal yield, leaf chlorophyll content anthocyanin level in roselle and protein content in soybeans was statistically significant. The comparison of the means showed that conservation tillage provides better results than conventional tillage in terms of number of bolls per plant of Roselle (271.77) and soybean (13.77), biological yield in Roselle (20.1 t.ha-1) and soybean (6.85 t.ha-1), sepal yield (16.1 t.ha-1), leaf chlorophyll content (33.24), anthocyanin (4.7 μmol.g-1) in Roselle and protein content in soybean (37.51 mg). Moreover, the maximum utilization of LER was due to no-tillage (2.86). The highest ratio of land parity was obtained from 100% soybean 50% Roselle (3.78).

The highest proportion of LER was obtained from 100% soybean 50% Roselle, which indicated superior cropping compared to sole crop. Also, in most of the studied traits, the conservation tillage system compared with conventional tillage resulted in higher value. In general, based on the results of this study, systems with no-tillage and also 100% Roselle+50% soybean be recommended.