عنوان مقاله [English]
Sunlight is the main source of energy in Agro ecosystems. Light is absorbed by leaves and this energy is stored during the process of photosynthesis in chemical bonds of organic compounds and finally converts to the plant biomass. In order to increase the efficiency of this process and understanding how light changes within the plant canopy is necessary to be aware of how changes in light absorption within a farming system, especially when considering various intercropping systems, agroforestry systems and even non-crop species management. Available reports have shown that the higher resources use efficiency in intercropping systems, especially light, water and nitrogen.
Materials and Methods
This study was aimed to investigate radiation absorption and use efficiency in substitution intercropping of milk thistle (Silybum marianum L.) and fennel (Foenicolum vulgar L.). The experiment was set up with five treatments in a randomized complete block design with three replications at the farm of the Faculty of Agriculture, Ferdowsi University of Mashhad, Iran, during 2012- 2013 growing season. In order to implement an ecological and low input system, no chemical inputs (fertilizers and pesticides) was applied. The experiment constituted 5 treatments: sole crop of milk thistle and fennel, intercropping (75% milk thistle-25% fennel), intercropping (50% milk thistle-50% fennel) and intercropping (25% milk thistle-75% fennel). Crops were harvested every eight days corresponding to 6 harvests starting with the development of the fourth leaf and ending at the early flowering. Above ground dry matter (DM) was determined after oven drying at 70 ˚C for 48 h. Leaf area was determined on the same harvested area used for the measurement of above ground dry matter. Leaf area of the Milk thistle was determined by LI3100 area meter. The green area index of Fennel was also calculated, according to the equation 1.
GAI = M × LWR/SLW (Equation 1)
GAI: green area index, M: daily dry matter allocated to the leaf + stem, LWR: leaf weight ratio and SLW: specific leaf weight.
Incident and transmitted radiation of the canopy was measured using the Sun scan Canopy Analysis System (Accu PAR LP-80). The light extinction coefficient (LEC) was determined from the slope of the linear regression between the natural logarithm of radiation transmission and leaf area index. According to the equation 2.
Ii/Io = e-K.LAI (Equation 2)
Io:amount of radiation on the top of canopy, Ii: amount of radiation at the bottom of canopy, K: light extinction coefficient and LAI: leaf area index.
The daily light absorption for both species was calculated according to the equation 3 t0 5.
Ii = Io (1-exp((-KS.LS) + (-KF.LF))) (Equation 3)
Is= Ii( ) (Equation 4)
IF = Ii- Is (Equation 5)
Io: amount of radiation on the top of canopy, Ii: amount of radiation at the bottom of canopy, Is: amount of absorbed radiation by milk thistle, IF: amount of absorbed radiation by fennel, Ks: light extinction coefficient of milk thistle KF: light extinction coefficient of fennel and Ls: leaf area index of milk thistle and LF: leaf area index of fennel.
Radiation use efficiency (RUE) was computed by the linear regression between dry matter accumulation (g.m-2) and cumulative amount of radiation absorption (MJ.m-2). The data statistical analysis and draw the figures were performed by Minitab, V16, Excel and Edraw MaxV5.0. Means were also compared by HSD test at the 5% probability level.
Results and Discussion
Results indicated that radiation use efficiency of milk thistle throughout the growing season was variable from 1.91 to 2.36 g.MJ-1 and in intercropping treatment (50% milk thistle-50% fennel) was at the highest amount. The amount of radiation use efficiency in fennel was variable from 0.71 to 1.39 g.MJ-1. The best recommendable treatment for intercropping of milk thistle and fennel was (50% milk thistle-50% fennel), in which case radiation use efficiency of milk thistle was at the highest level (2.36 g.MJ-1) and radiation use efficiency of fennel was higher than sole cropping (0.93 g.MJ-1). Based on the findings of this study it seems that enhancing diversity in agronomic practices is an effective operational approach to increasing the efficiency of resources.
The authors acknowledge the financial support of the project (Grant number 26556) by Vice President for Research and Technology, Ferdowsi University of Mashhad, Iran.