Effect of relay intercropping of chickpea (Cicer arietinum L.) with barley (Hordeum vulgare L.) on biochemical traits and yield under late season drought stress

Intercropping is an old cropping practices, possibly as old as the settled agriculture, and is widespread especially in low-input cropping systems. One of the most popular intercropping practices is the cultivation of certain annual legumes with cereals. Intercropping of two or more crop species not only improves yield on a given land area by making more efficient use of the available growth resources but also enhances biological activities in the soil and suppresses weeds, pests and diseases. Intercropping of barley and chickpea improves the use of plant growth resources, i.e. species do not compete precisely for the same niches.Relay intercropping refers to a cropping system in which the lifecycle of one crop overlaps that of another crop. Usually the second crop is planted after the first crop has reached its reproductive stage of growth but before it is ready for harvest. The purpose of this experiment was to detect the most suitable intercropping system and appropriate planting dates for chickpea and barley for sustainable production of these plants under water stress conditions at late growing season.

An experiment was carried out as a factorial split plot based on randomized complete block design with three replications at College of Agriculture and Natural Resources of Darab, Shiraz University during 2017-2018 growing season. The cropping systems included of two factors. The main plot was two water regimes including cutting off irrigation at the beginning of milk development stage and normal irrigation. Sub plot was 8 relay intercropping ratios as additive series consisted of monoculture of Zehak six-rowed barley cultivar (b), monoculture of Darab chickpea cultivar (c) cultivation of barley on December (b1), cultivation of barley on January (b2), cultivation of chickpea on December (c1), cultivation of chickpea on January (c2) and different combinations of relay intercropping consisted of cultivation of barley on December+chickpea on December (b1c1), cultivation of barley on December+chickpea on January (b1c2), cultivation of barley on January+chickpea on December (b2c1) and cultivation of barley on January+chickpea on January (b2c2) with a ratio of 1:1. Two weeks after drought stress the traits of chlorophyll a, b, catalase, peroxidase, were measured and at crop maturity, plants were hand harvested to measure biological yield, yield and yield components including number of pods/plant, number of seed/plant, 1000-seed weight, grain protein and land equivalent ratio. Finally, analysis of variance (ANOVA) was performed using SAS v. 9.4 software and the means compared by LSD test at 5 % probability level (p≤0.05).

Analysis of variance showed that late season drought stress had a significant effect on all plant traits except the number of seed/pod, 1000-seed weight and chickpea seed protein. In chickpea drought stress reduced the amount of chlorophyll a in all treatments and minimum amount of chlorophyll a was achieved in intercropping of barley on January. Also drought stress reduced the amount of chlorophyll b in all treatments except for the cultivation of chickpea on January. Interestingly, drought stress increased the amount of catalase (74.04%) and peroxidase enzymes (81.36%) in intercropping of barley on December+chickpea on January and barley on December+chickpea on December, respectively. Water stress increased 58% and 25% land equivalent ratio chickpea and total compared to the normal irrigation conditions. Finally, the maximum seed yield was obtained under drought stress conditions in barley on December+chickpea on January intercropping.

The result of this study showed that in general, late season drought stress reduced the amount of chlorophyll a and the maximum and minimum amount of reduction was 46.6 and 22.3% in intercropping barley on December+chickpea on January and barley on January+chickpea on January, respectively. Also drought stress reduced the amount of chlorophyll b in all treatments except chickpea on January, while drought stress increased the amount of catalase and peroxidase enzymes with the maximum increase of 74.04 and 81.36% intercropping barley on December+chickpea on January and barley on December+chickpea on December respectively. In this experiment, in barley on December+chickpea on January intercropping treatment, drought stress increased 58% and 25% land equivalent ratio of chickpea and total compared to the normal irrigation conditions, respectively. The results can be recommended for intercropping in some areas. Therefore, relay intercropping can greatly increase the economic efficiency and productivity of agricultural land use.