Effects of Different Tillage Systems, Nitrogen Fertilizer Rates, and Mycorrhiza Inoculation on some Soil Physical Properties and Yield of Mung Bean (Vigna radiata L.)

Tillage intensity and tillage system can affect biological, physical, and chemical properties of the soil. Suitable soil management is essential to achieve sustainable agricultural production especially in drought-prone regions. More application of machineries in a tillage system will result in more soil compaction which in turn increases soil bulk density and decreases its air and water permeability. Additionally, it has been well documented that the compact soil hampers the downward growth of the crop roots. The soil with good physical quality will provide aeration and water as well as non-impeditive mechanical resistance for root proliferation. Moldboard plowing is currently applied in around 65% of tillage practices although the agricultural extension services have tried to convince farmers to apply reduced tillage system by replacing moldboard plow with chisel plow to mitigate adverse effects of moldboard plowing especially in arid and semi-arid regions. Conservation tillage practices, especially reduced tillage, have been introduced to Iranian farmers since 1999. Mycorrhiza is the product of an association between a fungus and plant root that enhance the tolerance levels of plants against the drought, salinity and high heavy metal contents. The aim of the present study were to evaluate the effects of tillage systems, nitrogen levels, and mycorrhiza inoculation on yield and yield components of mung bean and soil criteria.

The experiment was conducted in Darehshahr research field in two growing seasons (2017 and 2018). The experimental layout was split plot based on a randomized complete block design with three replications. Treatments consisted of three tillage systems as conventional, conservation and no tillage as main plot, four nitrogen levels including 0% (as control), 33%, 66% and 100% of recommended fertilizer as sub plot, and two levels of mycorrhiza fungi inoculation (Contains arbuscular mycorrhiza fungi of Glomus mosseae strains, counting 107 to 108 (CFU / g.) Prepared by Soil and Water Research Institute) (no symbiosis (as control) and with symbiosis) as sub-sub-plot. Studied traits were yield components (such as 1000-seed weight, No. of seeds per pod, No. of pods per plant), seed yield and harvest index of mung bean and moisture content, cone index and organic carbon percent of soil. For analysis of variance SAS 9.4 was used. All the means were compared according to Duncan test (p≤0.05).

The results revealed that the highest 1000-seed weight (57.48 g) was obtained from no-tillage and the highest number of seeds per pod (10.64 seeds per pod) and the number of pods per plant (61.04 pods per plant) were obtained from conservation tillage. The highest seed yield was obtained from conservation tillage + application of 100% N fertilizer with 2941 kg.ha-1. The highest seed weight, number of seeds per pod, and number of pods per plant were obtained from 66% N fertilizer application. Mycorrhiza inoculation increased harvest index, seed yield and its components. The soil bulk density in the no-tillage system had the highest value. The maximum and the minimum soil moisture contents were observed for non-tillage and conventional tillage systems, respectively.highest soil cone index (2.25 MPa) was obtained from no-tillage and 66% N fertilizer and the lowest (1.07 MPa) was for conventional tillage system+ without nitrogen application. The highest and the lowest soil organic carbon were related to no-tillage and conventional tillage systems with 0.68% and 0.32%, respectively.

In general, the conservation tillage system+ application of 66% N fertilizer and inoculation with mycorrhiza had a relative advantage impact on yield and related traits. In addition, the soil physical traits and organic carbon content were improved affected as declined tillage systems. The long-term field experiment points out the beneficial impacts of reduced tillage and no tillage systems that, in addition to preserving both soil physical (such as cone index) and chemical criteria (and organic carbon), fertility and biological activity, could increase yield and exhibit a comparable yield over a long-term period as in conventional plough. Currently, there is no mung bean variety appropriate to Iran. Improving some varieties with higher yield which are tolerant to warm climate and water deficiency seems essential to improve the sustainability of local seed production. Investigating into the effect of mung bean tillage and fertilizer consumption on the weed type and density is also suggested for future studies.