Impact of salinity and organic amendments on soil properties, C pools and N mineralization in Vertisol

Sanjay Arora and Kiran Vaghasiya

Central Soil Salinity Research Institute, Regional Research Station, Bharuch 392012, Gujarat

An incubation laboratory experiment was conducted to ascertain the effect of soil amendments including industrial wastes on soil properties and nutrient mineralization with respect to time under different levels of salinity (2 and 8 dS/m). The treatment included, farmyard manure (FYM), horse manure (HM), vermicompost (VC), fly ash (FA), biological sludge (BS), phosphogypsum (PG), ETP sludge (ETPSL) and pressmud (PM). The incubation was carried out at field capacity for 10 weeks at 28±1oC in triplicate in boxes. One set of each box was removed weekly and soil was processed for analysis. After addition of this amendments and industrial waste add water into two part 45 box treated with water of 2.0 dS/m EC and 45 box treated with water of 8.0dS/m EC to an amount equal to 50% of water holding capacity (WHC) / Field capacity (FC).

The loss in weight due to the moisture loss was replenished. The boxes were kept for incubation at 28ºC enabling decomposition of amendments and mineralization of nutrients. After incubation sampling was performed at 1, 2, 4, 6 and 8 weeks and the soils were analyzed for different for soil properties.

Soil pH did not show any variation among the treatments irrespective of the time of incubation. The soil pH values ranged from 7.24 to 8.05 at salinity level 2dS/m and 7.22 to 7.80 at 8 dS/m did not show any significant difference indicating that the different nutrient sources used, behaved almost in a similar way. However, with respect time, there was decrease in soil pH in upto 6 week at both the salinity levels, under different treatments. From the data it is indicated that increase the soil salinity under addition of soil amendments and industrial waste with 8dS/m water treatments than that of with 2dS/m water treatments. Soil EC values ranged from 1.40 to 0.70dS/m at salinity level 2dS/m while 2.50 to 3.40dS/m at salinity of 8dS/m. In control, EC sharply increased from 0.5dS/m to 2.7 dS/m when salinity was imposed. Similarly in all the treatments EC was enhanced under 8dS/m by 2 to 3 times as compared to soil receiving water of EC 2dS/m. Irregular trend was noted in soil EC with respect to incubation periods among all the treatment at both levels of salinity. Soil OC(%) values ranged from 0.25 to 2.75 in salinity level 2dS/m and 0.32 to 1.85 with 8dS/m water treatments The data shows that, organic carbon (%) shows higher values with 2dS/m water treatments than that of 8dS/m water treatments in all the imposed treatments. With time, it was observed that there was build up of organic carbon in 2nd

to 4th week and through decline in the most of the cases. At 2dS/m salinity, maximum OC was observed in VC amended soil followed by fly ash and HM. however, at 8dS/m salinity maximum OC was observed in VC amended soil followed by HM, FYM and fly ash amended soils.

As, compared to the control (0.42% OC), there was build up of 1.79% at the 4 th week in soils amended with VC and imposed salinity of 2dS/m while only at 2nd week of incubation, PG resulted in the maximum OC content. At 8dS/m salinity, 1.9% OC was observed in soil amended with VC followed by 1.79% OC in HM amended soil at 8dS/m which was attained only after 4 th

week of incubation.

The effect of different organic amendments and industrial waste was studied, in respect of total carbon content in soil. From the data presented in above graph it is evident that highest total carbon (%) was observed in soil under treatment of vermicompost at salinity level 2dS/m. Whereas, the highest total carbon (%) was noted in soil under treatment of phosphogypsum (PG) and biological sludge (BS) at salinity level 8dS/m. There was net decline in Total C after 4th week of incubation in above all the treatments. Maximum build up of Total C was observed in PM treated soil at 2dS/m or 8dS/m salinity, while minimum in case of BS at 2dS/m and VC at 8dS/m. Maximum of 16.7% Total C was observed in VC amended soil at 8 th week incubation salinity level of 2dS/m which was 4.7% higher in magnitude over control. Similarly at salinity level 8dS/m, maximum of 16.7% Total C was observed in PG amended soil at 8 th week of incubation.

There was decrease in mineral N content of soil in all the treatments when salinity was imposed. It was observed that maximum mineral N content was observed at 8 th week of incubation in soil amended with horse manure (HM) followed by vermicompost (VC) and farm yard manure (FYM) at both the salinity levels. However, as compared to control, minimum amount of mineral N was noted in fly ash application. Among industrial wastes, N was mineralized in biological sludge (BS) than ETPSL or Press mud (PM) at both the levels of salinity.

Decrease in available nitrogen status was observed when salinity was imposed from 2dS/m to 8dS/m. Higher Nitrogen status was found in the soil which gives treatment of ETP sludge and VC with salinity level 2dS/m. Whereas, nitrogen level in soil with salinity level 8dS/m there is no major changes found under different treatments. Over all there was increase in nitrogen content at 1&2 weeks after incubation in some cases while in 4 to 6th week in others.

At salinity level of 2dS/m, maximum amount 0.952 mg/kg of available N was observed in 2nd

week of soil incubated with ETP sludge which further decreased to 0.728 mg/kg at 6 th&8th weeks. Increasing salinity level to 8dS/m resulted in decline available N content under all amendments and was maximum of 0.508 mg/kg in VC amended soil after 6th week of incubation.

Available Phosphorus content (mg/kg) of the soil with the addition of soil amendments and industrial waste showed highest values under treatment of phosphogypsum and ETP sludge at salinity level of 2dS/m. Whereas at salinity level of 8dS/m, highest values was observed in the treatment of phosphogypsum (PG) and farm yard manure (FYM).With respect to the period of incubation, more accumulation of available P content was observed at later periods as compared to initial. After 8 weeks, 0.252 mg/kg was observed in soils amended with PG at 2dS/m as well as in same treatment (0.230 mg/kg) at 8dS/m which was more than that 1/3rd time higher than initial value (0.180 mg/kg).

Available Sulphur content (mg/kg) of the soil with the addition of soil amendments and industrial waste resulted in highest value under treatment of phosphogypsum (PG) at both the salinity levels i.e. 2dS/m as well as 8dS/m, in comparison with another soil amendments and industrial waste application.

With the passage of incubation time, maximum of 28.07 mg/kg of S was obtained at 8 th week .In soils amended with PG at 2dS/m salinity while increased in salinity resulted in early release of this quantity of Available S which was attained at 4th week with further decline slightly to 27.4 mg/kg at 8th week.

Available boron content (mg/kg) of the soil was influenced with the application of soil amendments and industrial wastes. It was highest under treatment of press mud (PM) and horse manure (HM) at the salinity level of 2dS/m where as the higher values were obtained under treatment of press mud (PM), biological sludge (BS), horse manure (HM) and fly ash (FA) at salinity level of 8dS/m in comparison with other soil amendments and industrial wastes.

Overall, there was non-uniform trend in case of boron with incubation period in all the amendments both at 2dS/m and higher salinity of 8dS/m.

Alkaline phosphatase activity is the considered as a major constituent of soil biochemical properties. Alkaline phosphatase contents (µg/g/h) of the soil amended with organic amendments and industrial waste was found to be maximum in treatment of horse manure (HM) as compared to other amendments and industrial waste at the salinity level of 2dS/m.

At 8dS/m salinity level the alkaline phosphatase content (µg/g/h) of the soil was maximum in soil under treatment of phosphogypsum (PG) and horse manure (HM) as compare with other amendments and industrial wastes.

With respect to time of incubation, it was observed that alkaline phosphatase increased at 4 th and 6th week of incubation in all treatment over early stages of incubation at 8dS/m salinity level. Compare to alkaline phosphatase activity in control (~6 µg/g/h), there was increase up to 66.7 µg/g/h in HM amended soil at 2dS/m observed after 8th week of incubation while it was maximum of 70 µg/g/h in PG treated soil observed in soil after 6th week of incubation.