Pasture Species as an Option for Soil Organic Carbon Sequestration to Restore Abandoned Croplands in Nepal
Cropland abandonment is a human-induced land use change that is emerging globally in the last century. The rate of cropland abandonment is increasing in Nepal in the last decade, impacting soil functions and productivity. Restoration options have been actively sought by land managers and policymakers, and the potential of pasture establishment has been seen as a potential option to maintain soil quality while also providing a productive base for landholders. Following abandonment, changes in geomorphology and secondary vegetation succession can have a significant impact on soil organic carbon (SOC). Few studies have been conducted in Nepal to understand the impact and restoration of post-abandonment land. In this work, abandoned croplands, forest, pasture, and existing cropped land were examined in Gorkha and Kavre districts of Nepal with the aim of understanding the impacts of cropland abandonment by measuring the change in SOC across soil depths. A field experiment was undertaken in Gorkha district of Nepal where four pasture species were grown in a prior cropland abandoned for 2 years, in order to understand the potential of pasture species for carbon (C) sequestration. To explore the mechanism of SOC formation by pasture roots, a greenhouse experiment at University of New England, Australia was also conducted in which four pasture species were grown in two contrasting soil types (Ferrosol and Chromosol). Abandoned cropland in Nepal subject to secondary vegetation succession had accumulated significant amounts of SOC, particularly the labile fraction (particulate organic carbon), compared with existing cropland, especially after 10 years of abandonment and that SOC values were on the trajectory towards those of forest and pasture. Around 23% of SOC has been recovered with secondary succession in more than 10 years abandoned cropland compared to the currently cropped land. Pasture establishment on abandoned cropland increased the SOC in which the labile carbon increased in the top-soil (0-20 cm) and stable carbon in sub-soil (20-40 cm). Pasture roots contribute to form new carbon through dissolved organic carbon formation and root exudation that is mostly fixed on the stable SOC fractions (mineral-associated organic carbon) in both Chromosol and Ferrosol. It is concluded that vegetation cover in abandoned cropland increased labile carbon in the surface soil which had been preferentially lost in the early years of abandonment. With the pasture establishment on abandoned cropland, SOC can be stabilised in sub-soil with the higher fixation of new carbon in the mineral soil matrix. So, we recommend that land managers and policymakers integrate a pasture component in abandoned cropland restoration program that has ability to restore abandoned cropland through increased SOC.
Spatial variability of soil properties under different land use in the Dang district of Nepal
Increased nutrient mining, soil erosion, and limited nutrient management has led to declines in soil quality and reduced productivity in many parts of Nepal. A study was conducted in the eastern part of the Dang district of Nepal in 2015 to assess the variability of selected soil properties of three different land use types (agricultural, agroforestry, and grassland) and to map their spatial distribution. A total of 120 soil samples were collected from 0-15 cm depth and analyzed for soil fertility parameters: pH, organic matter (OM), nitrogen (N), phosphorus (P), potassium (K), boron (B), and zinc (Zn). Results revealed that the average value of the soil pH significantly (P < 0.05) varied from agroforestry to agricultural land use. Soil OM and N contents were in the medium range in all land use with minor variation, with the highest average OM and N found in grassland (2.87% and 0.14%), followed by agricultural land (2.64% and 0.13%), and agroforestry (2.45% and 0.12%). Soil P showed a significant variation between agroforest (18.99 kg ha−1) and grassland (8.49 kg ha−1). Soil K content was high in grassland (144.44 mg kg−1) and low in agricultural land (120.95 mg kg−1) but was not statistically significant. Micronutrient B was low (0.28-0.35 mg kg−1) and Zn was very low (0.14 mg kg−1). The interpolated soil maps thus generated may assist farmers in identifying the expected nutrient levels for their localities and encourage them to modify their management practices to improve productivity and lift income.
Pasture species as an option for soil organic carbon sequestration to restore abandoned cropland in Nepal - Dataset
The dataset is composed of four datasets. First, there was a dataset derived from a literature search database from a systematic literature review. The variables were created according to the objectives of the work. The second dataset was generated from the land use assessment, where soil samples were taken from various geospatial points. The third dataset was generated during a field experiment, and the fourth dataset was generated during a greenhouse experiment and laboratory analysis. The description sheet of the physical soil samples stored at the university is also included.