Exploring the variability of soil nutrient outflows as influenced by land use and management practices in contrasting agro-ecological environments

Impact of Soil and Water Conservation Measures on Soil Physicochemical Characteristics and Crop Productivity: Evidence From Korekore Watershed in the Central Highlands of Ethiopia

This study investigates the effects of physical and chemical soil degradation on crop productivity in the Korekore Watershed. The watershed was categorized into level, sloping, and steep slope gradients. Within each slope gradient, one cultivated land managed with soil and water conservation and one cultivated land without soil and water conservation were selected. Selected soil physicochemical analyses were performed on 18 disturbed and undisturbed soil samples and were taken from the top 0-20 cm depths from each cultivated land with three replications. The soil degradation index (SDI) was evaluated based on the percent changes in soil properties of cultivated land without soil and water conservation to that of the cultivated land managed with soil and water conservation. The crop productivity index was determined by analyzing the percentage growth rate and its standard deviation. Soil bulk density and moisture content improved undercultivated land managed with SWC practices. Significantly higher (p ≤ 0.05) soil organic carbon (SOC) content (2.02%), total N (0.12%), available P (4.69 ppm), and exchangeable K (1.33 cmolc/kg) were observed in cultivated land managed with SWC as compared to cultivated land without SWC measures. The value of the SDI (+243.9%) for the watershed has demonstrated that soil degradation has improved and soil and water conservation measures had a significant impact on crop yields. The average crop yield rate (CYR) (30%) was found to be lower than the estimate provided by the central statistics agency in Ethiopia. A higher CYR was observed in cultivated land managed with soil and water conservation practices. It can be concluded that physical and chemical soil degradation significantly impacts crops unless counterbalanced by soil and water conservation measures. Therefore, it is recommended to implement well-integrated watershed management practices to improve soil quality and enhance crop productivity.

Modeling canopy water content in the assessment for rainfall induced surface and groundwater nitrate contamination: The Bilate cropland sub watershed

Nitrate contamination in surface and groundwater remains a widespread problem in agricultural watersheds is primarily associated to high levels of percolation or leakage from fertilized soil, which allows easy infiltration from soil into groundwater. This study was aimed to predict canopy water content to determine the nitrate contamination index resulting from nitrogen fertilizer loss in surface and groundwater. The study used Geographically Weighted Regression (GWR) model using MODIS 006 MOD13Q1-EVI Earth observation data, crop information and rainfall data. Satellite data collection was synchronized with regional crop calendars and calibrated to plant biomass. The average plant biomass during observed plant growth stages was between 0.19 kg/m2 at the minimum and 0.57 kg/m2 at the maximum. These values are based on the growth stages of crops and provide a solid basis for monitoring and validating crop water productivity data. The simulation results were validated with a high correlation coefficient (R2 = 0.996, P < 0.0005) for the observed rainfall in the growing zone compared to the predicted canopy water content. The nitrate contamination index assessment was conducted in 2004, 2008, 2009, 2010, 2011, 2013, 2014, 2015, 2018 and 2020. Canopy water content and root zone seasonal water content were measured in (%) per portion as indicators of the NO-3-N-nitrate contamination index in these years (0.391, 0.316, 0.298, 0.389, 0.380, 0.339, 0.242, 0.342 and 0.356).

Effects of agricultural land use on soil nutrients and its variation along altitude gradients in the downstream of the Yarlung Zangbo River Basin, Tibetan Plateau

Agricultural development in alpine ecosystems can cause significant changes in soil nutrients. With large altitude spans, the combined effect of the two is still unclear in existing research. To answer this problem, this study took the downstream of the Yarlung Zangbo River Basin (YZRB) as the study area, and designed a comparative soil sampling scheme along the altitude gradient. We compared soil nutrient characteristics facility agricultural land (FA) and field cultivated land (FC), using grassland (GL), the main source of agriculture expansion, as a reference. A total of 44 sampling areas were designed within an altitude range of 800-3500 m to reveal the effects of agricultural land development along the altitude gradient on soil nutrients. Research found that the FA significantly improved soil nutrient levels, with most nutrient indicators higher than those of FC and GL (P < 0.05), while the above indicators of FC were only slightly higher than GL. Moreover, the effects of agricultural development decreased with soil depth, and mainly occurred within the 0-30 cm soil layer (P < 0.05). With increasing altitude, most of soil nutrients first decreased and then increased and differences in soil nutrients among different land use modes first expanded and then shrank. This may be related to differences in farmland management methods, vegetation coverage, and temperature under different altitude gradient constraints. Especially in middle-altitude areas, the FA not only breaks through the low-temperature limitations of the plateau, but also has the advantage of large-scale development, which is suggested for future agricultural intensification in the plateau.

Predicting runoff and sediment responses to climate-resilient land use and management scenarios

Soil erosion is the predominant agent affecting ecosystem services in the Ethiopian highlands. However, land management interventions aimed at controlling erosion in the region are hampered, mainly by a lack of watershed-based appropriate management practices and anticipated climate changes. This study examined the effectiveness of different land use changes and management scenarios in decreasing runoff and sediment loss under current and future climates in the drought-prone humid watershed of the Ethiopian highlands. We employed a modeling approach integrating observed data at watershed and plot scales with Soil and Water Assessment Tool. In the first step, we evaluated the impact of land use changes between 2006 and 2017 on runoff and sediment loss. Then, we developed five land use and management scenarios based on watershed land capabilities and selected land management practices. Model parameters were modified based on runoff and sediment loss results obtained from experimental plots of biophysical and agronomical land management practices in the watershed. The runoff and sediment loss were simulated under current (2014-2019) and future climates (the 2050s) for each land use and management scenario. Results revealed that land use changes (mainly an increase in Acacia decurrens plantations by 206%) alone between 2006 and 2017 reduced runoff by 31% and sediment loss by 45%. Under the current climate, the five land use and management scenarios reduced runoff by 71-95% and sediment loss by 75-96% compared to the baseline scenario. Under the future climate (2050s), these scenarios decreased runoff by 48-90% and sediment loss by 54-91%. However, their effectiveness was slightly decreased (5-23%) as a result of increases in rainfall (10-46%) and mean temperature (1.7-1.9 °C) in the 2050s. The scenario of improving vegetation cover through forage production and plantations in appropriate areas plus best land management practices was the most effective and climate-resilient of the five scenarios. This study suggests that evaluating the impact of land use and management practices under future climate change shows promise for guiding effective and sustainable interventions to adapt to climate change.

Farmland nutrient pollution and its evolutionary relationship with plantation economic development in China

Contradiction between growing plantation economic demand and agro-ecological degradation has always restricted sustainable development of agricultural countries. This study applied the unit inventory analysis to evaluate the productions and discharges of farmland non-point source (FNPS) nitrogen (TN) and phosphorus (TP) among China's nine national-level agricultural districts over 1999-2019. On this basis, we quantified the evolutionary relationship between plantation economic output and FNPS pollution based on optimal regression fitting. The results showed that over 1999-2019, farmland cumulative TN and TP discharges for the whole China were approximately 15807 × 10⁴ t and 1312 × 10⁴ t, with prominent district heterogeneity. According to FNPS discharge magnitudes, China's agricultural districts can be classified into three categories: high, moderate and slight discharge zones. Huang-Huai-Hai Plain and Middle-lower Yangtze Plain were identified as the main severely-polluted districts. Mineral fertilizer is the primary contributor to FNPS pollution. Annual FNPS load showed a trend of increasing followed by decreasing, and the peak interval was recorded in 2014-2016. Spatiotemporal dynamics in FNPS discharge intensities were disparate from that in discharge magnitudes. SC has the highest TN discharge intensity, with an annual average intensity of 0.068 t/ha, followed by MLYP (0.044 t/ha) and HHHP (0.041 t/ha). HHHP has the highest TP discharge intensity, with an annual average intensity of 0.0051 t/ha, followed by SC (0.0038 t/ha) and MLYP (0.0031 t/ha). District-based agro-ecological restoration strategies were accordingly proposed considering FNPS discharge magnitude and intensity concurrently. In most agricultural districts, with the growing economic output in plantation, the FNPS load showed an increase followed by a decrease or to leveling off. Furthermore, with the increasing TN/TP economic partial productivity, the FNPS TN/TP discharge intensities reached the climax, then declined or tended to be flattening out.

Seasonal and diurnal soil respiration dynamics under different land management practices in the sub-tropical highland agroecology of Ethiopia

The temporal dynamics of soil respiration change in response to different land management practices are not well documented. This study investigated the effects of soil bunds on the monthly and diurnal dynamics of soil respiration rates in the highlands of the Upper Blue Nile basin in Ethiopia. Six plots (with and without soil bunds, three replicates) were used for measurement of seasonal soil respiration, and 18 plots were used for measurement of diurnal soil respiration. We collected seasonal variation data on a monthly basis from September 2020 to August 2021. Diurnal soil respiration data were collected four times daily (5 a.m., 11 a.m., 5 p.m., and 11 p.m.) for 2 weeks from 16 to 29 September 2021. A Wilcoxon signed-rank test showed that seasonal soil respiration rates differed significantly (p < 0.05) between soil bund and control plots in all seasons. In plots with soil bunds, seasonal soil respiration rates were lowest in February (1.89 ± 0.3 µmol CO₂ m^-2 s^-1, mean ± SE) and highest in October (14.54 ± 0.5 µmol CO₂ m^-2 s^-1). The diurnal soil respiration rate was significantly (p < 0.05) higher at 11 a.m. than at other times, and was lowest at 5 a.m. Seasonal variation in soil respiration was influenced by soil temperature negatively and moisture positively. Diurnal soil respiration was significantly affected by soil temperature but not by soil moisture. Further study is required to explore how differences in soil microorganisms between different land management practices affect soil respiration rates.

Nano-fertilizers: A sustainable technology for improving crop nutrition and food security

Excessive use of synthetic fertilizers cause economic burdens, increasing soil, water and atmospheric pollution. Nano-fertilizers have shown great potential for their sustainable uses in soil fertility, crop production and with minimum or no environmental tradeoffs. Nano-fertilizers are of submicroscopic sizes, have a large surface area to volume ratio, can have nutrient encapsulation, and greater mobility hence they may increase plant nutrient access and crop yield. Due to these properties, nano-fertilizers are regarded as deliverable 'smart system of nutrients'. However, the problems in the agroecosystem are broader than existing developments. For example, nutrient delivery in different physicochemical properties of soils, moisture, and other agro-ecological conditions is still a challenge. In this context, the present review provides an overview of various uses of nanotechnology in agriculture, preference of nano-fertilizers over the conventional fertilizers, nano particles formation, mobility, and role in heterogeneous soils, with special emphasis on the development and use of chitosan-based nano-fertilizers.

A joint standard-exceeding risk assessment of multiple pollutants based on robust geostatistics with categorical land-use type data: A case study of soil nitrogen and phosphorus

Joint standard-exceeding risk and its spatial uncertainty of soil available nitrogen (AN) and available phosphorus (AP) under the specific constraints are essential for guiding the joint regulation of pollutants but were rarely considered by previous studies. Moreover, traditionally-used spatial simulation models are not only non-robust but also ignoring valuable categorical information (e.g., land-use types), which may hinder the acquisition of high-precision spatial simulation results. This study first established optimally robust semi-variogram estimators to identify the spatial outliers of soil AN and AP in Jintan County, China. Then, robust sequential Gaussian simulation (RSGS) with land-use types (RSGS-LU) was proposed and further compared with RSGS, SGS-LU, and SGS in the spatial simulation accuracy. Last, a joint standard-exceeding probability model under the specific constraints was proposed, and the corresponding high-risk areas were delineated for the joint regulation of soil AN and AP. Results showed that: (i) 23 and 17 spatial outliers were identified for soil AN and AP, respectively; (ii) removing outliers or combining land-use types could improve the spatial simulation accuracy of soil AN and AP; (iii) RSGS-LU generated the highest spatial simulation accuracy for both soil AN and AP; (iv) the area with the joint standard-exceeding (AP > 30 mg kg^-1∪ AN > 130 mg kg^-1) probability >75% accounted for 9.98% of the county's area; (iv) the area with the joint standard-exceeding (AP > 30 mg kg^-1∩ AN > 130 mg kg^-1) probability >75% accounted for 2.29% of the county's area. It is concluded that RSGS-LU and joint standard-exceeding probability model under the specific constraints could provide more accurate and flexible spatial decision support for the joint regulation of soil AN and AP at a regional scale. Moreover, the methods recommended in this study also provide valuable tools for the joint standard-exceeding risk assessment of other multiple soil pollutants.