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As governments continue to address climate change when formulating policy, there remains a need to determine if such a change exists in the historical record to inform clear indices for monitoring the present climate for site-specific interventions. This study characterised trends and anomalies in rainfall and dry spells, providing local information often projected from satellites or regional data in data-scarce regions. From 1961 to 2007, daily rainfall records in Central Malawi were used to calculate indices for low-(Balaka), medium-(Bunda, Chitedze, KIA), and high-altitude (Dedza) sites, which were then subjected to Mann–Kendall's, Cramer's, and Spearman-Rho's trend tests. Significant decreasing trends in terms of wet days and growing season length were evident across locations. Seasonal and extreme rainfall, dry spells, and inter-seasonal and near-decadal anomalies were not consistently or inevitably significant. Unexpectedly, rainfall anomalies were largest in Bunda and KIA, which have mild climatic regimes, while the lowest were in Balaka, a rainfall-averse zone. The relationship between El Niño-Southern Oscillation (ENSO) and extreme rainfall and dry spell events did not reach statistical significance. In conclusion, extreme precipitation and dry spell events show varied intensities and proportions rather than increased frequency. The disparate results largely justify the need for in-depth local-scale assessments for agroclimatic applications. [ABSTRACT FROM AUTHOR]

Biochar application to a structurally poor tropical soil could potentially alter the soil's aggregate strength and hydraulic properties. However, very few field studies have investigated the impact of biochar on the aggregate strength and hydraulic properties of tropical soils. A field experiment was therefore conducted to investigate the short-term effects of rice straw biochar on soil hydraulic properties and aggregate stability of an Acrisol in Ghana. The biochar was broadcast at rates of 10 t [ha.sup.-1] and 20 t [ha.sup.-1] as single applications that were incorporated into the top 20 cm of the soil using a spade and then the soil was levelled using a rake. Field saturated hydraulic conductivity and laboratory-measured soil water retention, aggregate stability and water-repellency were determined 10 months after the biochar application. Biochar increased aggregate stability against fast wetting by up to 33% compared to the control. This implies that biochar might improve the stability of aggregate of an Acrisol against slaking and erosivity of heavy rainfall. However, aggregate stability against slow wetting and mechanical breakdown after pre-wetting were unaffected by the biochar. Biochar did not affect field saturated hydraulic conductivity, water retention characteristics and water-repellency. Further field studies on weathered tropical soils with low native soil organic matter is recommended to elucidate the effect of repeated biochar addition on soil hydraulic and aggregate characteristics. Keywords: aggregate stability, biochar, carbon sequestration, hydraulic conductivity, hydrophobicity, organic amendment, pyrolysis, soil water retention, tropical soils, water repellency., Introduction Biochar, a carbon-rich by-product from pyrolysis of biomass, has gained wide research interest due to its potential to promote agricultural productivity, carbon sequestration and soil remediation by absorbing organic [...]

In the Vietnamese Mekong Delta, soil quality and crop yield are steadily declining under rice monocultures with three crops per year. The objective of this study was to evaluate the medium-term effects of rotating rice with upland crops and adding organic amendments on rice yield, and to relate this to soil quality. A field trial with split-plot design including two factors and three replicates was carried out from 2017 to 2020, over the course of nine consecutive cropping seasons. Crop rotations and organic amendments were applied as main-plot and subplot factors, respectively. The rotations were (1) rice–rice–rice (R–R–R), (2) soybean–rice–rice (So–R–R), and (3) sesame–rice–rice (Se–R–R), while organic amendment treatments included (i) no amendment (NO-AM), (ii) compost of rice straw and cow manure (RS+CM), and (iii) sugarcane compost (SGC); the composts were applied at a rate of 2.0 t ha−1. The rotation cycle started with the so-called spring–summer (SS) season, followed by the summer–autumn (SA) season and ending with the winter–spring (WS) season. Rice yield significantly (p < 0.05) increased under organic amendments after nine growing seasons (2019–2020 WS), with an increment of 5.1% for RS+CM (7.07 ton/ha) and 6.1% for SGC (7.14 ton/ha). Contrary to our expectation, rotations with upland crops did not significantly increase rice yield. Rice yield significantly and positively correlated with an integrated soil quality index–SQI (r = 0.85) for the topsoil (0–15 cm), but not for the subsoil (15–30 cm). The increased availability of soil nutrients (Si and marginally also P) and improved soil physical properties probably induced by organic amendments, along with other soil properties under study, cumulatively attributed to enhanced rice yield. Repeated organic amendments thus becomes an effective management practice in improving soil quality under rice-based systems and could be applied to sustain rice yield in rice-producing regions with similar soil types and climatic conditions. Use of a SQI involving several soil quality indicators enables us to quantify the overall importance of soil fertility for rice yield versus other factors, and it provides an effective means of quantifying the integrated effect of improved management. Moreover, integrating a wide range of soil quality indicators in a SQI ensures its applicability across diverse settings, including different crop rotations and various soil types. [ABSTRACT FROM AUTHOR]

With climate change expected to intensify the occurrence and severity of droughts, the control of groundwater table (GWT) depth and capillary rise on topsoil moisture may render a critical driver of biological activity. Consequently, GWT depth could influence topsoil carbon mineralization. In this study, undisturbed 200 cm long soil columns of three different textures (loamy sand, sandy loam and silt loam) were subjected to two artificial GWT depths (–165 cm and –115 cm) in the laboratory. We examined (1) moisture supply by capillary rise along the soil profile and specifically into the top 20 cm soil, and (2) consequently the effect of GWT on decomposition of an added 13C-enriched substrate (ryegrass) over a period of ten weeks, with limited water applications representing a dry summer. A 50 cm difference in GWT depth (–165 cm vs. –115 cm) resulted in different topsoil moisture for the sandy loam (31 % vs. 38 % Water-filled pore space (WFPS)) and silt loam (33 % vs. 43 % WFPS) soils. In the loamy sand soil, GWT-induced moisture differences appeared only up to 85 cm above the GWT. The expected acceleration of mineralization of the added ryegrass under a shallower GWT was not confirmed. In contrast, C mineralization pulses after the wetting events were even higher for the drier –165 cm GWT soils. For the silt loam soil, where capillary rise supply had the largest contribution to topsoil moisture, a lower mineralization rate of the stable Cryegrass pool was also found with shallower GWT. These findings suggest that a potential capillary rise effect of increased topsoil moisture on ryegrass mineralization might have been counteracted by other processes. We postulate that the Birch effect might have been magnified following the rewetting of drier topsoils under deeper GWT levels, ultimately enhancing mineralization compared to where the soil remains consistently wetter under shallower GWT levels. Based on our findings, including the process of texture-specific capillary supply from the GWT can be required to adequately simulate moisture in the topsoil during droughts as they occurred over the past summers in North-West Europe, depending on GWT and texture combination. However, the net effect on topsoil C mineralization is complex and correct simulation of C mineralization may require further integration of specific processes connected to fluctuating soil moisture state, such as the Birch effect. [ABSTRACT FROM AUTHOR]