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Alkaline phosphomonoesterase (ALP) mainly originates from soil microbial secretion and plays a crucial role in the turnover of soil phosphorus (P). To examine the response of ALP-encoding microbial communities (analysed for the biomarker of the ALP gene, phoD ) of soils and derivative soil fractions to different fertilisation regimes, soil samples were collected from a long-term experimental field (over 35 years). The different organic P (Po) pools of soil fractions and the ALP activity of soil were also determined. Compared with chemical-only fertilised soils, the ALP activity was 232–815% higher in organic-amended soils, and the highest enzyme activity was observed in the organic-only fertilised treatment. The abundance of the phoD gene harbouring in soil fractions, determined by quantitative PCR (qPCR), was affected by different fertilisations. The highest abundance of the phoD gene was generally detected in the 2–63-μm-sized fraction (silt), but most phoD -encoding microbial species were associated to the 0.1–2-μm-sized fraction (clay) in the chemical-only fertilised soil. The contents of labile Po (LPo), moderately labile Po (MLPo) and fulvic acid-associated Po (FAPo) were significantly correlated with the phoD gene abundance, whereas only LPo content was significantly correlated with the ALP activity. The dominant phoD -encoding phylas were Actinobacteria and Proteobacteria , according to a high-throughput sequencing. Bradyrhizobium , a N 2 -fixer identified as a phoD- encoding genus, showed the highest abundance in fertilised soils. The abundance of Bradyrhizobium , Streptomyces , Modestobacter , Lysobacter , Frankia and Burkholderia increased with the organic-only amendment and was significantly correlated with the ALP activity. According to structure equation models (SEM), pH and LPo content significantly and directly affected the ALP activity; the soil organic C (C org ) content was related to composition and abundances of phoD- harbouring microbial communities; since both microbial properties were correlated to the ALP activity, the C org content was indirectly related to the ALP activity. In conclusion, soil management practices can be used to optimise the contents of soil available P and the organic P with regulation of soil ALP activity and the community composition of corresponding microbes.

BackgroundUnderstanding the yearly, seasonal, monthly, and weekly rainfall variability is crucial for improved agricultural practice in Ethiopia, where agriculture depends on rainfall. In particular, knowledge of rainfall onset, withdrawal, amount, distribution, and the length of the crop growing period would protect farmers from crop damage due to climatic anomalies. This study collected and described 39 years of rainfall data using the Markov chain model. Based on the rainfall probability levels at different threshold values, the length of the dry and wet spells and the length of the growing period were determined.ResultsThe study shows dependable rainfall at a 75% probability level commences in June. The chance of receiving greater than 10 mm at a 50% probability level starts in week 10 (5 March–11 March), with much discontinuity up to week 21st (21 May–27 May). The dependable weekly rainfall begins the week of 22 May (28th May–3rd June) with a probability of greater than 20 mm. The study revealed that the short rainy season rainfall (February to May) is unreliable for growing crops at Ghinchi as opposed to other highland areas of Ethiopia. The major crop growing season is therefore confined to periods of the long rainy season (weeks 22nd to 39th, or 28th May–30th September). The water balance for the study area indicates that the moisture availability index is greater than 0.5, and potential evapotranspiration is lower than precipitation during these months.ConclusionsClimate change and rainfall variability is creating a problem with crop production constraints in the rain-fed agricultural production system in the highlands of Ethiopia. Physical properties of the soil coupled with the unfavorable soil-rainfall relationship limit increased crop production on vertisols. Improving the drainage system and capturing rainfall variability in agronomic-relevant terms is essential. Improving the physical limitations of the soil, adapting to rainfall variability, and practicing improved agronomic practices may help farmers overcome the production problem. This study provides critical information on rainfall variability concerning vertisol management and crop production. However, to overcome the problem, technological support is needed from researchers and policymakers.

Microclimatic conditions change dramatically as forests age and impose strong filters on community assembly during succession. Light availability is the most limiting environmental factor in tropical wet forest succession; by contrast, water availability is predicted to strongly influence tropical dry forest (TDF) successional dynamics. While mechanisms underlying TDF successional trajectories are not well understood, observational studies have demonstrated that TDF communities transition from being dominated by species with conservative traits to species with acquisitive traits, the opposite of tropical wet forest. Determining how functional traits predict TDF tree species’ responses to changing environmental conditions could elucidate mechanisms underlying tree performance during TDF succession. We implemented a 6-ha restoration experiment on a degraded Vertisol in Costa Rica to determine (1) how TDF tree species with different resource-use strategies performed along a successional gradient and (2) how ecophysiological functional traits correlated with tree performance in simulated successional stages. We used two management treatments to simulate distinct successional stages including: clearing all remnant vegetation (early-succession), or interplanting seedlings with no clearing (mid-succession). We crossed these two management treatments (cleared/interplanted) with two species mixes with different resource-use strategies (acquisitive/conservative) to examine their interaction. Overall seedling survival after 2 yr was low, 15.1–26.4% in the four resource-use-strategy × management-treatment combinations, and did not differ between the management treatments or resource-use-strategy groups. However, seedling growth rates were dramatically higher for all species in the cleared treatment (year 1, 69.1% higher; year 2, 143.3% higher) and defined resource-use strategies had some capacity to explain seedling performance. Overall, ecophysiological traits were better predictors of species’ growth and survival than resource-use strategies defined by leaf and stem traits such as specific leaf area. Moreover, ecophysiological traits related to water use had a stronger influence on seedling performance in the cleared, early-successional treatment, indicating that the influence of microclimatic conditions on tree survival and growth shifts predictably during TDF succession. Our findings suggest that ecophysiological traits should be explicitly considered to understand shifts in TDF functional composition during succession and that using these traits to design species mixes could greatly improve TDFrestoration outcomes.

Incipient groundwater salinization has been identified in many arid and semi-arid regions where groundwater is increasingly used for irrigation, but the dominant processes at stake in such context are yet uncertain. Groundwater solutes originates from various sources such as atmospheric inputs, rock dissolution and fertilizer residues, and their concentration is controlled by hydrological processes, in particular evapotranspiration. Here, we propose a deconvolution method to identify the sources and processes governing the groundwater Chloride concentration in agricultural catchments, using the relative variations of Sodium and chloride and using a neighbouring pristine catchment as a reference for the release rate of Na by weathering. We applied the deconvolution method to the case of the Kabini Critical Zone Observatory, South India, where groundwater was sampled in 188 farm tubewells in the semi-arid catchment of Berambadi and in 5 piezometers in the pristine catchment of Mule Hole. In Berambadi, groundwater composition displayed a large spatial variability with Cl contents spanning 3 orders of magnitude. The results showed that the concentration factor due to evapotranspiration was on average about 3 times more than in the natural system, with higher values in the valley bottoms with deep Vertisols. Linked with this process, large concentration of Chloride originating from rain was found only in these areas. At the catchment scale, about 60 percent of the Chloride found in groundwater originates from fertilizer inputs. These results show that Potassium fertilization as KCl is an important source of groundwater salinization in semi-arid context, and stress that identifying dominant drivers is crucial for designing efficient mitigation policies.

Understanding the distribution and release dynamics of potassium (K) in calcareous soils is essential for efficient nutrient management in arid and semi-arid regions. This study investigates K forms and their release behavior in ten agricultural soil pedons from the Darab region in southern Iran, characterized by diverse physiographic settings and soil orders (Entisols, Inceptisols, Aridisols, and Vertisols). Dominant clay minerals identified through X-ray diffraction included illite, smectite, and chlorite. The surface horizons showed greater average concentrations of soluble K (0.63%), exchangeable K (5.06%), and non-exchangeable K (6.5%), whereas structural K was most abundant in subsurface horizons (89.32%). Cumulative K release, assessed through successive CaCl₂ extractions, ranged from 267.7 to 572.4 mg/kg in surface soils and 145.2 to 433 mg/kg in subsurface layers. Release kinetics of non-exchangeable K were effectively described by the power function and pseudo-second-order models, indicating both rapid and sustained release phases. Among the studied soils, pedon 6 (Inceptisol) exhibited the highest release rate, as reflected in its b parameter suggesting enhanced K availability and faster equilibrium attainment. These findings underscore the critical influence of soil mineralogy on potassium dynamics and support the development of site-specific fertilization strategies.

Soil aggregates govern soil organic carbon (SOC) sequestration. But, sparse understanding about the process leads to inaccuracy in predicting potential of soil to stabilize C in warming world. We appraised effects of 43 years of fertilization on relative temperature sensitivity of SOC decomposition (Q₁₀) in soil aggregates to know whether SOC quality or quantity governs Q₁₀. Treatments were: fallow, control, 100% recommended dose of nitrogen (N), N and phosphorus (NP), N, P and potassium (NPK), and NPK + farmyard manure (FYM) (NPK + FYM). Macroaggregates, microaggregates and silt + clay (s + c) fractions were incubated for 16 weeks at 25, 35 and 45 °C, SOC quality (R₀) and Q₁₀ were computed. SOC mineralization from macro- and micro- aggregates were 34 and 28% higher than s + c across the treatments. The s + c fraction of NPK + FYM had ~ 41, 40 and 24% higher C decay rate than NPK plots at 25, 35 and 45 °C, respectively. For s + c fraction Q₁₀ increased over other aggregates. Mean Q₁₀ of s + c fraction was ~ 18.3 and 17.5% higher than macro and micro-aggregate-C, respectively. R₀ was the lowest for NPK + FYM, suggesting longterm manuring with balanced NPK significantly enhance recalcitrance of C. We observed Q₁₀ of macroaggregates and s + c fraction is controlled by C quality but C quantity governs Q₁₀ of microaggregates in Vertisol. Specifically, microaggregates of NPK + FYM were more temperature sensitive, and could be vulnerable to C loss. Hence, practices facilitating microaggregate formation should be avoided. Thus, we recommend manure application for facilitating C sequestration.

The influence of biochar on nitrogen (N) transformation processes in soil is not fully understood. This study assessed the influence of four biochars (wood and poultry manure biochars synthesized at 400°C, nonactivated, and at 550°C, activated, abbreviated as: W400, PM400, W550, PM550, respectively) on nitrous oxide (N2O) emission and N leaching from an Alfisol and a Vertisol. Repacked soil columns were subjected to three wetting–drying (W–D) cycles to achieve a range of water‐filled pore space (WFPS) over a 5‐mo period. During the first two W–D cycles, W400 and W550 had inconsistent effects on N2O emissions and the soils amended with PM400 produced higher N2O emissions relative to the control. The initially greater N2O emission from the PM400 soils was ascribed to its higher labile intrinsic N content than the other biochars. During the third W–D cycle, all biochar treatments consistently decreased N2O emissions, cumulatively by 14 to 73% from the Alfisol and by 23 to 52% from the Vertisol, relative to their controls. In the first leaching event, higher nitrate leaching occurred from the PM400‐amended soils compared with the other treatments. In the second event, the leaching of ammonium was reduced by 55 to 93% from the W550‐ and PM550‐Alfisol and Vertisol, and by 87 to 94% from the W400‐ and PM400‐Vertisol only (cf. control). We propose that the increased effectiveness of biochars in reducing N2O emissions and ammonium leaching over time was due to increased sorption capacity of biochars through oxidative reactions on the biochar surfaces with ageing.

Safflower (Carthamus tinctorius L.) is an edible oilseed crop mainly cultivated in marginal lands. This study evaluates safflower crop water requirements to understand its feasibility to cultivate under rainfed ecosystem through a field experiment undertaken at the International Crops Research Institute for the Semiarid Tropics research farm, India. Eight improved and stress-tolerant safflower cultivars (five spiny and three non-spiny) were evaluated in Vertisols at three soil depths, that is, shallow: <0.60 m, medium: 0.60–1.20 m, and deep:1.20–1.80 m, over 3 years (2009–2012). Wet, normal, and deficit rainfall years were experienced during 2009/2010, 2010/2011, and 2011/2012, respectively. Soil moisture, crop yield, and growth parameters were measured, and field-scale hydrology was captured through a calibrated one-dimensional water balance model. Safflower responded to available residual soil moisture which varied with soil depth and rainfall received in different years. Total crop water use was 300–320 mm during the postrainy season, of which about 70% was extracted in deep Vertisols and 55% in medium Vertisols through residual soil moisture. In addition, 30% of water requirement was met through postrainy season rainfall. Safflower grown in shallow Vertisols could only meet 40% of crop water requirement. Spiny cultivar NARI-H-15 grown in deep soil recorded a maximum yield of 1890 kg ha−1 in the wet year. Seed yield from spiny cultivars grown in deep and medium soils was nearly similar (1500–1600 kg ha−1) during wet and normal years; a significant reduction in yield (>50%) occurred in shallow soils and also during a rainfall deficit year. Spiny cultivars produced 10%–50% higher seed yield compared to non-spiny cultivars. Growing safflower in medium and deep Vertisols provides opportunities for crop intensification.

Zinc (Zn) deficiency prevails in different soils and crops of the world. Soil Zn deficiency adversely affects growth, yield and micronutrients (Zn, copper (Cu), iron (Fe) and manganese (Mn)) concentration in different crops including pigeonpea ( Cajanus cajan L. Millsp.), a protein rich legume crop grown consumed in different parts of the world. Therefore, we carried out a 2-years field experiment on a Zn-deficient Vertisol with 20 different pigeonpea genotypes and 3 levels of Zn treatments in a split-plot design with 3 replications, to study the effect of Zn application on yield, micronutrients concentration and uptake by pigeonpea genotypes. The 3 levels of Zn treatments were no Zn (no Zn fertilizer was applied), soil Zn (20 kg Zn ha −1 ) and soil + foliar Zn. Compared to no Zn application, soil and soil + foliar application of Zn enhanced mean grain yield by 15 and 24%, stover yield by 13 and 29% and total biomass yield of pigeonpea genotypes by 13 and 29%, respectively. Soil + foliar application of Zn significantly increased mean grain Zn concentration by 33% compared to no Zn application. Soil and soil + foliar Zn application led to reduction in mean grain Cu concentration by 9 and 10%, respectively, and did not significantly increase or decrease grain Fe and Mn concentration. Soil and soil + foliar application of Zn significantly increased mean grain Zn, Fe and Mn uptake by pigeonpea genotypes compared to no Zn application. Soil + foliar application of Zn had significantly higher mean grain Zn, Fe and Mn uptake compared to soil Zn application. The grain, stover and total biomass yield, micronutrients concentration in grain and stover and micronutrients uptake by the genotypes were different under various treatments. The genotypes ICPL 87119, BDN 2, JKM 7, Virsa Arhar 1, DT 23 and AAUT 2007–10 under soil application of Zn and ICPL 87119, BDN 2, JKM 7 and Virsa Arhar 1 under soil + foliar application of Zn were found promising for cultivation to obtain higher grain yield and micronutrients uptake.

Production of exopolysaccharides (EPS) can be used as a criteria for the isolation of stress tolerant microorganisms. In the present study, EPS-producing fluorescent pseudomonads were isolated from alfisols, vertisols, inseptisols, oxisols, and aridisols of different semiarid millet growing regions of India and were screened in vitro for drought tolerance in trypticase soy broth supplemented with different concentrations of polyethylene glycol (PEG6000). Out of the total 81 isolates, 26 could tolerate maximum level of stress (−0.73 MPa) and were monitored for the amount of EPS produced under maximum level of water stress. The strain GAP-P45, isolated from alfisol of sunflower rhizosphere, showed the highest level of EPS production under water stress conditions, was identified as Pseudomonas putida on the basis of 16S rDNA sequence analysis, and was used as seed treatment to study its effect in alleviating drought stress effects in sunflower seedlings. Inoculation of Pseudomonas sp. strain GAP-P45 increased the survival, plant biomass, and root adhering soil/root tissue ratio of sunflower seedlings subjected to drought stress. The inoculated bacteria could efficiently colonize the root adhering soil and rhizoplane and increase the percentage of stable soil aggregates. Scanning electron microscope studies showed the formation of biofilm of inoculated bacteria on the root surface and this, along with a better soil structure, might have protected the plants from the water stress.