Interest in the use of biochar in agriculture has increased exponentially during the past decade. Biochar, when applied to soils is reported to enhance soil carbon sequestration and provide other soil productivity benefits such as reduction of bulk density, enhancement of water-holding capacity and nutrient retention, stabilization of soil organic matter, improvement of microbial activities, and heavy-metal sequestration. Furthermore, biochar application could enhance phosphorus availability in highly weathered tropical soils. Converting the locally available feedstocks and farm wastes to biochar could be important under smallholder farming systems as well, and biochar use may have applications in tree nursery production and specialty-crop management. Thus, biochar can contribute substantially to sustainable agriculture. While these benefits and opportunities look attractive, several problems, and bottlenecks remain to be addressed before widespread production and use of biochar becomes popular. The current state of knowledge is based largely on limited small-scale studies under laboratory and greenhouse conditions. Properties of biochar vary with both the feedstock from which it is produced and the method of production. The availability of feedstock as well as the economic merits, energy needs, and environmental risks—if any—of its large-scale production and use remain to be investigated. Nevertheless, available indications suggest that biochar could play a significant role in facing the challenges posed by climate change and threats to agroecosystem sustainability.
Establish a common threshold in P saturation across a geographic diversity of soils.• Predict water-soluble P from soil P storage capacity to guide fertilizer strategies.• Relate runoff P concentration with soil P storage capacity. ABSTRACTLoss of legacy soil phosphorus (P) due to historical over-application of fertilizers and manures can result in eutrophication of water bodies. The soil P storage capacity (SPSC) has been proposed as a tool to estimate the capacity of humid region soils to act as either sinks or sources of P to runoff or leaching. The SPSC is based on a threshold molar ratio of extractable P/(Al+Fe), called the soil P saturation ratio (PSR), above which water-soluble P abruptly increases. Objectives were to (i) document consistency of the threshold PSR for a wide geographic range of acid soils, (ii) determine applicability of a SPSC vs. water-soluble P predictive equation to soils from various regions, and (iii) relate SPSC with water quality parameters. Surface samples were collected from acidic, humid-region soils encompassing multiple physiographic provinces of the United States. Water quality data, including dissolved reactive P and total P, were obtained from various study sites. Phosphorus, Fe, and Al in Mehlich 3 solutions were determined, and PSR and SPSC calculated. The threshold PSR based on 186 samples is 0.1, indicating a common threshold across the geographic range of this study. Phosphorus concentrations in runoff related closely with SPSC, PSR, and M3-P values of soils that were the source of the runoff. However, SPSC has the additional potential of estimating extent of legacy P loss at excessive concentrations for soils of eastern and central United States. Results support general applicability of PSR and SPSC for acid soils.Abbreviations: DRP, dissolved reactive phosphorus; ICP-OES, inductively coupled plasma-optical emission spectrometry; M3-Al, Mehlich 3-extractable aluminum; M3-Fe, Mehlich 3-extractable iron; M3-P, Mehlich 3-extractable phosphorus; PSR, phosphorus saturation ratio; SPSC, soil phosphorus storage capacity; STP, soil test phosphorus; TP, total phosphorus.
Conventional agricultural practices that use excessive chemical fertilizers and pesticides come at a great price with respect to soil health, a key component to achieve agricultural sustainability. Organic farming could serve as an alternative agricultural system and solve the problems associated with the usage of agro‐chemicals by sustainable use of soil resources. A study was carried out to evaluate the impact of organic vs. conventional cultivations of basmati rice on soil health during Kharif (rainy) season of 2011 at Kaithal district of Haryana, India, under farmers' participatory mode. Long‐term application of organic residues in certified organic farms was found to improve physical, chemical, and biological indicators of soil health. Greater organic matter buildup as indicated by higher soil organic carbon content in organic fields was critical to increase soil aggregate stability by increasing water holding capacity and reducing bulk density. Proper supplementation of nutrients (both major and micro nutrients) through organic residue addition favored biologically available nutrients in organic systems. Further, the prevalence of organic substrates stimulated soil microorganisms to produce enzymes responsible for the conversion of unavailable nutrients to plant available forms. Most importantly, a closer look at the relationship between physicochemical and biological indicators of soil health evidenced the significance of organic matter to enzyme activities suggesting enhanced nutrient cycling in systems receiving organic amendments. Enzyme activities were very sensitive to short‐term (one growing season) effects of organic vs. conventional nutrient management. Soil chemical indicators (organic matter and nutrient contents) were also changed in the short‐term, but the response was secondary to the biochemical indicators. Taken together, this study indicates that organic farming practices foster biotic and abiotic interactions in the soil which may facilitate in moving towards a sustainable food future.
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