Dirt, soil, call it what you want-it's everywhere we go. It is the root of our existence, supporting our feet, our farms, our cities. This fascinating yet disquieting book finds, however, that we are ...running out of dirt, and it's no laughing matter. An engaging natural and cultural history of soil that sweeps from ancient civilizations to modern times,Dirt: The Erosion of Civilizationsexplores the compelling idea that we are-and have long been-using up Earth's soil. Once bare of protective vegetation and exposed to wind and rain, cultivated soils erode bit by bit, slowly enough to be ignored in a single lifetime but fast enough over centuries to limit the lifespan of civilizations. A rich mix of history, archaeology and geology,Dirttraces the role of soil use and abuse in the history of Mesopotamia, Ancient Greece, the Roman Empire, China, European colonialism, Central America, and the American push westward. We see how soil has shaped us and we have shaped soil-as society after society has risen, prospered, and plowed through a natural endowment of fertile dirt. David R. Montgomery sees in the recent rise of organic and no-till farming the hope for a new agricultural revolution that might help us avoid the fate of previous civilizations.
In agricultural systems, maintenance of soil organic matter (SOM) has long been recognized as a strategy to reduce soil degradation. No‐tillage and manure amendments are management practices that can ...increase SOM content and improve soil aggregation. We investigated the effects of 10‐yr of different tillage systems and N sources on soil aggregate‐size distribution and aggregate‐associated C and N. The study was a split‐plot design replicated four times. The main plot treatment was tillage (no‐tillage, NT; conventional tillage, CT) and the subplot treatment was N source (manure, M; NH4NO3 fertilizer, F). The experiment was established in 1990 on a moderately well‐drained Kennebec silt loam (Fine‐silty, mixed, superactive mesic Cumulic Hapludoll) with continuous corn (Zea mays L.). In 1999, soil samples were collected (0‐ to 5‐cm depth) from the field treatments and separated into four aggregate‐size classes (>2000, 250–2000, 53–250, and 20–53 μm) by wet sieving. Labile C and N content of all aggregate‐size fractions were measured using 28‐d laboratory incubations of intact and crushed aggregates. No‐tillage and M treatments significantly increased total C and N and the formation of macroaggregates. Conventional tillage in comparison with NT significantly reduced macroaggregates with a significant redistribution of aggregates into microaggregates. Aggregate protected labile C and N were significantly greater for macroaggregates, (>2000 and 250–2000 μm) than microaggregates (53–250 and 20–53 μm) and greater for M than F indicating physical protection of labile C within macroaggregates. No‐tillage and M a lone each significantly increased soil aggregation and aggregate‐associated C and N; however, NT and M together further improved soil aggregation and aggregate‐protected C and N.
Determination of soil particle‐size distribution (PSD) by sieving, hydrometer, and pipette methods as well as by laser diffraction (LD) suffers from inherent flaws, mainly due to the difficulty in ...defining the size of irregularly shaped particles. Therefore these methods yield only estimates of PSD. The objective of this study was to determine whether a functional relationship exists between the PSDs obtained by the combined sieve‐pipette method and those obtained by LD. Samples from 42 California soils were analyzed. For the LD measurements a Beckman–Coulter LS‐230 apparatus with a 750‐nm laser beam that measures particles in the range of 0.04 to 2000 μm was used, employing the Mie theory for the PSD calculations. Values of 1.5 and 0.2 for the real part and the imaginary term of the refractive index (RI), respectively, gave satisfactory results for the optical model calculations. Volume percentage of the clay‐size fraction obtained by LD was generally lower than mass percentage of the clay fraction derived by the pipette method. The opposite trend was noted for the silt‐size fraction. Coefficients of determination for the regression equations for the clay, silt, and sand fractions determined by the two methods were 0.702, 0.689, and 0.821, respectively. Good agreement between measured and calculated LD values for one size class was accompanied by poor agreement between measured and calculated values for the other. The LD method provides a continuous PSD curve, which enables a detailed data analysis and a flexible application of different particle‐size dependent classification systems.
Biochar (B) application to sandy soils improves its productivity and mitigates climate change. A pot experiment was conducted to investigate the potential effects of maize stalks biochar applied to a ...zucchini (Cucurbita pepo L. var.Hybrid fadwa) grown on a calcareous sandy soil. Plastic pots were filed with three kilograms of the studied soil and amended by the biochar at levels of 0 (control, unamended soil), 6.3 (B1), 12.6 (B2), and 25.5 (B3) g pot‒1. The pots were planted with zucchini plants and designed in a complete randomized design with three replications. Amending the soil with the biochar significantly increased the soil organic matter, fresh fruit yield, nitrogen use effiency (NUE) and agronomic efficiency of applied nitrogen (AE N) of zucchiniplants. Biochar additions improved the fresh fruits by 26.7, 55, and 195.0 % for B1, B2 and B3 treatments respectively, over the control. The NUE of the plants increased owing to the application of biochar to the soil from 69.2 mg fruit/mg N at the control treatment to 77.1, 84.3 and 131.4 mg fruit/mg N for B1, B2 and B3 treatments, respectively. So, it is recommended to apply biochar as an amendment to the calcareous sandy soil in order to improve its fertility.
Arsenic adsorption on amorphous Al and Fe oxides and the clay minerals, kaolinite, montmorillonite, and illite was investigated as a function of solution pH and As redox state, i.e., arsenite As(III) ...and arsenate As(V). Arsenic adsorption experiments were carried out in batch systems to determine adsorption envelopes, amount of As(III), As(V), or both adsorbed as a function of solution pH per fixed total As concentration of 20 μM As. Arsenate adsorption on oxides and clays was maximal at low pH and decreased with increasing pH above pH 9 for Al oxide, pH 7 for Fe oxide and pH 5 for clays. Arsenite adsorption exhibited parabolic behavior with an adsorption maximum around pH 8.5 for all materials. There was no competitive effect of the presence of equimolar arsenite on arsenate adsorption. The competitive effect of equimolar arsenate on arsenite adsorption was small and apparent only on kaolinite and illite in the pH range 6.5 to 9. The constant capacitance model was able to fit the arsenate and arsenite adsorption envelopes to obtain values of the intrinsic As surface complexation constants. These intrinsic surface complexation constants were then used in the model to predict competitive arsenate and arsenite adsorption from solutions containing equimolar As(III) and As(V) concentrations. The constant capacitance model was able to predict As adsorption from mixed As(III)‐As(V) solutions in systems where there was no competitive effect.
Soil C sequestration can improve soil quality and reduce agriculture's contribution to CO2 emissions. The long‐term (12 yr) effects of tillage system and N fertilization on crop residue production ...and soil organic C (SOC) sequestration in two dryland cropping systems in North Dakota on a loam soil were evaluated. An annual cropping (AC) rotation spring wheat (SW) (Triticum aestivum L.)–winter wheat (WW)–sunflower (SF) (Helianthus annuus L.) and a spring wheat‐fallow (SW‐F) rotation were studied. Tillage systems included conventional‐till (CT), minimum‐till (MT), and no‐till (NT). Nitrogen rates were 34, 67, and 101 kg N ha−1 for the AC system and 0, 22, and 45 kg N ha−1 for the SW‐F system. Total crop residue returned to the soil was greater with AC than with SW‐F. As tillage intensity decreased, SOC sequestration increased (NT > MT > CT) in the AC system but not in the SW‐F system. Fertilizer N increased crop residue quantity returned to the soil, but generally did not increase SOC sequestration in either cropping system. Soil bulk density decreased with increasing tillage intensity in both systems. The results suggest that continued use of a crop‐fallow farming system, even with NT, may result in loss of SOC. With NT, an estimated 233 kg C ha−1 was sequestered each year in AC system, compared with 25 kg C ha−1 with MT and a loss of 141 kg C ha−1 with CT. Conversion from crop‐fallow to more intensive cropping systems utilizing NT will be needed to have a positive impact on reducing CO2 loss from croplands in the northern Great Plains.
Resumen: En la acuaponía el uso de sustrato permite la colonización de bacterias nitrificantes y actúa como biofiltro. El diámetro de partículas del sustrato puede ser determinante en la colonización ...del sustrato por las bacterias y puede afectar el desarrollo y rendimiento de las plantas; razón por la que en esta investigación se planteó la hipótesis de que tamaño de partícula del tezontle afecta la colonización de bacterias y el desarrollo y crecimiento de las plantas. El experimento consistió de recipientes de 120 L como estanques para los peces, y de 12 tinas de 240 L para el sustrato y una bomba para oxigenación auxiliar a los estanques de los peces. Se establecieron 3 cultivos en cada tina: tomate, pepino y lechuga. Estos cultivos fueron trasplantados en 3 granulometrías de tezontle: diámetro menor a 1 cm, mayor a 5 cm y mezcla 50:50% de ambos tamaños con tres repeticiones por tratamiento. Se realizó un análisis de la varianza y prueba de Tukey. No hubo efecto del diámetro de partícula del sustrato en la altura, diámetro de tallo y lecturas SPAD en las plantas de tomate, pepino y lechuga. El diámetro de partícula del sustrato no afectó el rendimiento ni firmeza, acidez titulable y grados Brix en los frutos de tomate. Tampoco hubo efecto sobre rendimiento y de calidad de frutos de pepino. En lechuga el peso fresco correspondiente al sustrato con partículas menores a 1 cm fue 55% mayor al de partículas mayores a 5 cm: 89.87 y 50.12 g por planta, respectivamente. El diámetro de partícula no afecta el rendimiento ni la calidad de los cultivos establecidos, sin embargo, en términos prácticos el tezontle fino menor a un cm es recomendable porque tiene mayor capacidad retención de humedad y mayor superficie para que las bacterias colonicen el medio.
Implications of no-till (NT) management on soil C dynamics, soil fertility, and crop yields have been discussed, but an up-to-date synthesis of NT impact on soil physical properties based on a ...comprehensive compilation of global published studies is not available. Yet, an understanding of changes in soil physical properties after NT adoption is important to manage soils, agricultural production, and environmental quality. We compared data on soil physical properties among NT, reduced till (RT), and conventional till (CT) systems, discussed factors influencing tillage system effects, and underscored research needs. No-till had mixed effects on soil bulk density and penetration resistance but reduced Proctor bulk density (compactibility) by 4 to 13% in the 0 to 15 cm depth, suggesting that NT can reduce the susceptibility of the soil to compaction. No-till increased wet aggregate stability by 1 to 97%, water infiltration by 17 to 86%, and available water by 44%. It reduced or had no effect on soil temperature during the growing season but increased soil thermal conductivity. The latter indicates that NT can increase the soil's ability to conduct heat. No-till induced some slight water repellency, which can reduce soil aggregate slaking and enhance C storage. However, NT had no consistent effects on saturated hydraulic conductivity, soil consistency, and shear strength. Reduced till effects on soil properties were intermediate in values between NT and CT. No-till benefits for reducing compaction risks and improving structural quality increased in the long term. Changes in soil physical properties appear to be mainly confined to the upper 10 cm depth. Reviews on NT and soil C have also concluded that NT can cause stratification of soil organic C in the upper 5 or 10 cm depth. Thus, NT-induced increases in near-surface (<10 cm depth) soil organic C concentration most likely improved wet aggregate stability and available water capacity, and reduced compactibility. One-time tillage of NT soils does not seem to negatively affect soil physical properties. Addition of companion practices (i.e., cover crops, C amendments) can enhance NT performance. Overall, NT management can have positive effects on soil physical properties with the extent depending on soil textural class and management duration.
•No-till management generally improves soil physical properties.•Changes in soil properties in reduced till are between no-till and tilled systems.•No-till benefits for improving soil properties increase with time.•Companion practices such as cover crops can enhance no-till performance.•One-time tillage of no-till soils may not negatively affect soil properties.
BACKGROUND: Plant biostimulants are diverse substances and microorganisms used to enhance plant growth. The global market for biostimulants is projected to increase 12 % per year and reach over ...$2,200 million by 2018. Despite the growing use of biostimulants in agriculture, many in the scientific community consider biostimulants to be lacking peer-reviewed scientific evaluation. SCOPE: This article describes the emerging definitions of biostimulants and reviews the literature on five categories of biostimulants: i. microbial inoculants, ii. humic acids, iii. fulvic acids, iv. protein hydrolysates and amino acids, and v. seaweed extracts. CONCLUSIONS: The large number of publications cited for each category of biostimulants demonstrates that there is growing scientific evidence supporting the use of biostimulants as agricultural inputs on diverse plant species. The cited literature also reveals some commonalities in plant responses to different biostimulants, such as increased root growth, enhanced nutrient uptake, and stress tolerance.
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