Crop yield and SOC responses to biochar application were dependent on soil texture and crop type in southern Quebec,Canada

Changes to soil nutrient availability and increases for crop yield and soil organic C (SOC) concentration on biochar‐amended soil under temperate climate conditions have only been reported in a few publications. The objective of this work was to determine if biochar application rates up to 20 Mg ha^?1 affect nutrient availability in soil, SOC stocks and yield of corn (Zea mays L.), soybean (Glycine max L.), and switchgrass (Panicum virgatum L.) on two coarse‐textured soils (loamy sand, sandy clay loam) in S Quebec, Canada. Data were collected from field experiments for a 3‐y period following application of pine wood biochar at rates of 0, 10, and 20 Mg ha^?1. For corn plots, at harvest 3 y after biochar application, 20 Mg biochar ha^?1 resulted in 41.2% lower soil NH on the loamy sand; the same effect was not present on the sandy clay loam soil. On the loamy sand, 20 Mg biochar ha^?1 increased corn yields by 14.2% compared to the control 3 y after application; the same effect was not present on the sandy clay loam soil. Biochar did not alter yield or nutrient availability in soil on soybean or switchgrass plots on either soil type. After 3 y, SOC concentration was 83 and 258% greater after 10 and 20 Mg ha^?1 biochar applications, respectively, than the control in sandy clay loam soil under switchgrass production. The same effect was not present on the sandy clay loam soil. A 67% higher SOC concentration was noted with biochar application at 20 Mg ha^?1 to sandy clay loam soil under corn.     

Sweet Sorghum [Sorghum bicolor (L.) Moench] Biomass Production for Biofuel and the Effects of Soil Types and Nitrogen Fertilization

This research aimed to determine the optimum nitrogen fertilization rate on three soils for producing biomass sweet sorghum (Sorghum bicolor cultivar M81E) and corn (Zea mays cultivar P33N58) grain yield and to compare their responses. The research was conducted in Missouri in rotations with soybean, cotton, and corn. Seven rates of nitrogen (N) were applied. Sweet sorghum dry biomass varied between 11 and 27.5 Mg ha^?1) depending on year, soil type, and N rate. Nitrogen fertilization on the silt and sandy loam soils had no effect (P > 0.05) on sweet sorghum yield grown after cotton and soybean. However, yield increased in the clay soil. Corn grain yielded from 1.3 to 12.9 Mg ha^?1, and 179 to 224 kg N ha^?1 was required for maximum yield. Increasing biomass yield required N application on clay but not on silt loam and sandy loam in rotations with soybean or cotton.     

Soybean Micronutrient Content in Irrigated Plants Grown in the Midsouth

Concentrations and contents of iron (Fe), boron (B), zinc (Zn), manganese (Mn), and copper (Cu) were determined for two MG IV and one MG V irrigated soybean (Glycine max L. Merr.) cultivars grown on clay and sandy loam soils in 2011 and 2012. Plants were sampled at V3, R2, R4, R6, and R8, tissues separated, dried, weighed, and nutrient concentrations determined. Nutrient contents were calculated. No cultivar, site, or year differences in nutrient concentrations or contents were observed. Iron had the greatest concentration and content of all followed by B, Zn, Mn, and Cu. Maximum concentrations and contents in leaves occurred at R4 and later declined. Concentrations and contents in stems remained constant or increased while pods rapidly increased until (R8). A 3328 kg ha^?1 seed yield will remove 325.0 g Fe ha^?1, 153.9 g B ha^?1, 175.6 g Zn ha^?1, 100.0 g Mn ha^?1, and 52.5 g Cu ha^?1.     

Organic Nitrogen Source Addition for Improving the Physicochemical Properties of Sandy Loam Soil and Maize Performance

Poor quality of sandy loam soils ?is the main reason for low crop yield. Improvement of physicochemical properties of these soils is very challenging. Addition of organic sources may improve the soil properties. Therefore, this study investigated the adequacy of poultry-manure-compost (PMC) and pressmud-compost (PrMC) at 0 (control), 2, 4, 6, 8, and 10 t ha^?1 for improving the physicochemical properties of sandy loam soil and maize performance. An increasing trend in most soil and crop traits was seen with increasing compost levels. For 10 t PMC ha^?1, soil inorganic-N (512%), organic-carbon (78%), and water-holding capacity (65.36%) improved maximum. This resulted in the maximum mean crop growth rate (43.85%), stover yield (94%), grain protein (21%), and nitrogen use efficiency (30.6 kg kg^?1). Contrarily, grain oil (?7%) was lowest at 10 t PMC ha^?1. Consequently, 10 t PMC ha^?1 could be much effective to improve the physicochemical properties of sandy loam soils and maize performance.     

Response of soil exchangeable and crop potassium concentrations to variable fertilizer and cropping regimes in long-term field experiments on different soil types

Annual potassium (K) balances have been calculated over a 40‐year period for five field experiments located on varying parent materials (from loamy sand to clay) in south and central Sweden. Each experiment consisted of a number of K fertilizer regimes and was divided into two crop rotations, mixed arable/livestock (I) and arable only (II). Annual calculations were based on data for K inputs through manure and fertilizer, and outputs in crop removal. Plots receiving no K fertilizer showed negative K balances which ranged from 30 to 65 kg ha^?1 year^?1 in rotation I, compared with 10–26 kg ha^?1 year^?1 for rotation II. On sandy loam and clay soils, the K yield of nil K plots (rotation I) increased significantly with time during the experimental period indicating increasing release of K from soil minerals, uptake from deeper soil horizons and/or depletion of exchangeable soil K (K_ex). Significant depletion of K_ex in the topsoil was only found in the loamy sand indicating a K supply from internal sources in the sandy loam and clay soils. On silty clay and clay soils, a grass/clover ley K concentration of ～2% (dry weight) was maintained during the 40‐year study period on the nil K plots, but on the sandy loam, loam and loamy sand, herbage concentrations were generally less than 2% K.     

Changes in carbon stocks of Danish agricultural mineral soils between 1986 and 2009

To establish a national inventory of soil organic carbon (SOC) stocks and their change over time, soil was sampled in 1986, 1997 and 2009 in a Danish nation‐wide 7‐km grid and analysed for SOC content. The average SOC stock in 0–100‐cm depth soil was 142 t C ha^?1, with 63, 41 and 38 t C ha^?1 in the 0–25, 25–50 and 50–100 cm depths, respectively. Changes at 0–25 cm were small. During 1986–97, SOC in the 25–50‐cm layer increased in sandy soils while SOC decreased in loam soils. In the subsequent period (1997–2009), most soils showed significant losses of SOC. From 1986 to 2009, SOC at 0–100 cm decreased in loam soils and tended to increase in sandy soils. This trend is ascribed to dairy farms with grass leys being abundant on sandy soils while cereal cropping dominates on loamy soils. A statistical model including soil type, land use and management was applied separately to 0–25, 25–50 and 50–100 cm depths to pinpoint drivers for SOC change. In the 0–25 cm layer, grass leys added 0.95 t C ha^?1 year^?1 and autumn‐sown crops with straw incorporation added 0.40 t C ha^?1 year^?1. Cattle manure added 0.21 t C ha^?1 year^?1. Most interestingly, grass leys contributed 0.58 t C ha^?1 year^?1 at 25–50 cm, confirming that inventories based only on top‐soils are incomplete. We found no significant effects in 50–100 cm. Our study indicates a small annual loss of 0.2 t C ha^?1 from the 0–100 cm soil layer between 1986 and 2009.     

Macro-Nutrient Concentration and Content of Irrigated Soybean Grown in the Early Production System of the Midsouth

Macro-nutrients in soybean (Glycine max L. Merr.) have not been extensively researched recently. Concentrations and contents of nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur (N, P, K, Ca, Mg, and S) were determined for three irrigated cultivars grown using the early soybean production system (ESPS) on two soils (a sandy loam and a clay) in the Mississippi Delta during 2011 and 2012. Data were collected at growth stages V3, R2, R4, R6, and R8. No change in macro-nutrients due to soil type or years occurred and modern cultivars were similar to data collected >50 years ago. Mean seed yield of 3328 kg ha^?1 removed 194.7 kg N ha^?1, 16.5 kg P ha^?1, 86.0 kg K ha^?1, 17.5 kg Ca ha^?1, 9.0 kg Mg ha^?1, and 10.4 kg S ha^?1. Increased yields over the decades are likely due to changed plant architecture and/or pests resistance, improved cultural practices, chemical weed control, and increased levels of atmospheric carbon dioxide (CO₂). Yield improvements by genetically manipulating nutrient uptake appear to be unlikely.     

Influence of Sulfur Fertility on Wheat Yield Performance on Alluvial and Upland Soils

Abstract: In recent years, sulfur (S) deficiencies in winter wheat (Triticum aestivum L.) have become more common, particularly on coarse‐textured soils. In Study I, field experiments were conducted in 2001/2002 through 2003/2004 on Mississippi River alluvial soils (Experiment I) and an upland, loessial silt loam (Experiment II) to evaluate the influence of spring S rates of 0, 5.6, 11.2, and 22.4 kg ha^?1 and a fall rate of 22.4 kg sulfate (SO₄)‐S ha^?1 on grain yield of three varieties. In Study II, field experiments were conducted in 2001/2002 and 2004/2005 on alluvial soils to evaluate the influence of spring S rates of 0, 5.6, 11.2, and 22.4 kg SO₄‐S ha^?1 in fields where S‐deficiency symptoms were present. Grain yield response to applied S occurred only on alluvial, coarse‐textured, very fine sandy loam soils (Study II) that had soil SO₄‐S levels less than the critical level of 8 mg kg^?1 and organic‐matter contents less than 1 g kg^?1 in the 0‐ to 15‐, 15‐ to 30‐, and 30‐ to 45‐cm depths. Soil pH increased with soil depth. Optimum S rate was 11.2 kg SO₄‐S ha^?1 in 2001/2002 and 5.6 kg SO₄‐S ha^?1 in 2004/2005. On the upland, loessial silt loam soil, soil SO₄‐S levels accumulated with depth, whereas organic‐matter content and pH decreased. In the loessial soils, average soil SO₄‐S levels in the 15‐ to 30‐ and 30‐ to 45‐cm soil depths were 370% greater than SO₄‐S in the surface horizon (0 to 15 cm).     

Catch Crop and Animal Slurry in Spring Barley Grown with Straw Incorporation

Abstract

Four rates of straw (0, 4, 8 and 12 t ha^?1 yr^?1) were incorporated in a field experiment with continuous spring barley. The experiment was conducted on a sandy soil (5.5% clay) and a sandy loam soil (11.2% clay). After eight years, the straw incorporation was combined with catch-crop growing with and without winter application of animal slurry and also spring fertilization with mineral fertilizer (0, 50, 100 or 125 kg N ha^?1 yr^?1). The combined experiment was conducted for three lyears on the sandy soil and for four years on the sandy loam soil. The effects on barley dry matter yield and N uptake are presented together with the long-term effects of the straw incorporations on crop growth and soil C and N. Grain yield on the sandy loam was unaffected by straw incorporation. On the sandy soil the highest straw application rates reduced grain yield in the unfertilized barley. When the barley received mineral fertilizer at recommended levels (100 kg N ha^?1 yr^?1), grain yield on this soil was also unaffected by the high straw rates. Including a catch crop had a positive effect on the grain yield of barley on both soils. The total N uptake in grain and straw generally increased with straw application up to 8 t ha^?1 yr^?1. With the highest straw application rate (12 t ha^?1 yr^?1), the total N uptake decreased but still exceeded N uptake in barley grown with straw removal. The barley accumulated higher amounts of N when a catch crop was included. The total N uptake in the barley was significantly higher after animal slurry application. The extra N uptake, however, was much lower than the amounts of N applied with the slurry. Incorporation of straw had only a small influence on N uptake after slurry application. The straw, therefore, was not able to store the applied N during winter. In the two four-year periods before the combined experiment, grain yield on the sandy loam was generally negatively affected by straw incorporations. In the second period, N uptake began to show a positive effect of the straw. On the sandy soil, grain yield and N uptake during the whole period were generally positively affected by the straw incorporations except for the highest straw rate (12 t ha^?1 yr^?1). The sandy loam soil showed higher increases in C and N content after the repeated straw incorporations and catch-crop growing than the sandy soil. When application of animal slurry was combined with the catch crop, no further increases in soil C and N were found relative to soil where a catch crop was grown without slurry application. Large amounts of the N applied with the slurry may therefore have been lost by denitrification or nitrate leaching.     

Towards sustainable production of peppermint (Mentha piperita L.) through integrated use of vermicompost and cowpea green manuring with synthetic nitrogen fertilization

A field experiment with peppermint (Mentha piperita L.) was conducted in a sandy loam (Typic ustifluvent) soil during 2007 and 2008 at Lucknow, India. Ten treatments consisting of control (no synthetic or organic nitrogen fertilization), synthetic nitrogen fertilization (SN) 75, 150 and 225 kg ha^?1 alone, vermicompost (VC) 3 t + 37.5 kg SN ha^?1, VC 6 t + 75 kg SN ha^?1 and VC 9 t + 112.5 kg SN ha^?1 and intercropping of one, two and three rows of cowpea for green manuring in combination with 50, 100 and 150 kg SN ha^?1, respectively, were evaluated in a randomized block design. Integrated use of VC 9 t with 112.5 kg SN ha^?1 produced maximum essential oil (94.3 kg ha^?1), increased the herb and essential oil yields by 104 and 89%, respectively, over control and reduced SN use by 50%, without affecting the quality of essential oil. Application of VC and intercropping of cowpea for green manuring significantly improved the organic carbon, available N, P and K content in soil over SN alone. To get sustainable production of peppermint, application of VC 9 t ha^?1 along with 112.5 kg N ha^?1 through synthetic fertilizer is recommended for light textured sandy loam soils.     

Cation transport during unsaturated flow through two intact soils

In the quest for better understanding of cation movement through undisturbed soils, leaching experiments on 300-mm long undisturbed soil columns of two contrasting soils were carried out. One soil was a weakly-structured alluvial fine sandy loam, the other a well-structured aeolian silt loam. About 2000 mm of solutions of MgCl₂ and Ca(NO₃)₂ of 0·025 M were applied at unsaturated water flow rates of between 3 and 13 mm h^?1. Solute movement was monitored over several weeks by collecting effluent under suction at the base. In the sandy loam anion transport was influenced by exclusion from the double layer, whereas in the Ramiha soil anion adsorption occurred. Cation transport was described by coupling the convection-dispersion equation with cation exchange equations. Good simulations of the Mg²⁺ and Ca²⁺ concentrations in the effluent and on the exchange sites were obtained if 80% of the exchangeable cations, as measured using the 1 M ammonium acetate method, were assumed to be active. Local physical or chemical disequilibrium did not need to be explicitly taken into account. About 400 kg ha^?1 of native potassium was leached from the alluvial soil, but only about 10 kg ha^?1 was leached from the aeolian soil. The convection-dispersion equation coupled with exchange theory was found to describe cation transport under unsaturated flow through undisturbed soil satisfactorily.     

Impact of pig slurry on soil properties, water salinization, nitrate leaching and crop yield in a four-year experiment in Central Spain

Abstract. The repeated application of pig slurry to agricultural soils may result in an accumulation of salts and a risk of aquifer pollution due to nitrate leaching and salinization. Under Mediterranean conditions, a field experiment on a sandy loam soil (Typic Xerofluvent) was performed with maize (Zea mays) in 1998, 1999 and 2001 to study the effects of applying optimal (P1) and excessive rates (P3) of pig slurry on soil salinization, nitrate leaching and groundwater pollution. The rate of pig slurry was established considering the optimal N rate for maize in this soil (170, 162 and 176 kg N ha^?1 for 1998, 1999 and 2001, respectively). Pig slurry treatments were compared to an optimal N rate supplied as urea (U) and a control treatment without N fertilizer (P0). The composition of the slurries showed great variability between years. Mean NO₃^? leaching losses from 1998 to 2001 were 329, 215, 173 and 78 kg N ha^?1 for P3, P1, U and P0 treatments, respectively. The amount of total dissolved salts (TDS) added to the soil in slurry application between 1998 and 2001 was 2019 kg TDS ha^?1 for the P1 treatment and 6058 kg TDS ha^?1 for the P3 treatment. As a consequence, the electrical conductivity (EC) of the slurry‐treated soils was greater than that of the control soil. The EC correlated significantly with the sodium concentration of the soil solution. Over the entire experimental period, 2653, 2202 and 2110 kg Na ha^?1 entered the aquifer from the P3, P1 and P0 treatments, respectively. The P3 treatment did not significantly increase grain production in 1999 and 2001 compared with that achieved with the optimal N rate treatment (P1). This behaviour shows the importance of establishing application guidelines for pig slurry that will reduce the risk of soil and groundwater pollution.     

Potassium Leaching as Affected by Soil Texture and Residual Fertilization in Tropical Soils

Potassium (K) leaching is affected by soil texture and available K, among other factors. In this experiment, effects of soil texture and K availability on K distribution were studied in the presence of roots, with no excess water. Soils from two 6-year field experiments on a sandy clay loam and a clay soil fertilized yearly with 0, 60, 120, and 180 kg ha^?1 of K₂O were accommodated in pots that received 90 kg ha^?1 of K₂O. Soybean was grown up to its full bloom (R2). Under field conditions, K leaching below the arable layer increased with K rates, but the effect was less noticeable in the clay soil. Potassium leaching in a sandy clay loam soil was related to soil K contents from prior fertilizations. With no excess water, in the presence of soybean roots, K distribution in the profile was significant in the lighter textured soil but was not apparent on the heavier textured soil.     

Nitrogen Mineralization Potential as Influenced by Microbial Biomass,Cotton Residues and Temperature

Integrating information on nitrogen (N) mineralization potentials into a fertilization plan could lead to improved N use efficiency. A controlled incubation mineralization study examined microbial biomass dynamics and N mineralization rates for two soils receiving 56 and 168 kg N ha^?1 in a Panoche clay loam (Typic Haplocambid) and a Wasco sandy loam (Typic Torriorthent), incubated with and without cotton (Gossypium hirsutum L.) residues at 10 and 25°C for 203 days. Microbial biomass activity determined from mineralized carbon dioxide (CO₂) was higher in the sandy loam than in clay loam independent of incubation temperature, cotton residue addition and N treatment. In the absence of added cotton residue, N mineralization rates were higher in the sandy loam. Residue additions increased N immobilization in both soils, but were greater in clay loam. Microbial biomass and mineralization were significantly affected by soil type, residue addition and temperature but not by N level.     

Effect of Raw and NH4+-enriched Zeolite on Nitrogen Uptake by Wheat and Nitrogen Leaching in Soils with Different Textures

Leaching of nutrients in soil can change the surface and groundwater quality. The present study aimed at investigating the effects of raw and ammonium (NH₄⁺)-enriched zeolite on nitrogen leaching and wheat yields in sandy loam and clay loam soils. The treatments were one level of nitrogen; Z₀: (100 kg (N) ha^?1) as urea, two levels of raw zeolite; Z₁:(0.5 g kg^?1 + 100 kg ha^?1) and Z_2: (1 g kg^?1 + 100 kg ha^?1), and two levels of NH₄⁺-enriched zeolite; Z₃: (0.5 g kg^?1 + 80 kg ha^?1) and Z₄: (1 g kg^?1 + 60 kg ha^?1). Wheat grains were sown in pots and, after each irrigation event, the leachates were collected and their nitrate (NO₃^?) and NH₄⁺ contents were determined. The grain yield and the total N in plants were measured after four months of wheat growth. The results indicated that the amounts of NH₄⁺ and NO₃^? leached from the sandy loam soil were more than those from the clay loam soil in all irrigation events. The maximum and minimum concentrations of nitrogen in the drainage water for both soils were observed at control and NH₄⁺-zeolite treatments, respectively. Total N in the plants grown in the sandy loam was higher compared to plants grown in clay loam soil. Also, nitrogen uptake by plants in control and NH₄⁺-zeolite was higher than that of raw-zeolite treatments. The decrease in the amount of N leaching in the presence of NH₄⁺-zeolite caused more N availability for plants and increased the efficiency of nitrogen fertilizers and the plants yield.     

Liming and Cultivars Affect Root Growth,Nodulation, Leaf to Stem Ratio,Herbage Yield,and Elemental Composition of Alfalfa on an Acid Soil

Abstract

Soil acidity is one of the limiting factors affecting the production and sustainability of pastures and crops in many parts of the world. An on‐farm experiment was conducted in Australia to investigate the cultivar variation in alfalfa (lucerne) (Medicago sativa L.) with respect to soil acidity and response to applied lime. The experimental site was a brown sandy clay loam with a soil pH of 4.8 (1:5 calcium chloride). Ten cultivars (Hunter River, Hunterfield, Sceptre, Aurora, Genesis, Aquarius, Venus, PL90, PL55, and breeding line Y8804) were tested at two levels of lime (0 and 2 t ha^?1). Lime application significantly increased the root growth, nodulation, leaf retention, leaf to stem ratio, herbage yield, and crude protein content of alfalfa. Liming had a significant effect on elemental composition of alfalfa shoots. Aluminum (Al) concentration was reduced from 93 mg kg^?1 DM in nil lime treatment to 45 mg kg^?1 DM in +lime treatment. Similarly, manganese (Mn) and iron (Fe) shoot concentrations were reduced from 74 mg kg^?1 DM and 92 mg kg^?1 DM to 59 mg kg^?1 DM and 76 mg kg^?1 DM, respectively. Liming significantly improved the calcium (Ca) concentration of shoots, while there was a little effect on phosphorus (P) and zinc (Zn) concentrations of alfalfa shoots. Cultivars had differential response to lime application. Response to lime application was greater in Y8804 and Aurora alfalfa where yield increased by 32% and 31%, while yield increase was 11–22% in other cultivars. Cultivars also differed significantly in root growth, nodulation, leaf drop, leaf to stem ratio, crude protein content, and elemental composition of shoots. Cultivars with better performance in no liming treatment had comparatively lower shoot Al, Mn, and Fe concentrations compared with other cultivars.     

Grain yield,seed weight,seed N concentration,and nodule activity of soybean as influenced by defoliation and N fertilizer

It is unknown if nitrogen (N) fertilizer application will ameliorate the yield loss associated with severe defoliation of soybean [Glycine max (L.) Merr.] at the R5 stage of growth. The objective of this field study was to investigate the interaction of N fertilization rate and extent of defoliation on soybean yield, seed weight, seed N concentration, and nodule activity. Field experiments were conducted in 1988 and 1989 on a Drummer silty clay loam (Typic Haplaquolls). Treatment variables were three cultivars: BSR 101, Chamberlain, and Elgin 87; three N fertilizer rates applied one day after defoliation: 0, 84, and 168 kg N ha^‐1 as urea; and three levels of defoliation: 0, 50, and 75%. Grain yield was not significantly affected by N rate but did decrease with defoliation. Fertilizer N did not ameliorate the yield reduction associated with defoliation. Seed weight decreased linearly with increasing defoliation. Plants exposed to the most severe defoliation produced seed which weighed 1 g 100^‐1 seed less than seed from nondefoliated plants. In 1989 seed weight of only the nondefoliated plants increased slightly with N rate, seed weight was not affected by N rate for any other year by defoliation treatment combination. Seed N concentration was not affected by N rate. Seed N concentration increased with defoliation in 1988 but not in 1989. Seed N concentration was not affected by defoliation in 1989. N fertilizer application and defoliation decreased nodule activity. Defoliated plants utilized nitrates in preference to dinitrogen fixation. Fertilizer N increased the concentration of nitrates in the plant, but the increase did not ameliorate the yield loss. Developing pods and seed are the predominate sink. The additional energy presumably required for dinitrogen fixation did not exacerbate the yield loss.     

Effects of polyacrylamide,biopolymer and biochar on the decomposition of 14C‐labelled maize residues and on their stabilization in soil aggregates

The efficacy of applying plant residues to agricultural soils as a carbon (C) source for microorganisms and C sequestration is dependent on soil physiochemical properties, which can be improved by aggregation using soil conditioners. However, no attempt has been made to assess the effects of soil conditioners such as biochar (BC), biopolymer (BP) or polyacrylamide (PAM) on plant residue decomposition. We assessed the effects of BC, synthesized BP and anionic PAM on the decomposition of ¹⁴C‐labelled maize residues and on their stabilization in aggregate fractions in sandy and sandy loam soils. Polyacrylamide and BP were applied at 400 kg ha^?1 and BC was applied at 5000 kg ha^?1, and the soils were incubated for 80 days at 22°C. The conditioners improved the physical and biological properties of both soils, as shown by a 24% increase in the 1–2 mm aggregates. Biochar and BP accelerated the decomposition of plant residues as indicated by ¹⁴CO₂ efflux, and resulted in reduced stabilization of residues in both soils relative to that observed in the control and PAM treatments. The reduction in ¹⁴C incorporation and C stabilization in the BC‐ and BP‐treated soils was observed mainly in the < 0.25‐mm aggregates. This was confirmed by reduction of activity of hydrolytic enzymes (β‐cellobiosidase and β‐glucosidase). Decomposition of plant residues in sandy soil was more sensitive to BP and PAM application than that in sandy loam soil. Improved soil structure after applying BC and BP increased aeration and decreased the contact between plant residues and mineral soil particles and consequently accelerated plant residue decomposition and reduced C sequestration.     

Eucalyptus biochar application enhances Ca uptake of upland rice,soil available P,exchangeable K,yield, and N use efficiency of sugarcane in a crop rotation system

It was hypothesized that the application of eucalyptus biochar enhances nutrient use efficiencies of simultaneously supplied fertilizer, as well as provides additional nutrients (i.e., Ca, P, and K), to support crop performance and residual effects on subsequent crops in a degraded sandy soil. To test this hypothesis, we conducted an on‐farm field experiment in the Khon Kaen province of Northeastern Thailand to assess the effects of different application rates of eucalyptus biochar in combination with mineral fertilizers to upland rice and a succeeding crop of sugarcane on a sandy soil. The field experiment consisted of three treatments: (1) no biochar; (2) 3.1 Mg ha^?1 biochar (10.4 kg N ha^?1, 3.1 kg P ha^?1, 11.0 kg K ha^?1, and 17.7 kg Ca ha^?1); (3) 6.2 Mg ha^?1 biochar (20.8 kg N ha^?1, 6.2 kg P ha^?1, 22.0 kg K ha^?1, and 35.4 kg Ca ha^?1). All treatments received the same recommended fertilizer rate (32 kg N ha^?1, 14 kg P ha^?1, and 16 kg K ha^?1 for upland rice; 119 kg N ha^?1, 21 kg P ha^?1, and 39 kg K ha^?1 for sugarcane). At crop harvests, yield and nutrient contents and nitrogen (N) use efficiency were determined, and soil chemical properties and pH₀ monitored. The eucalyptus biochar material increased soil Ca availability (117 ± 28 and 116 ± 7 mg kg^?1 with 3.1 and 6.2 Mg ha^?1 biochar application, respectively) compared to 71 ± 13 mg kg^?1 without biochar application, thus promoting Ca uptake and total plant biomass in upland rice. Moreover, the higher rate of eucalyptus biochar improved CEC, organic matter, available P, and exchangeable K at succeeding sugarcane harvest. Additionally, 6.2 Mg ha^?1 biochar significantly increased sugarcane yield (41%) and N uptake (70%), thus enhancing N use efficiency (118%) by higher P (96%) and K (128%) uptake, although the sugar content was not increased. Hence, the application rate of 6.2 Mg ha^?1 eucalyptus biochar could become a potential practice to enhance not only the nutrient status of crops and soils, but also crop productivity within an upland rice–sugarcane rotation system established on tropical low fertility sandy soils.     

Co-inoculation of soybeans and common beans with rhizobia and azospirilla: strategies to improve sustainability

Plant–microorganism associations have long been studied, but their exploitation in agriculture partially or fully replacing chemical fertilizers is still modest. In this study, we evaluated the combined action of rhizobial and plant growth-promoting rhizobacteria inoculants on the yields of soybean and common bean. Seed inoculation with rhizobia (1.2?×?10⁶ cells seed^?1) was compared to co-inoculation with Azospirillum brasilense in-furrow (different doses) or on seeds (1.2?×?10⁵ cells seed^?1) in nine field experiments. The best in-furrow inoculant dose was 2.5?×?10⁵ cells of A. brasilense seed^?1 for both crops. Inoculation with Bradyrhizobium japonicum increased soybean yield by an average 222 kg?ha^?1 (8.4 %), and co-inoculation with A. brasilense in-furrow by an average 427 kg?ha^?1 (16.1 %); inoculation always improved nodulation. Seed co-inoculation with both microorganisms resulted in a mean yield increase of 420 kg?ha^?1 (14.1 %) in soybean relative to the non-inoculated control. For common bean, seed inoculation with Rhizobium tropici increased yield by 98 kg?ha^?1 (8.3 %), while co-inoculation with A. brasilense in-furrow resulted in the impressive increase of 285 kg?ha^?1 (19.6 %). The cheaper, more sustainable inoculated treatment produced yields equivalent to the more expensive non-inoculated + N-fertilizer treatment. The results confirm the feasibility of using rhizobia and azospirilla as inoculants in a broad range of agricultural systems, replacing expensive and environmentally unfriendly N-fertilizers.