Biochar and fertiliser applications influence phosphorus fractionation and wheat yield

The use of biochar in agriculture to achieve the dual benefits of improving soil quality whilst sequestering carbon (C) has received much attention. However, in low-intensity broadacre agricultural systems where yield is constrained by rainfall and costs associated with phosphorus (P) fertiliser, the application of biochar at rates commonly reported (>10 t ha^?1) are likely to be prohibitively expensive where yield benefits cannot be guaranteed. In marginal areas where calcareous soils dominate, biochar application has no liming effect, reducing its value compared to application in acidic soils. In the present study, we use a field experiment to investigate the interaction between P fertilisation and biochar banding at low application rates (<1 t ha^?1) on wheat yield and soil P fractionation (assessed by a modified Hedley method) in a highly alkaline Haplic Calcisol in a dryland broadacre cropping system. Our results demonstrate no statistically significant effect of low rate biochar banding on wheat yield in this highly P-constrained soil, but a significant effect of both biochar and fertiliser on P fractionation in both years of the study. Higher P fertiliser rates significantly increased wheat yield in all biochar treatments. The interactions between biochar, P fertiliser and P fractionation indicate shifts in potential P availability both as a result of P fertilisation and also biochar application. Further work is required in low productivity calcareous systems such as that studied here to elucidate the potential for biochar amendment to improve productivity and sequester C.     

Wheat straw and its biochar had contrasting effects on soil C and N cycling two growing seasons after addition to a Black Chernozemic soil planted to barley

Application of crop residues and its biochar produced through slow pyrolysis can potentially increase carbon (C) sequestration in agricultural production systems. The impact of crop residue and its biochar addition on greenhouse gas emission rates and the associated changes of soil gross N transformation rates in agricultural soils are poorly understood. We evaluated the effect of wheat straw and its biochar applied to a Black Chernozemic soil planted to barley, two growing seasons or 15 months (at the full-bloom stage of barley in the second growing season) after their field application, on CO₂ and N₂O emission rates, soil inorganic N and soil gross N transformation rates in a laboratory incubation experiment. Gross N transformation rates were studied using the ¹⁵N isotope pool dilution method. The field experiment included four treatments: control, addition of wheat straw (30 t ha^?1), addition of biochar pyrolyzed from wheat straw (20 t ha^?1), and addition of wheat straw plus its biochar (30 t ha^?1 wheat straw + 20 t ha^?1 biochar). Fifteen months after their application, wheat straw and its biochar addition increased soil total organic C concentrations (p?=?0.039 and <0.001, respectively) but did not affect soil dissolved organic C, total N and NH₄ ⁺-N concentrations, and soil pH. Biochar addition increased soil NO₃ ^?-N concentrations (p?=?0.004). Soil CO₂ and N₂O emission rates were increased by 40 (p?p?=?0.03), respectively, after wheat straw addition, but were not affected by biochar application. Straw and its biochar addition did not affect gross and net N mineralization rates or net nitrification rates. However, biochar addition doubled gross nitrification rates relative to the control (p?2 and N₂O emissions and enhance soil C sequestration. However, the implications of the increased soil gross nitrification rate and NO₃ ^?-N in the biochar addition treatment for long-term NO₃ ^?-N dynamics and N₂O emissions need to be further studied.     

Effects of cotton (Gossypium hirsutum L.) straw and its biochar application on NH3 volatilization and N use efficiency in a drip-irrigated cotton field

Reducing ammonia (NH₃) volatilization is a practical way to increase nitrogen (N) fertilizer use efficiency (NUE). In this field study, soil was amended once with either cotton (Gossypium hirsutum L.) straw (6 t ha^?1) or its biochar (3.7 t ha^?1) unfertilized (0 kg N ha^?1) or fertilized (450 kg N ha^?1), and then soil inorganic N concentration and distribution, NH₃ volatilization, cotton yield and NUE were measured during the next two growing seasons. In unfertilized plots, NH₃ volatilization losses in the straw-amended and biochar-amended treatments were 38–40% and 42–46%, respectively, less than that in control (i.e., unamended soil) during the two growing seasons. In the fertilized plots, NH₃ volatilization losses in the straw-amended and biochar-amended treatments were 30–39% and 43–54%, respectively, less than that in the control. Straw amendment increased inorganic N concentrations, cotton yield, cotton N uptake and NUE during the first cropping season after application, but not during the second. In contrast, biochar increased cotton N uptake and NUE during both the first and the second cropping seasons after application. Furthermore, the effects of biochar on cotton N uptake and NUE were greater in the second year than in the first year. These results indicate that cotton straw and cotton straw biochar can both reduce NH₃ volatilization and also increase cotton yield, N uptake and NUE. In addition, the positive effects of one application of cotton straw biochar were more long-lasting than those of cotton straw.     

Role of Plant Growth-Promoting Rhizobacteria (PGPR), Biochar,and Chemical Fertilizer under Salinity Stress

Pot experiment was conducted under axenic conditions in a growth chamber with 14 h photoperiod at 22/26°C to evaluate the role of biochar, phosphate-solubilizing rhizobacteria (Pseudomonas sp.), and chemical fertilizer under induced salt stress (150 mM sodium chloride (NaCl)). Factorial randomized complete plot designs with three replications were used. Biochar and fertilizer were mixed in soil (5:1) while Pseudomonas sp. was applied as seed soaking. Salt stress applied at 3 leaf stage significantly reduced (27%) soil moisture and increased electrolyte leakage, Na and potassium (K) uptake, proline, and antioxidant enzymes. Biochar and Pseudomonas sp. decreased the sodium by 24% and 50%, respectively, and increased proline, soil moisture content, and peroxidase (POD) activity. Fertilizer treatment increased the electrolyte leakage by 73%. The effect of fertilizer was 3–4× higher for proline and POD activity in combined treatment with biochar and Pseudomonas. The fertilizer effect can be augmented by the application of Pseudomonas sp. and biochar to alleviate salt stress.     

Effect of Primary Biomethanated Spentwash on Soil Properties,Nutrient Uptake,and Yield of Wheat on Sodic Soil

The experiment on the effect of primary biomethanated spentwash (PBSW) on soil properties, nutrient uptake and yield of wheat on sodic soil was carried out at a research farm of Post Graduate Institute, Mahatma Phule Krishi Vidyapeeth, Rahuri, Maharashtra state, India, during the post-monsoon season. The experimental soil was sodic calcareous having Sawargaon series of isohyperthermic family of Vertic Haplustepts. The experiment was laid out in a randomized block design with nine treatments and three replications. The treatments consisted of varying doses of PBSW (100, 200, 300, 400 and 500 m³ ha^?1), absolute control, farmyard manure (FYM) 5 t ha^?1 + RDF-AST (recommended dose of fertilizer as per soil test), FYM 5 t ha^?1 + 50% GR (gypsum requirement) + RDF-AST and FYM 5 t ha^?1 + 100% GR + RDF-AST. The results revealed that the physical properties, namely bulk density and hydraulic conductivity, were improved in sodic soil due to the application of increased doses of PBSW. A significant reduction in pH, calcium carbonate and exchangeable sodium percentage (ESP) and an increase in organic carbon, cation-exchange capacity (CEC) and electrical conductivity (EC) were observed in the soil, due to the addition of PBSW. The available soil nitrogen (N), phosphorus (P), potassium (K) and micronutrient iron, manganese, copper and zinc (Fe, Mn, Cu and Zn) content after the harvest of wheat was the highest in the 500 m³ ha^?1 treatment compared with all the other treatments. The exchangeable calcium (Ca²⁺), magnesium (Mg²⁺) increased significantly and exchangeable Sodium (Na⁺) reduced significantly with increased doses of PBSW. The saturation paste extract analysis also showed the same trend. A significant increase in the EC of the saturation paste of extract of the soil was observed in all PBSW treatments and it was the highest (4.75 dS m^?1) in PBSW application @ 500 m³ ha^?1. The application of PBSW @ 500, 400, 300 and 200 m³ ha^?1 resembled the treatments of FYM + gypsum @ 100 GR + RDF-AST, FYM + gypsum @ 50 GR + RDF-AST and FYM + RDF-AST, respectively, regarding the biological properties of sodic soil. The PBSW application @ 500 m³ ha^?1 had recorded the highest grain (47.33 q ha^?1) and straw (72.72 q ha^?1) yield and the maximum total uptake of N, P, K, Fe, Mn, Cu, and Zn by wheat, which was at par with the treatment of FYM (5 t ha^?1) + gypsum @ 100% GR + RDF-AST.     

Biochar and crop residue application to soil: effect on soil biochemical properties,nutrient availability and yield of rice (Oryza sativa L.) and wheat (Triticum aestivum L.)

In the recent past, biochar and crop residues have attracted lots of attention as a viable strategy for maintaining soil health. This paper evaluates the comparative effect of two different doses (equivalent to 2 and 5 t C ha^?1) of each of pine needle and Lantana biochar (PBC and LBC), wheat residue and lentil residue (WR and LR) on soil biological properties, nutrient availability and yield of rice and wheat in pot culture. Energy-dispersive X-ray spectroscopy (EDS) revealed higher C content of biochar than crop residues. Evaluation of biochemical quality reflected high recalcitrance indices of C and N for both PBC and LBC. Application of LBC and PBC increased the wheat grain yield significantly by 6.2%–24.2% over control. Both PBC and LBC significantly increased N and P uptakes in grain over the control and crop residues. Both biochars recorded a significant decrease of 33.9 and 71,7% in β-glucosidase activity in comparison to control at termination of study. PBC and LBC also resulted in more soil available N, P and K in soil at different intervals. The geometric mean of enzyme activities (GMea) reflected improved soil quality by PBC and LR and reduction by LBC application.     

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.     

Soil management for raising crop water productivity in rainfed production systems in Lao PDR

This study investigated the impacts of organic- and clay-based soil amendments, and their combinations on crop water productivity (CWP) using maize as a test crop. On-station field trials were established over two consecutive years at the Naphok and Veunkham sites in Laos. At each site, 10 treatments were applied in a randomized complete block design with three replications. The treatments were control, rice husk biochar (10 t ha^?1), bentonite clay (10 t ha^?1), compost (4 t ha^?1), clay-manure compost (10 t ha^?1), rice husk biochar compost (10 t ha^?1), bentonite clay + biochar, bentonite-clay + compost, biochar + compost, and bentonite clay + biochar + compost. All treatments were applied in 2011. Significant (p < 0.05) treatment effects in CWP and growing period evapotranspiration were determined. At Naphok, differences between the amended and control plots in CWP varied between 0.1 and 0.6 kg m^?3 in 2011 and from 0.1 to 0.4 kg m^?3 in 2012, whereas differences at Veunkham varied between 0.3 and 1.0 kg m^?3 in 2011 and from 0.05 to 0.29 kg m^?3 in 2012. At both sites, CWP in 2012 was significantly lower than 2011. Our results illustrate that organic- and clay-based soil amendments improve CWP, indicating that soil-based interventions could be suitable options for improving agricultural productivity.     

Soil carbon fractions in response to straw mulching in the Loess Plateau of China

Straw mulching has been used to conserve soil water and sustain dryland crop yields, but the impact of the quantity and time of mulching on soil C fractions are not well documented. We studied the effects of various amounts and times of wheat (Triticum aestivum L.) straw mulching on soil C fractions at 0–10- and 10–20-cm depths from 2009 to 2017 in the Loess Plateau of China. Treatments were no mulching (CK), straw mulching at 9.0 (HSM) and 4.5 Mg ha^?1 (LSM) in the winter wheat growing season, and straw mulching at 9.0 Mg ha^?1 in the summer fallow period (FSM). Soil C fractions were soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). All C fractions at 0–10 and 10–20 cm were 8–27% greater with HSM and LSM than FSM and CK. Both SOC and POC at 0–10 cm increased at 0.32 and 0.27 Mg ha^?1 year^?1 with HSM and at 0.40 and 0.30 Mg C ha^?1 year^?1 with LSM, respectively, from 2009 to 2017. Winter wheat grain yield was lower with HSM and LSM, but total aboveground biomass was greater with HSM than other treatments. All C fractions at most depths were correlated with the estimated wheat root residue returned to the soil and PCM at 0–10 and 0–20 cm was correlated with wheat grain yield. Wheat straw mulching during the growing season increased soil C sequestration and microbial biomass and activity compared with mulching during the fallow period or no mulching, regardless of mulching rate, due to increased C input, although it reduced wheat grain yield. Continuous application of straw mulching over time can increase soil C sequestration by increasing nonlabile C fractions while decreasing labile fractions. Straw mulching at higher rate and mulching during the summer fallow period had no additional benefits in soil C sequestration.     

Influence of nitrogen fertilizer forms and crop straw biochars on soil exchange properties and maize growth on an acidic Ultisol

Effects of repeated application of urea (UN) and calcium nitrate (CN) singly and together with crop straw biochars on soil acidity and maize growth were investigated with greenhouse pot experiments for two consecutive seasons. Canola straw biochar (CB), peanut straw biochar (PB) and wheat straw biochar (WB) were applied at 1% of dried soil weight in the first season. N fertilizers were applied at 200 mg N kg^?1. In UN treatments, an initial rise in pH was subjected to proton consumption through urea hydrolysis, afterwards nitrification of NH₄⁺ caused drastic reductions in pH as single UN had soil pH of 3.70, even lower than control (4.27) after the 2nd crop season. Post-harvest soil analyses indicated that soil pH, soil exchangeable acidity, NH₄⁺, NO₃^? and total base cations showed highly significant variation under N and biochar types (P < 0.05). Articulated growth of plants under combined application with biochars was expressed by 22.7%, 22.5%, and 35.7% higher root and 25.6%, 23.8%, and 35.9% higher shoot biomass by CB, PB and WB combined with CN over UN, respectively. Therefore, CN combined with biochars is a better choice to correct soil acidity and improve maize growth than UN combined with biochars.     

Soil temperature,growth and yield of maize (Zea mays L.) as affected by wheat straw mulch

Maize crop is grown mostly in tropical/subtropical environments where drought adversely affects its production. A field experiment was conducted on sandy loam soil for four years (1999 – 2002) to study the effect of wheat straw mulch (0 and 6 t ha^?1) and planting methods (flat and channel) on maize sown on different dates. Maximum soil temperature without mulch ranged from 32.2 – 44.4°C in channel and 31.6 – 46.4°C in flat planting method. Mulching, however, lowered soil temperature by 0.8 – 7.0°C in channel and 0 – 9.8°C in flat planting. Mulching, on an average, improved leaf area index by 0.42, plant height by 14 cm, grain yield by 0.24 t ha^?1 and biomass by 1.57 t ha^?1, respectively. Mulching improved grain yield only in flat sowing. Interaction between sowing date and planting method was significant. Seasonal variation in biomass were significantly correlated (p = 0.05) with mean air temperature during 0 – 45 days after planting (DAP) (r = ?0.95), pan evaporation during 0 – 15 DAP (r = 0.79) and negative correlation with rainfall in entire cropping season (r = ?0.89), whereas biomass increase with mulch in different cropping seasons had negative relation (r = ?0.74) with amount of rain during 0 – 15 DAP.     

Effect of Low‐Rate Commercial Humic Acid on Phosphorus Availability,Micronutrient Uptake,and Spring Wheat Yield

Abstract

A greenhouse study was conducted to determine the effects of low‐rate commercial humic acid (HA) on phosphorus (P), iron (Fe), and zinc (Zn) availability and spring wheat yields, in both a calcareous soil and a noncalcareous soil. In Phase I, soluble P concentrations were monitored at 1.9, 3.8, and 5.7 cm from a monoammonium phosphate (MAP) fertilizer band that had either been coated with one of two HA products at the equivalent of 1.7 kg HA ha^?1, a label rate, or left uncoated. Sampling occurred periodically up to 48 d after fertilizer application. In Phase II, uptake of P, Fe, and Zn and grain yield were measured in soils that had been fertilized with 7.5 or 25 kg P ha^?1, either coated with HA or left uncoated. In Phase I, only three significant differences (P=0.05) out of 66 comparisons were found in soluble P concentrations between HA and control treatments at time points ranging from 4 to 48 d after fertilization. In addition, no significant differences were found in nutrient uptake, shoot biomass, or grain yield between HA and control treatments. These greenhouse results suggest that low commercial HA rates (～1.7 kg HA ha^?1) may be insufficient to enhance spring wheat growth.     

Soil phosphorous buffer coefficient as influenced by time and rate of P addition

Abstract

This study was conducted to investigate the effect of time and rate of phosphorus (P) addition on phosphorus availability and phosphorus buffer coefficient in some calcareous soils. Phosphorus was added to the samples at rates of 0, 50, 100, 200, 400, 600 and 800 mg P kg^?1 soil. The samples were incubated for 0.041, 1, 7, 14, 21, 30, 60 and 90 days at constant temperature and moisture. Extractable phosphorus was determined after the incubation. The results showed a sharp decrease in available P within 1 h after P addition. There was a linear relation between added P and extractable P in all soils. The buffer coefficients of soils were estimated by Olsen P for above incubation periods. Generally the buffer coefficient decreased with increasing time of incubation. The results indicated that inputs of between 23 – 59 mg kg^?1 are required to raise Olsen P by 10 mg kg^?1 in these calcareous soils, which assuming 2500 t soil ha^?1, gives a required input of 58 – 148 kg P ha^?1.     

Is burial of wheat straw in ditches a way to reduce CH4 emissions from rice cultivation?

Abstract

Burial of wheat straw in ditches and incorporation of wheat straw are the two main ways of returning wheat straw prior to rice cultivation in China. To examine the effect of burying wheat straw in ditches on CH₄ emissions from rice cultivation, a field experiment was conducted at Yixing, Jiangsu, China in 2004. CH₄ flux was measured using a closed-chamber technique in three treatments (CK, no wheat straw application; WI, evenly incorporating 3.75 t ha^?1 wheat straw into the 0.1 m topsoil; WD, burying 3.75 t ha^?1 wheat straw in 0.14-m deep by 0.25-m wide ditches). Seasonal CH₄ emissions ranged from 49.7 to 218.4 kg CH₄ ha^?1. The application of wheat straw in these two ways significantly increased CH₄ emissions by 4.0-fold and 4.4-fold, respectively (P < 0.05). Although CH₄ flux from the non-ditch area in the WD treatment was as low as that in the CK treatment, it was counter-balanced by extremely high CH₄ flux from the ditch, which was approximately 6.0-fold as much as that from WI, leading to comparability between treatments WI and WD in total CH₄ emissions (P > 0.05). No significant difference was observed between the three treatments in grain yield (P > 0.05). The results indicated that burial of wheat straw in ditches is not a way to reduce CH₄ emission from rice cultivation.     

Effect of soybean inoculation with Bradyrhizobium and wheat inoculation with Azotobacter on their productivity and N turnover in a Vertisol

A long-term field experiment was conducted for 8 years on a Vertisol in central India to assess quantitatively the direct and residual N effects of soybean inoculation with Bradyrhizobium and wheat inoculation with Azotobacter in a soybean–wheat rotation. After cultivation of soybean each year, its aerial residues were removed before growing wheat in the same plots using four N levels (120, 90, 60 and 30 kg ha^?1) and Azotobacter inoculation. Inoculation of soybean increased grain yield by 10.1% (180 kg ha^?1), but the increase in wheat yields with inoculation was only marginal (5.6%; 278 kg ha^?1). There was always a positive balance of soil N after soybean harvest; an average of +28 kg N ha^?1 yr^?1 in control (nodulated by native rhizobia) plots compared with +41 kg N ha^?1 yr^?1 in Rhizobium-inoculated plots. Residual and direct effects of Rhizobium and Azotobacter inoculants caused a fertilizer N credit of 30 kg ha^?1 in wheat. Application of fertilizers or microbial inoculation favoured the proliferation of rhizobia in crop rhizosphere due to better plant growth. Additional N uptake by inoculation was 14.9 kg N ha^?1 by soybean and 20.9 kg N ha^?1 by wheat crop, and a gain of +38.0 kg N ha^?1 yr^?1 to the 0–15 cm soil layer was measured after harvest of wheat. So, total N contribution to crops and soil due to the inoculants was 73.8 kg N ha^?1 yr^?1 after one soybean–wheat rotation. There was a total N benefit of 13.8 kg N ha^?1 yr^?1 to the soil due to regular long-term use of microbial inoculants in soybean–wheat rotation.     

Effect of biochar amendment on soil physical,chemical and biological properties and groundnut yield in rainfed Alfisol of semi-arid tropics

The aim of this study was to evaluate the effect of biochar and organic soil amendments on soil physicochemical and microbial load, carbon sequestration potential, nutrient uptake and yield of groundnut in acidic red soil under rainfed condition. Biochar was prepared from red gram, cotton, maize stalk and mesquite wood using pilot scale slow pyrolysis biochar unit. The above sources of biochar at the rate of 2.5 and 5 t ha^?1 and enriched farmyard manure 0.75 t ha^?1, composted coir pith 10 t ha^?1 and arbuscular mycorrhizae 100 kg ha^?1 were applied as basal with required nitrogen, phosphorous and potassium fertilizer. Biochar amendment at the rate of 5 t ha^?1 reduced the bulk density from 1.41 to 1.36 g cm^?3 and increased the soil moisture 2.5%. With respect to soil chemical changes, it raised soil pH from 5.7 to 6.3; increased the cation exchange capacity 1.4 cmol⁺ kg^?1 and enhanced the carbon buildup 4.4 t ha^?1. The significant differences in bacteria, fungi and actinomycetes population were observed between biochar and control. The nitrogen, phosphorous and potassium were better utilized under biochar and composted coir pith, which was 21, 5 and 20 kg ha^?1 higher than control. The experimental results suggested that application of biochar to acidic red soil favoured good soil physical, chemical and biological environment, and these positive changes influenced growth and yield attributes and enhanced pod yield 29% over control.     

Effect of Sheep Manure and Its Produced Vermicompost and Biochar on the Properties of a Calcareous Soil after Barley Harvest

ABSTRACT

Conversion of manures to vermicompost and biochar may alleviate some negative effects of manure application to soil but the efficiency of the produced vermicompost and biochar as compared to their feedstocks is not well-known. In the current investigation, we compared the effects of sheep manure and its derived vermicompost and biochar (pyrolyzed at 400°C for 4 h) on the properties of a calcareous soil that planted with five cultivars of barley (Behrokh, Khatam, Reyhaneh03, Fajr 30 and Nimrooz) for 60 days. Different soil properties and availability of nutrients and barley yield were determined after plant harvest. The biochar significantly increased barley yield rather than control (4.20 vs. 3.57 g pot^?1), but sheep manure and vermicompost had no effect on it (3.51 and 3.37 g pot^?1, respectively). Fajr 30 and Nimrooz (3.52 and 3.42 g pot^?1, respectively) had significantly lower yield than other cultivars. Biochar increased soil pH up to 8.2. Soil salinity was increased by application of all organic materials (increase to 16–36%). Cation exchange capacity (CEC) and organic matter content of soil were also increased by all organic materials application (0.4–0.9 cmol kg^?1 and 0.33–0.50%, respectively). All organic materials increased total nitrogen (N), but this increase was the highest with sheep manure application (53%). The availability of phosphorus (P) and potassium (K) was increased significantly by application of all organic materials, and this increase was the highest with biochar application (19 and 309 mg kg^?1, respectively). Biochar application had no effect on the availability of micronutrients, but application of sheep manure and vermicompost increased the availability of iron (Fe) (0.62 and 0.48 mg kg^?1, respectively) and zinc (Zn) (0.18 and 0.37 mg kg^?1, respectively). Generally, organic materials may change the status of soil nutrients via change in soil pH, organic matter content, release of nutrients, increase in soil CEC and formation of soluble complex with nutrients.     

Crop Utilization of Nitrogen in Swine Lagoon Sludge

Swine lagoon sludge is commonly applied to soil as a source of nitrogen (N) for crop production but the fate of applied N not recovered from the soil by the receiver crop has received little attention. The objectives of this study were to (1) assess the yield and N accumulation responses of corn (Zea mays L.) and wheat (Triticum aestivum) to different levels of N applied as swine lagoon sludge, (2) quantify recovery of residual N accumulation by the second and third crops after sludge application, and (3) evaluate the effect of different sludge N rates on nitrate (NO₃-N) concentrations in the soil. Sludge N trials were conducted with wheat on two swine farms and with corn on one swine farm in the coastal plain of North Carolina. Agronomic optimum N rates for wheat grown at two locations was 360 kg total sludge N ha^?1 and the optimum N rate for corn at one location was 327 kg total sludge N ha^?1. Residual N recovered by subsequent wheat and corn crops following the corn crop that received lagoon sludge was 3 and 12 kg N ha^?1, respectively, on a whole-plant basis and 2 and 10 kg N ha^?1, respectively, on a grain basis at the agronomic optimum N rate for corn (327 kg sludge N ha^?1). From the 327 kg ha^?1 of sludge N applied to corn, 249 kg N ha^?1 were not recovered after harvest of three crops for grain. Accumulation in recalcitrant soil organic N pools, ammonia (NH₃) volatilization during sludge application, return of N in stover/straw to the soil, and leaching of NO₃ from the root zone probably account for much of the nonutilized N. At the agronomic sludge N rate for corn (327 kg N ha^?1), downward movement of NO₃-N through the soil was similar to that for the 168 kg N ha^?1 urea ammonium nitrate (UAN) treatment. Thus, potential N pollution of groundwater by land application of lagoon sludge would not exceed that caused by UAN application.     

Humic substrates application in diluted form enhanced availability of phosphorus (P) and its uptake by tea bushes in the tea-growing soil of Northeast India

Tea (Camellia sinensis L.) is an evergreen perennial crop, which is cultivated for its shoots in acidic soil under sub-tropical humid climatic condition. The availability of phosphorus (P) to plants is naturally limited in acidic tea-growing soils. Humic substrates (HS) are often applied to enhance availability of nutrients, especially P in horticultural and vegetable crop fields. However, its effect on soil of a perennial crop like tea was not studied before. In this study, application of HS enhanced P availability mainly by facilitating growth of phosphate-solubilizing bacteria (PSB) and enhancing phosphatase activity in soil. Application of same amount of HS in diluted form was more effective to enhance PSB population and phosphatase activity, which in turn increased P availability in soil and P uptake by tea bushes. This experiment indicated that application of 1.5 kg HS ha^?1 as 0.3% solution might be applied to enhance P availability to improve P availability and P uptake by plants in tea-growing soil.