Potential of Carbon Dioxide Biosequestration of Saline–Sodic Soils during Amelioration under Rice–Wheat Land Use

Potential for carbon dioxide (CO₂) biosequestration was determined during the reclamation of highly saline–sodic soils (Aridisols) after rice (2003) and wheat (2003–2004) crops at two sites in District Faisalabad, Pakistan. Two treatments were assessed: T₁, tube-well brackish water only; and T₂, soil-applied gypsum at 25% soil gypsum requirement?+?tube-well brackish water. The irrigation water used at both sites had different levels of salinity (EC 3.9–4.5 dS m^?1), sodicity (SAR 21.7–28.8), and residual sodium carbonate (14.9 mmol_c L^?1). Composite soil samples were collected from soil depths of 0–15 and 15–30 cm at presowing and postharvest stages and analyzed for pH, EC_e, and sodium adsorption ratio (SAR). After rice harvest, there was no significant effect of gypsum application on EC_e, pH, and SAR at both sites, except pH at 0–15 cm depth decreased significantly with gypsum at site 1. After wheat harvest, EC_e, pH, and SAR decreased significantly with gypsum at site 1, whereas the effect of gypsum on these parameters was not significant at site 2. Compared to initial soil, EC_e and SAR in soil decreased considerably after rice or wheat cultivation, particularly at site 1, whereas pH increased slightly due to cultivation of these crops. For rice, the total CO₂ sequestration was significantly increased with gypsum application at both sites and ranged from 1499 to 2801 kg ha^?1. The total sequestration of CO₂ was also significantly increased with gypsum application in wheat at both sites and ranged from 2230 to 3646 kg ha^?1. The amounts of CO₂ sequestered by crops due to gypsum application were related to seed and straw yield responses of rice and wheat to gypsum, which were greater at site 1 than site 2. Also, the yield response to applied gypsum was greater for rice than wheat at site 1, whereas the opposite was true at site 2. Overall, the combined application of gypsum with brackish water reduced soil EC_e and SAR compared to brackish water alone, particularly at site 1. Our findings also suggest that the reclamation strategies should be site specific, depending on soil type and quality of brackish water used for irrigation of crops. In conclusion, the use of gypsum is recommended on brackish water–irrigated salt-prone soils to improve their quality, and for enhancing C biosequestration and crop production for efficient resource management.     

Potassium Quantity–Intensity Parameters and Their Correlation with Bean Plant Indices in Some Calcareous Soils

Plant availability of potassium (K) in soils is controlled by dynamic interactions among its different pools. Potassium quantity–intensity (Q/I) parameters were determined to relate them to bean plant indices in a pot experiment. The results showed that the activity ratio at equilibrium (AR^k) ranged from 0.015 to 0.358 (mmol L^?1)^0.50, the potential buffering capacity (PBC) ranged from 7.54 to 26.32 mmol kg^?1/(mmol L^?1)^0.50, the labile K (Δk°) ranged from 9.1 to 112.2 mg kg^?1, and the K adsorbed at specific sites (Kx) ranged from 6.51 to 69.69 mg kg^?1. The results of pot experiment showed that some K Q/I parameters were significantly correlated with some plant indices. Also, the correlation study showed that readily exchangeable K was significantly correlated with K Q/I parameters except K_x. The results of this research show that the K Q/I method can be used for estimating of soil K availability for bean.     

Influence of Inorganic Phosphorus,VAM Fungi,and Irrigation Regimes on Crop Productivity and Phosphorus Transformations in Okra (Abelmoschus esculentus L.)–Pea (Pisum sativum L.) Cropping System in an Acid Alfisol

The present investigation was carried out at CSK Himachal Pradesh Agricultural University, Palampur, India, during 2009–2011 to economize inorganic phosphorus (P) and water needs of an okra (Abelmoschus esculentus)–pea (Pisum sativum) cropping system through vesicular arbuscular mycorrhizal (VAM) fungi (Glomus mosseae) in a Himalayan acid Alfisol. The field experiment was replicated three times in a randomized block design comprising 14 treatments consisting of 12 treatment combinations of two VAM levels [0 and 12 kg ha^?1], three phosphorus levels [50, 75, and 100% of recommended soil-test-based nitrogen (N)–P–potassium (K)], and two irrigation regimes [40 and 80% of available water-holding capacity of field soil (AWC)], in addition to one treatment with “generalized recommended NPK dose with generalized recommended irrigations (GRD)” and one treatment based on “farmers’ practice of plant nutrition and irrigation management in the region.” This article presents crop productivity and P dynamics studies during the second crop cycle of okra–pea sequence (2010–2011) and statuses of different P fractions in the soil after the second pea crop harvest during 2010–2011. Crop productivity and P uptake data in okra–pea sequence indicated that application of VAM + 75% P dose at either of two irrigation regimes did not differ significantly than GRD treatment and VAM + 100% P dose. It suggests an economy of about 25% inorganic P dose through VAM fungi. The treatments imbedded with VAM inoculation enhanced the P uptake in okra–pea system, on an average by 21% over the GRD and non-VAM-inoculated counterparts. Further, integrated application of P, VAM, and irrigation regimes evaluated in okra–pea sequence for 2 years led to greater status of water-soluble P (21%), sodium bicarbonate (NaHCO₃)–inorganic phosphorus (Pi) (11%), sodium hydroxide (NaOH)–Pi (9%), hydrochloric acid (HCl)–extractable–P (20%) over non-VAM-inoculated counterparts and low status of organic P (NaHCO₃-P_o and NaOH-P_o), all of which appreciably contributed to available P supply to plants in the present study in an acid Alfisol. The correlation coefficient reveals that contribution of inorganic P forms is highly correlated to crop productivity and total P uptake in okra and pea crops besides soil available P in the present study. Overall, it is concluded that VAM inoculation in okra–pea cropping system significantly enhanced the P availability to plants by way of enriching the labile-P pool such as water-soluble P and P loosely bound to aluminium (Al-P) and iron (Fe-P) on adsorption complexes and by P mineralization from organic matter in an Himalayan acid Alfisol.     

Effects of Conjunctive Nutrient Management on Soil Fertility and Overall Soil Quality Index in Submountainous Inceptisol Soils under Rainfed Maize (Zea mays L.)–Wheat (Triticum aestivum) System

The present long-term study was initiated to quantify the long-term effects of conjunctive nutrient management on soil quality, identify key indicators, and assess soil quality indices under a rainfed maize–wheat system in marginal Inceptisol soils in India. Results of the study revealed that soil organic carbon was significantly influenced by the conjunctive nutrient-management treatments. Among the nine treatments, the application of 100% recommended dose of nitrogen (RDN) (80 kg N ha^?1), 15 kg N (compost) + 20 kg N ha^?1 (inorganic), 25 kg N (compost), and 15 kg N (compost) + 10 kg N ha^?1 (green leaf) resulted in greater organic carbon contents of 5.57, 5.32, 5.27, and 5.26 g kg^?1, which were greater by 29.5%, 24%, 23%, and 22%, respectively, over the control. The greatest soil quality index (1.61) was observed with application of 25 kg nitrogen (N; compost) as well as with application of 15 kg N (compost) + 10 kg N ha^?1 (green leaf). The order of percentage contribution of key indicators toward soil quality indices was available potassium (K) (34%) > available phosphorus (P) (32%) > available N (13%) > microbial biomass carbon (12%) > exchangeable calcium (Ca) (9%). The linear regression equation revealed the principal role of soil quality indicators in maize crop yield. The methodology and the results of the study could be of great relevance in improving and assessing soil quality not only for the study locations but also for other climatically and edaphically identical regions across the world.     

Evaluation of Extractants and Quantity–Intensity Relationship for Estimation of Available Potassium in Some Calcareous Soils of Western Iran

Accurate estimation of the available potassium (K⁺) supplied by calcareous soils in arid and semi‐arid regions is becoming more important. Exchangeable K⁺, determined by ammonium acetate (NH₄OAc), might not be the best predictor of the soil K⁺ available to crops in soils containing micaceous minerals. The effectiveness of different extraction methods for the prediction of K‐supplying capacities and quantity–intensity relationships was studied in 10 calcareous soils in western Iran. Total K⁺ uptake by wheat grown in the greenhouse was used to measure plant‐available soil K⁺. The following methods extracted increasingly higher average amounts of soil K⁺: 0.025 M H₂SO₄ (45 mg K⁺ kg^?1), 1 M NaCl (92 mg K⁺ kg^?1), 0.01 M CaCl₂ (104 mg K⁺ kg^?1), 0.1 M BaCl₂ (126 mg K⁺ kg^?1), and 1 M NH₄OAc (312 mg K⁺ kg^?1). Potassium extracted by 0.01 M CaCl₂, 1 M NaCl, 0.1 M BaCl₂, and 0.025 M H₂SO₄ showed higher correlation with K⁺ uptake by the crop (P < 0.01) than did NH₄OAc (P < 0.05), which is used to extract K⁺ in the soils of the studied area. There were significant correlations among exchangeable K⁺ adsorbed on the planar surfaces of soils (labile K⁺) and K⁺ plant uptake and K⁺ extracted by all extractants. It would appear that both 0.01 M CaCl₂ and 1 M NaCl extractants and labile K⁺ may provide the most useful prediction of K⁺ uptake by plants in these calcareous soils containing micaceous minerals.     

Changes in Fractions of Iron,Manganese, Copper,and Zinc in Soil under Continuous Cropping for More Than Three Decades

The effect of continuous cropping with maize and wheat on soil characteristics and various forms of micronutrient cations in an Incetisol over the years was studied in an ongoing long‐term experiment in New Delhi, India. The soil samples collected in the years of 1993, 1995, 1997, 1999, 2001, 2003, and 2004 were analyzed for different fractions of iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) by following a sequential extraction procedure. The pH, electrical conductivity (EC), and calcium carbonate (CaCO₃) content of the soil varied from 8.28 to 8.53, 0.40 to 0.43 dSm^?1, and 0.92 to 1.05%, respectively. Organic carbon content ranged from 0.38 in the control to 0.67% in 100% NPK + farmyard manure (FYM). Diethylenetriaminepentaacetic acid (DTPA)–extractable Fe and Mn (but not Zn and Cu) in soil declined from their respective initial (1971) values as a result of intensive cropping for more than three decades. It also resulted in a decrease in the concentrations of all the four metallic cations bound to organic matter, in addition to Fe and Zn, associated with carbonates in all the treatments in surface soil.     

Boron Fertilization and Evaluation of Four Soil Extractants: Russet Burbank Potato

Yield‐response correlations with old and improved soil extraction methods for boron (B) are needed. Russet Burbank potato (Solanum tuberosum L.) was grown with two, four, and six B treatments applied in 2004, 2005, and 2006, respectively. Zero and 1.1, 2.2, or 3.4 kg B ha^?1 soil and 0.22 or 0.28 kg B ha^?1 foliar treatments were applied. Boron fertilization did not significantly increase tuber yield or quality despite initially low hot‐water‐extractable B (0.34–0.50 mg kg^?1), although postseason B for unfertilized treatments increased (0.51–0.57 mg kg^?1). Soil‐applied B generally reflected B application relative to the untreated control and the low foliar rates in all three years for the four soil extractions utilized [hot water, pressurized hot water, diethylenetriaminepentaacetic acid (DTPA)–sorbitol, and Mehlich III]. Boron content of potato petiole did reflect application of B in 2 years, but tuber and peel tissues did not consistently reflect application of B.     

Quantity–Intensity Relationships of Potassium in Soils under Some Guava Orchards on Marginal Lands

Quantity–intensity relations of potassium (K) were worked out for guava orchard soils. Equilibrium activity ratio of potassium (AR_e ^k) ranged from 0.46?×?10^?3 to 21.30?×?10^?3 (mol L^?1)^0.5. The majority of the samples had less than 1?×?10^?3 (mol L^?1)^0.5, indicating K depletion in these soils due to continuous K mining. AR_e ^k was significantly and positively correlated with available forms of K, K saturation percentage, labile K (K_L), and specific-site K (K_X) and negatively correlated with free energy of exchange (–ΔG). The potential buffering capacity (PBC₀ ^K) of K varied from 8.8 to 286.2 cmol kg^?1/(mol L^?1)^0.5. PBC₀ ^K was positively and significantly correlated with clay content. Sixty percent of the soils had ΔK⁰ values of less than 0.1 cmol kg^?1. High K_G (Gapon selectivity coefficent) indicated high affinity for K in these soils. Leaf K was positively and significantly correlated with ΔK⁰, K_L, and K_X and negatively correlated with –ΔG.     

Soil Organic Carbon,Phosphorous, and Potassium Status in Rice–Wheat Soils of Different Agro-climatic Zones in Indo-Gangetic Plains of India

The status of available macronutrients [phosphorus (P) and potassium (K)] and soil organic carbon (SOC) of the surface soil under a rice–wheat cropping system was studied in 40 districts of the Indo-Gangetic Plains (IGP) of India. The soil samples were collected from the farmers' fields in four transects (Trans-, Upper, Middle, and Lower Gangetic Plains) of the IGP. The selection of farmers, villages, blocks, and districts within an agro-climatic zone (ACZ) was done on the basis of a multistage statistical approach. The available macronutrients were characterized as low, medium, and high. In Trans-Gangetic Plains, SOC, available P, and available K were in the ranges of 0.06–0.86%, 6.7–85.1 kg ha^?1, and 50–347 kg ha^?1, respectively. In Upper Gangetic Plains, the respective values were in the ranges of 0.05–2.55%, 4.5–155.0 kg ha^?1, and 45 to 560 kg ha^?1. Similarly, in Middle Gangetic Plains, these values were in the ranges of 0.04–2.01%, 4.7–183.7 kg ha^?1, and 72–554 kg ha^?1, respectively. In Lower Gangetic Plains, respective values were 0.12–1.78%, 2.2–112.0 kg ha^?1, and 83–553 kg ha^?1. In Trans-Gangetic plains, the majority of the soils in the midplains ACZ representing intensively cultivated rice–wheat system area were low to medium in SOC and available P, whereas available K status was medium to high. Irrespective of the agroclimatic variations, more than 90% of the soils were low to medium in SOC and available P with a marginal deficiency of K. The majority of the coarse-textured soils in Shiwaliks were found to have low to medium SOC and available P, whereas less intensively cultivated arid zone soils were high in SOC, available P, and available K. In Upper and Middle Gangetic Plains, the majority of the soils tested medium for SOC and medium to high in available P and K. The dominance of medium status of available P in these soils could be due to mining of soil P by the rice–wheat cropping system practiced in these regions for more than 300 years. In Lower Gangetic Plains, the SOC was medium to high in most of the soils, whereas available P and K were high. Recent introduction of the rice–wheat system on intensive scale in these traditionally rice-growing areas resulted in less mining of SOC, P, and K.     

Comparison of Conductimetric and Colorimetric Methods with Distillation–Titration Method of Analyzing Ammonium Nitrogen in Total Kjeldahl Digests

The distillation–titration method (DTM) is a standard procedure used by most laboratories to measure ammonium-nitrogen (NH₄-N) in the total Kjeldahl N (TKN) digests of various kinds of agricultural and environmental samples. These samples may have TKN contents ranging from less than 100 ppb to as high as percentage levels. However, the DTM procedure generally leads to a very low throughput because it is labor intensive and time-consuming. At the current practical quantitation limit (PQL) of 300 ppb established at the Feed and Environmental (FEW) Laboratory, University of Georgia, the DTM procedure is less applicable to low TKN surface water samples. In this study, we therefore compared the performance of diffusion conductivity method (DCM) and colorimetric method (CM) with DTM in measuring NH₄-N in the TKN digests of 29 different samples representing surface waters, lagoons, manures, poultry litters, and environmental wastes. Acceptable accuracy and precision were achieved for various QC samples by all three methods. For widely different sample matrices and TKN contents, the NH₄-N in the TKN digests measured by DCM and CM both agreed well with that measured by DTM. However, the linear working range of CM is limited within 0.2 to 5.0 ppm, whereas DCM is linear at a wider range of 0.01 to 2000 ppm. With DCM, the PQL of TKN is at 13 ppb, much less than the 300 ppb in DTM and 520 ppb in CM. Both DCM and CM require increasing the pH of the working TKN digest to a highly alkaline range. To meet such pH requirement, the minimum dilution need for DCM is twofold, where as that CM is fourfold. Because of greater mandatory dilution requirement coupled with a greater PQL, CM may often fail to measure NH₄-N in the working TKN digest of some low TKN surface water samples. On the other hand, with some environmental waste samples containing TKN at percentage level, CM would require multistep dilution of the digests prior to measurement, thus allowing dilution-related error as well as requiring additional labor. In contrast, DCM can measure both low TKN surface waters and high TKN environmental wastes without any major limitations. Moreover, DCM may work well without any adjustment of sample background in the calibration standards. Thus DCM appears to be an attractive alternative to the labor-intensive and time-consuming DTM for measuring NH₄-N in the TKN digests of various kinds of agricultural and environmental samples in the analytical services laboratories.