S.P. Datta

Monitoring changes in soil organic carbon pools, nitrogen, phosphorus, and sulfur under different agricultural management practices in the tropics

Soil organic matter not only affects sustainability of agricultural ecosystems, but also extremely important in maintaining overall quality of environment as soil contains a significant part of global carbon stock. Hence, we attempted to assess the influence of different tillage and nutrient management practices on various stabilized and active soil organic carbon pools, and their contribution to the extractable nitrogen phosphorus and sulfur. Our study confined to the assessment of impact of agricultural management practices on the soil organic carbon pools and extractable nutrients under three important cropping systems, viz. soybean–wheat, maize–wheat, and rice–wheat. Results indicated that there was marginal improvement in Walkley and Black content in soil under integrated and organic nutrient management treatments in soybean–wheat, maize–wheat, and rice–wheat after completion of four cropping cycles. Improvement in stabilized pools of soil organic carbon (SOC) was not proportional to the applied amount of organic manures. While, labile pools of SOC were increased with the increase in amount of added manures. Apparently, green manure (Sesbania) was more effective in enhancing the lability of SOC as compared to farmyard manure and crop residues. The KMnO4-oxidizable SOC proved to be more sensitive and consistent as an index of labile pool of SOC compared to microbial biomass carbon. Under different cropping sequences, labile fractions of soil organic carbon exerted consistent positive effect on the extractable nitrogen, phosphorus, and sulfur in soil.

Diagnosis and Amelioration of Iron Deficiency under Aerobic Rice

ABSTRACT Iron (Fe) deficiency is one of the serious nutritional disorders in aerobically grown rice on upland alkaline and calcareous soils, which leads to a decline in productivity. With a view to resolve the Fe-deficiency syndrome in aerobic rice, the influence of soil moisture regimes, farmyard manure (FYM) and applied Fe on the release of Fe was assessed under an incubation study. A field experiment was also conducted to evaluate the relative effectiveness of soil and foliar applications of Fe in alleviating Fe deficiency using four rice cultivars (‘IR 36’, ‘IR 64’, ‘IR 71525-19-1-1’ and ‘CT 6510-24-1-2’). Results of incubation study indicated that the application of FYM marginally improved the diethylene triamine pentaacetic acid (DTPA)-Fe status of soil over control. However, application of iron sulfate (FeSO4 · 7H2O) at 14 mg Fe/kg with FYM released as much Fe as did the application of 27 mg Fe/kg as FeSO4 7H2O alone. Comparatively higher amounts of Fe were released under water saturation than that under drier soil moisture regimes and the effect of incubation period in releasing Fe was pronounced only under water saturation. Under field study, supplementation of Fe through integrated or inorganic source caused improvement in the DTPA and ammonium acetate (NH4OAc) extractable Fe similar to that recorded under incubation. The foliar application of Fe (3% FeSO4 7H2O solution, thrice at 40, 60, and 75 days after sowing of rice, i.e., 45 kg FeSO4.7H2O/ha) was most effective and economical in correcting Fe deficiency in aerobic rice, followed by soil application of 150 kg FeSO4.7H2O + 10 t FYM/ ha and 305 kg FeSO4.7H2O/ha. Among the rice cultivars, ‘CT 6510-24-1-2’ and ‘IR 71525-19-1-1’ performed better under aerobic condition compared to ‘IR 36’ and ‘IR 64’. Differential response of rice cultivars to applied Fe was not related to Fe-nutrition; rather it was apparently related with inherent ability of cultivars to grow under water-stress condition. Ferrous iron (FeII) content in rice plants proved to be a better index of Fe-nutrition status compared to total plant Fe and chemically extractable soil Fe. The FeII concentration of ≥ 37 mg kg−1 in plants (on dry weight basis) appeared to be an adequate level at 60 days after sowing for direct seeded rice grown under upland aerobic condition.

Fractionation and colorimetric determination of boron in soils

We attempted to modify and evaluate existing sequential fractionation schemes for B involving the use of chemicals, which subsequently do not interfere with the measurement of B by colorimetry. Also evaluated was the contribution of various soil B fractions to the amount of B extracted by hot CaCl2, CaCl2-mannitol, salicylic acid, ammonium acetate, HCl, and tartaric acid. For this purpose, 17 soils with diverse properties were used. The extraction scheme proposed here partitioned B into five pools, (i) readily soluble, (ii) specifically adsorbed, (iii) oxide bound, (iv) organically bound, and (v) residual boron, respectively extracted with 0.01 M CaCl2, 0.05 M KH2PO4, 0.175 M NH4-oxalate (pH 3.25), 0.5 M NaOH, and HF + H2SO4 + HClO4. The procedure of elimination of color from extracts of oxide bound, organically bound, and residual B fractions was also evolved. Relationships of individual B fractions with physicochemical properties of the experimental soils confirmed the general validity of the proposed fractionation scheme. The relationships of different B fractions with extractable B in soils suggest that hot CaCl2 and salicylic acid may be better extractants for available B in soils. Fraktionierung und colorimetrische Bestimmung von Bor in Boden Ein bestehendes sequenzielles Fraktionierungsverfahren fur Bor in Boden wurde in Anbetracht des Fehlens eines ICP-Gerates modifiziert, um B colorimetrisch mit Azomethin-H und Carmin bestimmen zu konnen. Hierzu mussten auch Verfahren zur Eliminierung der Eigenfarbung der Bodenextrakte entwickelt werden. Das hier vorgestellte Extraktionsschema differenziert in (i) leicht losliches B, (ii) spezifisch adsorbiertes B, (iii) oxid-gebundenes B, (iv) organisch gebundenes B und (v) Residual-B. Insgesamt 17 verschiedene Boden wurden auch jeweils mittels heiser CaCl2, CaCl2 mit Mannitol, Salicylsaure, Ammoniumazetat, HCl und Weinsaure extrahiert und das so extrahierte B den oben genannten B-Fraktionen zuzuordnen versucht. Aufgrund der gefundenen Beziehungen wurden heises CaCl2 und Salicylsaure als die geeigneten Extraktionsmedien fur pflanzenverfugbares B in Boden ermittelt.

EFFECT OF APPLIED LIME AND BORON ON THE AVAILABILITY OF NUTRIENTS IN AN ACID SOIL

Productivity of resources on acid soils occupying one fourth of the total area in India is abysmally low. Lime is applied to such soils with the primary objective of increasing the productivity of crops by enhancing the availability of native and applied plant nutrients. Greenhouse pot experiments and laboratory experiments were conducted to evaluate the effects of lime and boron (B) on the availability of nutrients in soils and their uptake by plants. The application of lime enhanced the available nitrogen (N,), phosphorus (P), calcium (Ca), magnesium (Mg), sulfur (S), and zinc (Zn) content in soils, which was reflected in their uptake by sunflower (Helianthus annus). On the contrary, availability of copper (Cu), iron (Fe), and manganese (Mn) in soil was reduced due to liming. Sunflower responded very well in terms of dry matter yield to B application to the extent of 175% and 188% under 1 and 2 mg kg−1 applied levels of B, respectively. Dry matter yield of sunflower was reduced to the tune of 29.2 and 42.7% under 2/3 and 1 lime requirement (LR), respectively, over control. Lime application at 1/3 LR with 2 mg kg−1 of applied B emerged as an optimum combination in acid soils.

Chemical fractions and bioavailability of nickel in alluvial soils.

The present study was undertaken to sequentially fractionate nickel (Ni) in soils of divergent physicochemical char acteristics and evaluate the contribution of different fractions towards plant uptake. For this, fifteen bulk surface (0–15 cm) soil samples were collected from the cultivated fields of northwestern Indo-Gangetic alluvial plains. A pot experiment was conducted with these soils to assess the contribution of soil Ni fractions to plant uptake using soybean as test crop. Results showed that residual Ni was the most dominant fraction in soil constituting 3.19–63.6% of total Ni. The water soluble plus exchangeable Ni accounted for only 0.70–4.04% of total soil Ni. Organically bound Ni varied from 1.60–6.85% of total Ni; these values are relatively lower as compared to those reported for temperate soils. Correlation studies showed that the free iron oxide (Fe 2 O 3 ) and soil organic carbon correlated with various fractions of Ni in soil. Water soluble plus exchangeable and organically bound are the dominant fractions which contributed positively and manganese oxide (MnO 2 ) bound and residual fractions contributed negatively towards the phytoavailability of Ni in soil.

Soil boron status: impact of lime and fertilizers in an Indian long-term field experiment on a Typic Paleustalf

In Indian agriculture, nitrogen (N) and phosphorus (P) fertilizers are predominantly used by the farmers, often ignoring secondary and micronutrients. Significance of boron (B) in nutrient management studies has been increasingly underlined under intensive cropping systems particularly in acid soils. In order to understand the distribution of soil native B in different fractions and their contribution to plant B uptake as influenced by nutrient management, soil samples collected after wheat (2009–2010) from a long-term experiment (LTE) continuing since 1972–1973 on Typic Paleustalf of Ranchi were subjected to sequential fractionation of soil B. Treatments included N alone, NP, NPK, 150% of recommended NPK, NPK + farmyard manure (FYM), NPK + lime, and an unfertilized-control. Five soil B fractions were determined along with hot CaCl2-extractable (available) B. Averaged across the treatments, the soil had low organic carbon (C), pH and cation exchange capacity (CEC), and high free sesquioxides. Total B content was 21.7 mg kg−1. Among different B fractions, residual B was the major contributor to total B and other fractions collectively shared 7% of total B only. Application of N alone depleted readily soluble, specifically adsorbed and organically bound B bringing the contents even below unfertilized-control. Conjoint use of lime or FYM with NPK increased significantly these fractions, whereas a decrease in oxide bound B was noticed under these treatments. Available B was positively correlated with these fractions indicating their significance in controlling B availability in the soil. The study revealed that use of lime or FYM helped modifying the distribution of soil B in different fractions by way of changing soil pH and organic C content, resulting in enrichment of plant available pool. A drastically low available B content in different treatments receiving fertilizers alone, however, suggested the necessity of B fertilization at prescribed rates for maintaining soil B fertility as also high crop yields.

Safe limit of arsenic in soil in relation to dietary exposure of arsenicosis patients from Malda district, West Bengal- A case study

Safe limit of arsenic in soil in relation to dietary exposure of arsenicosis patients was established in Malda district of West Bengal. Out of 182 participants examined, 80 (43.9%) participants showed clinical features of arsenicosis, characterized by arsenical skin lesion (pigmentation and keratosis), while 102 participants did not have any such lesion (control). Experimental results of the twenty eight soils (own field) of the participants showed the mean Olsen extractable and total arsenic concentration of 0.206 and 6.70mgkg-1, respectively. Arsenic concentration in rice grain ranged from 2.00 to 1260μgkg-1 with the mean value of 146μgkg-1. The hazard quotient (HQ) for intake of As by human through consumption of rice varied from 0.03 to 3.52. HQ exceeds 1.0 for drinking water and rice grain grown in the study area in many cases. As high as 77.6% variation in As content in rice grain could be explained by the solubility-free ion activity model. Toxic limit of extractable As in soil for rice in relation to soil properties and human health hazard, associated with consumption of rice grain by human, was established. For example, the permissible limit of Olsen extractable As in soil would be 0.43mgkg-1 for rice cultivation, if soil pH and organic carbon content were 7.5% and 0.50%, respectively. However, the critical limit of Olsen extractable As in soil would be 0.54mgkg-1, if soil pH and organic carbon were 8.5% and 0.75%, respectively. The conceptual framework of fixing the toxic limit of arsenic in soils with respect to soil properties and human health under modeling-framework was established.

Solubility Relationships of Iron and Evaluation of its Fertility Status in Degraded Soils

ABSTRACT This study was conducted to determine the solubility of iron (Fe) and identify the solid phases responsible for controlling its solubility in these soils by using Baker soil test (BST) computer program. The results indicated that the ferric ion (Fe3+) activity in all the soils, except the acidic ones, nearly approached the theoretical solubility line of known minerals, namely soil-Fe, amorphous-Fe, maghemite, and lepidocrocite. Solubility of Fe in acid soils of Ranchi (soil 3) and Cooch-Behar (soil 6) did not match the theoretical solubility lines of any of the known minerals. The acidic soils of Ranchi and Cooch-Behar were sufficient for Fe with respect to both quantity and intensity factor based on BST rating, while alkaline (soil 1) and calcareous (soil 5) were sufficient in reserve Fe; deficiency of iron still could be suspected because of high pH. These findings elucidate the role of solid phase controlling iron solubility in soil solution of degraded soils.

Long-term irrigation with zinc smelter effluent affects important soil properties and heavy metal content in food crops and soil in Rajasthan, India

ABSTRACT Use of wastewater for irrigating agricultural crops is on the rise, particularly in the developing countries. The present study was undertaken to assess the long-term effect of irrigation with zinc smelter effluent on important soil properties including heavy metal status. Metal concentration in the edible parts of the crops grown on smelter effluent-irrigated soils was also measured. For this purpose, the agricultural lands which have been receiving the zinc smelter effluent irrigation for about five decades at Debari, Udaipur, India were selected. The adjacent tubewell water-irrigated fields were selected as reference. Long-term irrigation with smelter effluent resulted into significant buildup of ethylenediaminetetraacetic acid extractable Zn (57.7 fold), Cu (4.51 fold), Fe (3.35 fold), Mn (1.77 fold), Ni (1.20 fold), Pb (45.1 fold), and Cd (79.2 fold) in soils over tubewell water-irrigated fields. Total Zn, Cu, Mn, Ni, Pb, and Cd content in effluent-irrigated soils was also increased by 27.0, 1.60, 1.40, 1.30, 26.2, and 167 fold, respectively. Risk assessment indicated a very high to moderate potential ecological risk due to Cd, Pb, and Zn in soils close to the immediate vicinity of the smelter plant. Cadmium and Pb concentrations in edible parts of almost all the crops grown on effluent-irrigated soils were above the safe limit of CODEX commission. On an average, soil pH dropped by 0.31 units due to smelter effluent irrigation. Smelter effluent irrigation resulted into significant increase in soil organic carbon, electrical conductivity, and CaCO3 content. On an average, there was decrease in available N (21.0%) and P (20.8%) content in effluent-irrigated soils over the tubewell water-irrigated ones. An increase in available K (102%) and S (26.0 fold) was recorded in effluent-irrigated soils. Long-term irrigation with zinc smelter effluent resulted into reduced microbial activities in soil as evidenced from the level of microbial biomass carbon and dehydrogenase activity. In view of the buildup of heavy metals and subsequent imbalance in essential plant nutrients in smelter effluent-irrigated soils, appropriate remediation-cum-fertilization strategy needs to be adopted for better soil health and plant nutrition.

Boron Fractions in a Vertic Ustochrept as Influenced by Thirteen Years of Fertilization and Manuring

Soil and plant samples were collected after harvest of wheat in 2010 from a long-term experiment on groundnut-wheat sequence that continued since 1996–97 on a Vertic Ustochrept at Junagadh Agricultural University, in order to study the distribution of boron (B) in different fractions and their contribution towards B availability in soil and B uptake by wheat. Treatments included N alone, NP, NPK, 150% of recommended NPK, NPK+farmyard manure (FYM) and an unfertilized control. Five soil B fractions were determined along with hot CaCl2-extractable (available) B. Specifically adsorbed and organically bound B fractions were significantly greater under continuous use of NPK+FYM compared with other treatments, resulting in higher values of available B under NPK+FYM treatment. Soil organic C and cation exchange capacity were the important soil characteristics that governed the distribution of soil B in different fractions. Organically bound B appeared pivotal regarding availability of native B for plant uptake.