R.K. Rattan

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.

Critical limits of deficiency and toxicity of zinc in paddy in a typic ustipsamment

Abstract A pot culture experiment was conducted to establish the critical limits of deficiency and toxicity of Zn in a Typic Ustipsamment from tropical India. Critical limits of Zn deficiency and toxicity were 0.39, and 12 μg/g with DTPA‐TEA‐CaCl2, 2.2 and 26 μg/g with EDTA‐(NH4)2Co3 and 0.78 and 12 μg/g with HC1 (0.05 N), respectively. Critical concentrations in the rice plants associated with deficiency and toxicity were 16 and 190 μg/g.

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.

Distribution of Zinc Fractions in Some Major Soils of India and the Impact on Nutrition of Rice

Abstract Speciation study of microelements in soils is useful to assess their retention and release by the soil to the plant. Laboratory and greenhouse investigations were conducted for five soils of different agro‐ecological zones (viz., Bhuna, Delhi, Cooch‐Behar, Gurgaon, and Pabra) with diverse physicochemical properties to study the distribution of zinc (Zn) among the soil fractions with respect to the availability of Zn species for uptake by rice plant. A sequential extraction procedure was used that fractionated total soil Zn into water‐soluble (WS), exchangeable (EX), specifically adsorbed (SA), acid‐soluble (AS), manganese (Mn)‐oxide‐occluded (Mn‐OX), organic‐matter‐occluded (OM), amorphous iron (Fe)‐oxide‐bound (AFe‐OX), crystalline Fe‐oxide‐bound (CFe‐OX), and residual (RES) forms. There was a wide variation in the magnitude of these fractions among the soils. The studies revealed that more than 90% of the total Zn content occurred in the relatively inactive clay lattice and other mineral‐bound form (RES) and that only a small fraction occurred in the forms of WS, EX, OM, AFe‐OX, and CFe‐OX. Rice (Oryza sativa L.) cultivars differ widely in their sensitivity to Zn deficiency. Results suggested that Zn in water‐soluble, organic complexes, exchange positions, and amorphous sesquioxides were the fractions (pools) that played a key role in the uptake of Zn by the rice varieties (viz., Pusa‐933‐87‐1‐11‐88‐1‐2‐1, Pusa‐44, Pusa‐834, Jaya, and Pusa‐677). Isotopic ally exchangeable Zn (labile Zn) was recorded higher in Typic Ustrochrept of Pabra soil, and uptake of Zn by rice cultivars was also higher in this soil. The kinetic parameters such as maximum influx at high concentrations (Imax) and nutrient concentration in solution where influx is one half of Imax (Km) behaved differentially with respect to varieties. The highest Imax value recorded was 9.2×10−7 µmol cm−2 s−1 at the 5 mg kg−1 Zn rate for Pusa‐933‐87‐1‐11‐88‐1‐2‐1, and the same was lowest for Pusa‐44, being 4.6×10−7 µmol cm−2 s−1 at the 5 mg kg−1 Zn rate. The Km value was highest for Pusa‐44 (2.1×10−4µmol cm−2 s−1) and lowest for Pusa‐933‐87‐1‐11‐88‐1‐2‐1 (1.20×10−4µmol cm−2 s−1). The availability of Zn to rice cultivars in Typic Ustrochrepts of Bhuna and Delhi soils, which are characterized by higher activation energy and entropy factor, was accompanied by breakage of bonds or by significant structural changes.

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.

A new approach for estimating the phytotoxicity limits

A pot experiment was carried out on a Typic ustipsamment to study the effect of Cd concentration on the yield of wheat (Triticum aestivum) and soybean (Glycine max). Cd levels taken were 1, 5, 10, 20, 40, 80, and 160 μg g-1 of soil. Three different statistical procedures were employed to evaluate the phytotoxicity limits. The non-linear regression technique was found to be more effective in calculating C0 (threshold concentration) and C100 (toxic concentration) in comparison to Cate and Nelson (1971) and Beckett and Davis (1977) procedures. This technique was unaffected by the nature of the distribution of the data and did not require any initial value of concentration as a starting point.

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 Effect of Tillage, Water and Nutrient Management Practices on Mineral Nitrogen, Available Phosphorus and Sulphur Content under Rice-Wheat Cropping System

The Indo-Gangetic plains of South Asia depends on rice-wheat based cropping system for their food security. Sustainable management of this system is difficult because of differential requirements in respect of soil and environmental conditions. A judicious and scientific management of this system in relation to tillage, water and nutrient is crucial for sustaining productivity. The present paper aims to study the interactive effects of tillage, water and nutrient management practices on mineral nitrogen (N), available phosphorus (P) and sulphur (S) content in soil under rice-wheat cropping system after completion of 7th cropping cycle. Soil samples were collected from a long-term field experiment which was initiated in 2001 at Indian Agricultural Research Institute (IARI) farm. The experiments consisted of two tillage, three water and seven nutrient management practices, which were allocated to main, sub and sub-sub plots (split-split plot design), respectively. Results indicated that, mineral N and available P content in soil was higher in puddled soil as compared to non-puddled condition. The P content in soil decreased with moisture content whereas, available S increased. Organic source of nutrients could not maintain the level of mineral N in soil even as that recorded in control whereas, plots that received FYM and crop residue along with mineral fertilizers showed significantly higher mineral N content than the plot where nutrients were supplied through chemical fertilizers. Integration of crop residues along with mineral fertilizers had a beneficial effect on the availability of P in soil.