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3.2.1 Long-term Impact of Rice-Wheat and Maize-Wheat Cropping Systems on the Stability of Humus-Carbon in the Soil

Kinetics of carbon release was studied on the naturally occurring clay-humus complexes extracted from the soils by sodium hydroxide - sodium pyrophosphate solution extraction.

Results showed that the release of carbon (Qt)at a given time from clay-humus complex followed very closely the Elovich reaction kinetics:

Qt = (1/β)ln(αβ) +(1/β)ln t

with α and β coefficients signifying the initial rate of release and the coefficient of stability, respectively. The α and β values of clay-humus complex of different layers of two profiles from the contiguous area (one under rice–wheat and the other under maize–wheat for long time) were estimated. The average stability of the humus from the samples of rice–wheat cropping system was higher (β= 8.814) than that from maize–wheat cropping system ((β= 8.019). The average release of carbon from rice–wheat cropping system was lower (0.71%) than that from maize–

wheat cropping system. In another set of experiments, the stability of carbon in the rhizosphere soil of wheat was lower, and carbon release coefficient was higher than that in the non-rhizosphere wheat soil. This is corroborated by the observations that the fraction of labile carbon was more in the rhizosphere than in the non-rhizosphere soil during wheat cropping.

3.2.2 Influence of Rice Cropping on the Clay Mineralogy of Two Divergent Soils

Clay fractions were isolated from soil samples collected from different depths of four profiles two from BCKV farm, Mohanpur (WB) and two from PAU farm, Ludhiana (Punjab).

Among the two nearby profiles collected from the contiguous places, one was under long-term continuous rice cultivation and the other from adjoining cultivated upland conditions.

The X-ray diffraction studies confirmed the presence of pure phase mica (8.8 o2θ), vermiculite (6.1 o2θ), kaolinite (12.4

o2θ) and smectite (4.88 o2θ) (glycerol solvated). Other prominent peaks found were in the range of (11.2-11.3) o2θ, (9.2-9.3) o2θ and (8.2-8.3) o2θ, which were ascribed to randomly interstratified kaolinite-mica, kaolinite smectite and mica-vermiculite, respectively. On an average, the Mohanpur soil exhibited more advanced stage of weathering compared

to the Ludhiana soil, and rice cultivation at the same site accelerated the weathering process.

3.2.3 Sulphate Sorption Characteristics of Acid Soils of Eastern India

A study was undertaken to relate sulphate (SO4) sorption characteristics of five acid soils (two Alfisols, two Ultisols and one Inceptisol) with the soil properties. The pH of soils varied from 4.81 to 6.34. The organic carbon content ranged from 0.38 to 1.03%. The CEC was found to vary from 4.0 to 11.0 cmol(p+) kg-1 and the clay content varied from 12.6 to 23.9%. The water extractable sulphate S and the phosphate extractable sulphate S ranged from 5.21 to 28.00 and 12.75 to 81.50 mg kg-1, respectively.

The simple regressions showed that the Langmuir equation (r value, 0.94 0.99**) gave the best fit over Freundlich (r value, 0.84 0.97**) for all the soils. Sulphate sorption maximum (b) and constant related to bonding energy (K) calculated from Langmuir equation are presented in the following table. The sulphate sorption maximum value was found in the order: Alfisol > Ultisol > Inceptisol. The results indicated that SO4 –S sorption maximum (b) had strong negative relationship with pH (0.892**). The sulphate sorption maximum was significantly related to clay (0.912**).

There was a negative correlation between sulphate sorption maximum and organic carbon content (0.823**). The mechanism by which high organic carbon content inhibits the sulphate sorption on soil constituents involves the increase in dissolved organic carbon (DOC) concentration in soil solution. This increased DOC competes with sulphate ions for sorption sites and thereby decreases the sulphate sorption.

Sulphate sorption maximum had a significant negative relation

with water extractable sulphate S (0.972**) and a positive relation with phosphate extractable S (0.842**). The overall results indicate that the sulphate sorption capacity in moderate to strongly acid soils depended upon the soil pH, organic carbon, and native water and phosphate extractable sulphate pools.

3.2.4 Stability of Clay Minerals in Relation to Pedogenic Progression in Different Agro- Ecosystems

Profile soil samples from one cultivated and two adjoining forest areas of Nagpur, Maharashtra, belonging to semi-arid eco-region in the Deccan Plateau, were collected.

Semi–quantitative analysis of the clay minerals present in soils at different depths was done. The mineralogical studies revealed that, in general, in forest soils, there was more inter- stratification of mica-kaolinite and mica-smectite. This inter- stratification was less in the adjoining cultivated field. The more inter-stratification in forest soils might be due to more weathering caused by acid leaching of organic acids present in these soils. The conversion was more particularly in lower depth (60-100 cm) and on surface soils (0-15 cm).

Computation of the weathering stage of the soil samples from the semi-quantitative clay-mineral analysis and Jackson’s weathering sequences showed that in the surface soil the weathering stage was less advanced in the case of cultivated soils than that of the adjoining forest soils. Average weathering stage in surface soil of forest area indicated the sequence of transformation as mica ... vermiculite ... smectite. In the cultivated surface soils, the weathering was less advanced and followed the sequence mica ... vermiculite.

3.2.5 Ion Exchange Resin Method for Estimation of Plant Available Soil Phosphorus

The hydroxide (OH-)-saturated exchange resin bags with shaking period ranging from half-an-hour to 24 hours were evaluated on 27 soil samples for soybean crop against standard check of Olsen and CaCl2.2H2O reagents as extractants for phosphorus. Pot experiment was conducted on soybean var.

PK 1042 during kharif 2007 with two levels of phosphorus, viz. 0 (control) and 40 mg P2O5 kg-1 as KH2PO4. The dry matter yield (dried to a constant weight at 65OC) of the 45 days’ old plants was recorded. Phosphorus content in the di-acid plant digests was determined. Data obtained showed that the phosphorus levels and soils significantly influenced dry matter yield, content and uptake of P by soybean. However, the interaction effect was non-significant. Soil P content extracted

Langmuir constants of S sorption in five acid soils

Soil /Location Sulphate Bonding Max. buffering r-value sorption energy capacity

maximum (b) cons. (K) (bXK) (L kg-1) (L mg-1)

Alfisol 125.00 0.089 11.13 0.99**


Ultisol 110.23 0.912 10.05 0.97**


Ultisol 115.38 0.950 10.96 0.97**


Inceptisol 84.83 0.104 8.82 0.99**


Alfisol 120.23 0.078 9.38 0.94**


by all the extractants gave highly significant positive correlation with most of the biological indices of soybean with the sole exception of OH- resin bags with ½ hr shaking. The critical limitsby promising extractants, viz., Olsen’s, OH- resin bags with 1 hr shaking, OH- resin bags with 6 hours shaking and OH- resin bags with 24 hours shaking were found to be 9.38, 4.60, 5.40 and 10.75 mg P kg-1 soil for soybean, respectively. The critical concentration of P in 45 days’ old soybean plant tissues was found to be 0.26% on dry weight basis.

3.2.6 Soil Biodiversity Assessment for Enhancing Carbon Sequestration and Nitrogen Cycling under Different Tillage Systems and Crop Rotations

Soil samples from four different rotations, viz., maize–

(wheat/linseed/mustard/chickpea)–greengram under conventional or no-tillage with or without residues treatments at the IARI research farm were studied in the rabi season of 3rd year of the experiment (2007-2008) for the assessment of C and N sequestration; and also for different biochemical and biodiversity indicators. The results revealed a range (0.39- 0.54%) of soil organic C (SOC) in the samples. Incorporation of residues with conventional tillage (CT + R) or retention on the surface under zero tillage (ZT + R) had higher SOC than the conventional or zero tillage systems without residue.

Growing linseed showed better C sequestration in soil than wheat, mustard or chickpea; and linseed under ZT + R had the highest SOC (0.54%) among the treatments. The average potential N mineralization (PNM) rate narrowly ranged from 1.4 mg kg-1 soil day-1 in ZT to 2.5 mg kg-1 soil day-1 in CT + R.

The highest PNM of 2.6 mg kg-1 soil day-1 was exhibited in the system with chickpea under CT + R treatment.

The tillage and residue management practices had strong influence on the microbial biomass C (MBC), microbial quotient (ratio of MBC to SOC) and metabolic activity of microbial community (ratio of deydrogenase activity to MBC).

These parameters invariably followed the order: ZT + R>

CT+R> ZT> CT, and, as in the case of SOC, ZT + R under linseed had the highest MBC, dehydrogenase and MQ. The MBC was strongly associated (R2=0.68**) with SOC, whereas deydrogenase had significantly higher correlation with MBC (R2 = 0.60**) indicating that metabolic activity of the microbial communities was more strongly influenced by the pool of microbial biomass or metabolic quotient (R2 = 0.45**)than the SOC (R2 = 0.30*).

With respect to microbial population, the average density of bacteria followed the order: CT + R> ZT + R> CT> ZT. In the case of fungi, the order was: ZT + R > CT + R > ZT > CT.

Soil organic C, microbial biomass C and dehydrogenase activity in soil as influenced by tillage and residues management practices in different maize-based cropping systems

Proportionately higher fungal population under ZT + R indicates the higher contribution of fungi to residues decomposition and mineralization of nutrients.

3.2.7 Effect of Mineral Fertilizers and Organic Manure on the Soil Quality Index and Productivity under Soybean–Wheat Cropping Sequence

An attempt was made to monitor the soil quality and crop productivity under soybean-wheat cropping sequence as influenced by the application of organic manure and mineral fertilizers. The treatments consisted of three levels of N, viz., 0, 30 and 45 kg ha-1 for soybean and 0, 120 and 180 kg ha-1 for wheat. The entire amount of N was supplied to both the crops through urea and farmyard manure (FYM) alone or in combination of 1:1 ratio. Since the continuity of carbon supply depends on both the total pool size and lability, carbon management index (CMI) was computed. Results indicated that supplementation of N through FYM significantly improved the soil quality as evident from the carbon management index compared to that under integrated or inorganic sources after completion of five cropping cycles.

Substantial improvement in the status of soil fertility parameters like available P and micronutrient cations was also discernible under organic and integrated inputs. However, FYM could not sustain the same yield level, particularly of wheat as that obtained with chemical fertilizers. Relatively higher amount of mineral N in soil and elevated N content in plant under chemical fertilizers compared to those under FYM at critical growth stages of wheat were responsible for higher crop yield. Hence, there is a need to integrate carbon–based soil quality index with the fluxes of mineral N in soil during the crop growth to have its true reflection on the productivity of the system.

3.2.8 Relative Efficacy of Soil and Foliar Application of Iron in Correcting Iron Deficiency under Aerobically Grown Rice

A field trial on diagnosis and amelioration of Fe deficiency under aerobically– grown rice was conducted using Pusa Sugandh 3, IR 64, IR 55419 and IR 55423 as test rice cultivars. Apart from control, Fe management treatments consisted of soil application of 150 kg FeSO4/ ha, and foliar application of 3% FeSO4 solution. Results indicated that two foliar sprays of Fe (3% FeSO4;30 kg FeSO4/ha) at 30 and 45 days after sowing (DAS) were more

effective and economical in correcting Fe deficiency compared to soil application of 150 kg FeSO4/ha. However, both the methods of Fe application were equally effective in maintaining Fe2+ in plants at 35 DAS. The Fe2+ content of > 46 mg kg-1 in plants (on dry-weight basis) appeared to be adequate at 35 DAS for direct - seeded rice. Among the rice cultivars, Pusa Sugandh 3, IR 55419 and IR 55423 performed better under aerobic condition compared to IR 64.

3.2.9 Effect of Tillage, Water and Nutrient Management Practices on Available Micronutrient Status of Soil under Rice-Wheat and Maize-Wheat Cropping Sequences

Status of available micronutrient cations of surface soil (0-15 cm) as influenced by tillage-water-nutrient management practices was monitored after harvest of rice and maize under rice–wheat and maize–wheat cropping sequences, respectively, in the fifth cropping cycle. Results indicated that there was a substantial improvement in available iron (Fe) status in puddled soil (19.4 mg kg-1) compared to that in unpuddled ones (10.6 mg kg-1) after harvest of rice under rice–wheat cropping sequence. Among the water management treatments, continuous submergence and irrigation one day after drainage was equally effective in maintaining available Fe status in soil which was superior to irrigation after 3 days of drainage. Available Mn was depleted as a result of continuous submergence, particularly under unpuddled condition. These results clearly suggested that puddling coupled with intermittent drainage was not only a water-saving option but also an effective management practice in maintaining adequate fertility status of soil in respect of micronutrient cations, particularly Fe and Mn.

Under maize–wheat cropping sequence, bed planting significantly improved the available Zn and Cu status of soil (1.25 mg kg-1) as compared to that in conventional tillage (0.95 mg kg-1). Two and three irrigations were equally effective in maintaining available Zn and Fe status of soil, which were significantly superior to irrigating maize crop once. However, on an average, available Fe (DTPA-Fe) content across the treatments was below the generalized critical limit of deficiency, i.e, 4.5 mg kg-1. This suggests that there is a need for inclusion of Fe in fertilization schedule for maximizing the productivity under maize–wheat cropping sequence. Substitution of 25% of recommended dose of N by sewage sludge marginally increased the Zn, Cu and Fe status of soil.

3.2.10 Influence of Continuous Irrigation with Yamuna Water on Soil Chemical Environment

Soils irrigated with water from Yamuna river in Rainy Well near ITO, Delhi for more than two decades exhibited a significant build-up of total as well as DTPA-extractable Fe, Cu, Pb and Ni contents compared to those irrigated with tube well water. On the other hand in soils of Sarai Kale Khan (near Nizamuddin bridge, Delhi), an increase was observed only in total-Fe, -Zn, -Cd and DTPA- Fe, -Zn, -Pb contents.

Though total Cu did not vary significantly in tube well and Yamuna water irrigated soils of Sarai Kale Khan, there was a significant decrease in the DTPA-Cu. The elevated heavy metals in both total and available pools in Yamuna water irrigated soils resulted in increased metal (Fe, Zn, Cu, Cd, Pb, Ni) concentration in guava fruit in Rainy Well, while Fe, Zn and Pb increased in tomato and Fe and Pb in wheat biomass in Sarai Kale Khan. Although long-term sewage irrigation contaminated the soils with heavy metals, it improved the soil fertility through a significant increase in the available P (35%), available K (28%), and available S (617%) contents in soils of Rainy Well.

Basanti showed the highest yield in the Cd-spiked soil, while Pusa Bold showed the highest content of Cd. In the case of Pb, the cultivars RH 8113, GM 2, PBR 97 of B. juncea, GSL 1 of B. napus and Pusa Gaurav belonging to B. carinata were found to be promising. Among these, the cultivar RH 8113 showed the highest yield as well as contents of Pb. The cultivars belonging to B. juncea, RLM 619, Krishna, Basanti, Kranti and GM 2 were better accumulators of Zn than others.

Among these, Kranti showed the highest yield, while Krishna showed the highest content of Zn. These screened species would be a valuable research material for choosing further efficient cultivars for the purpose of phytoremediation of heavy metal contaminated soils.

3.2.12 Release of Mineral Nitrogen from Sewage Sludge and Rice Straw

Laboratory incubation studies revealed that the soil amended with rice straw recorded the lowest content of mineral N up to 30 days of incubation; the mineral-N content, however, increased over control at 45 and 60 days but remained lowest among the amendments tried. Application of sewage sludge recorded the highest content of mineral inorganic N (NH4 + NO3-N). Sewage sludge and rice straw in a ratio of 1:3 recorded the highest content of mineral N. From this study, it can be concluded that application of these materials in soil requires a minimum of 15-30 days’ time for release of mineral N in sewage sludge alone and mixed with rice straw, and 60 days in rice straw direct incorporation;

otherwise, the crop sown immediately after these treatments may suffer from nitrogen deficiency.

3.2.13 Effect of Enriched Paddy Straw Compost on Nutrition of Cowpea and Soil Health

Five composts were prepared from paddy straw alone and by mixing 2% N, 2% N + 2% P, 2% N + 2% K and 2%

N + 2% P + 2% K with paddy straw. The sources of N, P and K used for enrichment were urea, rock phosphate and mica, respectively. These composts were evaluated for their effect on yield, and nutrient uptake by cowpea cv. Pusa Komal, and soil fertility and biological health. Nitrogen dose of 60 mg N/kg soil was supplied either through compost alone or 75% N through compost + 25% N through urea or 50% N through compost + 50% N through urea under various treatments. Results showed that dry matter yield was significantly higher than that of control in all enriched compost treated pots. Maximum dry matter yield (40.67 g/

pot) was observed in the treatment where N had been applied

Metal contents in different crops irrigated with tube well water and Yamuna water

Soils Metal content in crops (mg kg-1)

Fe Mn Zn Cu Cd Pb Ni

Rainy Well Soil, Guava fruit

Tube well water 343.5 35.5 23.2 21.8 1.77 13.1 22.4 Yamuna water 338.5* 37.8ns 35.8* 25.3* 2.08* 18.5* 26.2*

Sarai Kale Khan Soil, Tomato fruit

Tube well water 28.9 28.9 58.2 31.5 1.02 11.2 14.0 Yamuna water 32.5ns 32.5ns 62.6* 23.0ns 0.88ns 16.6* 12.0ns

Sarai Kale Khan Soil, Wheat biomass

Tube well water 29.3 38.7 28.7 15.1 0.39 5.65 9.5 Yamuna water 86.3* 25.6ns 26.8ns 7.9* 0.40ns 7.75* 8.0ns

ns – not significant, * t test showing significant difference at 5% level

3.2.11 Screening of Brassica Cultivars for their Phyto-extracting Ability

In a net house experiment, 28 cultivars belonging to three Brassica species, namely, Brassica carinata, B. napus and B. juncea were tested for screening efficient phytoextractor for Cd, Pb and Zn. The cultivars Pusa Jaikisan, Pusa Bold, Rohini and Basanti of B. juncea and Pusa Swarnima of B. carinata emerged as promising accumulators of Cd.

in the ratio of 50:50 through NPK-enriched compost and urea. Application of NPK-enriched compost in conjunction with urea N (25% N or 50% N) was associated with significant increase in total N uptake by cowpea over that of control. Application of N through NPK-enriched compost alone or in conjunction with urea (25% and 50% N) gave maximum uptake of P. Similar trend was observed in the K uptake by cowpea. The NPK-enriched compost in conjunction with 50% N through urea recorded maximum uptake of Zn, Cu, Mn and Fe. Application of enriched compost was associated with enhanced availability of major as well as micronutrients in the soil. Enriched compost treated soil samples showed a significant increase in organic C content and microbial biomass C (MBC) over those of control. Maximum increase in organic C (0.63%) and MBC (249 mg/kg) was observed where N had been applied in the ratio 50:50 by the NPK-enriched compost and urea.

Significant increase in the dehydrogenase activity was also observed in the enriched composts. Mineralization of C and N from cowpea decomposition

Above-ground portion of cowpea plant of 30 days (5 g fresh weight, 1.5 g dry weight) and 60 days (5 g fresh weight, 2 g dry weight) was decomposed in 200 g soil. Besides this, rice straw (2%) plus cowpea was kept for comparison. Initially organic C recorded higher values in the amended soil which, however, got stabilized at the end of the experiment. An appreciable increase in microbial biomass carbon (MBC) was found in the cowpea-amended soil followed by soil with cowpea and rice straw treatment.

3.2.14 Effect of Enriched Composts on Pearl Millet

Four enriched composts, viz., (i) ordinary rice straw (RS) compost (100% RS); (ii) enriched compost (100% RS) + rock phosphate (RP @ 4% P) + waste mica (@ 4% K) + phosphorus solubilizing micro-organisms (PSM); (iii) enriched compost (75% RS + 25% mungbean straw, MS) + RP (@ 4% P) + waste mica (@ 4% K) + PSM; and (iv) enriched compost (50% RS + 50% MS) + RP (@ 4% P) + waste mica (@ 4% K) + PSM along with one control and 100% recommended dose of NPK fertilizer (RDF) were evaluated in a field experiment on pearl millet. Application of different enriched composts and inorganic fertilizers recorded significantly higher grain, straw and total biomass yield of pearl millet. The highest grain yield (2.79 t ha-1)

was observed in treatment where 50% RDF was applied through inorganic fertilizers along with application of 5 t ha-1 of enriched compost prepared using 50% rice straw + 50% mungbean straw + RP @ 4% P + mica @ 4% K + PSM. Under this treatment, maximum uptake of N, P and K was observed. Higher yield and nutrient uptake in the soil receiving enriched compost prepared with 50% rice straw + 50% mungbean straw + RP @ 4% P + waste mica @ 4% K + Aspergillus awamori along with 50% recommended dose of fertilizer may be attributed to the overall improvement in the biological, physical and chemical properties of the soil, which favorably influenced the crop growth.

3.2.15 Dynamics of Potassium Release in Soil Fertilized with Microbially Treated Waste Mica and its Uptake by Sudan Grass

Greenhouse experiments were conducted to study the dynamics of K release from waste mica treated with microbial cultures, viz., Bacillus mucilaginosus, Azotobacter chroococcum and Rhizobium spp., and evaluate its effectiveness on yield and uptake by Sudan grass (Sorghum vulgare var Sudanensis) on two Alfisols, one each from Bhubaneswar and Hazaribagh. The crop was harvested five times at one-month interval. Biomass yield was recorded and the K content in Sudan grass was assessed. Soil samples were drawn after each cutting and analyzed for different pools of K. Results revealed that introduction of microbial cultures along with mica recorded higher yield and K uptake by Sudan grass in both the soils compared to those in mica alone. Treatment receiving Bacillus mucilaginosus proved to be effective in increasing the yield, uptake and recovery of K by Sudan grass.

Treatment receiving mica along with Bacillus mucilaginosus also resulted in significantly higher water soluble and exchangeable K but lower amount of non- exchangeable K in both the soils. Alfisol from Hazaribagh recorded higher amounts of water soluble, exchangeable, non-exchangeable and total K than Alfisol from Bhubaneswar. Results on release kinetics of K in Alfisol from Bhubaneswar showed significant release of K from mica treated with microbial culture (Bacillus mucilaginosus). The X-ray diffraction analysis revealed that mica treated with Bacillus mucilaginosus underwent the highest dissolution in both the soils. This bio- intervention of waste mica could be an alternative and viable technology to utilize waste mica as a cheaper source of K fertilizer.