Hema Singh

Effect of residue placement and chemical fertilizer on soil microbial biomass under tropical dryland cultivation

Four treatments (control, chemical fertilizer, wheat straw, and wheat straw+fertilizer) were established on the dryland experimental farm of the Institute of Agricultural Sciences, Banaras Hindu University. Organic in C in the different treatments ranged from 0.69 to 0.93%, total N from 0.08 to 0.11%, and total P from 0.018 to 0.021. The application of straw significantly increased the soil water-holding capacity. The maximum effect on the microbial biomass was realized with the straw+fertilizer treatment, followed by straw and then by the fertilizer treatment. During the study microbial biomass C ranged from 144 to 491 μg g-1 dry soil, biomass N from 14.6 to 50.1 μg g-1, and biomass P from 7.2 to 17.6 μg g-1 soil. Microbial biomass C, N and P represented 3.2–4.6% of total C, 2.6–3.8% of total N, and 5.8–8.2% of total P in the soil, respectively, in all cases the highest proportion occurred in the straw+fertilizer treatment and the lowest in the control. Microbial biomass C, N, and P were positively correlated with each other. Microbial biomass C and N increased by 77% in straw+fertilizer-treated plots relative to the control. The increase in microbial biomass P in the straw+fertilizer treatment over the control was 81%. The increase in the microbial biomass is expected to enhance nutrient availability in the soil, as the microbial biomass acts both as a sink and a source of plant nutrients.

Nitrogen and phosphorus availability and mineralization in dryland reduced tillage cultivation: Effects of residue placement and chemical fertilizer

Abstract Proper residue management may help augment soil fertility in dryland farming systems in the developing countries. We report on the effect of residue placement and chemical fertilizer on available nutrient pools (N and P) and N-mineralization in dryland reduced tillage cultivation. Four treatments (control, fertilizer, straw, and straw + fertilizer) were initiated in June 1990 under dryland farming conditions (rice and lentil rotation) in an attempt to improve nutrient availability and plant growth. Plant available pools (N and P) and N-mineralization rates were measured periodically. Available N ranged from 7.0 to 25.5 μg Ng −1 dry soil, maximum values were found for the fertilizer treated plots (45–66% greater than control) followed in decreasing order by straw + fertilizer, straw and control plots. N-mineralization rate ranged from 2.7 to 24.2 μg g −1 month −1 . The increase in nitrogen mineralization in straw + fertilizer treatment was 97% over the control. The rate of N-mineralization was greatest during the wet period of the year. It increased exponentially with increase in soil moisture content from 5–23%, indicating that the N-mineralization process is moisture limited in these drylands. At similar moisture content, straw + fertilizer treatment resulted in greater rate of N-mineralization compared to the control. Available P ranged from 7.9 to 17.7 μg Pg −1 dry soil. From 26 to 69% increase in available P was found in straw + fertilizer treated plots. Both available P and mineralization rates were maximum in straw + fertilizer treated plots and minimum in control plots. In conclusion, straw + fertilizer application substantially increased available nutrient pools, and also the rate of N-mineralization, particularly in the wet period.

Effect of plant residue and fertilizer on grain yield of dryland rice under reduced tillage cultivation

Use of reduced tillage practices and inputs of organic materials, rather than chemical fertilizers, has been suggested as a method of ‘low input agriculture’ to achieve sustainability in dryland agriculture. This study evaluated the effects of incorporation of plant residue and chemical fertilizer under reduced tillage on biomass and grain yield of dryland (rainfed) rice (Oryza sativa L.). Four treatments were established: (a) a no-input control; (b) chemical fertilizer 80 kg N ha−1, 40 kg P ha−1, and 30 kg K ha−1; (c) air-dried wheat straw (organic C 378 g kg−1, total N 4.8 g kg−1, total P 0.9 g kg−1, C/N ratio 75.5) at 20 Mg ha−1 (the amount of N in straw was equivalent to that applied with chemical fertilizer); (d) wheat straw + fertilizer, straw applied at 10 Mg ha−1 and rate of fertilizer 50% of (b). The soil type at the site is a Inceptisol and, a silt loam, pH 6.7 and water holding capacity 405 g kg−1. Straw and fertilizer treatments were applied about 3 weeks before planting. Inorganic N (nitrate + ammonium-N) concentrations in the control, fertilizer, straw, and straw + fertilizer amended soils were 7.2, 11.6, 8.6 and 11.5 μg g−1, respectively. Available P was greatest in the straw + fertilizer treated plots (16.7 μg g−1) followed by fertilizer (16.0 μg g−1), straw (14.2 μg g−1) and the control (12.0 μg g−1). The rates of N-mineralization in the straw + fertilizer, fertilizer and straw treatments were 16.6, 14.3 and 11.2 μg g−1 month−1, respectively. Microbial biomass C, N and P were 66, 77 and 49% greater, respectively, in the straw + fertilizer treated plots than in the control. Total crop biomass ranged from 6.79–9.91 Mg ha−1 and grain yield ranged from 1.08–1.46 Mg ha−1, both in the order: control < straw < fertilizer < fertilizer + straw. There were strong positive relationships between grain yield and microbial biomass (r= 0.84, P < 0.001), N-mineralization (r=0.85, P < 0.001), and available P (r=0.84, P < 0.001). The combined input of straw and fertilizer could be an ideal practice to improve soil fertility and thereby the productivity of rice under dryland (rainfed) conditions.

Effect of dust load on the leaf attributes of the tree species growing along the roadside.

Dust is considered as one of the most widespread air pollutants. The objective of the study was to analyse the effect of dust load (DL) on the leaf attributes of the four tree species planted along the roadside at a low pollution Banaras Hindu University (BHU) campus and a highly polluted industrial area (Chunar, Mirzapur) of India. The studied leaf attributes were: leaf area, specific leaf area (SLA), relative water content (RWC), leaf nitrogen content (LNC), leaf phosphorus content (LPC), chlorophyll content (Chl), maximum stomatal conductance (Gsmax), maximum photosynthetic rate (Amax) and intrinsic water-use efficiency (WUEi). Results showed significant effect of sites and species for DL and the leaf attributes. Average DL across the four tree species was greater at Chunar, whereas, the average values of leaf attributes were greater at the BHU campus. Maximum DL was observed for Tectona grandis at Chunar site and minimum for Syzygium cumini at BHU campus. Across the two sites, maximum value of SLA, Chl and Gsmax were exhibited by S. cumini, whereas, the greatest value of RWC, LNC, LPC, Amax and WUEi were observed in Anthocephalus cadamba. A. cadamba and S. cumini exhibited 28 and 27 times more dust accumulation, respectively, at the most polluted Chunar site as compared to the BHU campus. They also exhibited less reduction in Amax due to dust deposition as compared to the other two species. Therefore, both these species may be promoted for plantation along the roadside of the sites having greater dust deposition.

On the possibilities of premonitory swarms for three sequences of earthquakes of the Burma—Szechwan region

Abstract Short term spatial and temporal variations in seismicity prior to the three sequences of earthquakes of m b ⩾ 5.8 of the Burma—Szechwan region are studied. Six years (1971–1976) of ISC seismicity data, as reported in the Regional Catalogue of Earthquakes, are considered. During the period, six earthquakes of body wave magnitude m b ⩾ 5.8 occurred in four sequences. Of these, three sequences are preceded by swarm activity in the epicentral regions. Evison (1977b) suggested that the swarm before the sequences of large shocks is a possible long-term precursor. He derived the conclusion by analyzing earthquakes in New Zealand and California. The analysis of the seismicity data for the region under investigation supports Evisons view and suggests that a relation between swarms and sequences of large events exists. The precursory time period (i.e. the time from beginning of the swarm to the main shock) for the Szechwan earthquakes of m b = 5.9 (Feb. 6, 1973) and m b = 5.8 (May 10, 1974) and the Burma earthquake of m b = 6.2 (Aug. 12, 1976) are 305, 317 and 440 days, respectively.

Eco-physiological performance of two invasive weed congeners ( Ageratum conyzoides L. and Ageratum houstonianum Mill.) in the Indo-Gangetic plains of India

Morphological (easily measureable) and physiological (hard to measure) traits of two closely related invasive alien congeners—Ageratum conyzoides L. and Ageratum houstonianum Mill. were studied with a perspective that which species will be potentially be more successful as an invader in the Indo-Gangetic plains of India. Leaf construction cost (LCC) is considered as a quantifiable measure of energy demand for biomass production and is related to energy use efficiency as it include component of both morphological and physiological traits. We hypothesised that a low LCC would give the invaders growth advantage by utilizing energy efficiently. Low LCC of A. houstonianum on mass basis (0.54xa0g glucose gu2009−u20091) and area basis (20.48xa0gxa0mu2009−u20092) gives insight into the success of this invasive weed over A. conyzoides. The present study gives evidence that how the morphological traits are linked to physiological traits that could directly affect invasive attributes of the invader, which in turn would be crucial to prioritize species for ecosystem management.

Effect of environmental conditions on decomposition in eight woody species of a dry tropical forest

Litter decay is a significant part of carbon budget. Due to strong environmental control, the changes in the environment may drastically influence the litter decay rates. Litter decomposition of eight dry tropical woody species, viz. Shorea robusta, Buchanania lanzan, Diospyros melanoxylon, Lagerstroemia parviflora, Lannea coromandelica, Terminalia tomentosa, Holarrhena antidysenterica and Lantana camara was studied to document the effect of intra-annual changes in the environment. Litter decomposition was monitored at monthly intervals at five sites using litter bag technique over an annual cycle in a dry tropical deciduous forest of Vindhyan highland, India. Weight loss differed among species and through months, and ranged from 15.38% in L. camara at Kotwa site in January to 30.72% in T. tomentosa at Hathinala site in August. Peak weight loss occurred in August and averaged 46.2% across species and sites. Nitrogen and phosphorus mineralization rates also varied significantly from species to species. T. tomentosa having higher nitrogen content and lower C/N ratio than other species exhibited faster weight loss. Nitrogen and phosphorus contents of litter showed significant positive correlation with weight loss. C/N ratio was negatively related to decay constant, and the weight loss was positively related to the soil surface temperature as well as soil moisture content.

Soil Carbon Dynamics Under Changing Climate—A Research Transition from Absolute to Relative Roles of Inorganic Nitrogen Pools and Associated Microbial Processes: A Review

Abstract It is globally accepted that soil carbon (C) dynamics are at the core of interlinked environmental problems, deteriorating soil quality and changing climate. Its management remains a complex enigma for the scientific community due to its intricate relationship with soil nitrogen (N) availability and moisture-temperature interactions. This article reviews the management aspects of soil C dynamics in light of recent advances, particularly in relation to the availability of inorganic N pools and associated microbial processes under changing climate. Globally, drastic alterations in soil C dynamics under changing land use and management practices have been primarily attributed to the variation in soil N availability, resulting in a higher decomposition rate and a considerable decline in soil organic C (SOC) levels due to increased soil CO2 emissions, degraded soil quality, and increased atmospheric CO2 concentrations, leading to climate warming. Predicted climate warming is proposed to enhance SOC decomposition, which may further increase soil N availability, leading to higher soil CO2 efflux. However, a literature survey revealed that soil may also act as a potential C sink, if we could manage soil inorganic N pools and link microbial processes properly. Studies also indicated that the relative, rather than the absolute, availability of inorganic N pools might be of key importance under changing climate, as these N pools are variably affected by moisture-temperature interactions, and they have variable impacts on SOC turnover. Therefore, multi-factorial studies are required to understand how the relative availability of inorganic N pools and associated microbial processes may determine SOC dynamics for improved soil C management.

A new insight into the warming potential of organically amended agro-ecosystems

Organic fertilization enhances the global warming potential of the soil, which is primarily attributed to higher CO2 emission from the soil. However, long-term studies under organic fertilization to observe its impact on soil’s warming potential with respect to CO2 efflux are limited in the dry tropical ecosystem. Therefore, we observed the changes in soil organic matter (C, N), soil CO2 efflux (SCE), soil moisture, microbial biomass C, and dehydrogenase activity in the plots under 1, 3, 5, and 10xa0years of organic fertilization, designated as OM1, OM3, OM5, and OM10, respectively. Also, a nearby native forest was taken as a standard reference system (NF) in the present study for comparative purpose. We observed that organic fertilization significantly (Pxa0≤xa00.05) increased soil organic carbon (SOC), soil organic nitrogen (SON), SCE, moisture, microbial biomass C, and dehydrogenase activity, whereas decreased the SOC/SON ratio after 10xa0years, which also approached closer to NF. However, only the plots under 10xa0years of organic fertilization showed SCE significantly (Pxa0≤xa00.05) similar to NF. It indicates that long-term organic fertilization is required for the improvement in soil properties. SCE showed a significantly (Pxa0≤xa00.05) higher value (on average, by 61%) in OM10 site as compared to OM1. However, SCE on unit C basis (SCER) showed no change (Pxa0>xa00.05). This increase in SCE after 10xa0years of organic fertilization might be attributed to the significant (Pxa0≤xa00.05) increase in SOC, soil moisture, microbial biomass C, and dehydrogenase activity. However, no change in SCER after 10xa0years shows that organic fertilization has possibly been misinterpreted with respect to their impact on soil’s global warming potential. It might be attributed to the C protective nature of the organic fertilization. Overall, our results contradict with the often publicized higher warming potential of the organically amended systems. This indicates that organic fertilization does not increase the soil’s global warming potential, which is often misrepresented because SCE is not observed with respect to the existing SOC content.

Contrasting leaf phenology of woody species of dry tropical forest

We studied selected leaf traits [leaf area (LA), leaf water content (LWC), leaf fresh weight (LFW), leaf dry weight (LDW), specific leaf area (SLA) and chlorophyll content] of eight woody species (Shorea robusta, Buchanania lanzan, Diospyros melanoxylon, Lagerstroemia parviflora, Lannea coromandelica, Terminalia tomentosa, Holarrhena antidysenterica and Lantana camara) dominant at four sites in a dry tropical deciduous forest over complete two annual cycles (2008–2010). Our results showed that leaf traits varied across species (1.7–11.5 fold), months (1.2–1.5 fold) and sites (1.1–1.3 fold). However, leaf traits showed smaller variation between sites than between species. Leaf lifespan varied from 7 months (L. coromandelica) to 12 months (S. robusta). On the same sites, species differed in the length of deciduous period. The maximum LA, LDW, LFW and LWC were recorded for the semi-evergreen species, SLA for long-deciduous species and chlorophyll content for short-deciduous species, respectively. The coefficient of variation was maximum for LDW and minimum for chlorophyll content. Among the eight woody species, T. tomentosa exhibited the greatest LA, LDW, LFW and LWC. LA, LWC, LFW, LDW, SLA, LD, SD, MD & SE confirm.