Bioavailability of selenium to forage crops in a sandy loam soil amended with Se-rich plant materials

Greenhouse experiments were conducted to study the bioavailability of selenium (Se) to sorghum (Sorghum bicolor L.), maize (Zea mays L.) and berseem (Trifolium alexandrinum L.) fodders in a sandy loam soil amended with different levels of Se-rich wheat (Triticum aestivum L.) and raya (Brassica juncea L. Czern) straw containing 53.3 and 136.7microg Seg(-1), respectively. Each of the fodder crops was grown after incorporation of Se-rich materials either individually or in a sequence - sorghum-maize-berseem by incorporating Se-rich straws only to the first crop. Application of Se-rich straws to each crop, even at the greatest rate of 1%, did not have any detrimental effect on dry matter yield of different crops. With increase in the level of wheat straw from 0% to 1%, Se content in sorghum and maize plants increased to greatest level of 1.3 and 1.5microg g(-1), respectively, at 0.3% of applied straw and thereafter it decreased consistently. In case of raya straw, the greatest Se content in sorghum (2.3microg g(-1)) and maize (3.0microg g(-1)) was recorded at 0.3% and 0.4% of the applied straw, respectively. Unlike sorghum and maize fodders, Se content in all the four cuts of berseem continued to increase with increase in the level of applied straws and for different cuts of berseem it varied from 1.6 to 2.3 and 3.4 to 4.3microg g(-1) in case of wheat and raya straw, respectively. Similar variations in Se content of different fodder crops were recorded when these were grown in the sequence - sorghum-maize-berseem; but Se content was 2-4 times lower than when each crop was grown with fresh application of Se-rich straw. None of the fodders absorbed Se in levels toxic for animal consumption (>5microg g(-1)) even at the greatest level of applied straw. Of the total Se added through Se-rich straws, utilization of Se was not more than 2% in case of sorghum and maize crops and up to 5% in case of berseem. At the time of sowing of sorghum, hot water soluble Se (HWS-Se) in soils treated with different levels of Se-rich wheat and raya straw, respectively, varied from 18 to 36 and 18 to 79microg kg(-1). Whereas in case of berseem, it varied from 33 to 101 and 33 to 154microg kg(-1), respectively. HWS-Se present at the sowing time of berseem was significantly correlated with Se content of all the four cuts in the soil treated with Se-rich straws; the coefficients of correlation 'r' varied between 0.79 (p0.05) and 0.99 (p0.001). Selenium-rich materials supplied significant amounts of S, P and micronutrients to the growing fodder crops. These investigations suggest that Se-rich raya and wheat straw may be disposed off safely in soils used for growing fodders.     

Chemical methods and phytoremediation of soil contaminated with heavy metals

The effects of chemical amendments (calcium carbonate (CC), steel sludge (SS) and furnace slag (FS)) on the growth and uptake of cadmium (Cd) by wetland rice, Chinese cabbage and wheat grown in a red soil contaminated with Cd were investigated using a pot experiment. The phytoremediation of heavy metal contaminated soil with vetiver grass was also studied in a field plot experiment. Results showed that treatments with CC, SS and FS decreased Cd uptake by wetland rice, Chinese cabbage and wheat by 23-95% compared with the unamended control. Among the three amendments, FS was the most efficient at suppressing Cd uptake by the plants, probably due to its higher content of available silicon (Si). The concentrations of zinc (Zn), lead (Pb) and Cd in the shoots of vetiver grass were 42-67%, 500-1200% and 120-260% higher in contaminated plots than in control, respectively. Cadmium accumulation by vetiver shoots was 218 g Cd/ha at a soil Cd concentration of 0.33 mg Cd/kg. It is suggested that heavy metal-contaminated soil could be remediated with a combination of chemical treatments and plants.     

Terbuthylazine persistence in an organic amended soil

The aim of this work was to study the effect of the application of a solid waste from olive oil production (alperujo) on the movement and persistence of the herbicide terbuthylazine (N2-tert-butyl-6-chloro-N4-ethyl-1,3,5-triazine-2,4-diamine). An experimental olive grove was divided in two plots: (i) Plot without organic amendment (blank) and (ii) Plot treated with alperujo during 3 years at a rate of 17920 kg of alperujo ha(- 1). Terbuthylazine was applied to both plots at a rate of 2 kg ha(- 1) a.i. Triplicates from each plot were sampled at 3 depths (0-10, 10-20 and 20-30 cm), air-dried, remains of olive leaves, grass roots, and stones removed and sieved through a 5 mm mesh sieve. Terbuthylazine was extracted with methanol 1:2 weight:volume ratio, the extracts were evaporated to dryness, resuspended in 2 mL of methanol, filtered and anylized by high performance liquid chromatography (HPLC). Higher amounts of terbuthylazine were detected at each sampling depth in plots treated with alperujo. The increase in soil organic matter content upon amendment with alperujo slightly increased sorption, suggesting that other factors beside sorption affect terbuthylazine degradation rate in organic amended soils.     

Weed interference on maize (Zea mays) under no tillage system

A field trial was carried out in Brazil in March 2002 with the aim to evaluate the effects of different timing and extension of weedy period on maize productivity. The hybrid Pioneer 30K75 was sowed under 7 t ha(-1) mulching promoted by glyphosate spraying. The treatments were divided in two groups: In the first group, weeds were maintained since the maize sowing until different periods in the crop cycle: 0, 14, 28, 42, 56, 70, and 150 days (harvesting time). In the second group, the maize crop was kept weed free for the same periods of the first group. Weed control was done through hand hoeing. A complete randomized blocks experimental design with five replications was used for plots distribution in the field. Nonlinear regression model was used to study the effects of weedy or weedfree periods on maize productivity. Weed community included 13 families and 31 species. Asteraceae, Poaceae, and Euphorbiaceae were the most abundant families. Results showed that under no tillage condition with 7 t ha(-1) mulching at sowing time, the maize crop could cohabit with weed community for 54 days without any yield lost. On the other hand, if the crop was kept weed free for 27 days, the weed interference was not enable to reduce maize production. According to these results one weed control measure between 27 and 54 days after crop emergence could be enough to avoid any reduction in maize productivity.     

Heavy metal mobility in runoff water and absorption by eggplant fruits from sludge treated soil

Sewage sludge addition to agricultural lands requires judicious management to avoid environmental risks arising from heavy metal and nitrate contamination of surface water and accumulation in edible plants. A field study was conducted on a silty-loam soil of 10% slope at Kentucky State University Research Farm. Eighteen plots of 22 x 3.7 m each were separated using metal borders and the soil in six plots was mixed with sewage sludge and yard waste compost mix (SS-YW) at 15 t acre(-1), six plots were mixed with sewage sludge (SS) at 15 t acre(-1), and six unamended plots that never received sludge were used for comparison purposes. Plots were planted with eggplant, Solanum melongena L. as the test plant. The objectives of this investigation were to: 1) assess the effect of soil amendments on the transport of NO3, NH4, and heavy metals (Cd, Cr, Ni, Pb, Zn, Cu, and Mo) into surface water; 2) investigate the effect of soil amendments on heavy metal bioavailability in eggplant fruits at harvest; and 3) assess chemical and physical properties of soil following addition of soil amendments and their impact on the yield and quality of eggplant fruit. SS-YW treatments reduced runoff water by 63% while plots incorporated with sewage sludge alone reduced runoff water by 37% compared to control treatment. The SS-YW treatments transported more mineral nitrogen (NO3-N and NH4-N) in runoff water than SS treatments. Total marketable yield (lbs acre(-1)) and number of eggplant fruits were greatest in SS-YW treatments. This response may be due to improved soil porosity, water, and nutrient retention of the soil amended with SS-YW mixture. Concentrations of heavy metals in soil amended with sludge were below the U.S. Environmental Protection Agency (USEPA) limits. Chromium, Ni, Zn, and Cu were taken up by eggplant fruits but their concentrations were below the Codex Commission allowable levels.     

Residue determination and dissipation of ioxynil octanoate in maize and soil

A simple and efficient residue analysis method for direct determination of ioxynil octanoate in maize and soil was developed and validated with High Performance Liquid Chromatography-Ultra Violet (HPLC-UV). The samples were extracted with mixtures of acetonitrile and deionized water followed by Solid Phase Extraction (SPE) to remove co-extractives prior to analysis by HPLC-UV. The recoveries of ioxynil octanoate extracted from maize and soil samples ranged from 86 %-104 % and 84 %-96 %, respectively, with relative standard deviation (RSD) less than 7.84% and sensitivity of 0.01 mg kg(-1). The method was applied to determine the residue of ioxynil octanoate in maize and soil samples from experimental field. Data had shown that the dissipation rate in soil was described as pseudo-first-order kinetics and the half-life (t(1/2)) was less than 1.78 days. No ioxynil octanoate residue (<0.01 mg kg(-1)) was detected in maize at harvest time withholding period of 60 days after treatments of the pesticide. Direct confirmation of the analytes in field trial samples was realized by Liquid Chromatography-Mass Spectrometry (LC-MS).     

Weed Interference on Maize (Zea mays) Under No Tillage System

Abstract

A field trial was carried out in Brazil in March 2002 with the aim to evaluate the effects of different timing and extension of weedy period on maize productivity. The hybrid Pioneer 30K75 was sowed under 7 t ha^?1 mulching promoted by glyphosate spraying. The treatments were divided in two groups: In the first group, weeds were maintained since the maize sowing until different periods in the crop cycle: 0, 14, 28, 42, 56, 70, and 150 days (harvesting time). In the second group, the maize crop was kept weed free for the same periods of the first group. Weed control was done through hand hoeing. A complete randomized blocks experimental design with five replications was used for plots distribution in the field. Nonlinear regression model was used to study the effects of weedy or weedfree periods on maize productivity. Weed community included 13 families and 31 species. Asteraceae, Poaceae, and Euphorbiaceae were the most abundant families. Results showed that under no tillage condition with 7 t ha^?1 mulching at sowing time, the maize crop could cohabit with weed community for 54 days without any yield lost. On the other hand, if the crop was kept weed free for 27 days, the weed interference was not enable to reduce maize production. According to these results one weed control measure between 27 and 54 days after crop emergence could be enough to avoid any reduction in maize productivity.     

L-asparaginase and L-glutaminase activities in submerged rice soil amended with municipal solid waste compost and decomposed cow manure

The field study was conducted to evaluate the effect of municipal solid waste compost (MSWC) as a soil amendment on L-asparaginase (LA) and L-glutaminase (LG) activities. Experiments were conducted during the wet seasons of 1997, 1998 and 1999 on rice grown under a submerged condition, at the Agriculture Experimental Farm, Calcutta University at Baruipur, West Bengal, India. The treatments consisted of control, no input; MSWC, at 60 Kg N ha(- 1); well-decomposed cow manure (DCM), at 60 Kg N ha(- 1); MSWC (30 Kg N ha(- 1)) + Urea (U) (30 Kg N ha(- 1)); DCM (30 Kg N ha(- 1)) + U (30 Kg N ha(- 1)) and Fertilizer, (at 60:30:30 NPK kg ha(- 1)) through urea, single superphosphate and muriate of potash respectively). LA and LG activities alone and their ratio with organic-C (ratio index value, RIV), straw and grain yield were higher in DCM than MSWC-treated soils, due to higher amount of biogenic organic materials like water-soluble organic carbon, carbohydrate and mineralizable nitrogen in the former. The studied parameters were higher when urea was integrated with DCM or MSWC, compared to their single applications. The heavy metals in MSWC did not detrimentally influence the above-measured activities of soil. In the event of long term MSWC application, changes in soil quality parameters should be monitored regularly, since heavy metals once entering into soil persist over a long period.     

Effect of organic amendment on degradation and formation of bound residues of methabenzthiazuron in soil under constant climatic conditions

Abstract

The degradation of [phenyl‐U‐¹⁴C]methabenzthiazuron (MBT) and formation of bound residues in the surface soil of an orthic luvisol were studied under constant climatic conditions (20°C, 40 % of maximum water holding capacity). In two treatments (with and without preincubation in the soil) maize straw was amended at a rate of 1.5 g/100 g dry soil in addition to the application of MBT. The mineralization of uniformly labeled maize straw was studied simultaneously. In additional flasks, MBT was incubated at 0, 10 and 30°C with and without addition of maize straw.

The turnover of the amended maize straw led to an enhanced dissipation of MBT which was mainly due to the formation of bound residues. This corresponded to a higher microbial activity in the soil after straw amendment and the intensive mineralization of the radiolabeled maize straw. About 2–3 % of the applied radioactivity from the radiolabeled maize straw was measured in the soil microbial biomass 10 and 40 days after application whereas ¹⁴C from MBT was only incorporated into soil microbial biomass in the treatments with straw amendment.

Within the bound residue fractions relatively more radioactivity was measured in fulvic and humic acids after straw amendment. Increasing temperatures promoted the dissipation of MBT and the formation of bound residues in both treatments, but without amendment of maize straw these effects were far less pronounced. The laboratory scale degradation experiment led to similar results as were found in a corresponding lysimeter study. Differences that were observed could be explained by different temperature regimes of the experiments and time of aging in soil.     

Impact of biochar application to a Mediterranean wheat crop on soil microbial activity and greenhouse gas fluxes

Biochar has been recently proposed as a management strategy to improve crop productivity and global warming mitigation. However, the effect of such approach on soil greenhouse gas fluxes is highly uncertain and few data from field experiments are available. In a field trial, cultivated with wheat, biochar was added to the soil (3 or 6 kg m⁻²) in two growing seasons (2008/2009 and 2009/2010) so to monitor the effect of treatments on microbial parameters 3 months and 14 months after char addition. N₂O, CH₄ and CO₂ fluxes were measured in the field during the first year after char addition. Biochar incorporation into the soil increased soil pH (from 5.2 to 6.7) and the rates of net N mineralization, soil microbial respiration and denitrification activity in the first 3 months, but after 14 months treated and control plots did not differ significantly. No changes in total microbial biomass and net nitrification rate were observed. In char treated plots, soil N₂O fluxes were from 26% to 79% lower than N₂O fluxes in control plots, excluding four sampling dates after the last fertilization with urea, when N₂O emissions were higher in char treated plots. However, due to the high spatial variability, the observed differences were rarely significant. No significant differences of CH₄ fluxes and field soil respiration were observed among different treatments, with just few exceptions. Overall the char treatments showed a minimal impact on microbial parameters and GHG fluxes over the first 14 months after biochar incorporation.     

Effects of municipal solid waste compost and mineral fertilizer amendments on soil properties and heavy metals distribution in maize plants (Zea mays L.)

Soil amendments based on crop nutrient requirements are considered a beneficial management practice. A greenhouse experiment with maize seeds (Zea mays L.) was conducted to assess the inputs of metals to agricultural land from soil amendments. Maize seeds were exposed to a municipal solid waste (MSW) compost (50 Mg ha⁻¹) and NPK fertilizer (33 g plant⁻¹) amendments considering N plant requirement until the harvesting stage with the following objectives: (1) determine the accumulation of total and available metals in soil and (2) know the uptake and ability of translocation of metals from roots to different plant parts, and their effect on biomass production. The results showed that MSW compost increased Cu, Pb and Zn in soil, while NPK fertilizer increased Cd and Ni, but decreased Hg concentration in soil. The root system acted as a barrier for Cr, Ni, Pb and Hg, so metal uptake and translocation were lower in aerial plant parts. Biomass production was significantly enhanced in both MSW and NPK fertilizer-amended soils (17%), but also provoked slight increases of metals and their bioavailability in soil. The highest metal concentrations were observed in roots, but there were no significant differences between plants growing in amended soil and the control soil. Important differences were found for aerial plant parts as regards metal accumulation, whereas metal levels in grains were negligible in all the treatments.     

Influence of seedling roots, environmental factors and soil characteristics on soil CO2 efflux rates in a 2-year-old loblolly pine (Pinus taeda L.) plantation in the Virginia Piedmont

To understand the role of managed forests in carbon sequestration an understanding of factors controlling soil CO2 efflux will be necessary. This study examined the influence of seedling roots, environmental factors, nutrient availability, and soil characteristics on soil CO2 efflux patterns in a 2-year-old pine plantation in the Virginia Piedmont. Efflux rates were measured both near the base of seedlings and midway between rows in plots that had received fertilization and mulch treatments in a factorial combination. Soil CO2 efflux rates were consistently higher near the base of seedlings, fertilization increased seedling growth with no significant effect on rates. and mulching increased winter efflux rates. In a regression analysis of seasonal soil CO2 efflux, soil temperature explained 42.2% of the variance followed by the interaction of soil temperature and moisture and of soil temperature and plot position, which together explained an additional 9.8% of the observed variance in seasonal rates. During March 2000 measurements, the spatial pattern of soil CO2 efflux between plots was most influenced by differences in soil nitrogen and pine root biomass. Furthermore, spatial differences observed in mean annual efflux rates were found to be highly influenced by the amount of soil coarse fragments in the upper soil profile.     

Terbuthylazine persistence in an organic amended soil

The aim of this work was to study the effect of the application of a solid waste from olive oil production (alperujo) on the movement and persistence of the herbicide terbuthylazine (N²-tert-butyl-6-chloro-N⁴-ethyl-1,3,5-triazine-2,4-diamine). An experimental olive grove was divided in two plots: (i) Plot without organic amendment (blank) and (ii) Plot treated with alperujo during 3 years at a rate of 17920 kg of alperujo ha^{? 1}. Terbuthylazine was applied to both plots at a rate of 2 kg ha^{? 1} a.i. Triplicates from each plot were sampled at 3 depths (0–10, 10–20 and 20–30 cm), air-dried, remains of olive leaves, grass roots, and stones removed and sieved through a 5 mm mesh sieve. Terbuthylazine was extracted with methanol 1:2 weight:volume ratio, the extracts were evaporated to dryness, resuspended in 2 mL of methanol, filtered and anylized by high performance liquid chromatography (HPLC). Higher amounts of terbuthylazine were detected at each sampling depth in plots treated with alperujo. The increase in soil organic matter content upon amendment with alperujo slightly increased sorption, suggesting that other factors beside sorption affect terbuthylazine degradation rate in organic amended soils.     

Environmental and potential health effects of growing leafy vegetables on soil irrigated using sewage sludge and effluent: a case of Zn and Cu

The use of sewage sludge and effluent as a source of nutrients and water for crop production is increasing worldwide. A study was conducted in 2001 at Pension farm (near Harare) to determine the effect of long term (>30 yrs) application of sewage sludge and effluent on Zn and Cu accumulation in top soil, uptake of these metals by lettuce (Lactuca sativa L.) and mustard rape (Brassica juncea L.), and dry matter yield. Application of sewage sludge/effluent significantly (p<0.001) increased total Zn (13.7-1563.9 mg kg(-1)) and Cu (2.5-133.3 mg kg(-1)) in the top soil (0-20 cm depth) compared to the control. Sewage sludge/effluent addition significantly (p<0.001) increased Zn uptake by both test crops, while Cu uptake was significant in the first crop of lettuce and the second crop of mustard rape. Based on the dietary patterns of poor urban households in Zimbabwe, the maximum possible intake of Cu will only constitute 40% the Maximum Daily Intake (MDI). The toxicological implications for Zn will however be more severe, exceeding the MDI by 77% through exposure by lettuce consumption and by 251% consumption of mustard rape. It was concluded that long-term addition of sewage sludge/effluent to soil at Pension farm had increased the concentration of Zn and Cu in top soil to levels that pose environmental concern. The consumption of leafy vegetables produced on these soils pose a health risk to poor communities that reside around the study site, especially children, through possible Zn toxicity.     

The interactions between plant growth,vegetation structure and soil processes in semi-natural acidic and calcareous grasslands receiving long-term inputs of simulated pollutant nitrogen deposition

Regular applications of ammonium nitrate (35-140 kg N ha(-1) year(-1)) and ammonium sulphate (140 kg N ha(-1) year(-1)) to areas of acidic and calcareous grassland in the Derbyshire Peak District over a period of 6 years, have resulted in significant losses in both overall plant cover, and the abundance of individual species, associated with clear and dose-related increases in shoot nitrogen content. No overall growth response to nitrogen treatment was seen at any stage in the experiment. Phosphorus additions to the calcareous plots did however lead to significant increases in plant cover and total biomass, indicative of phosphorus limitation in this system. Clear and dose-related increases in soil nitrogen mineralization rates were also obtained, consistent with marked effects of the nitrogen additions on soil processes. High nitrification rates were seen on the calcareous plots, and this process was associated with significant acidification of the 140 kg N ha(-1) year(-1) treatments.     

Potential of conservation agriculture modules for energy conservation and sustainability of rice-based production systems of Indo-Gangetic Plain region

Rice-based cropping systems are the most energy-intensive production systems in South Asia. Sustainability of the rice-based cropping systems is nowadays questioned with declining natural resource base, soil degradation, environmental pollution, and declining factor productivity. As a consequence, the search for energy and resource conservation agro-techniques is increasing for sustainable and cleaner production. Conservation agriculture (CA) practices have been recommended for resource conservation, soil health restoration and sustaining crop productivity. The present study aimed to assess the different CA modules in rice-based cropping systems for energy conservation, energy productivity, and to define energy-economic relations. A field experiment consisted of four different tillage-based crop establishment practices (puddled-transplanted rice followed by (fb) conventional-till maize/wheat (CTTPR-CT), non-puddled transplanted rice fb zero-till maize/wheat (NPTPR-ZT), zero-till transplanted rice fb zero-till maize/wheat (ZTTPR-ZT), zero-till direct-seeded rice fb zero-till maize/wheat (ZTDSR-ZT)), with two residue management treatments (residue removal, residue retention) in rice–wheat and rice–maize rotations were evaluated for energy budgeting and energy-economic relations. Conservation-tillage treatments (NPTPR-ZT, ZTTPR-ZT, and ZTDSR-ZT) reduced the energy requirements over conventional tillage treatments, with the greater reduction in ZTTPR-ZT and ZTDSR-ZT treatments. Savings of energy in conservation-tillage treatments were attributed to reduced energy use in land preparation (69–100%) and irrigation (23–27%), which consumed a large amount of fuel energy. Conservation-tillage treatments increased grain and straw/stover yields of crops, eventually increased the output energy (6–16%), net energy (14–26%), energy ratio (25–33%), and energy productivity (23–34%) as compared with CTTPR-CT. For these energy parameters, the treatment order was ZTDSR-ZT ≥ ZTTPR-ZT > NPTPR-ZT > CTTPR-CT (p < 0.05). Crop residue retention reduced net energy, energy ratio, and energy productivity when compared with residue removal. Our results of energy-economic relations favored the “conservative hypothesis,” which envisages that energy and monetary investments are not essentially the determinants of crop productivity. Thus, zero tillage-based crop establishments (ZTTPR-ZT, ZTDSR-ZT) in rice-based production systems could be the sustainable alternative to conventional tillage-based agriculture (CTTPR-CT) as they conserved non-renewable energy sources, reduced water requirement, and increased crop productivity.

     

Effect of buffer strips and soil texture on runoff losses of flufenacet and isoxaflutole from maize fields

The influence of buffer strips and soil texture on runoff of flufenacet and isoxaflutole was studied for two years in Northern Italy. The efficacy of buffer strips was evaluated on six plots characterized by different soil textures; two plots had Riva soil (18.6% sand, 63.1% silt, 18.3% clay) while the remaining four plots had Tetto Frati (TF) soil (37.1% sand, 57% silt, 5.9% clay). Additionally, the width of the buffer strips, constituted of spontaneous vegetation grown after crop sowing, was also compared for their ability to abate runoff waters. Chemical residues in water following runoff events were investigated, as well as their dissipation in the soil. After the first runoff events, concentrations of herbicides in water samples collected from Riva plots were as much as four times lower in waters from TF plots. On average of two growing seasons, the field half-life of flufenacet in the upper soil layer (5 cm) ranged between 8.1 and 12.8 days in Riva soil, 8.5 and 9.3 days in TF soil. Isoxaflutole field half-life was less than 1 day. The buffer strip was very affective by the uniformity of the vegetative cover, particularly, at the beginning of the season. In TF plots, concentration differences were generally due to the presence or absence of the buffer strip, regardless of its width.     

Using thermal units for estimating critical period of weed competition in off-season maize crop

Brazilian off-season maize production is characterized by low yield due to several factors, such as climate variability and inadequate management practices, specifically weed management. Thus, the goal of this study was to determinate the critical period of weed competition in off-season maize (Zea mays L.) crop using thermal units or growing degree days (GDD) approach to characterize crop growth and development. The study was carried out in experimental area of the University of S?o Paulo, Brazil, with weed control (C), as well as seven coexistence periods, 2, 4, 6, 8, and 12 leaves, flowering, and all crop cycle; fourteen treatments were done. Climate data were obtained from a weather station located close to the experimental area. To determine the critical period for weed control (CPWC) logistic models were fitted to yield data obtained in both W and C, as a function of GDD. For an arbitrary maximum yield loss fixed in 2.5%, the CPWC was found between 301 and 484 GDD (7-8 leaves). Also, when the arbitrary loss yield was fixed in 5 and 10%, the period before interference (PBI) was higher than the critical weed-free period (CWFP), suggesting that the weeds control can be done with only one application, between 144 and 410 GDD and 131 and 444 GDD (3-8 leaves), respectively. The GDD approach to characterize crop growth and development was successfully used to determine the critical period of weeds control in maize sown off-season. Further works will be necessary to better characterize the interaction and complexity of maize sown off-season with weeds. However, these results are encouraging because the possibility of the results to be extrapolated and because the potential of the method on providing important results to researchers, specifically crop modelers.     

Microbial biomass and enzyme activities in submerged rice soil amended with municipal solid waste compost and decomposed cow manure

We studied the suitability of municipal solid waste compost (MSWC) application to submerged rice paddies in the perspective of metal pollution hazards associated with such materials. Experiments were conducted during the wet seasons of 1997, 1998 and 1999 on rice grown under submerged condition, at the Agriculture Experimental Farm, Calcutta University at Baruipur, West Bengal, India. The treatments consisted of control, no input; MSWC, at 60 kgNha(-1); well decomposed cow manure (DCM), at 60 kgNha(-1); MSWC (30 kgNha(-1)) +Urea (30 kgNha(-1)); DCM (30 kgNha(-1)) +U (30 kgNha(-1)) and Fertilizer, (at 60:30:30 NPK kgha(-1) through urea, single superphosphate and muriate of potash respectively). Soil microbial biomass-C (MBC), MBC as percentage of organic-C (ratio index value, RIV), urease and acid phosphatase activities were higher in DCM than MSWC-treated soils, due to higher amount of biogenic organic materials like water soluble organic carbon, carbohydrate and mineralizable nitrogen in the former. The studied parameters were higher when urea was integrated with DCM or MSWC, compared to their single applications. Soil MBC, urease and acid phosphatase activities periodically declined up to 60 day after transplanting (DAT) and then increased after crop harvest. The heavy metals in MSWC did not detrimentally influence MBC, urease and acid phosphatase activities of soil. In the event of long term MSWC application, changes in soil quality parameters should be monitored regularly, since heavy metals once entering into soil persist over a long period.