Effect of rice variety on methane emission from an Indonesian paddy field

Variations in CH₄ emission from a Sumatra paddy field in which 8 popular modern varieties in Indonesia were grown were compared in the 1994/1995 rainy season. Total amounts of CH₄ emitted during the period of rice growth were in the ranges of 32.6-41.7 and 51.3–64.6 g CH₄ m^-2 for the plots amended with chemical fertilizer only and those amended with both rice straw and chemical fertilizer, respectively. The mean CH₄ emission rate was highest in the plot with the variety Bengawan solo and lowest in the plots with the varieties Atomita-4 and Way seputih among the plots which received chemical fertilizer, while highest in the plot with Way seputih and lowest in the plot with Bengawan solo among the plots amended with both rice straw and chemical fertilizer. The increase in the mean CH₄ emission rates by rice straw application was higher for the plots planted with Way seputih (1.98 times) and Atomita-4 (1.77 times) than for the plots with Bengawan solo (1.23 times) and IR-64 (1.35 times). The plots with Walanai and Cisanggarung recorded intermediate mean emission rates and the increase in CH₄ emission by rice straw application was also intermediate (1.57–1.64 times). It was noteworthy that Way seputih and Atomita-4 were derived from the variety Cisadane, Bengawan solo and IR-64 from the variety IR-54, and Walanai and Cisanggarung from the varieties IR-36 and Pelita 1-1, respectively.

The amounts of CH. emitted for 1 kg grain production ranged from 53 (Atomita-4) to 74 (Kapuas and Walanai) and from 89-93 (IR-64, Bengawan solo, and Atomita-4) to 121 (Kapuas) g CH₄ kg^-1 of grain for the plots amended with chemical fertilizer and those amended with rice straw and chemical fertilizer, respectively.     

Dissolved organic nitrogen and carbon in pastoral soils: the New Zealand experience

Dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) in soils are increasingly recognized as important components of nutrient cycling and biological processes in soil‐plant ecosystems. The aims of this study were to: (i) quantify the pools of DON and DOC in a range of New Zealand pastoral soils; (ii) compare the effects of land use changes on these pools; and (iii) examine the seasonal variability associated with these two components of dissolved organic matter. Soil samples (0–7.5 cm depth) from 93 pastoral sites located in Northland, Waikato, Bay of Plenty and Otago/Southland, New Zealand, were collected in autumn. Adjacent sites under long‐term arable cropping or native vegetation and forestry land use were also sampled at the same time to estimate the impacts of different land use on DON and DOC in these soils. Twelve dairy and 12 sheep and or beef pastures were sampled in winter, spring, summer and autumn for a 2‐year period to study the seasonal fluctuations of DON and DOC. A field incubation study was also carried out in a grazed pasture to examine fluctuations in the concentrations of and and DON levels in soil. Other soil biological properties, such as microbial biomass‐C, biomass‐N and mineralizable N, were also measured. Pastoral soils contained the greatest amounts of DON (13–93 mg N kg⁻¹ soil, equivalent to 8–55 kg N ha⁻¹) and DOC (73–718 mg C kg⁻¹ soil, equivalent to 44–431 kg C ha⁻¹), followed by cropping and native vegetation and forestry soils. The DON concentration in soils was found to be more seasonally variable than DOC. There was approximately 80% fluctuation in the concentration of DON in winter from the annual mean concentration of DON, while DOC fluctuated between 23 and 28% at the dairy and the sheep and beef monitoring sites. Similar fluctuations in the concentrations of DON were also observed in the field incubation studies. These results indicate that DON is a dynamic pool of N in soils. There was a strong and significant positive correlation between DON and DOC in pastoral soils (r = 0.71, P < 0.01). There were also significant positive correlations between DON and total soil C (r = 0.59, P < 0.01), total soil N (r = 0.62, P < 0.01) and mineralizable N (r = 0.47, P < 0.01). The rather poor correlations between total soil C and N with DOC and DON, suggest other biogeochemical processes may be influencing concentrations of DOC and DON in these soils. Given the size of DON and DOC pools in the pastoral soils, we suggest that these pools of C and N should be taken into account when assessing the impact of pastoral land use on soil C and N enrichment of surface and groundwater.     

Expression Pattern of Vascular Endothelial Growth Factor in Canine Folliculogenesis and its Effect on the Growth and Development of Follicles after Ovarian Organ Culture

In this study, the expressions of VEGF in dog follicles were detected by immunohistochemistry and the effects of VEGF treatment on the primordial to primary follicle transition and on subsequent follicle progression were examined using a dog ovary organ culture system. The frozen‐thawed canine ovarian follicles within slices of ovarian cortical tissue were cultured for 7 and 14 days in presence or absence of VEGF. After culture, the ovaries were fixed, sectioned, stained and counted for morphologic analysis. The results showed that VEGF was expressed in the theca cells of antral follicles and in the granulosa cells nearest the oocyte in preantral follicle but not in granulosa cells of primordial and primary follicles; however, the VEGF protein was expressed in CL. After in vitro culture, VEGF caused a decrease in the number of primordial follicles and concomitant increase in the number of primary follicles that showed growth initiation and reached the secondary and preantral stages of development after 7 and 14 days. Follicular viability was also improved in the presence of VEGF after 7 and 14 days in culture. In conclusion, treatment with VEGF was found to promote the activation of primordial follicle development that could provide an alternative approach to stimulate early follicle development in dogs.     

Interactions between 14C-labelled atrazine and the soil microbial biomass in relation to herbicide degradation

A laboratory incubation experiment was set up to determine the effects of atrazine herbicide on the size and activity of the soil microbial biomass. This experiment was of a factorial design (0, 5, and 50 g g^–1 soil of non-labelled atrazine and 6.6×10³ Bq g^–1 soil of ¹⁴C-labelled atrazine) x (0, 20, and 100 g g^–1 soil of urea-N) x (pasture or arable soil with a previous history of atrazine application). Microbial biomass, measured by substrate-induced respiration and the fumigation-incubation method, basal respiration, incorporation of ¹⁴C into the microbial biomass, degradation of atrazine, and ¹⁴C remaining in soil were monitored over 81 days. The amount of microbial biomass was unaffected by atrazine although atrazine caused a significant enhancement of CO₂ release in the non-fumigated controls. Generally, the amounts of atrazine incorporated into the microbial biomass were negligible, indicating that microbial incorporation of C from atrazine is not an important mechanism of herbicide breakdown. Depending on the type of soil and the rate of atrazine application, 18–65% of atrazine was degraded by the end of the experiment. Although the pasture soil had twice the amount of microbial biomass as the arable soil, and the addition of urea approximately doubled the microbial biomass, this did not significantly enhance the degradation of atrazine. This suggests that degradation of atrazine is largely independent of the size of the microbial biomass and suggests that other factors (e.g., solubility, chemical hydrolysis) regulate atrazine breakdown. A separate experiment conducted to determine total amounts of ¹⁴C-labelled atrazine converted into CO₂ by pasture and arable soils showed that less than 25% of the added ¹⁴C-labelled atrazine was oxidised to ¹⁴CO₂ during a 15-week period. The rate of degradation was significantly greater in the arable soil at 24%, compared to 18% in the pasture soil. This indicates that soil microbes with previous exposure to atrazine can degrade the applied atrazine at a faster rate.     

Agroforestry Impacts on Soil Fertility in the Rima'a Valley,Yemen

Yemen is one of the world's least developed countries and experiences problems of scarcity of natural agricultural resources as well as soil erosion and degradation. Agroforestry systems (AFS) are being promoted as a more appropriate land use system than monocropping systems (MCS) worldwide. Unfortunately, long-term studies on agroforestry and other land use systems (LUS) do not exist in Yemen. Agroforestry in the Rima'a region has started to deteriorate and many farmers turned to (MCS). This study was conducted in the Rima'a Valley, near Alsharq town, Dhamar, Yemen. The study evaluates the soil nutrients, organic matter (OM), and other soil properties such as pH, bulk density, and porosity under AFS and compares it with soil under MCS. Standard procedures for soil sampling and analyzing were used to collect and analyze 36 composite samples from Site 1 and 36 composite samples from Site 2 from six cropping systems (treatments). The results showed that there were significant variations in relation to LUS. Agroforestry practices—mixed trees with coffee (S1), and Cordia africana L. with coffee (S2) have higher nitrogen concentration (0.17–0.26%) as compared to the Ziziphus spina-christi L. with maize (S3) and the monocropping maize (S5), (<0.16% in both Sites 1 and 2). Similar results were seen on the effect of the different LUS on the soil P, K, and OM contents at the two sites (p < .01). While soil N, P, and soil K were higher under agroforestry systems S1, and S2 in both sites, it was the lowest in S5 in both sites. It can be concluded that agroforestry has more favorable effects on soil fertility and other soil properties. The government should establish programs and campaigns to disseminate AFS technology and promote the importance of agroforestry in soil conservation.     

Genetic architecture of plant height in maize phenotype‐selected introgression families

This study aimed at developing, characterizing and evaluating two maize phenotypic‐selected introgression libraries for a collection of dominant plant height (PHT)‐increasing alleles by introgressing donor chromosome segments (DCS) from Germplasm Enhancement of Maize (GEM) accessions into elite inbred lines: PHB47 and PHZ51. Different backcross generations (BC₁‐BC₄) were developed and the tallest 23 phenotype‐selected introgression families (PIFs) from each introgression library (PHB47 or PHZ51) were selected for single nucleotide polymorphism genotyping to localize DCS underlying PHT. The result shows that most PIFs carrying DCS were significantly (α = 0.01) taller than the respective recurrent parent. In addition, they contained larger donor genome proportions than expected in the absence of selection or random mating across all BC generations. The DCS were distributed over the whole genome, indicating a complex genetic nature underlying PHT. We conclude that our PIFs are enriched for favourable PHT‐increasing alleles. These two libraries offer opportunities for future PHT gene isolation and allele characterization and for breeding purposes, such as novel cultivars for biofuel production.     

Dissolved organic matter leaching in some contrasting New Zealand pasture soils

Leaching of dissolved organic matter (DOM) from pastoral soils is increasingly seen as an important but poorly understood process. This paper examined the relationship between soil chemical properties, microbial activity and the losses of dissolved organic carbon (DOC) and nitrogen (DON) through leaching from six pasture soils. These soils differed in carbon (C) (4.6–14.9%) and nitrogen (N) (0.4–1.4%) contents and in the amount of organic C and N that had accumulated or been lost in the preceding 20+ years (i.e. −5131 to +1624 kg C ha⁻¹ year⁻¹ and −263 to +220 kg N ha⁻¹ year⁻¹, respectively). The paper also examined whether between‐soil‐type differences in DOC and DON leaching was a major explanatory factor in the observed range of soil organic matter (SOM) changes in these soils. Between 280 and 1690 kg C ha⁻¹ year⁻¹ and 28–117 kg N ha⁻¹ year⁻¹ leached as DOC and DON, respectively, from the six soils in a lysimeter study, with losses being greater from two poorly drained gley soils. Losses of C and N of this magnitude, while at the upper end relative to published data, could not fully explain the losses at Rawerawe, Bruntwood and Lepperton sites reported by Schipper et al. (2007) . The study highlights the leaching of DOM as a significant pathway of loss of C and N in pasture soils that is often ignored or given little attention in predictive models and nutrient budgeting. Leaching losses of DOC and DON alone, or in combination with slightly increased respiration losses of SOM given a 0.2°C increase in the mean annual soil temperature, do not fully explain long‐term changes in the SOM observed at these sites. When soils examined in the present study were separated on the basis of drainage class, the losses of DOC by leaching were correlated with both total and hot‐water extractable C (HWC), the latter being a measure of the labile SOM fraction. Basal microbial CO₂ respiration rates, which varied between 1 and 3.5 µg CO₂‐C g⁻¹ soil hour⁻¹ in surface soils (0–75‐mm depth), was also linked to HWC and the quantities of C lost as DOC. Adoption of the HWC method as an approach that could be used as a proxy for the direct measurement of the soil organic C lost by leaching as DOC or respired needs to be examined further with a greater number of soils. In comparison, a poor relationship was found between the hot‐water extractable N (HWN) and loss of DON by leaching, despite HWN previously being shown to be a measure of the mineralizable pool of N in soils, possibly reflecting the greater competition for N than C in these soils.     

Induction of novel variants through physical and chemical mutagenesis in Barbeton daisy (Gerbera jamesonii Hook.)

Summary

Gerbera (Gerbera jamesonii) is an attractive ornamental flower of high economic importance. The present investigation was aimed at generating novel flower colour variants in the gerbera cultivar ‘Harley’ through physical and chemical mutagenesis. In vitro-raised shoot cultures of gerbera, established from petiole explants, were exposed to different doses of γ-rays (1.5, 2.0, 2.5, 5.0, 10.0, 15.0, 20.0, or 30.0 Gy) using a Cobalt-60 source emitting 2.51 kGy h^–1. To induce mutations through chemical mutagenesis, different concentrations of ethylmethane sulphonate [EMS; 0.1, 0.2, 0.5, 0.8, or 1.0% (v/v)] were administered for 10 min or for 20 min. The LD50 values calculated for shoot survival and the induction of mutations were approx. 6.5 Gy for γ-rays and 0.65% (v/v) EMS for 10 min, or ≤ 0.1% (v/v) EMS for 20 min. Investigations revealed a negative correlation between mutagen dose and plant survival, both in vitro and after acclimatisation. Morphological variants showing changes in leaf shape, leaf size, scape length, flower diameter, and flower colour were obtained. Significantly, early flowering was induced in all mutated plants compared to non-mutated plants.The high frequencies of colour variants obtained using Bγ-rays, or the application of EMS to in vitro-raised shoot cultures could be an effective way to improve gerbera cultivars.     

Effects of long-term compost and fertilizer application on stability of aggregate-associated organic carbon in an intensively cultivated sandy loam soil

The study examined the influence of compost and mineral fertilizer application on the content and stability of soil organic carbon (SOC). Soil samples collected from a long-term field experiment were separated into macroaggregate, microaggregate, and silt + clay fractions by wet-sieving. The experiment involved seven treatments: compost, half-compost N plus half-fertilizer N, fertilizer NPK, fertilizer NP, fertilizer NK, fertilizer PK, and control. The 18-year application of compost increased SOC by 70.7–121.7%, and mineral fertilizer increased by 5.4–25.5%, with no significant difference between control soil and initial soil. The C mineralization rate (rate per unit dry mass) in microaggregates was 1.52–2.87 mg C kg⁻¹ day⁻¹, significantly lower than in macroaggregate and silt + clay fractions (P < 0.05). Specific C mineralization rate (rate per unit SOC) in silt + clay fraction amounted to 0.48–0.87 mg C g⁻¹ SOC day⁻¹ and was higher than in macroaggregates and microaggregates. Our data indicate that SOC in microaggregates is more stable than in macroaggregate and silt + clay fractions. Compost and mineral fertilizer application increased C mineralization rate in all aggregates compared with control. However, compost application significantly decreased specific C mineralization rate in microaggregate and silt + clay fractions by 2.6–28.2% and 21.9–25.0%, respectively (P < 0.05). By contrast, fertilizer NPK application did not affect specific C mineralization rate in microaggregates but significantly increased that in silt + clay fractions. Carbon sequestration in compost-amended soil was therefore due to improving SOC stability in microaggregate and silt + clay fractions. In contrast, fertilizer NPK application enhanced SOC with low stability in macroaggregate and silt + clay fractions.