Modeling the Impacts of Soil Organic Carbon Content of Croplands on Crop Yields in China

This study quantified the impacts of soil organic carbon （SOC） content on the grain yield of crops using a biogeochemical model （DNDC, denitrification-decomposition）. Data on climate, soil properties, and farming management regimes of cropping systems were collected from six typical agricultural zones （northeast, north, northwest, mid-south, east and southwest regions of China, respectively） and integrated into a GIS database to support the model runs. According to the model, if the initial SOC content in the cropland was increased by 1 g C kg^-1, the crop yield may be increased by 176 kg ha^-1 for maize in the northeast region, 454 kg ha^-1 for a maize-wheat rotation in the north region, 328 kg ha^-1 for maize in the northwest region, 185 kg ha^-1 for single-rice in the mid-south region, 266 kg ha^-1 for double-rice in east region, and 229 kg ha^-1 for rice and wheat rotation in southwest region. There is a great potential for enhancing the crop yield by improving the SOC content in each region of China.     

Biochemical analysis of a chlorfenapyr-selected resistant strain of Tetranychus urticae Koch

Tetranychus urticae Koch has recently developed resistance to chlorfenapyr in Australia and Japan, but no attempt has yet been made to describe the biochemical mechanisms involved in chlorfenapyr resistance. In this study a laboratory-selected chlorfenapyr-resistant strain was investigated. Resistance to chlorfenapyr was associated with a strong increase in esterase activity and P450 mono-oxygenase (MO) activity but a decrease in 3,3',5,5'-tetramethylbenzidine (TMBZ) peroxidation activity. Differences in esterase activities between susceptible and resistant strains increased with increasing carbon number of the aliphatic side-chain of the nitrophenol substrate. A 4.4-fold increase in the O-deethylation of 7-ethoxy-4-trifluoromethyl coumarin (7-EFC) mediated by P450 MOs was detected. Remarkably, the resistant strain showed only half of the total TMBZ peroxidation activity found in the susceptible strain. The activity of these enzymes was further determined on different crosses and back-crosses of both strains. Results indicated that activities correlated with chlorfenapyr susceptibility and could be considered as biochemical markers. Esterase isozymes of both strains and their crosses were separated with isoelectric focusing (IEF) and visualised after activity staining. It was clear that two distinct zones of enhanced esterase activity were present in the chlorfenapyr-resistant strain (EST 11, pI = 4.88 and EST 16, pI = 4.71). EST 11 was identified with inhibitors as a carboxylesterase. The relative presence and intensity of these esterase zones changed in the different crosses and could be seen as a marker for chlorfenapyr resistance. Glutathione-S-transferase and glucose-6-phosphate dehydrogenase activities were not significantly different between strains. A twofold decrease in TMBZ peroxidase activity in the resistant strain could reflect decreased activation of chlorfenapyr. On the basis of these results the involvement of P450 MOs and esterases in the activation and detoxification of chlorfenapyr in T. urticae is challenged and discussed.     

Effects of dietary Ca/P ratio, P level and microbial phytase supplementation on nutrient digestibilities in growing pigs: precaecal, post-ileal and total tract disappearances of OM,

Eight female pigs (26–61 kg) provided with a simple T-cannula about 10 cm proximal to the ileo-caecal valve, were used in two experiments to investigate the effects of Ca/P ratio, P level and supplementation with phytase (500 FTU/kg) on precaecal, post-ileal and total tract disappearances of organic matter (OM), phosphorus (P) and calcium (Ca). In experiment 1, two Ca/P ratios and two P levels were tested according to a 2 × 2 factorial arrangement within a Latin square design. In experiment 2, the diets of experiment 1 were supplemented with phytase (500 FTU/kg). There was a substantial absorption of OM, P and Ca in the post-ileal tract for all diets. Precaecal and total tract disappearances of OM were reduced by phytase addition (−4.4 and −0.8%, respectively). Supplementation with phytase resulted in an improvement of total tract and post-ileal P disappearances by 10.3 and 12.1%, respectively, without affecting precaecal P disappearance. Addition of feed phosphate resulted in a higher precaecal disappearance of P (+10.8%), resulting in a higher total tract disappearance of P (+5.9%). Addition of limestone had little effect on disappearances of OM, P and Ca, but reduced activity of supplemental phytase and had a negative influence on growth performance. Precaecal, post-ileal and total tract Ca disappearances were hardly affected by the examined dietary factors. The results might indicate that P from feed phosphate is absorbed primarily prececally and that P from phytate, liberated by microbial phytases, is dominantly absorbed post-illeally.     

Identification of commercial chicory cultivars for hydroponic forcing and their phenetic relationships revealed by random amplified polymorphic DNAs and amplified fragment length polymorphisms

One‐hundred and twenty‐four amplified fragment length polymorphism (AFLP) and 49 random amplified polymorphic DNA (RAPD) markers have been used to distinguish between 20 and 23 commercial chicory cultivars, respectively. These were all Cichorium intybus var. foliosum F₁ hybrids, currently used in hydroponic forcing. Five‐hundred and twenty RAPD primers (OPERON) were tested, of which 156 resulted in reproducible patterns and 26 yielded polymorphisms. Two‐hundred and fifty‐six AFLP primer‐combinations were tested and six combinations were selected for identification purposes. Similarity indices were measured and clustering has been done using pairwise comparison. Both types of marker provide similar conclusions. Two major clusters are formed, representing late and early cultivars. All cultivars were identified using 10 informative RAPD primers or three AFLP primer combinations. A low degree of polymorphism was detected between some early cultivars, suggesting a narrow genetic base in their breeding strategy.     

Development of simple sequence repeat (SSR) markers in Eucalyptus from amplified inter-simple sequence repeats (ISSR)

Eucalyptus spp. are widely used in exotic plantations. Since many of these trees are derived from vegetative propagation, the routine identification of clones has become increasingly important. The most widely used molecular based method for fingerprinting these clones is by random amplified polymorphic DNAs (RAPDs). Although this technique is useful, its results are not very repeatable, especially between laboratories. The aim of this study was to develop microsatellite markers that are highly repeatable, and to investigate their value in Eucalyptus fingerprinting. Typically, this process involves the expensive procedure of constructing an enriched genomic library. However, we used an intersimple sequence repeat (ISSR) polymerase chain reaction (PCR)‐based enrichment technique for microsatellite‐rich regions. With this relatively inexpensive method, microsatellite‐rich regions were amplified directly from genomic DNA, after which PCR products were cloned and sequenced. From these microsatellite‐rich sequences, primer sets were constructed to amplify mono‐, di‐, tri‐, hexa‐and nona‐nucleotide repeats. These markers were all inherited in a Mendelian fashion in the progeny of a test cross between two Eucalyptus grandis trees. The primer sets developed were also able to amplify the corresponding microsatellite loci from five different Eucalyptus spp., namely E. grandis, E. nitens, E. globulus, E. camaldulensis and E. urophylla.     

Charts for Guiding Irrigation in Real Time

In order to adjust correctly the irrigationcalendar to actual weather and waterlimiting conditions, farmers requireguidelines to help them in their day to daydecisions. In this paper a procedure isoutlined to present such guidelines in theform of a single chart. On the chartinformation concerning the irrigationinterval and irrigation duration ispresented. Tables guide the user (i) toadjust the irrigation interval to theactual weather conditions throughout thegrowing season and (ii) to select theduration of the water application as afunction of the characteristics of theirrigation system. In case of watershortage during a particular period,additional data informs the user on thesensitivity of the crop to water stress. Anexample is presented for drip irrigatedtomatoes in the region of Tunis on afluvisol.     

Nitrous oxide emission from herbicide-treated soybean

 The emission of N₂O from soybean plants treated with the herbicides dichlorophenoxyacetic acid (2,4-D) and bromoxynil was studied. The N₂O flux from 2,4-D- and bromoxynil-treated soybean was 14.1 ng N₂O-N g^–1 fresh weight h^–1 and 19.7 ng N₂O-N g^–1 fresh weight h^–1, respectively, i.e. approximately twice that of the controls. The NO₂ ^–-N concentration in 2,4-D- and in bromoxynil-treated soybean was about 8 μg N g^–1 fresh weight, i.e. fivefold the concentration found in control plants. The NO₃ ^– content in herbicide-treated soybean did not differ significantly from that of the control plants. Consequently, the accumulation of NO₂ ^–-N during the assimilation of NO₃ ^–-N was thought to cause the observed N₂O release. Probably, N₂O is a by-product produced during either the reaction of NO₂ ^–-N with plant metabolites or NO₂ ^–-N decomposition. Final conclusions must await further experiments. Received: 5 November 1999     

The origin of carbonates in termite mounds of the Lubumbashi area, D.R. Congo

The origin of carbonate accumulations in termite mounds is a controversial issue. This study is an attempt to elucidate the processes of carbonate precipitation in Macrotermes mounds built on Ferralsols in Upper Katanga, D.R. Congo, whereby a differentiation between pedogenic and inherited carbonates is considered. Carbonate features were investigated for a 9 m deep termite-mound profile, and for an 18 m wide cross-section through a termite mound and the adjacent soil, using field and laboratory techniques. Field evidence for a pedogenic origin includes morphological type (soft powdery materials, nodules, and coatings on ped surfaces) and distribution patterns of the carbonates. Thin-section studies reveal that the carbonates occur predominantly as impregnative orthic nodules and less commonly as coatings, both clearly pedogenic; calcareous pellets are interpreted as locally reworked pedogenic carbonates. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray spectrometry (SEM-EDS) and stable isotope (δ¹³C) analyses show that all isolated carbonate features consist of high-Mg calcite (4.9-12.3 mol% MgCO₃) with δ¹³C signatures ranging from − 13.2‰ to − 11.5‰. Weddellite (CaC₂O₄. 2H₂O) is identified in a thin-section and by XRD analysis, and appears to be locally transformed into calcite. The stable isotope composition of carbon suggests that calcite precipitated in equilibrium with soil CO₂ generated during decomposition of soil organic matter, and locally most likely during oxidation of oxalate. This study proves that carbonates which accumulated in Macrotermes mounds are pedogenic precipitates, whose deposition is partly related to microbial decay of organic matter, subsequently redistributed to some extent by abiotic dissolution-reprecipitation and termite activity.