Estimation of evaporation from arid-irrigated region using MODIS satellite imagery

For sustainable development of irrigated agriculture in arid regions, improvement of water use efficiency is essentially required to maintain current production levels and meet food and fiber for population growth in future. To achieve high water use efficiency, a key consideration is to reduce unnecessary soil water loss due to evaporation. In this article, regional daily evaporation over Hetao Irrigation District in a typical arid region during the irrigation period of 2009 was determined by a developed maximum surface temperature model combining Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery. The results showed that maximum land surface temperature (LST) from MODIS satellite imagery was relatively higher in the western and middle parts than that of the eastern part of the district. At the same time, the mean minimum LST was shown somewhat higher in the eastern part. Mean daily evaporation was relatively higher in the eastern part, which showed water consuming is higher in the eastern part of the district. During the irrigation period of 2009, the total income water (irrigation water and rainfall) amount is 590.3 mm, and the outcome water (drainage discharge and evaporation) amount is 497.5 mm. The surplus of 92.8 mm in the irrigated season is considered to be consumed in winter season. Throughout the irrigated season, income and outcome almost equals each other. The daily evaporation distribution map could specify particular water consuming areas over the district where high daily evaporation may be occurred.     

Soil properties affected by combinations of soil solarization and organic amendment

A field experiment was conducted to investigate the effects on soil properties of solarization combined with rice bran additive. The treatments included control (bare soil), black polyethylene film mulch (BM), clear polyethylene film mulch (CM), rice bran mixture (RBMx), rice bran mulch (RBM), rice bran mixture and black polyethylene film mulch (RBMx + BM), rice bran and black polyethylene film mulch (RBM + BM), rice bran mixture and clear polyethylene film mulch (RBMx + CM), and rice bran and clear polyethylene film mulch (RBM + CM). Initially, 15 kg m⁻² of rice bran was applied to each treatment as the organic amendment. A cover of black or clear polyethylene film was then used to begin the soil solarization process. Approximately 49 days later, the polyethylene film was removed and five broccoli seedlings per replication were planted 6 weeks later. The combination of rice bran mixture with the clear/transparent polyethylene film mulch (RBMx + CM) raised both the mean and maximum soil temperatures over 0–30 cm of soil depth. Maximum soil temperature under the RBMx + CM treatment was the highest of all treatments (77°C) and were about 32°C greater than under the control, while it was only 52°C under RBM + BM treatment. Combining rice bran with clear/transparent polyethylene film mulch during the soil solarization process is recommended for raising soil temperatures. Further investigation over a longer period of soil solarization process with rice bran–organic amendment and polyethylene film mulch combinations is required to more accurately determine their effects on soil properties and crop production.     

Groundwater flow and transport and potential sources of groundwater nitrates in the Ryukyu Limestone as a mixed flow aquifer in Okinawa Island, Japan

We investigated the groundwater flow and the transport and potential source of groundwater nitrates in the typical karst setting of the Ryukyu Limestone aquifer in the southern part of Okinawa Island, Japan. Analysis of groundwater hydrographs indicated that this is a ??mixed flow?? aquifer with the coexistence of slow diffuse flow in the matrices and rapid conduit flow in the caves and caverns. This relationship is indicated by the travel time of groundwater flow: 70?days in the matrices of the aquifer and 6?days through the caves and caverns. The conduit flow system was also confirmed by the distribution of relatively low concentrations of ²²²Rn near caverns. The sampling sites were categorized into upland field (UF) type and residential area (RA) type according to the land-use ratio on the upstream side with a 600-m influential radius, and cave and cavern (CC) type according to the hydrogeologic setting near two large caverns, even though the CC type should be categorized as the UF type from the viewpoint of land use. Cross plots of NO₃-N versus SO₄ ^2? showed that the predominant source of UF groundwater nitrates was chemical fertilizer. A difference was observed in average ??¹⁵N values between UF (8.9??) and RA (10.0??). On the other hand, the average ??¹⁵N value for CC (10.5??) was similar to that for RA, indicating that CC nitrates were not related to the surrounding land use. This phenomenon is considered as evidence that CC groundwater nitrates were carried by rapid groundwater flow through caves and caverns from residential areas located higher upstream compared to the influential areas. According to previous studies, animal and human waste was considered the predominant sources of RA and CC groundwater nitrogen. The contribution ratio of chemical fertilizer (R _CF) was calculated using mass balance equations under assumed predictability. There was a relatively high correlation between the rate of upland areas and of residential areas and R _CF. Average R _CF for UF, RA and CC was 41, 27, and 25%, respectively.     

Phylogeny and nitrogen fixation potential of Bradyrhizobium species isolated from the legume cover crop Pueraria phaseoloides (Roxb.) Benth. in Eastern Cameroon

Pueraria is an herbaceous, perennial legume crop originating in Asia. Pueraria phaseoloides (Roxb.) Benth. (tropical kudzu) is frequently introduced into production systems and is used as green manure, a cover crop and a forage plant, making it important economically. We used P. phaseoloides as a trap crop to study and characterize soil rhizobia in Eastern Cameroon. Bacteria were isolated from fresh nodules collected from field-grown P. phaseoloides roots. The 16S-23S rRNA internal transcribed spacer (ITS) sequences from 30 bacterial isolates were amplified by polymerase chain reaction (PCR) and the reaction products were sequenced. Phylogenetic analysis revealed that all isolates were ascribed to the genus Bradyrhizobium and were grouped into three clusters of Bradyrhizobium sp. strains, one cluster of B. yuanmingense strains, and one cluster of B. elkanii strains. Acetylene reduction assay (ARA) results indicated that the B. yuanmingense strains had significantly higher nitrogen fixation potential and that they could be used as inoculants to enhance nitrogen fixation in Pueraria grown in Eastern Cameroon.     

Phosphite (phosphorous acid): Fungicide, fertilizer or bio-stimulator?

Phosphite (     ; Phi), a reduced form of phosphate (     ; Pi), is widely marketed as either a fungicide or fertilizer or sometimes as a biostimulant. This is confusing for both distributors and growers. The present paper explores data from various studies to clarify that Phi does not provide plant P nutrition and thus cannot complement or substitute Pi at any rate. In addition, Phi itself does not have any beneficial effect on the growth of healthy plants, regardless of whether it is applied alone or in combination with Pi at different ratios or different rates. The effect of Phi on plants is not consistent, but is strongly dependent on the Pi status of the plants. In most cases, the deleterious effect of Phi is evident in Pi-starved, but not Pi-sufficient, plants. Plants fertilized with Pi allowing for approximately 80–90% of its maximum growth might still be at risk of the effect. This negative effect becomes more pronounced under more seriously Pi-deficient conditions. Although a number of studies have shown positive crop responses to Phi, these responses are likely to be attributable to the suppression of plant diseases by Phi and/or to Pi formed from oxidation of Phi by microbes. In addition, indirectly providing P by Phi-to-Pi oxidation is not an effective means of supplying P to plants compared with Pi fertilizer. An understanding of these issues will aid the right selection of fertilizer as well as minimize the harmful effects of Phi use on crops.     

Intragenomic variation in the internal transcribed spacer regions between 16S–23S rRNA genes among the three copies of Sinorhizobium fredii strains

The soybean-nodulating Sinorhizobium fredii strain has been reported to possess three copies of rRNA gene operons. In the present study, we investigated the diversity of the 16S–23S rDNA internal transcribed spacer (ITS) regions of S. fredii strains. Based on the sequences of the ITS regions, we divided the sequences of the S.   fredii strains into two groups, type A and type B. A dot-matrix analysis indicated that the region flanked by tRNA-Ile and tRNA-Ala is longer in type A than in type B, whereas type B sequences possess longer regions upstream of tRNA-Ile and downstream of tRNA-Ala than those of the type A sequence. Restriction fragment length polymorphism of polymerase chain reaction product (PCR-RFLP) of the ITS region in the cloned plasmids as templates could reconstruct the PCR-RFLP pattern from the total DNA as a template. The results of Southern hybridization using the insert sequence between tRNA-Ile and tRNA-Ala in type A as a probe indicated differences in the copy numbers of the type A ITS regions among the strains tested. These results indicated that S. fredii strains possess the type A and type B sequences of the ITS regions at ratios of 3:0, 2:1, 1:2 or 0:3. These S. fredii strains may be useful biological materials for the study of intraspecific variations.     

Effect of phosphite–phosphate interaction on growth and quality of hydroponic lettuce (Lactuca sativa)

Although the fungicidal properties of phosphite have been recognized, its potential as a fertilizer is still being debated. The information on how phosphite affects the growth and quality of plants in relation to phosphate (P_i) also remains unknown. This study was conducted to investigate the effect of phosphite in relation to P_i on growth and quality parameters of lettuce (Lactuca sativa L.). The results showed that addition of phosphite to the nutrient solution at different rates ranging from 0.05 to 2 mM significantly increased total P, water‐extractable P_i, and phosphite in both shoots and roots, but did not improve plant growth under various P_i supplies (0.05, 0.1, 0.15, and 0.3 mM as P_i levels for approximately 50%, 80%, 90%, and 100% of the maximum plant growth, respectively), indicating that phosphite was well absorbed by roots and mobile inside the plants, but did not provide any P nutrition. Also, no stimulating effect of any P_i–phosphite combination was observed. The effect of phosphite on plant growth was strongly dependent on the level of P_i supply. In general, application of phosphite up to 2 mM did not influence the growth of P_i‐sufficient plants. However, plants fertilized with P_i for about 90% of maximum growth were still vulnerable to phosphite at 2 mM. The negative effect of phosphite was found even at concentrations as low as 0.2 mM, when plants were supplied with P_i adequate for about 80% of maximum growth or less. At 0.05 mM, phosphite had marginal effects on plant growth under all the P_i levels. Although phosphite itself had little influence on the ascorbate and mineral concentrations of lettuce, its application to P_i‐deficient plants may decrease the mineral concentrations of plants brought about by the inhibitory effect of phosphite on root growth and hence nutrient uptake. Since phosphite is an effective fungicide for lettuce, care should be taken on P_i supplies prior to application of phosphite products to minimize the harmful effects.     

Horizontal and vertical variations in survival rates of juvenile bivalves,Anadara kagoshimensis (Tokunaga, 1906), Ruditapes philippinarum (Adams & Reeve, 1850) and Atrina sp., experimentally caged in the inner area of the Sea of Ariake,Japan

International Aquatic Research - In the inner area of the Sea of Ariake, rearing experiments were conducted to examine how the survival rates of juveniles of three bivalve species (Anadara...