: The effects of relative light intensity (RLI) on the growth, yield and curcumin content of turmeric (Curcuma longa L.) were examined in Okinawa, Japan. The plants were shaded with white nets with different mesh sizes for maintaining respective RLI. Five RLI, 100 (without shading), 82, 79, 73 and 59% in 200482, 79, 73 and 59% in −200582, 79, 73 and 59% in and four RLI, 100, 68, 52 and 48% in 200582, 79, 73 and 59% in −2006 were evaluated. In the fi rst experiment, plant height increased markedly, but the number of leaves and tillers, and SPAD value increased slightly in the plants grown at 59−82% RLI compared with control (without shading). Turmeric shoot biomass and yield increased significantly at 59−82% RLI and they were highest at 73% RLI in the fi rst experiment. Curcumin content of turmeric increased markedly at 59−73% RLI as compared with the control in the fi rst experiment. Similar results in plant growth, shoot biomass, yield and curcumin content were obtained in the second experiment, but the effects of RLIs were smaller than in the fi rst experiment because of late planting. This study indicates that turmeric is a partial shadetolerant plant that could be cultivated at around 59−73% RLI for higher yield and curcumin content in Okinawa. However, the degree of RLI required for better turmeric cultivation may vary with the place, year and irradiance level.

Profitable turmeric (Curcuma longa L.) production requires adequate nutrients. We have investigated the effect of inoculation with arbuscular mycorrhizal fungi (AMF) on growth, nutrient uptake, yield and curcumin production of turmeric under field and glasshouse conditions. Although AMF inoculation slightly increased plant height, leaf number and shoot N content, no statistical differences were observed in vegetative growth parameters, biomass production, nutrient uptake and curcumin content compared to control plants under field conditions. It was difficult to determine the exact effect of inoculated AMF on turmeric growth because of indigenous AMF. On the other hand, turmeric showed better response to AMF inoculation under greenhouse conditions. AMF inoculation resulted in higher biomass production and nutrient uptake of turmeric. Moreover the concentration of curcumin, contained in the rhizome of turmeric, increased in AMF treatment. These results indicate that AMF inoculation has beneficial effects on turmeric growth and curcumin production. AMF inoculation to turmeric field would be effective when indigenous soil populations of AMF are low or native AMF are no longer effective.

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Maize plants are well colonized with arbuscular mycorrhizal fungi (AMF), which contribute mineral nutrients absorption from soil. However little is known about their role in nitrogen (N) absorption especially from amino acids, which reach a considerable quantity in soils. This experiment was conducted to investigate N acquisition from amino acids through AMF symbiosis. AMF inoculation clearly increased the N content of maize supplied with amino acids (Glu, Ala and Pro). Further study of xylem sap revealed that the composition of amino acids was changed by AMF inoculation. These results indicate that AMF contribute N from amino acids, and may affect the nitrogen assimilation of host plants.

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A field experiment was conducted in Okinawa, Japan from 2005 to 2007 to evaluate the effect of purple nutsedge and other weeds on turmeric growth and yield and determine the effective weed-control period to minimize crop interference. Treatments consisted of all weeds removed at 70, 115, and 160 d sequentially after planting (DAP), all weeds except purple nutsedge removed at these three dates, plus weedy and weed-free controls. Purple nutsedge density increased until 115 DAP when grown alone with turmeric and thereafter decreased markedly, whereas it increased only until 70 DAP when grown with other weeds. Weed reinfestation in turmeric that was sequentially weeded was high until 115 DAP, but thereafter was negligible. In the weedy control, the weed infestation was severe until 160 DAP. Plant height and leaf and tiller number per plant of turmeric increased rapidly from 70 to 160 DAP. Season-long weed infestation significantly reduced shoot biomass and rhizome yield of turmeric, but both were similarly high among treatments of weed-free turmeric, all weed removal, and removal of all weeds except purple nutsedge. Purple nutsedge (> 3,000 plants/m2) did not significantly reduce turmeric yield, whereas the combined weed species reduced yield by greater than 40%. Thus, crop interference by purple nutsedge was not high, and other weeds could be removed during 70 to 160 DAP for reduced labor requirements and higher yield of turmeric.

Legume-grass mixed cropping has significant advantages that affect crop yield and soil resources. Generally, grasses grown with legumes take up more nitrogen than those grown under sole cropping. We focused on the effect of cutting hairy vetch during a vigorous growth stage on N uptake in oat under mixed cropping. We evaluated the amounts of N transferred from hairy vetch to oat by using a 15 N dilution method. Cutting hairy vetch increased the number of tillers and dry weight of oat, but total N content was not significantly higher than that under mixed cropping without cutting. In contrast, the amount of N transferred to oat was increased by cutting. Estimated amounts of N transferred to oat were 2.7 g m -2 with cutting of hairy vetch and 0.8 g m -2 without cutting. Cutting half of the oats under sole cropping did not indicate the transfer of rhizodeposited N in oat to the residual plants. In addition, cutting hairy vetch increased the amounts of accumulated solar radiation in the middle canopy of the mixed cropping plots. Therefore, in a hairy vetch and oat mixed cropping system, cutting of the hairy vetch might enhance growth of oat due to the transfer of N from hairy vetch and the reduction of light interception to the oat canopy. N fertility enhancement of the soil by cutting of the legume would be valuable for low-input crop production.

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