Atmospheric CO2 concentration effects on rice water use and biomass production

Numerous studies have addressed effects of rising atmospheric CO2 concentration on rice biomass production and yield but effects on crop water use are less well understood. Irrigated rice evapotranspiration (ET) is composed of floodwater evaporation and canopy transpiration. Crop coefficient Kc (ET over potential ET, or ETo) is crop specific according to FAO, but may decrease as CO2 concentration rises. A sunlit growth chamber experiment was conducted in the Philippines, exposing 1.44-m2 canopies of IR72 rice to four constant CO2 levels (195, 390, 780 and 1560 ppmv). Crop geometry and management emulated field conditions. In two wet (WS) and two dry (DS) seasons, final aboveground dry weight (agdw) was measured. At 390 ppmv [CO2] (current ambient level), agdw averaged 1744 g m-2, similar to field although solar radiation was only 61% of ambient. Reduction to 195 ppmv [CO2] reduced agdw to 56±5% (SE), increase to 780 ppmv increased agdw to 128±8%, and 1560 ppmv increased agdw to 142±5%. In 2013WS, crop ET was measured by weighing the water extracted daily from the chambers by the air conditioners controlling air humidity. Chamber ETo was calculated according to FAO and empirically corrected via observed pan evaporation in chamber vs. field. For 390 ppmv [CO2], Kc was about 1 during crop establishment but increased to about 3 at flowering. 195 ppmv CO2 reduced Kc, 780 ppmv increased it, but at 1560 ppmv it declined. Whole-season crop water use was 564 mm (195 ppmv), 719 mm (390 ppmv), 928 mm (780 ppmv) and 803 mm (1560 ppmv). With increasing [CO2], crop water use efficiency (WUE) gradually increased from 1.59 g kg-1 (195 ppmv) to 2.88 g kg-1 (1560 ppmv). Transpiration efficiency (TE) measured on flag leaves responded more strongly to [CO2] than WUE. Responses of some morphological traits are also reported. In conclusion, increased CO2 promotes biomass more than water use of irrigated rice, causing increased WUE, but it does not help saving water. Comparability with field conditions is discussed. The results will be used to train crop models. (Résumé d'auteur

Growth of PB 260 Clone (Hevea Brasiliensis (Willd. Ex a. Juss.) Muell-Arg.) in Different Potting Media and Fertilization Scheme

Rubber is an important commodity for Indonesia. Currently, a problem encountered in the propagation of rubber planting materials is the availability of ideal soils with optimum nutrition as the planting medium. Peat can be used as a growing medium but it still has weaknesses such as high level of acidity and poor in nutrient content. This study was aimed to assess the performance of rubber budded stump grown on modified potting medium and applied with different forms and rates of fertilizers. The nursery experiment consisted of 17 treatments and arranged in a randomized complete block design. After rubber nursery stage, the performance of the rubber budded stump were also monitored in the field for 10 months. Results showed that mixture of peat and soil with the application of recommended rate of solid or liquid fertilizer produced rubber budded stump with bigger stem diameter and taller plants. The potting medium stimulated early root development which led to higher nutrient uptake. These budded stump also performed better in field, showed higher leaf nutrient concentration after 6 months and produced bigger stem diameter after 10 months

Land Suitability Evaluation of Abandoned Tin-mining Areas for Agricultural Development in Bangka Island, Indonesia

Kepulauan Bangka Belitung, Indonesia is one of the tin mineral-producer in the world. Agricultural crops could be a wise option for the reclamation since abandoned tin-mining lands have a high potency to be used as agricultural lands. This study was aimed to evaluate of the land/soil characteristics of abandoned tin-mining areas and to establish land suitability of the land area for agriculture used to formulate appropriate land development measures and amelioration strategies for utilization of mined areas for crop production. The land evaluation was conducted by comparing the land characteristics in every type of abandoned tin-mining areas with its crop requirements. The current suitability showed that in general food crops, vegetable crops, fruit crops, and industrial crops were consider as not suitable (N). Spice and medicinal crops [pepper (Piper nigrum L.) and citronella (Andropogoh nardus L. Rendle)] were consider as not suitable (N), while the Jatropha (Jatropha curcas L.) and Kemiri Sunan (Aleurites moluccana L. Willd) crops were considered as marginally suitable (S3) in abandoned tin-mining areas. The forest crops and forage crops were considered as marginally suitable (S3). The water availability, soil texture, and low soil fertility were considered as the limiting factors of all crops to get optimum production. For agricultural development, the soil physical and chemical properties of abandoned tin-mining land must be improved through integrated farming

Molecular dissection of connected rice populations revealed important genomic regions for agronomic and biofortification traits

Breeding staple crops with increased micronutrient concentration is a sustainable approach to address micronutrient malnutrition. We carried out Multi-Cross QTL analysis and Inclusive Composite Interval Mapping for 11 agronomic, yield and biofortification traits using four connected RILs populations of rice. Overall, MC-156 QTLs were detected for agronomic (115) and biofortification (41) traits, which were higher in number but smaller in effects compared to single population analysis. The MC-QTL analysis was able to detect important QTLs viz: qZn5.2, qFe7.1, qGY10.1, qDF7.1, qPH1.1, qNT4.1, qPT4.1, qPL1.2, qTGW5.1, qGL3.1, and qGW6.1, which can be used in rice genomics assisted breeding. A major QTL (qZn5.2) for grain Zn concentration has been detected on chromosome 5 that accounted for 13% of R2. In all, 26 QTL clusters were identified on different chromosomes. qPH6.1 epistatically interacted with qZn5.1 and qGY6.2. Most of QTLs were co-located with functionally related candidate genes indicating the accuracy of QTL mapping. The genomic region of qZn5.2 was co-located with putative genes such as OsZIP5, OsZIP9, and LOC_OS05G40490 that are involved in Zn uptake. These genes included polymorphic functional SNPs, and their promoter regions were enriched with cis-regulatory elements involved in plant growth and development, and biotic and abiotic stress tolerance. Major effect QTL identified for biofortification and agronomic traits can be utilized in breeding for Zn biofortified rice varieties

Growth plasticity of Junglerice (Echinochloa colona) for resource use when grown with different rice (Oryza sativa) planting densities and nitrogen rates in dry-seeded conditions

Junglerice is one of the world's most problematic C4 grass weeds present in dry-seeded rice in many countries. A screenhouse study was conducted to determine the effect of four rice planting densities (0, 100, 200, and 400 plants m) and four nitrogen (N) rates (0, 50, 100, and 150 kg ha) on the growth and morphological plasticity of junglerice. Junglerice plant height was reduced by 15 to 35%, tiller number by 54 to 77%, leaf number by 61 to 85%, leaf area by 69 to 90%, leaf biomass by 63 to 88%, stem biomass by 70 to 92%, and inflorescence biomass by 66 to 94% at rice planting densities ranging from 100 to 400 plants m relative to the junglerice plants grown alone. However, all these growth parameters increased with increasing N rates. Junglerice biomass increased by 125 to 472%, whereas rice biomass increased by 122 to 285% with the application of 50 to 150 kg N ha. Additional N favored junglerice biomass production relative to rice. Rice crop interference (200 to 400 plants m) reduced junglerice growth and biomass and overshaded the junglerice plants when no N was applied. Increasing N application resulted in taller plants and higher biomass of junglerice, while it reduced root-shoot weight ratio. These results suggest that increasing N rate increased the competitive ability of the junglerice over rice regardless of crop planting density. Information generated in this study could be useful in devising appropriate combinations of planting density and fertilizer management strategies for cultural junglerice management, particularly in situations where junglerice species are more responsive than rice to N

Efficacy and economics of different herbicides, their weed species selectivity, and the productivity of mechanized dry-seeded rice

A field study was conducted in 2012 and 2013 at the International Rice Research Institute (IRRI) farm in Los Baños, Philippines, to evaluate the economic performance of PRE oxadiazon and pendimethalin, early POST butachlor plus propanil and thiobencarb plus 2,4-D, and late POST herbicides bispyribac-sodium and fenoxaprop plus ethoxysulfuron applied solely or sequentially. All herbicide treatments with PRE or early POST herbicides reduced total weed density by 85-100% and biomass by 80-100%, whereas late POST treatments reduced weed density by 32-50% and biomass by 40-62% compared with the nontreated weedy check. The highest grain yield was achieved in weed-free plots (5.9-6.1 t ha) and the lowest in weedy plots (0.2 t ha). Among the herbicide treatments, rice treated with oxadiazon, thiobencarb plus 2,4-D, and butachlor plus propanil followed by the late POST herbicides had grain yield increments of 23-25, 20 to 26, and 18 to 23 times that of the yield in weedy plots, respectively. The economic analysis showed that the sole application of oxadiazon provided the highest net profit and benefit-cost ratio in both years, which was similar to the treatments involving oxadiazon or early POST herbicides, followed by the sequential application of late POST herbicides

Growth analysis and biomass partitioning of Cyperus iria in response to rice planting density and nitrogen rate

Cyperus iria is a weed of rice with widespread occurrence throughout the world. Because of concerns about excessive and injudicious use of herbicides, cultural weed management approaches that are safe and economical are needed. Developing such approaches will require a better understanding of weed biology and ecology, as well as of weed response to increases in crop density and nutrition. Knowledge of the effects of nitrogen (N) fertilizer on crop-weed competitive interactions could also help in the development of integrated weed management strategies. The present study was conducted in a screenhouse to determine the effects of rice planting density (0, 5, 10, and 20 plants pot−1) and N rate (0, 50, 100, and 150 kg ha−1) on the growth of C. iria. Tiller number per plant decreased by 73–88%, leaf number by 85–94%, leaf area by 85–98%, leaf biomass by 92–99%, and inflorescence biomass by 96–99% when weed plants were grown at 20 rice plants pot−1 (i.e., 400 plants m−2) compared with weed plants grown alone. All of these parameters increased when N rates were increased. On average, weed biomass increased by 118–389% and rice biomass by 121–275% with application of 50–150 kg N ha−1, compared to control. Addition of N favored weed biomass production relative to rice biomass. Increased N rates reduced the root-to-shoot weight ratio of C. iria. Rice interference reduced weed growth and biomass and completely suppressed C. iria when no N was applied at high planting densities (i.e., 20 plants pot−1). The weed showed phenotypic plasticity in response to N application, and the addition of N increased the competitive ability of the weed over rice at densities of 5 and 10 rice plants pot−1 compared with 20 plants pot−1. The results of the present study suggest that high rice density (i.e., 400 plants m−2) can help suppress C. iria growth even at high N rates (150 kg ha−1)

Ecological significance of rice (Oryza sativa) planting density and nitrogen rates in managing the growth and competitive ability of itchgrass (Rottboellia cochinchinensis) in direct-seeded rice systems

Current understanding is that high planting density has the potential to suppress weeds and crop-weed interactions can be exploited by adjusting fertilizer rates. We hypothesized that (a) high planting density can be used to suppress Rottboellia cochinchinensis growth and (b) rice competitiveness against this weed can be enhanced by increasing nitrogen (N) rates. We tested these hypotheses by growing R. cochinchinensis alone and in competition with four rice planting densities (0, 100, 200, and 400 plants m-2) at four N rates (0, 50, 100, and 150 kg ha-1). At 56 days after sowing (DAS), R. cochinchinensis plant height decreased by 27-50 %, tiller number by 55-76 %, leaf number by 68-84 %, leaf area by 70-83 %, leaf biomass by 26-90 %, and inflorescence biomass by 60-84 %, with rice densities ranging from 100 to 400 plants m-2. All these parameters increased with an increase in N rate. Without the addition of N, R. cochinchinensis plants were 174 % taller than rice; whereas, with added N, they were 233 % taller. Added N favored more weed biomass production relative to rice. R. cochinchinensis grew taller than rice (at all N rates) to avoid shade, which suggests that it is a "shade-avoiding" plant. R. cochinchinensis showed this ability to reduce the effect of rice interference through increased leaf weight ratio, specific stem length, and decreased root-shoot weight ratio. This weed is more responsive to N fertilizer than rice. Therefore, farmers should give special consideration to the application timing of N fertilizer when more N-responsive weeds are present in their field. Results suggest that the growth and seed production of R. cochinchinensis can be decreased considerably by increasing rice density to 400 plants m-2. There is a need to integrate different weed control measures to achieve complete control of this noxious weed

Effect of pre-emergence herbicides and timing of soil saturation on the control of six major rice weeds and their phytotoxic effects on rice seedlings

The study evaluated the effects of pre-emergence herbicides and their rates [oxadiazon (0.5 and 1 kg ai ha), pendimethalin (1 and 2 kg ai ha), and pretilachlor with safener (0.6 kg ai ha)], and time of soil saturation establishment after herbicide application [1, 3, 5, and 7 days after spray (DAS)] in controlling the six major rice weeds, and their phytotoxic effects on rice seedling growth. All herbicides provided 100% control of Echinochloa colona, Echinochloa crus-galli, Leptochloa chinensis, Cyperus iria, and Amaranthus spinosus. Murdannia nudiflora was 100% controlled by oxadiazon and pretilachlor with safener, but poorly controlled (22-75%) by pendimethalin. Pendimethalin at 2 kg ai ha was more effective than at 1 kg ai ha in reducing the biomass of the stem, leaf, and root of M. nudiflora irrespective of timing of soil saturation. Rice plant height was reduced to a maximum (77-96%) by pendimethalin at 2.0 kg ai ha followed by oxadiazon at 1.0 kg ai ha (38-70%) compared to the non-treated control. In contrast, the tallest rice plants were observed in the non-treated control and those treated with pretilachlor with safener which had 80-100% rice plant survival. The lowest rice plant survival of 0, 6, 7, and 16% was found in the soil applied with pendimethalin at 2 kg ai ha and saturated at 1, 3, 5, and 7 DAS, respectively, which was followed by oxadiazon at 1 kg ai ha. All herbicides except pretilachlor with safener reduced SPAD values with early soil saturation, which improved with delay in soil saturation timing. Pendimethalin at 2 kg ai ha reduced the SPAD values of rice plants by 100-164% relative to the non-treated control and produced the highest phytotoxicity symptoms. Pendimethalin also reduced rice shoot biomass more than oxadiazon, which was compounded by early soil saturation after herbicide application. Pretilachlor with safener was the only herbicide that exhibited low phytotoxic symptoms on rice plants and did not reduce leaf, stem, root, and shoot biomass of rice. Percent reduction in rice leaf, stem, root, and shoot biomass by the different herbicides was in the order of pendimethalin 2 > oxadiazon 1 > pendimethalin 1 > oxadiazon 0.5 > pretilachlor with safener 0.6 kg ai ha. Each herbicide treatment reduced rice growth parameters as soil saturation was delayed in the order of 1 DAS > 3 DAS > 5 DAS > 7 DAS. The study suggests that soil water content and herbicide rates are important factors in influencing herbicide phytotoxicity in rice. The application of herbicides should be avoided when the soil is too wet, and irrigation should be delayed at least one week after herbicide application

Agronomic indices, growth, yield-contributing traits, and yield of dry-seeded rice under varying herbicides

Dry-seeded rice (DSR) is an emerging resource-conserving technology in many Asian countries, but weeds remain the major threat to the production of DSR systems. A field study was conducted in 2012 and 2013 at the International Rice Research Institute (IRRI), Los Baños, Philippines, to evaluate the performance of sole and sequential applications of preemergence (oxadiazon and pendimethalin), early postemergence (butachlor + propanil and thiobencarb + 2,4-D), and late postemergence herbicides (bispyribac-sodium and fenoxaprop + ethoxysulfuron) with different modes of action in comparison to manual weeding in DSR. The sequential applications of all preemergence and postemergence herbicides reduced weed density and biomass by 80–100% compared to the nontreated plots. The sole application of postemergence herbicides reduced weed density by only 44–54% and weed biomass by 51–61%, whereas oxadiazon alone reduced weed density and biomass by 96–100%. All herbicide treatments and manual weeding significantly affected tiller number, biomass, crop growth rate, agronomic indices, yield-contributing parameters (panicle density and filled grains), and yield (biological and grain) of rice. The highest grain yield was obtained in the manually weeded plots (5.9–6.1 t ha−1) and the plots treated with oxadiazon alone (5.4–5.6 t ha−1) and oxadiazon followed by postemergence herbicides (5.2–5.8 t ha−1). The lowest paddy yield (0.22 t ha−1) was achieved in the nontreated plots followed by the plots treated with the sole application of bispyribac-sodium and fenoxaprop + ethoxysulfuron. The results suggest that oxadiazon is the best broad-spectrum and economically effective herbicide when applied alone or in combination with other effective postemergence herbicides with different modes of action, depending on the weed species present in the field