Noboru Nakata

Responses of three wheat genotypes to high soil temperature during grain filling

Abstract High temperatures limit wheat (Triticum aestivum L.) production in many areas around the world. Soil temperatures near the root zone could be as high as the air temperature during wheat grain filling. The objectives of this study were to investigate the effects of high soil temperature on grain yield and related traits of wheat genotypes and to examine their differential responses. Three genotypes, Imam, Fang and Siete Cerros were grown under three temperature conditions in the daytime during grain-filling period: (i) normal air temperature/normal soil temperature (26/26°C), (ii) normal air temperature/high soil temperature (26/38°C) and (iii) high air temperature/high soil temperature (38/38°C). The night temperature was 18/18°C in all treatments. Temperatures during the daytime were increased at a rate of 4°C hr-1 from 18°C to the designated temperature, which was kept for at least 4 hr around noon. The 26/38°C and 38/38°C treatments significantly decreased the chlorophyll content (SPAD) of flag leaves, grain-filling duration, and increased carbohydrate remobilization or loss from the stem and the root, but with varying degrees among genotypes. Grain yield, biomass, grain weight, grains number spike-1 and harvest index at the 38/38°C treatment were significantly lower than at the other two treatments. In Imam, the grain yield was lower at 26/38°C than at 26/26°C, while in Siete Cerros the grain yield, grain weight, grain number spike-1 and harvest index were lower at the 38/38°C treatment than at the other two treatments. These results indicated that high temperature of soil alone (26/38°C) or high temperature of both air and soil (38/38°C) decreased the chlorophyll content and grain-filling duration, and increased carbohydrate remobilization. Genotypic differences in the responses to high soil temperature (26/38°C) and high air/soil temperature (38/38°C) were also observed.

Physiological Response of Three Wheat Cultivars to High Shoot and Root Temperatures during Early Growth Stages

Abstract Understanding wheat (Triticum aestivum L.) response to high shoot/root temperature during the early growth stages is important for successful production in tropical and subtropical environments. This study examined the physiological response of wheat cultivars to high shoot and/or root temperatures during early growth stages. Three cultivars; Imam, Fang and Siete Cerros were grown in soil and hydroponically at three shoot/root temperatures (23/23, 23/35 and 35/35ºC for the soil experiment; and 22/22, 22/38 and 38/38ºC for the hydroponic experiment). Leaf dry weight and leaf area plant-1 were significantly decreased by high shoot/ root temperature (HS/HR, 35/35 and 38/38ºC) but was not affected by a normal shoot/high root temperature (NS/HR, 23/35 and 22/38ºC). The NS/HR (22/38ºC) and HS/HR (38/38ºC) treatments in the hydroponic experiment significantly decreased photosystem II quantum yield ( Φpsii), photosynthetic rate (Pn) and specific leaf area (SLA) compared with the normal shoot/normal root (NS/NR, 22/22ºC) temperature treatment. Chlorophyll accumulation was significantly decreased by NS/HR, but increased significantly by HS/HR in most of the measuring dates. The heat-tolerant cultivar, Fang, always had the highest chlorophyll content, Φpsii and Pn under all temperature treatments, while the heat-sensitive cultivar, Siete Cerros, always had the greatest reduction in these traits especially towards the end of the experiment. Imam and Fang responded to HS/HR in the hydroponic experiment by immediate and greater reductions in leaf dry weight, total leaf area and SLA during the first wk of the treatments compared with Siete Cerros. The response changed with the treatments duration such that Imam showed the least reduction and Siete Cerros was the most affected cultivar towards the end of the experiment. Thus, wheat cultivars differentially responded to high shoot/root temperature by reducing the leaf weight and area and hence accumulating more chlorophyll in the diminished leaves. The failure to undergo such changes led to significantly lower chlorophyll accumulation, Φpsii and Pn under high root temperature.

Agronomic and Environmental Performance of Rapeseed Oilcake in the Lowland Rice Farming of Japan

The use of organic manures as an alternative to chemical fertilizers is an option for the development of sustainable farming systems in Japan. The present study examined the effect of rapeseed oilcake (RO) not only on yield and yield components of rice (Oryza sativa L.) but also on soil fertility parameters and surface water quality in a paddy field by comparing them with the effects of conventional inorganic fertilizer (IF) and a control (CR), that is, natural (unfertilized) system. The long-term field experiment from 1990 to 2006 demonstrated the indigenous sustainability of paddy systems, because husked grain yield and shoot biomass in the CR plot remained at moderate levels (ave. 323 ± 56 g m−2 and 843 ± 166 g m−2, respectively) over 17 successive years. Meanwhile, the application of RO comparatively improved grain yield (ave. 538 ± 83 g m−2) and shoot biomass (ave. 1478 ± 187 g m−2) to almost the same level as with IF (ave. 538 ± 68 g m−2 and 1511 ± 173 g m−2, respectively) during the study period. Soil fertility assessment in the last experimental year (2006) indicated that RO could improve the soil quality to the same extent as IF because major fertility parameters showed similar values between the RO and IF plots. On the other hand, the application of IF induced a substantial increase in estimated load outflows of nitrogen (N) and phosphorus (P) from the paddy surface water (2.46 g N m−2; 0.38 g P m−2) as compared to the CR plot (0.92 g N m−2; 0.06 g P m−2). Outflows from the RO plot showed relatively lesser effluent loads (2.00 g N m−2; 0.14 g P m−2) than the IF plot. From the findings of this study, we concluded that RO is agronomically similar to but an environmentally better resource material than conventional IF in the lowland rice farming system in Japan.

Excessive application of farmyard manure reduces rice yield and enhances environmental pollution risk in paddy fields

ABSTRACT The present study examined the effect of excessive application of farmyard manure (FM) on rice production and environmental pollution in paddy fields of Japan. A long-term field experiment was conducted during the period 1976–2006 to examine the trends of rice yield and yield components as affected by the excessive FM application (20 Mg ha−1 year−1 containing 110 kg N, 180 kg P2O5, and 320 kg K2O). Rice growth, soil fertility, and surface water quality were also assessed in the final year (2006). The results obtained were compared with those of a conventional practice with recommended doses of inorganic fertilizer (IF), i.e. 85 kg N, 68 kg P2O5, and 53 kg K2O ha−1 year−1, and an unfertilized control (CR). The excessive FM application resulted in a gradual decrease in grain yield, which was mostly explained by the reduction of grain fertility under the luxuriant rice growth. This reduction may have been due to the higher accumulation of soil nutrients such as N, P, and K. Moreover, the excessive FM application increased chemical oxygen demand, total P, and soluble K concentrations in the paddy surface water and their effluent loads compared to the conventional practice with the recommended IF application.

Evaluation of conventional and prolonged-swelling sodium dodecyl sulfate sedimentation tests for the prediction of bread wheat quality under heat stress conditions.

In non-traditional, heat-stressed environments, wheat breeding programmes were mainly concerned with the introduction and adaptation of high-yielding, heat-tolerant cultivars regardless of the end-use quality. For the recently developed quality-oriented markets, new cultivars should combine the above-mentioned traits with good grain quality to improve economic feasibility of wheat production in these environments. This study aimed to examine the suitability of the conventional sodium dodecyl sulfate sedimentation (SDSS) test for predicting bread-making quality and to evaluate the effectiveness of a prolonged-swelling SDSS test in improving the predictability of end-use quality under heat stress conditions. Conventional and prolonged-swelling SDSS volumes were measured from whole meal of 15 bread wheat genotypes grown for two seasons under two sowing conditions at Gezira Research Farm, Wad Medani, Sudan. Results of correlations of SDSS volumes with total and insoluble protein contents, mixograph peak height and mixograph descending slope indicated the suitability of the SDSS test in predicting bread-making quality under heat-stress irrigated conditions. However, the absence of significant correlations with some quality attributes, such as mixograph peak time and mixograph curve width, demonstrated the non-exclusiveness of the SDSS test for predicting all bread-making quality attributes. The prolonged-swelling SDSS tests did not improve identification of differences among genotypes over the conventional test despite similarly predicting some quality attributes and showing relatively small increases in the correlation coefficient magnitudes with others. SDSS after 10 min from settlement (SDSS10) showed strong correlations with all other SDSS volumes at various times and with most of quality attributes. This suggested that SDSS10 could be used for evaluation of bread-making quality in early generations of the breeding programme in the hot irrigated conditions of Sudan and similar environments.