Nobuhito Sekiya

Stomatal density of cowpea correlates with carbon isotope discrimination in different phosphorus, water and CO2 environments

* Stomatal formation is affected by a plants external environment, with long-distance signaling from mature to young leaves seemingly involved. However, it is still unclear what is responsible for this signal. To address this question, the relationship between carbon isotope discrimination (Delta) and stomatal density was examined in cowpea (Vigna sinensis). * Plants were grown under various environments that combined different amounts of soil phosphorus (P), soil water, and atmospheric CO(2). At harvest, stomatal density was measured in the youngest fully expanded leaf. The (13)C : (12)C ratio was measured in a young leaf to determine the Delta in mature leaves. * Results indicated that stomatal density is affected by P as well as by amounts of water and CO(2). However, stomatal responses to water and CO(2) were complex because of strong interactions with P. This suggests that the responses are relative, depending on some internal factor being affected by each external variable. Despite such complicated responses, a linear correlation was found between stomatal density and Delta across all environments examined. * It is proposed that the Delta value is a good surrogate for the long-term mean of the intercellular (C(i)) to the atmospheric (C(a)) CO(2) concentration ratio (C(i) : C(a)) and may be useful in understanding stomatal formation beyond complicated interactions.

Applying hydraulic lift in an agroecosystem: forage plants with shoots removed supply water to neighboring vegetable crops

When a plant encounters spatially heterogeneous soil moisture within its root system, usually drier surface and moister subsurface soils, water can move between these layers through the root system, a plant process known as hydraulic lift or redistribution. The water thus transferred is available not only for the plant itself but also for its neighbors. We examined application of this process as a possible biological irrigation tool. As ‘donors’, we used perennial forage plants with their shoots removed to minimize the effect of light-interception by them on the ‘receiver’ plants growing alongside them. In a horizontally split-root experiment, where an upper container was filled with sand and a lower one with water, superior donor species could maintain the upper sand in a fully hydrated condition for several weeks, increasing stomatal conductance in the receivers. The effects were also confirmed in a water-limited agricultural field, as significant differences were found in canopy temperature and yield in neighboring crop plants in the presence or absence of donor root systems. These results suggest that deep-rooting associate plants with their shoots removed function as an irrigation tool and improve crop production in water-scarce environments.

Performance of a Number of NERICA Cultivars in Zanzibar, Tanzania: Yield, Yield Components and Grain Quality

Abstract The cultivars of NERICA (New Rice for Africa), which are characterized by early maturity and high yield potential under rainfed conditions, have the potential to increase rice production in Tanzania, where rice cultivation is greatly affected by a short rainy season. Trials were conducted in Zanzibar to examine the yield performances of 14 NERICA cultivars at five locations during the long-rains season (Masika) and at another five locations during the short-rains season (Vuli). The NERICA cultivars produced significantly higher yields than local cultivars at five locations. Yields of 12 NERICA cultivars were associated with rainfall (R2 = 0.367 to 0.732) such that they yielded well during Masika (109 to 343 g m-2) and poorly during Vuli (11 to 68 g m-2). Spikelet number per panicle and percentage of filled spikelets (% filled spikelets) accounted for 70 to 90% of the yield variation in all cultivars, suggesting that yield was determined mainly during the later part of the growth period. In some cultivars, yield was associated with rainfall during the later part of the growth period but the yield of the remainder was associated with rainfall during the early part. A selected group of farmers, extension workers and researchers evaluated grain quality. Some cultivars scored well, especially NERICA 1. We conclude that NERICAs are generally suitable for production during Masika and that NERICA 1 especially should be promoted due to its high grain quality. However, for double cropping of NERICAs, measures must be implemented for increasing or maintaining the water status of the soil during Vuli.

Water-extraction by split-roots of sesbania and pigeon pea exposed to spatially heterogeneous distribution of soil water.

Abstract Previous studies have suggested that the deep roots of sesbania (Sesbania sesban) function less efficiently in water acquisition than those of pigeon pea (Cajanus cajan) despite similar rooting depths. To investigate this phenomenon, both species were grown in a vertically split-root system. The top soil was watered at two-day intervals and the bottom soil was kept wet. Fifty-seven days after sowing, the watering to the top soil was withheld and the water uptake was monitored in both the layers. At any given rate of transpiration, the water influx rate per unit root surface (WIR/RS) was higher in the top soil than in the bottom soil in sesbania, despite the greater availability of water in the latter. By contrast, in pigeon pea, the WIR/RS was higher in the bottom soil than in the top soil. In sesbania, aerenchyma tissue was observed only in the cortex of the roots in the bottom soil. On the other hand, aerenchyma tissue was scarcely observed in pigeon pea roots, suggesting that the presence of aerenchyma tissue led to the reduced WIR/RS of sesbania roots in the bottom soil. Thermal image analysis showed that the stomata of sesbania leaves did not respond to water shortage. Instead, the sesbania leaves were shed in order to avoid desiccation, further reducing the potential to extract water. We therefore conclude that the water-extraction ability of deep roots was lower in sesbania than in pigeon pea as a result of aerenchyma formation and leaf shedding.

Effects of Partial Harvesting on Napier Grass: Reduced Seasonal Variability in Feedstock Supply and Increased Biomass Yield

Abstract The production of cellulosic bioethanol from non-edible plants is receiving increasing attention for its potential to avoid food–fuel competition. However, seasonal variability in feedstock supplies increases the costs of stockpiling and limits commercialization. The cellulosic energy plant Napier grass (Pennisetum purpureum) has conventionally been harvested three times per year (on a 4-month cycle) in Indonesia. To shorten this cycle, we examined an alternative system in which every four rows (rather than the entire crop) were alternately harvested every 2 months (partial harvesting). Results from a 20-month experiment indicated that partial harvesting was effective in shortening the supply cycle from 4 to 2 months. Moreover, partial harvesting significantly increased biomass yield, probably as a result of the border effect. Investigations into available light, atmospheric CO2 concentration, and soil volumetric water content suggested that partial harvesting allowed Napier grass to capture more light for biomass production.

Farmer-to-Farmer Extension Facilitated by Agricultural Training Institutions: A Case of NERICA Dissemination in Tanzania

Abstract The Kilimanjaro Agricultural Training Center (KATC) extension approach has disseminated cultivation techniques for irrigated rice across Tanzania. KATC provides training to extension officers and key farmers (KFs). It also helps subsequent farmer-to-farmer (FTF) extension from KFs to intermediate farmers (IFs) and then to other farmers (OFs). The long-term intensive training for irrigated rice was greatly simplified for the dissemination of NERICA1 that was recently released for rainfed rice fields. While the original approach involves a 12-day residential training and a season-long field follow-up, the simplified one only provides a 2-day residential training. Here, we investigated the extent to which the simplified approach diffused NERICA1. The FTF extension worked almost theoretically from KFs to IFs but not from KFs/IFs to OFs over three cropping seasons. However, the number of OFs gradually increased with little intervention, suggesting that this approach should have some mechanism that encourages participation of OF from an early dissemination stage.

Effects of Seed P-enrichment and Localized P-fertilizer Application on Soil-grown Wheat

Abstract We previously reported two methods of phosphorus (P) supply that improve crop growth. One is to apply P-fertilizer locally into soils and the other is seed P-enrichment by soaking seeds in P-solution. Here, we examined which of the two methods or a combination of the two is more effective for wheat grown in pots. Each method increased dry matter to a similar extent but with a different time interval. The effect of localized P-application was observed at 25 d after sowing (DAS), while that of seed-P enrichment was observed at 50 DAS. Despite the positive effects of both methods, their combination had no additive effect. At 50 DAS, the growth variations were explained by P content, which depended on root length. We therefore assume that increasing root length may be the common and biologically relevant feature of both methods and that either application alone is sufficient to achieve this effect.