Shuichi Asanuma’s research while affiliated with Nagoya University and other places

Abstract In this study, we analyzed the rice cultivation and management in the irrigation schemes of the National Irrigation Board (NIB) and in three small schemes managed by local farmers so called outgrowers, which are distributed near the Lake Victoria in Western Kenya. As a result, we found big differences between NIB schemes and outgrowers’ schemes in their farm size and production. In NIB scheme, the average farm size per household was approximately one hector and their yield was 4.5 kg/ha which is double size and 1.5 times higher yield comparing outgrowers. Our survey suggests that this higher yield is brought by large amount of fertilizer and pesticide input and also appropriate frequency and timing of weeding. Necessarily, total production of NIB farmers is bigger, and they succeeded to sale about 3.5 ton per household, whereas outgrowers achieved only around 30% of it. The expenditure for rice cultivation of NIB farmers was about twice as large as outgrowers, but due to their big sales volume, their cash income from rice production after removing production cost at least 5 times and at most 26 times of outgrowers’. In all schemes, labor costs was the major component of management expenses. Outgrowers spent for wage labors, while they paid small cost for fertilizer and agricultural chemicals. Additionally, to meet this cash demand, many of them sold their livestock which was their important assets.

This study evaluated the effect of three N fertilization levels 60 (low), 120 (medium), and 180 (high) kg N ha−1 and soil moisture content gradients created by a line-source sprinkler on the expression of plasticity in lateral root branching and dry matter production (DMP) of upland new rice for Africa (NERICA) 1 and 4. There were no significant differences in DMP between NERICA 1 and 4 under well-watered, mild drought, and severe drought conditions regardless of N level. In contrast, under moderate drought (12–21% v/v of soil moisture content [SMC] in 2011 and 16–24% v/v of SMC in 2012), NERICA 1 had significantly higher shoot dry weight, total root length (TRL), lateral root length, and branching index than NERICA 4 at medium and high N; however, there was no significant difference between the two NERICAs in DMP at low N. TRL of NERICA 1 was significantly higher under moderate drought than well-watered conditions, but only with medium and high N. Regardless of N level, moderate drought did not enhance NERICA 4’s root system. Thus, NERICA 1’s root system exhibited plastic development, promoting lateral root branching at medium and high N. These morphological changes were associated with the greater DMP in NERICA 1 than NERICA 4 under moderate drought, whereas the lack of such plasticity at low N meant genotypic differences in DMP were obscured. Our findings implied that N application can improve upland NERICA productivity under moderate drought conditions, but differences in variety and field conditions may influence efficacy.

To identify differences in root plasticity patterns of two upland New Rice for Africa (NERICA) varieties, NERICA 1 and 4, in response to drought under conditions with contrasting soil profile characteristics, soil moisture gradients were imposed using a sloping bed system with depths ranging 30–65 cm and a line-source sprinkler system with a uniformly shallow soil layer of 20 cm depth. Varietal differences in shoot and root growths were identified only under moderate drought conditions, 11–18% v/v soil moisture content. Further, under moderate drought soil conditions where roots could penetrate into the deep soil layer, deep root development was greater in NERICA 4 than in NERICA 1, which contributed to maintaining dry matter production. However, under soil conditions with underground impediment to deep root development, higher shoot dry weight was noted for NERICA 1 than for NERICA 4 at 11–18% v/v soil moisture content, which was attributed to increased lateral root development in the shallow soil layer in NERICA 1. Enhanced lateral root development in the 0–20-cm soil layer was identified in NERICA 1 even under soil conditions without an impediment to deep root development; however, this did not contribute to maintaining dry matter production in upland rice. Thus, we show different root developmental traits associated with drought avoidance in the two NERICA varieties, and that desirable root traits for upland rice cultivation vary depending on the target soil environment, such as the distribution of soil moisture and root penetration resistance.

New Rice for Africa (NERICA) is a general name for interspecific rice varieties derived from a cross between the high-yielding Asian rice (Oryza sativa L.) between locally adapted African rice (Oryza glaberrima Steud.). Eight NERICAs were evaluated for cold tolerance (CT) at the reproductive stage and compared with their O.sativa parents and three Japanese standard rice varieties over 3years. Cold tolerance was evaluated based on the filled grain ratio (FGR) after cold water irrigation. The FGR was greatly reduced by cold water irrigation. NERICA 1, 2 and 7 had higher FGR (51.9-57.9%), while NERICA 6, 15 and 16 had lower FGR (6.2-14.5%). NERICA 1, 2 and 7 were less affected by cold stress, with a 31% mean reduction in FGR, while NERICA 6, 15 and 16 were greatly affected, with their FGRs being reduced by more than 80%. NERICA 3 and 4 were moderately affected by cold stress, with about 45% reduction rate in FGR. FGR significantly influenced the grain weights of the varieties with strong positive correlations (r=0.83-0.91; P<0.001), and thus, similar trends in grain weights were observed. Grain weights were reduced by 61.7-96.4% under cold stress. NERICA 1, 2 and 7 showed significantly better performance than NERICA 3 and 4, while NERICA 6, 15 and 16 performed poorly under cold water irrigation. The Japanese varieties Koshihikari (very tolerant) and Ozora (moderately tolerant) were more affected by cold water irrigation than NERICA 1, 2 and 7. On the basis of the mean reduction rate (%) in FGR under cold stress, the varieties were classified as follows: NERICA 1, 2 and 7 as tolerant; NERICA 3 and 4 as moderately tolerant; and NERICA 6, 15 and 16 as susceptible to cold stress. However, NERICA 7 grain yields were lower under cold stress due to both greatly reduced number of panicles per plant and number of spikelets per panicle. Therefore, NERICA 1 and 2 are suitable candidates for production in the highland regions of East Africa and should be promoted for production.

This paper analyzes, from both economic and socio-cultural perspectives, the roles of livestock in the livelihoods of western Kenya's Luo people, who live in an area facing severe soil erosion due to overgrazing. Forty-five households within the study area were surveyed and studied through participatory observation over 10 months. We classified them into five groups depending on their livestock keeping and examined the groups' socioeconomic characteristics in order to link livestock to livelihoods. The results show that households in the two groups owning the most livestock included many paternal extended families and their widows. The former group tended to live under unfavorable economic conditions, with comparatively lower off-farm incomes and negative post-food-purchase incomes. On the centrally, the latter group did not show negative post-food-purchase income due to smaller number of family members. However, these both groups' households also obtained large shares of their livestock through socio-cultural methods, such as entrustment, gifts, and marriage payments. After obtaining higher incomes by selling these livestock, they were able to pay school fees for their children, allowing them to access to a better future through education. The results demonstrate the importance of socio-cultural methods for obtaining livestock, which work through reciprocity. This has clear policy implications: when devising countermeasures to overgrazing, policymakers must consider both economic and socio-cultural roles played by livestock.

In the study area located in Western Kenya near the Lake Victoria, severe soil erosion occurred and it thought to relate to vegetation degradation caused by overgrazing. The livestock density estimated by analyzing satellite image (1.39 TLU/ha for available grazing lands) was lower than that of measured for seven farmers’ grazing lands using GPSs (4.41 TLU/ha, 2011) with variation from 0.83 to 12.36 TLU/ha. Thus, it is clear that the grasslands used by farmers are limited compared with the area of estimated available land for grazing identified by analyzing the satellite image. According to growth-consumption rate model that was developed by the Nyangito et al. (2008) in southeastern Kenya, if livestock density reaches over 7 TLU/ha, pasture growth rate became lower than consumption rate. Grass biomasses of the grazing lands were kept low (less than 50 g/50 × 50 cm2) under high livestock density (three farmers out of seven were higher than 7 TLU/ha). In addition, rainfall pattern is very unstable and we observed stunted growth of grasses during dry spells. Therefore, we concluded that overgrazing. It means that inhibition of continuous re-growth of grasses due to high grazing pressure has been occurred even for small area and contributed to the soil erosion.