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 (20Mgha(-1)year(-1) containing 110kg N, 180kg P2O5, and 320kg 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. 85kg N, 68kg P2O5, and 53kg 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.

Silicon (Si) is known as a beneficial nutrient in the cultivation of rice, playing a key role in photosynthesis enhancement, lodging resistance and tolerance to various environmental stress. The present study aimed to examine available Si content in both lowland soils (n = 29) and neighboring upland soils (n = 21) collected from Benin and Nigeria and to evaluate the validity of the assessment results through a pot experiment. Our results revealed that the acetate-buffer method predicted Si concentration in rice straw at the harvest stage (R-2 = 0.68, P < 0.01) better than the anaerobic-incubation method (R-2 = 0.31, P > 0.05), and 76% of the uplands and 38% of the lowlands were deficient (< 50 mg/kg) in acetate-buffer soluble Si. These findings suggest that the Si-deficiency soils prevail across the study area, making rice plants starved for Si and prone to environmental stress.

The present study aimed to assess the dynamics of oxyhydroxides via termite mounds in a tropical savannah of Central Nigeria, where the soils often contain oxyhydroxides as a major component of soil minerals. To this end, the quantities of oxyhydroxides stored in mounds built by Macrotermes bellicosus (Smeathman) were compared to those stored in surface (Ap1) soils, and their turnover rates were estimated. Both the mound wall and nest of M. bellicosus were enriched two- to 10-fold with acidified ammonium oxalate soluble iron (Fe-o) and aluminum (Al-o) and dithionite-citrate-bicarbonate (DCB) soluble iron (Fe-d) and aluminum (Al-d) relative to the adjacent surface soil horizon. These oxyhydroxide contents were positively correlated with the clay content (P<0.05), suggesting that M. bellicosus preferentially used silicate clay-associated oxyhydroxides for mound construction. The Fe-d, Al-d and DCB-soluble manganese (Mn-d) preserved in the M. bellicosus mounds ran up to 112 +/- 25.6, 5.72 +/- 1.41 and 2.17 +/- 0.68kgha(-1), accounting for 1.91 +/- 0.23%, 1.00 +/- 0.60% and 0.35 +/- 0.09% of the total amount stored in the surface soil horizon, respectively. Furthermore, the estimated turnover rates of Fe-d, Al-d and Mn-d were 6.6, 0.33 and 0.14kgha(-1) year(-1), respectively. These findings suggest that the mound-building termites significantly impacted the dynamics of free oxyhydroxides in an African savannah soil.

奈良市内の都市近郊二次林において，コバノミツバツツジ (<I>Rhododendron reticulatum</I>) の開花を調査し，その影響要因について検討した。その結果，対象個体の樹高と胸高断面積，土壌交換性 K 含量，周辺競争個体との胸高断面積相対比が開花に影響していた。開花の有無を目的変数とする一般化線形モデルでは，1) 対象個体の樹高，2) 土壌交換性K含量，3) 半径3 m圏内の上層木との胸高断面積相対比が説明変数として選択され，予測精度は74.2％と良好であった。また，予測精度上位2つのいずれのモデルにおいても，半径3 m圏内の競争木との胸高断面積相対比が説明変数として選択され，半径3 m 圏内に位置する競争木の管理が本種の開花を促進する上で重要であることが示唆された。

ミミズ(Oligochaeta)やシロアリ(Isoptera)のような土壌無脊椎動物は土壌生態系改変者と呼ばれ,土壌物理環境を改変・撹乱することによって他の生物への資源の有効性に影響を及ぼしている.土壌生成過程における物理学的,化学的,生物学的な影響に対する関心が高いのに対して,生態系改変者が土壌鉱物の風化において直接的および間接的に重要な影響を及ぼしていることはあまり認識されていない.その直接的な影響は鉱物粒子の物理的破壊であり,分泌物質による化学的変質である.一方,土壌無脊椎動物の共生微生物によって生成される有機酸やキレート成分による鉱物の溶解など間接的な影響もある.本稿では,土壌生態系改変者が土壌鉱物の風化に及ぼす影響に関する既往の文献を総括し,このトピックにおける研究課題と将来の展望について議論する.

The present study aimed to examine the influence of termites (Isoptera) on soil clay mineralogy. To this end, we analyzed the clay mineralogy in the mound structures of <I>Macrotermes bellicosus</I> (Macrotermitinae) and in the adjacent natural (termite-free) soil horizons along an inland valley toposequence in central Nigeria, and compared them using differential X-ray diffraction approach. The results indicated that: (i) <I>M. bellicosus</I> modified soil clay mineralogy to minor extent regardless of the substantial enrichment of clay particles in the mound structures; (ii) the mound structures generally had a decreased abundance of quartz balanced with an increased abundance of phyllosilicate minerals such as smectite and/or kaolinite when compared with the adjacent near-surface (Ap2) horizons; and (iii) there was a subtle difference in clay mineralogy between the mound wall and the hive in spite of a large disparity in particle-size distribution. These findings suggest that soil clay mineralogy is not linked to the ecological requirements of <I>M. bellicosus</I> and the apparent change in the clay mineralogy in mound structures is caused by the preferential selection of fine soil particles during the mound construction rather than by a preference among clay mineral species.

This study investigated the influence of mound-building termites on soil particle dynamics on the land surface and in soil-forming processes by examining the amount of soil particles in mound structures of Macrotermes bellicosus in a highly weathered Ultisol of tropical savanna. Soil particle turnover via the mounds was estimated using particle stock data and soil turnover data from previous studies. A 4-ha study plot with six mounds of relatively uniform shape and size was investigated. Soil mass constituting the mounds was 6,166 +/- 1,581 kg mound(-1) within which the mound wall and nest body accounted for 5,002 +/- 1,289 and 1,164 +/- 293 kg, respectively. The mound wall contained a significantly larger amount of clay (252 +/- 9.97 g kg(-1)) balanced with a lower sand content (676 +/- 26.5 g kg(-1)) than in the adjacent surface (Ap1) horizon, (46.4 +/- 12.8 g clay kg(-1); 866 +/- 83.2 g sand kg(-1)); the nest body had much higher clay content (559 +/- 51.0 g kg(-1)) but less sand (285 +/- 79.2 g kg(-1)) than the mound wall. As a result, the mounds of M. bellicosus accumulated clay of 2,874 +/- 781 kg ha(-1) (corresponding to 2.52% of clay stock in the Ap1 horizon) along with an estimated clay turnover rate of 169 kg ha(-1) year(-1). These findings suggest a positive feedback effect from termite mound-building activity on soil particle dynamics in tropical savanna ecosystems: M. bellicosus preferentially use subsoilmaterial formound construction, resulting in relocation of illuvial clay in the subsoil to the land surface where clay eluviation from the surface soil and its illuviation in the subsoil are major soil-forming processes.

The role of mounds of the fungus-growing termite Macrotermes bellicosus (Smeathman) in nutrient recycling in a highly weathered and nutrient-depleted tropical red earth (Ultisol) of the Nigerian savanna was examined by measuring stored amounts of selected nutrients and estimating their rates of turnover via the mounds. A study plot (4 ha) with a representative termite population density (1.5 mounds ha(-1)) and size (3.7 +/- 0.4 m in height, 2.4 +/- 0.2 m in basal diameter) of M. bellicosus mounds was selected. The mounds were found to contain soil mass of 9249 +/- 2371 kg ha(-1), composed of 7502 +/- 1934 kg ha(-1) of mound wall and 1747 +/- 440 kg ha(-1) of nest body. Significant nutrient enrichment, compared to the neighboring topmost soil (Ap1 horizon: 0-16 cm), was observed in the nest body for total nitrogen (N) and exchangeable calcium (Ca), magnesium (Mg) and potassium (K), and in the mound wall for exchangeable K only. in contrast, available (Bray-1) phosphorus (P) content was found to be lower in both the mound wall and the nest body than in the adjacent topmost soil horizon. Consequently, the mounds formed by M. bellicosus contained 1.71 +/- 0.62 kg ha(-1) of total N, 0.004 +/- 0.003 kg ha(-1) of available P, 3.23 +/- 0.81 kg ha(-1) of exchangeable Ca, 1.11 +/- 0.22 kg ha(-1) of exchangeable Mg and 0.79 +/- 0.21 kg ha(-1) of exchangeable K. However, with the exception of exchangeable K (1.2%), these nutrients amounted to less than 0.5% of those found in the topmost soil horizon. The soil nutrient turnover rate via M. bellicosus mounds was indeed limited, being estimated at 1.72 kg ha(-1) for organic carbon (C), 0.15 kg ha(-1) for total N, 0.0004 kg ha(-1) for available P, 0.15 kg ha(-1) for exchangeable Ca, 0.05 kg ha(-1) for exchangeable Mg, and 0.06 kg ha(-1) for exchangeable K per annum. These findings suggest that the mounds of M. bellicosus, while being enriched with some nutrients to create hot spots of soil nutrients in the vicinity of the mounds, are not a significant reservoir of soil nutrients and are therefore of minor importance for nutrient cycling at the ecosystem scale in the tropical savanna.

The green revolution has yet to be realized in Sub-Saharan Africa (SSA) even 40 years after its success in tropical Asia, suggesting that there was a missing element in the basic principles underlying the Asian green revolution when they were transferred to SSA. The authors argue that this missing element is 'ecotechnology'. Ecotechnology improves the crop growing environment in farmers' fields and enables them to accommodate basic green revolution technologies such as modern varieties, chemical fertilizers and irrigation facilities. The authors focus on sawah ecotechnology, a sustainable rice production technology. The term 'sawah' refers to a levelled, bunded and puddled rice field under controlled submergence, and 'sawah ecotechnology' indicates the technology for designing, developing and managing the sawah system. The sawah system development potential is at least 20 million ha in the West Africa (WA) subregion only. Realizing this potential, WA can sustainably produce food for more than 300 million people, as well as enabling the conservation and restoration of hundreds of millions of hectares of upland forests, contributing to carbon sequestration and global warming mitigation in the future.

In this paper, we review the soil fertility characteristics and the nature of material in the West African lowlands in comparison with paddy soils in tropical Asia to examine their potential for rice cultivation. Soil samples collected from major lowland ecosystems, i.e., inland valleys (185 locations) and flood plains (62 locations), in 13 countries (Benin, Burkina Faso, Cameroon, Cote d'Ivoire, Ghana, Guinea, Niger, Nigeria, Liberia, Mali, Senegal, Sierra Leone, and Togo) generally show low values of pH, total C and N, available (Bary-2) P, exchangeable Ca and Mg, effective cation exchange capacity (ECEC), and clay content. These properties of the 87 topsoil samples selected from 247 collected samples are well associated with mineralogical composition. The clay and primary minerals predominantly consist of kaolinite and quartz, respectively, which suggests that the lowland soils in the region have low nutrient-holding capacity and a limited potential for inherent nutrient supply. In general, soil pH, available P, exchangeable bases (Ca, Mg, K, and Na), and ECEC decrease while total C, total N and exchange acidity (Al and FI) increase with increasing rainfall. This tendency is mostly explained by the enhanced biomass production and soil weathering sequence governed by the climate. In terms of rice production, the lowland soils in West Africa have lower values of general fertility parameters and poorer mineralogical characteristics compared to paddy soils in tropical Asia, which includes Bangladesh, Cambodia, India, Indonesia, Malaysia, Myanmar, Philippines, Sri Lanka, and Thailand. In addition, deficit levels of S and Zn for rice production are widely observed in the lowland soils in West Africa. These findings suggest that soil fertility characteristics show substantially less potential for rice production in West Africa than in tropical Asia.

There has been less concern about soil mineralogical alteration than about soil physical, chemical and biological changes induced by termite nest-building activity. Furthermore, much less attention has been paid to free sesquioxides than to phyllosilicate minerals. In the present study, we conducted field morphological observations and selective dissolution analysis to characterize free sesquioxides in termite (Macrotermes bellicosus) mounds as compared with surrounding pedons in different toposequence positions, i.e., seasonally flooded valley bottom, hydromorphic fringe and well-drained upland sites. Distinctive redoximorphic features, such as surface yellowish layers on mound structures from the fringe site, indicate possible alteration of iron sesquioxide forms in the mounds due to the transportation of soil from reductive (aquic subsoil) to oxidative (epigeal mound) environments by the nest-building activity of M. bellicosus. On the other hand, the iron-soluble content in the dithionite-citrate-bicarbonate (DCB) system (Fed) was generally higher in the mound structures than at the adjacent sub-surface (Ap2) horizon at each toposequence position, while there was less difference in the content of acid ammonium oxalate (AAO) extractable iron (Fe(o)) as compared to Fed. As a consequence, the iron activity index (Fe(d)/Fe(o) ratio) was found for the most part to be lower in the mound structures than in the neighboring Ap2 horizon. In addition, the content of Fe(d), AAO-soluble Al (Al(o)) and DCB-extractable Al (Al(d)) was significantly correlated with clay content in these soils. These findings suggest that M. bellicosus preferentially collects clay particles, probably from the clay-rich subsoils, such as the argillic horizon, which has been formed by the co-migration of phyllosilicate minerals and relatively crystalline sesquioxides. The species then likely incorporates them into the mounds, which induces an increase in the Fed content relative to that of Fe(o), resulting in a decreased iron activity index in the mound structures. (C) 2010 Elsevier GmbH. All rights reserved.

This paper examines the characteristics of a traditional farmer-managed irrigation system in Nigeria, through the presentation of a detailed case study. It documents the development of a traditional irrigation system in the inland valley of the Bida region in central Nigeria and the features of its operation and management. The physical structure and the composition of system Users were surveyed in detail. In addition, the characteristics of community management of several irrigation systems ill the region were investigated. Farmers were able to mobilize necessary local resources tor irrigation development and maintenance although they did this without any external support. The irrigation management institution in file area was highly linked to the local land tenure system. The involvement of landlords in the irrigation community greatly affected the performance of irrigation management. There was no clear definition of water rights. In times of water shortage, water was rotated and shared but water scrambling, had become a severe problem in recent years with the higher demand for off-season crops. Irrigation communities were organized informally without tiers of nested organizations. Unfairness in water distribution and contribution to system maintenance existed between top-enders and tail-enders of irrigation canals. Nevertheless, the multi-layered and fragmented land ownership of the region made coordination among different irrigation communities difficult and the unfairness problem could not be solved without institutional changes.

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.

Termites play a significant role in soil-forming processes of the tropics. The influence of termites on pedogenesis as affected by the toposequence, however, has rarely been explored. We investigated the soil physicochemical and morphological characteristics of epigeal mounds constructed by Macrotermes bellicosus (Smethman) compared with those of surrounding pedons along a toposequence (bottom, fringe and upland sites) of an inland valley in central Nigeria. The physicochemical and morphological properties of the mound soils varied according to structural units but were generally different from those of the adjacent pedons. The differences included finer texture, higher electrical conductivity, total N, exchangeable bases (Ca, Mg and K) and effective cation exchange capacity and lower C/N ratio and exchange acidity in the mound than the pedon at each toposequence position. This tendency to modify the soil properties was more prominent in the nest body where the termites actually live, that is, in the hives, royal cell and base-plate, than in the soils below the nest and the other mound parts, that is, the external wall, internal wall and pillars. We found this trend to a greater or lesser degree at all toposequence positions. Our findings suggest that: (1) M. bellicosus can manipulate the mound soils according to functional applications of structure units or environmental requirements for its livelihood, regardless of local soils; (2) M. bellicosus makes ecological patches (hot spots) at all toposequence positions in the same measure; (3) the influence of M. bellicosus on the pedogenesis is reduced in the lowlands compared with the uplands because the number and volume of the mounds were substantially lower in the bottom and fringe sites compared with the upland site.

The particle-size distribution and mineralogical composition of the clay (< 2 mu m) and fine-sand (0.25-0.10 mm) fractions in soils of two inland valleys in Abakaliki and Bende, Southeast Nigeria, were investigated to provide basic information on soil-forming processes and agricultural potentials. These soils were silty or clayey, deriving from Cretaceous or Tertiary shale materials. The particle-size distribution and its computation on a clay-free basis revealed relatively remarkable lithologic breaks in a couple of pedons. The effect of lithologic discontinuities on soil mineralogical composition was not, however, conspicuous. Petrographic investigation revealed that quartz predominantly comprised the fine-sand fraction in the soils at both study sites. Nevertheless, the clay mineralogical composition of the soils was a mixture of kaolinite, irregularly interstratified smectite-illite intergrades (S/I), hydroxyl-Al interlayered 2:1 type clays (HICs), vermiculite, smectite, halloysite and illite along with fine-sized quartz in Abakaliki. The soils of Bende predominantly contained smectite, which was partially interlayered with hydroxyl-Al and kaolinite. It is suggested that seasonal floodwater has slowed the disintegration of weatherable clay minerals inherited from the shale, while quartz originating from the sandstone is predominant in the fine-sand fraction. Additionally, a possible soil-forming process observed at the both study sites was ferrolysis, which was indicated by a clear decreasing pattern of HICs downward in the soil profiles. The entry of S/I and vertical distribution patterns for a couple of clay minerals in the pedon suggested that the soils in Abakaliki have developed under the significant influence of aeolian dust delivered by the Harmattan. The findings might describe a site-specific deposition pattern of Harmattan dusts as well as hydromorphic soil-forming processes in the wetlands of the inland valleys.

Inland valleys are a widespread topography in West Africa and have significant potential for agricultural development, especially wet rice cultivation. This study investigated the physicochemical and morphological properties of the soils of two inland valleys in Abakaliki and Bende, Southeast Nigeria, where the soils are derived from shale materials, and discusses their agricultural potential as well as the soil-forming process. Particle size analysis suggested that the soils at both sites were fine-silty, fine-loamy or clayey and, thus, would be able to retain a high amount of water. In contrast, the higher content of clay and silt in the Abakaliki soils would enhance much more water retention than the Bende soils. The soils in Abakaliki, except for some subsoil horizons, generally had acidic reactions, low contents of exchangeable bases (Ca, Mg, K and Na) and high amounts of exchangeable acidity (Al and H) for which leaching effects under high precipitation in the area would be implicated. Bray-1 P values in these soils were generally low under such acidic conditions, while organic C and total N were recorded at relatively high levels, in particular at the surface horizons, reflecting large biomass production under a humid climate. The Bende soils showed similar chemical properties to Abakaliki except for relative accumulation of exchangeable bases throughout the profile on the downslope possibly because of the rolling topography. This result suggested that geological fertilization (i.e. afflux of nutrients released during the soil formation in the upland into the lowland) was more beneficial in Bende than Abakaliki. From the findings of the present study, we concluded that soils in both Abakaliki and Bende had good texture for sawah development (leveled and bounded rice field with an inlet and an outlet for irrigation and drainage), but their poor chemical properties would be constraints for agricultural production.

The clay mineralogical composition of 87 topsoil (0-15 cm) samples from inland valleys (IVs) and flood plains (FPs) in seven West African countries, namely Cote d'Ivoire, Ghana, Guinea, Mali, Niger, Nigeria and Sierra Leone, was examined using X-ray diffraction analysis to gain basic information for the development of sustainable lowland agriculture in the region. The results of the present study revealed that the clay fraction (< 2 m) of these samples consisted of 68.4% of 7 angstrom minerals (low-activity clays such as kaolin minerals), 26.6% of 14 angstrom minerals (relatively high-activity clays such as smectite and vermiculite) and 5.1% of 10 angstrom minerals (illite or clay micas) and showed a high variability in the composition. With respect to the soil material classification based on the relative abundance of these three types of minerals, Type 7 (rich in 7 angstrom minerals) accounted for 42.5% of the total samples, while 39.7% of all the samples were Type 7-10 and 7-14 with a predominance of 7 angstrom minerals and with negligible amounts of 10 and/or 14 angstrom minerals, respectively. Type 14-7 accounted for 17.2% of the total samples and was only recorded in Nigeria. The other clay mineral types (i.e. Types 7-10-14, 14, 10, 10-7, 10-14 and 14-10) that were composed mainly of 10 and/or 14 angstrom minerals were hardly found in the West African lowland soils, whereas Types 14 and 7-10-14 were observed in a vertic soil of Southeast Ghana and in northern Ghana, respectively. In contrast, no significant differences in the clay mineralogical composition were found between the IV and FP soils. Geographical distribution of the soil types showed that the soils in the eastern part of West Africa contained more 14 angstrom and 10 angstrom minerals than those in the western part. Although the effect of agro-climatological differences was not conspicuous, soils in the Sahel and Sudan savanna zones showed a higher percentage of 14 angstrom clay minerals than those in the Guinea savanna and equatorial forest zones. The findings were as follows: (1) the low fertility status of the lowland soils in the region was closely associated with their poor mineralogical characteristics (i.e. predominance of 1:1 type clay minerals and a lower amount of 2:1 type clay minerals), (2) no significant differences in the mean clay mineralogical composition were observed between the IV and FP soils, indicating that the lower fertility of the IV soils mainly resulted from the lower clay content, (3) the clay mineralogy of the West African lowland soils was more strongly influenced by the nature of the parent materials than by the climatic conditions and relief.

土壌生成速度（SPR）測定法の有力候補である原位置宇宙線生成核種年代決定法（TCN法）と地球化学的マスバランス測定法（GMB法）について、その測定精度と適用範囲を明らかにし、SPR測定法を確立することを目的として、環境条件の異なる調査地においてSPRの測定を行った。その結果、GMB法については、米国、インドネシア、京都、奈良においてSPRを算出することができた。他方、TCN法については、試料の効率的前処理方法の開発まで進んだが、COVID-19の影響もあり、実施期間中に測定まで完了することができなかった。そのため、今後の課題として継続して取り組んでいく予定でいる。

植生や母岩の異なる集水域から得られた観測データを基に、関西圏に位置する森林生態系の土壌生成速度（SFR）を求めることができた。また、当初計画にはなかった既存データの再解析によって、SFRの推定精度を検討できた。これらの結果から長期にわたって集水域マスバランスデータの解析が可能となる米国ハバードブルック長期生態系モニタリングサイトにおける調査の必要性が生じ、関連データを入手し解析を進めることになった。総評として、本研究によってSFRの測定手法を完全に確立するまでには至らなかったが、集水域マスバランス法の信頼性や実用性の一部検証を完了でき、今後の研究へつながる成果を得ることができた。

「緑の革命」後50年間での熱帯アジアの水田土壌の肥沃度の長期的変化を明らかにすることを目的として、50年前に調査が行われたタイ・フィリピン・マレーシア・バングラデシュにおいてほぼ同一地点で土壌を採取して肥沃度特性を分析した。その結果、いずれの国においても可給態リン酸の大幅な増加が認められ、pHや有機物の変化は顕著ではなかった。また、全カリウムの有意な減少がタイで認められた。従って、全般的な土壌肥沃度の向上は認められたものの、収量増加に伴う養分収奪の増加により加速化されていることが予想される土壌養分の適切な管理が熱帯水田稲作の持続性を確保するためには不可欠であると結論された。

サブサハラアフリカ(SSA)の緑の革命は育種・肥料・農薬・灌漑等の近代科学技術だけでは実現せず、科学技術を受け入れる質をもつ農地基盤のインフラ整備が前提となる。17-18世紀の英国の農業革命は14-18世紀のエンクロージャーによる畑地整備が、20世紀のアジアの緑の革命は、それ以前の数百年以上に及ぶ農民による水田整備の歴史が前提であった。同様の農地整備が必要である。人口爆発に対処するには、2050年ころまでにSSAにおける数千万ha規模の灌漑水田開発を実現するイノベーションが必要である。農民の自力灌漑水田開発と稲作技術であるアフリカ水田農法Sawah Technologyは、これを可能にする。

本研究ではまず、土壌動物による鉱物風化作用に関する研究の現状と課題を明らかにするため、既往の研究のレビューを行った。また、ナイジェリア産のシロアリ塚土壌の試料を用いて、対照土壌との鉱物組成の比較を行なった結果、土壌動物が鉱物風化に及ぼす影響は小さいため、野外調査でその影響を定量的に調査することが難しいことを確認した。他方、熱帯の強風下土壌におけるシロアリの営巣活動に起因する遊離酸化鉱物の移動・集積が土壌生成過程で無視できない影響を及ぼすことを示唆した。この他、インドネシアの火山灰土壌地帯において、土地利用や管理主方が土壌動物相の変遷と非晶質鉱物の含有量に変化をもたらすことを明らかにした。