Toshiyuki Wakatsuki

Ecological Engineering for Sustainable Food Production and the Restoration of Degraded Watersheds in Tropics of Low pH Soils: Focus on West Africa

Since upland rice under shifting cultivation is common, the mean paddy yield in sub-Sahara Africa (SSA), especially West Africa, has been stagnated at 1.3–1.7 t ha−1 during the past 30 years of 1970–2000. There exist numerous small inland valley swamps (IVS), of which 10 million ha is capable of being turned into small scale irrigated rice fields, i.e., sawah* by simple and low cost ecological engineering technology with farmers self-support efforts. The fertility of lowland soils in West Africa was the lowest, particularly available phosphorous status was extremely poor and low pH as well as low exchangeable bases among the three tropics of Asia, Africa and Latin America. However, because of multi-functional mechanisms of soil and water conservation and replenishment of nutrients, sustainable productivity of 1 ha of lowland sawah system can be equivalent more than 10 ha of upland fields. Geological fertilization, nitrogen fixation, neutralization of pH and increase phosphorous availability are the important functions of the sawah system. Sustainable development of sawah systems in IVSs can contribute to increase food production and to restore the degraded watersheds of SSA. *Sawah: The term sawah refers to leveled rice field surrounded by bund with inlet and outlet connecting irrigation and drainage. The term originates from Malayo-Indonesian. The English term, Paddy or Paddi, also originates from the Malayo-Indonesian term, Padi, which means rice plant. The term, Paddy, refers to rice grain with husk in West Africa of SSA. Most of the paddy fields in the Asian countries correspond to the definition of the term sawah. Paddy field is almost equivalent to sawah for Asian scientists. However, the term paddy fields refers to just a rice field including upland rice field in West Africa of SSA. Therefore in order to avoid confusion between the terms rice plant, paddy, and the improved man-made rice growth environment through ecological engineering, the authors propose to use the term sawah.

Water Movement Characteristics in a Multi-Soil-Layering System

The Multi-Soil-Layering (MSL) system consists of soil units arranged in a brick-like pattern that are surrounded by layers of zeolite or alternating particles with a homogeneous size that allow a high hydraulic loading rate. Characteristics of the changes in the water movement, hydraulic retention time (HRT) and system weight during the wastewater treatment in the MSL system were investigated using a laboratory-scale MSL system (D10 × W50 × H73 cm). As the loading rate increased from 1,000 to 5,500 L m−2 d−1, wastewater preferentially flowed into the permeable layers in the MSL, which decreased the contact of the wastewater with the soil mixture layers. HRT was inversely related to the loading rate. HRT decreased from 20 to 1 h, as the loading rate increased from 250 to 6,000 L m−2 d−1. As an indicator of the system condition, the weight variation of the system was determined during the wastewater treatment. When the weight was stable, input and output of wastewater and decomposition of organic matter appeared to be equilibrated. When the weight increased, the system started to clog. Due to clogging, the efficiency of COD and phosphorus removal decreased, while the efficiency of nitrate removal increased.

Effect of heating treatments on nitrogen mineralization from sewage sludge

Abstract Heating of sewage sludge has multifunctional benefits for agricultural recycling of sludge, one of which is the heat-induced changes in N mineralization from the sludge. To enhance the understanding and practical use of this phenomenon, we subjected sewage sludge to heating treatments at 120°C or 180°C for 16 h with or without air-drying as a pretreatment. During the 84-day aerobic incubation period, N mineralization from the sludge mixed with samples of an Andosol, a Fluvisol, an Arenosol and an Acrisol was significantly accelerated by the heating of air-dried sludge at 120°C and was significantly retarded by heating at 180°C, regardless of the soil types and temperatures during the incubation period. More conventional heat-drying of moist sludge at 120°C or 180°C also exerted similar but less pronounced effects. These heat-induced changes were attributed to the transformation of sludge organic N, because volatilization of N during the heating treatments was negligible. Sequential extraction of sludge N enabled detection of the heat-induced N transformations accounting for some but not all of the incubation results, indicating that mineralization of N in the heated sludge materials was determined not only by chemical extractability but also by other factors. Our results suggest that heating of sewage sludge regulates the rate of N mineralization and presents a promising method for producing various organic N fertilizers from sewage sludge.

Performance of Rice Cultivars in Various Sawah Ecosystems Developed in Inland Valleys, Ashanti Region, Ghana

Experiments were conducted in 2001 and 2002 to evaluate the agronomic responses of 23 rice cultivars with various growth traits in order to select suitable cultivars based on the ecosystems and local farming systems, in the Ashanti region of Ghana. The ecosystems included irrigated sawah* (IS), rainfed sawah (RS) and unbunded and unleveled lowland (UBLL). Two input levels consisted of a high input level (HIL—90 kg N + 45 kg P2O5+ 45 kg K2O ha−1+ herbicide application at 21 d after transplanting (DAT)+ hand weeding at 42 DAT) and a low input level (LIL—20 kg N+farmers’ weed control practices). The results showed that the adoption of the high input level resulted in the increase of the rice grain yield by 100% with a mean yield of 4.2 Mg ha−1, compared with 2.1 Mg ha−1 for the low input level. Rice yield in IS exceeded that in UBLL by 323%, whereas the yield in RS exceeded that in UBLL by 130%. Under the rainfed systems (RS and UBLL), the early maturing cultivars, WAB 208-5-HB, Emokokoo, Bouake189, PSBRC 34 and PSBRC 66 were less affected by the terminal drought that characterized the end of the rainy season, compared with the medium maturing ones such as WITA 1, WITA 3 and IR58088-16-2-2. Interspecific WAB208-5-HB (O. glaberrima×O. sativa) out-yielded most of the improved Oryza sativa cultivars in the UBLL ecosystem under both high and low input regimes.

Distribution and changes in heavy metal contents of paddy soils in different physiographic units of Bangladesh

Abstract The distribution and changes in the background levels of V, Cr, Mo, Ni, Cu, Zn, Pb, U, and As were assessed using 66 archived surface (Ap horizon) soil samples (22 for 1967 and 44 for 1995) analyzed by RIX 2000 x-ray fluorescence spectrometry to determine whether a soil was polluted or not during the period 1967–1995 in Bangladesh. Distribution of the mean V content showed lower values (<15.6 mg kg−1) in the soils of the Old Himalayan Piedmont Plain (OHP), Barind Tract (BT), and Madhupur Tract (MT), values ranging between 115.6 and 169.0 mg kg−1 (mean ± SD / 2) in the Tista Floodplain (TF), Brahmaputra Floodplain (BF), Meghna River and Estuarine Floodplain (MF), Northern and Eastern Piedmont Plains (NEP), and Chittagong Coastal Plain (CCP), and higher values (>169.0 mg kg−1) in the Ganges Floodplain (GF) and Surma-Kushiyara Floodplain (SKF). The mean Cr contents were lower (<84.7 mg kg−1) in OHP, TF, BT, and MT, ranged between 84.7 and 107.1 mg kg−1 in GF, BF, MF, NEP, and CCP, and a higher content (>107.1 mg kg−1) was recorded in SKF. The mean Mo contents ranged between 2.01 and 2.11 mg kg−1 in all the physiographic units except for a lower content (<2.01 mg kg−1) in TF and a higher content (>2.11 mg kg−1) in the MT unit. The mean Ni contents were lower (<39.5 mg kg−1) in OHP, TF, and BT, ranged between 39.5 and 62.3 mg kg−1 in GF, BF, MF, MT, NEP, and CCP and a higher content (>62.3 mg kg−1) was recorded in SKF. The mean Cu contents were lower (<23.4 mg kg−1) in OHP, TF, BT, MT, and NEP, ranged between 23.4 and 39.8 mg kg−1 in MF, SKF, and CCP, and a higher content (>39.8 mg kg−1) was recorded in GF and BF. The mean Zn contents were lower (<60.3 mg kg−1) in OHP, BT, MT, and NEP, ranged between 60.3 and 90.9 mg kg−1 in TF, MF, and CCP, and a higher content (>90.9 mg kg−1) was recorded in GF, BF, and SKF. The mean Pb contents were lower (<21.7 mg kg−1) in TF, BT, and NEP, and ranged between 21.7 and 25.3 mg kg−1 in the other physiographic units. The mean U content was lower (<3.47 mg kg−1) in NEP and an almost uniform distribution between 3.47 and 5.29 mg kg−1 was observed in the other physiographic units except for a higher content (>5.29 mg kg−1) in TF. The mean As contents were lower (<6.2 mg kg−1) in OHP, TF, and BT, ranged between 6.2 to 8.7 mg kg−1 in BF, MT, MF, NEP, and CCP, and a higher content (>8.7 mg kg−1) was recorded in the GF and SKF soils. The contents of V, Cr, Mo, Ni, Cu, Zn, Pb, V, and As in the peat soil were 222.2, 111.1, 2.11, 63.4, 57.4, 108.8, 25.4, 5.28, and 12.3 mg kg−1, respectively. However, the distribution of the V, Cr, Mo, Ni, Cu, Zn, Pb, V, and As contents was in the range of 43.3–275.0, 61.0–176.0, 1.90–2.21, 14.0–134.0, 8.7–65.7, 27.8–138.0, 14.3–31.0, 2.23–5.93, and 3.9–14.0 mg kg−1, with mean values of 142.3, 95.9, 2.06, 51.0, 31.6, 75.6, 23.5, 4.38, and 7.5 mg kg−1, respectively, in 1995. The heavy metal contents of the surface soils were, generally, higher on the lower slopes than in the middle or upper parts of the landscapes. A wide variation in the changes of heavy metal contents was observed among the soils of different physiographic units in Bangladesh. Changes in the V, Cr, Mo, Ni, Cu, Zn, Pb, V, and As contents showed higher increases up to 33.1, 25.0, 15.38, 28.5, 35.5, 24.9, 19.0, 22.10, and 34.6% and higher decreases down to 24.3, 13.1, 2.56, 36.4, 51.0, 21.5, 12.3, 18.98, and 40.0% respectively, with mean values remaining almost unchanged (−1.87 to +6.81%) except for a decrease of 17.1% Cu during the period 1967–1995. Results of this study suggested that the soil properties (clay, total Fe and Al contents, ECEC, total C content, pH, total Sand P contents) are important factors regulating the natural background levels of heavy metals in the soils of Bangladesh.

Effect of long-term intensive rice cultivation on the available silica content of sawah soils: Java Island, Indonesia

Abstract The dramatic increases in rice productivity and cultivation intensity through the implementation of green revolution (GR) technology using high yielding varieties (HYVs) of rice and chemical fertilizers were not long lasting in Indonesia. The stagnancy of rice productivity in recent years without any scientific reasons presents a challenge for agronomists and soil scientists in Indonesia. This study describes the effects of long-term intensive rice cultivation on the change in available silica (Si) in sawah soil. The term sawah refers to a leveled and bounded rice field with an inlet and an outlet for irrigation and drainage. Soil samples collected by Kawaguchi and Kyuma in 1970 and new samples taken in 2003 from the same sites or sites close to the 1970 sites were analyzed and compared. From 1970 to 2003, the average content of available Si decreased from 1,512 ± 634 kg SiO2 ha−1 to 1,230 ± 556 kg SiO2 ha−1 and from 6,676 ± 3,569 kg SiO2 ha−1 to 5,894 ± 3,372 kg SiO2 ha−1 in the 0–20 cm and 0–100 cm soil layers, respectively. Cultivation intensity differences between seedfarms planted with rice three times a year and non-seedfarms rotating rice and upland crops appeared to affect the changing rates of available Si within the study period. In the 0–20 cm soil layer, the average content of available Si decreased from 1,646 ± 581 kg SiO2 ha−1 to 1,283 ± 533 kg SiO2 ha−1 (−22%) and from 1,440 ± 645 kg SiO2 ha−1 to 1,202 ± 563 kg SiO2 ha−1 (−17%) in seedfarms and non-seedfarms, respectively. Differences in topographical position also influenced the decreasing rate of available Si in this study. Using similar management practices and cultivation intensity, upland sampling sites lost more Si compared with lowland sites. Planted rice under a rain fed system with no Si addition from rain water in an upland position may be a reason for the higher loss of Si, particularly in non-seedfarms. The Si supply from irrigation water might have contributed to the slowdown in the decreasing rate of available Si in Java sawah soils.

Soil Profile Alteration in a Brown Forest Soil under High-Input Tea Cultivation

Received 7 November 2005. Accepted 4 April 2006. Corresponding author : S. S. Abe (shinabe@phanes.muses.tottori-u.ac.jp, fax +81-857-31-5367). Abbreviations : Av-P, available P; Et-B, HCl-extractable B; Et-Cu, HCl-extractable Cu; Et-Fe, HCl-extractable Fe; Et-Mn, HCl-extractable Mn; Et-Mo, HCl-extractable Mo; Et-Zn, HCl-extractable Zn; Ex-Al, exchangeable Al; Ex-Ca, exchangeable Ca; Ex-K, exchangeable K; Ex-Mg, exchangeable Mg; NF-0, native forest; TC, total C; TF-19, 19-yr tea fi eld; TF-34, 34-yr tea fi eld; TN, total N. Soil Profi le Alteration in a Brown Forest Soil under High-Input Tea Cultivation

Land use dynamics and nutrient characteristics of soils and plants along topo-sequences in inland valley watersheds of Ashanti region, Ghana

Abstract Surveys on land use dynamics were conducted over a 3-year period along various toposequences in benchmark inland valley watersheds of the Ashanti region, Ghana. Six typical land use systems were selected for more detailed studies, Le., primary forest (PF), cacao farm (CP), fallow (Fallow), mixed cropping (MC), and lowland rice-based systems including both traditional rice (TR) and sawah{ft1} (paddy)-based rice farming (Sawah). Topsoil samples (0-20 cm) and samples of leaves and bark of various plants were collected from these land use systems for nutrient characterization using laboratory analyses. The remaining primary and secondary forests cover only a patchy area, accounting for less than 20%, in forest reserves and surrounding areas. Cacao farms were developed both in the upland areas, middle slopes, and lowland areas, which occupied about 20% of the watershed. Lowland rice farming is estimated to account for about 10% of the watershed. Oil palm cultivation is also common in the lowland areas. The remaining land use systems were mostly fallow and mixed cropping of maize, cocoyam, cassava, and plantain. Plant leaves of various species in the lowland traditional rice area showed higher concentrations of phosphorus and potassium but lower calcium and strontium concentrations than those of the leaves in the upland surveyed plots, especially, the forest area. Nitrogen, sulfur, magnesium, and the other mineral elements, however, did not show any clear differences among the six land use systems. Bark samples tended to exhibit lower concentrations of nitrogen, phosphorus, sulfur, magnesium, sodium, silicon, aluminum, iron, manganese, and copper but higher concentrations of calcium and strontium. Cacao leaves showed silicon-accumulator characteristics and the magnesium concentration was high too. Cacao bark contained potassium and zinc in appreciable amounts in compared to the leaves. Topsoil samples of the primary forest and cacao farms in the upland areas showed higher levels of TC, TN, exchangeable Ca and Mg, and eCEC while the levels of available P showed a rather reverse trend compared to the lowland traditional and sawah rice plots. Topsoil samples of the fallow and mixed cropping plots at upland and fringe sites showed intermediate levels. The pH at the mixed cropping site was the lowest. These general fertility trends along upland and lowland topo-sequences were different from those of monsoon Asia and Japan. With the implementation of the sawah rice-based farming system, the inland valleys could contribute to the enhancement of sustainable food production in the country.

Rice Growth and Yield in Waste-Amended West African Lowland Soils

Abstract The use of organic materials as an alternative to or in combination with inorganic fertilizer is being advocated for use by small-holder rice farmers in sub-Saharan Africa as way to reduce the cost of inputs and stabilize yields of modern varieties grown in the lowlands. In this study, the effects of humified sludge (HS), poultry manure (PM), cattle manure (CM), a mixture of humified sludge and poultry, and cattle manures (MM), and inorganic fertilizer (IF) were evaluated on growth and yield of rice during the dry and wet seasons. Three lowland soils, Eutric Vertisol (EV), Eutric Fluvisol (EF), and Haplic Gleysol (HG), were amended with 90 kg N/ha from the above nutrient sources. Organic materials incorporation was done four weeks before transplanting with 21-day-old rice seedling whereas IF was split-applied as basal and at panicle initiation. Soil was flooded until 10 d before harvest. Plant height, number of tillers and panicles, days to 50% flowering, 1000-grain weight, biomass, and grain yield as well as harvest index were recorded. Soil electrical conductivity (EC) and pH were measured before amendments and at maximum tillering, flowering, and maturity stages during the wet season. Soil amendments with manure or fertilizer improved the growth and yield of rice. Flowering was delayed more than 7 d in Vertisol without organic amendment. Humified sludge, PM, and IF significantly enhanced tillering and plant height more than did other nutrient amendments, especially in Vertisol. Mean grain yield in the wet season was 17.4% better than in the dry season. For the dry and wet seasons, nutrient amendment effect on grain yield was ranked HS > PM > MM > IF > CM > Control and HS > PM > IF > CM > MM > Control, respectively. The superiority of HS and PM to the chemical fertilizer may be attributed to balanced and gradual release of plant nutrients, which were synchronized with demand at various growth stages of the rice plant.

Nutrient Distribution in the Profile of Valley Bottom Soils Cultivated to Rice in Ghana

ABSTRACT The consumption of rice has increased in Ghana recently, but supply cannot meet demand; hence, there is a large annual importation to make up for the deficit. In Ghana, rice is cultivated under three main systems, namely rain-fed upland conditions, irrigated conditions, and rain-fed lowland conditions. Due to unpredictable rainfall, production under rain-fed conditions has been very unstable. Fortunately, inland valley systems (IVs), which have been cited by many authors as the environment best suited for efficient and sustainable rice production, abound in this country. This study was therefore undertaken to determine the soil nutrient status, and to document a plant species distribution that is useful for nutrient cycling in the IVs of the Ashanti region of Ghana. The goal is to develop a sustainable sawah-rice production system. ** Valley bottom soil samples for laboratory analyses were collected from standard soil profiles in areas under use for rice cultivation or capable of supporting rice. Results showed these soils to be slightly acidic (topsoil mean pH = 5.7) with low exchangeable acidity [0.10 cmol(+)/kg]. Mean topsoil total carbon (C), nitrogen (N), and available phosphorus (P) (Bray 1) were 1.8%, 0.20%, and 4.4 mg/kg, respectively. Exchangeable cation [cmol (+)/kg] values of surface soils were 0.3 for potassium (K), 5.1 for calcium (Ca), 1.8 for magnesium (Mg), and 0.2 for sodium (Na), respectively. The concentrations of C, N, and most cations decreased down the profile. However, the overall fertility levels were well within the normal ranges for IVs of West Africa. The species dominating the valley bottoms were fairly similar in their carbon content. However, Manihot esculenta and Mallatus oppositifolium of the family Euphorbiaceae were higher than other species in N content. Species belonging to the family Euphorbiaceae were lower in P content (which ranged from 0.9 to 3.7 g/kg) while Physalis angulata and Manihot esculenta contained the highest (3.9 and 3.6 g/kg) P, respectively. The variable nutrient composition of these species has implications for nutrient cycling in the ecosystem. Knowledge of nutrient status of IVs will greatly assist in efforts at adopting the Asian type of sawah rice cultivation. If supported with appropriate farming practices that return crop residues to the soil and utilize inorganic fertilizer or organic manures, the inland valley ecology can contribute significantly to food security, especially of rice, and also conserve the environment. **The term sawah refers to bunded and leveled rice fields with both irrigation and drainage gates. It is of Malayo-Indonesia origin. The English term paddy originated from the Malayo-Indonesian word padi, meaning rice plant. It refers to unhusked rice in West Africa. Most of the paddy fields in the Asian countries fit the definition of sawah. However, the term paddy field refers only to a rice field, including upland rice fields in West Africa. To avoid any confusion between a rice plant paddy and the improved man made rice-growing environment, the authors use the term sawah.