The inter ac tion of land use and sea sonal mi cro cli mat ic events could explain the dif fer ences in soil qual ity char ac ter is tics which medi ate bio log i cal and phys i cal pro cesses of the soil under low input land use sys tems (plough plus har row, strip/heap till age, man ual clear ing/no till). It is hy poth es ised that in a humid trop i cal Alf isol, low input sys tem involv ing reduced till age meth ods, and min eral fer til izer and/or live stock manure use, would sup port a higher den sity of micro bial bio mass, soil aggre ga tion, organic C and total N and hence improve ment in soil qual ity. The dynam ics of biotic and abi otic soil prop er ties as affected by meth ods of seed bed prep a ra tion char ac ter ised by man ur al input and mi cro cli mat ic tran si tions from wet to dry sea son was stud ied in a maize field in a trop i cal rain for est Alf isol in Ak ure, a humid rain for est zone of Nige ria. Each year, tri als were car ried out dur ing the rainy (April–July) and late (September–December) sea sons of 2001 and 2002. Meth ods of seed bed prep a ra tion involv ing plough plus har row, strip/heap till age and no till age, and addi tion of dif fer ent gra di ents of manures (mineral N and/or plant debris and live stock litter) were imposed on the soil at the site of the exper i ment (of com pa ra ble phys i cal prop er ties of bulk den sity and texture). Among the treat ments, there were sig nif i cant dif fer ences in the val ues of water hold ing capac ity, aggre gate sta bil ity (macro-aggre ga tion), con cen tra tions of micro bial bio mass, organic C, total and min eral N and CEC. In the rainy and late sea son tri als, the strip/heap till age and the no till treat ments improved aggre gate sta bil ity (as mea sured by the per cent ages of aggre gates between 2 and 10 mm of soil) and water hold ing capac ity over plough + har row. For exam ple, in the rainy sea son trial, under treat ments involv ing strip/heap till age and the no till alone and in com bi na tion with live stock manur ing and res i due reten tion, the val ues of aggre gates between 2 and 10 mm range from (110–116; 113–119 g/kg) and water hold ing capac ity (0.11–0.14; 0.12–0.15 g/g) over plough + har row (107.3 g/kg; 0.11 g/g). Sim i lar trends were found in the val ues of soil micro bial bio mass C (377, 353; 547, 490 μg/g dry soil), soil organic C (3.8, 4.3; 5.2,5.5 g/g) and total N (2.9, 2.3; 2.9, 3.0 mg/g) for strip/heap and no till treat ments com pared to plough + har row (327.6 μg/g dry soil; 3.4 g/g; 2.8 mg/g). Although the %C micro bial to C organic ratio (an indicator of the utilisation of organic carbon by the microbes in terms of organic matter turn over rate) was sta ble for all treatments, its magnitude was not con stant but increased with increases in soil C concentration. The values of microbial bio mass carbon to organic carbon (Cmic: Corg) ratio were higher under plough ing and heap till age com bined with min eral N (0.096, 0.099) than in no-till treat ment (0.083) in the rainy sea son trial. Similar trends were obtained in the magnitudes of this param eter in the late sea son trial. Microbial bio mass correlated positively with both soil organic C (y = 0.393c − 6.7; r2 = 0.99; P< 0.05) and water hold ing capacity (y = 0.87c0.39; r2 = 0.94; P<0.05) and neg a tively with bulk density (y=−0.3c+1.9; r2 = 0.90; P<0.05), strong positive lin ear cor re la tion were also found between soil macro aggre gates and other soil prop er ties: micro bial bio mass C (y=0.41c−18.4; r2=0.95; P<0.05), organic C (y=0.61c−14.3; r2 = 0.97; P<0.05) and total N (y = 0.063c−10.8; r2 = 0.98; P<0.05). Huge responses of soil characteristics were obtained from low input land use systems (plough plus har row, strip/heap till age, manual clear ing/no till). These proper ties mediate many biological and physical processes of soil carbon, N mineralisation, soil aggregation and water hold ing capacity and microbial bio mass, and led to improvement in soil quality. The emerged trend was that the interaction of land use, clay content of the soil and seasonal micro climatic events could explain the heteroge neity of soil components among treatments.

Effects of Some Soil Management Systems on Soil Physical Properties, Microbial Biomass and Nutrient Distribution Under Rainfed Maize Production in a Humid Rainforest Alfisol

n Quantification of litter deposition and organic mantle accumulation are important steps on nutrient cycling studies. This study aimed to quantify litter deposition and organic mantle in a sabiAE (Mimosa caesalpiniifolia Benth) woodlot in an experimental farm in the Brazilian northeast region. Twenty 0.50 x 0.50 x 0.15 m wood collectors, to quantify litter deposition, were systematically distributed over the area elevated 30 cm above the soil. Deposited material was collected monthly from October 2000 to September 2001, and separated into leaves, twigs, flowers, pods and mixed portions. Undecomposed organic mantle was randomly sampled nearby collector boxes, to a total of 20 monthly samples, from which a 0.30 x 0.30 m composed sample was collected. The collected material was also hand separated into leaves, twigs, flowers,

http://www.scielo.br/pdf/rarv/v31n1/02.pdf

Deposição e acúmulo de matéria seca e nutrientes em serapilheira em um bosque de sabiá (Mimosa caesalpiniifolia Benth.)

Na pecuaria bovina sustentavel, tem sido utilizada a presenca de arvores associada as pastagens. Neste trabalho, objetivou-se avaliar a influencia de arvores de Sucupira - Branca (Pterodon emarginatus) em atributos fisicos e quimicos do solo e sobre a qualidade da forrageira em sistema silvipastoril. O estudo foi realizado no municipio de Nioaque-MS, Brasil. Em area ocupada com pastagem de Brachiaria decumbens sombreada predominantemente por Sucupira - Branca, foram escolhidas cinco arvores adultas representativas, no entorno das quais foram tracadas seis transectas locadas a ângulos de 60o entre uma e outra. Em intervalos de cinco metros ao longo dessas transectas foram centradas as parcelas de amostragem ate 30 m de distância, coletando-se ai amostras de serrapilheira, da graminea e do solo. Para a forragem, analisou-se: proteina bruta (PB), fibra em detergente neutro (FDN) e digestibilidade in vitro da materia seca (DIVMS). Para o solo, os atributos estudados foram: densidade do solo, macroporosidade, microporosidade, porosidade total, resistencia a penetracao, teores trocaveis de magnesio e potassio. Os dados foram submetidos a analises de regressoes simples e de correlacao. Concluiu-se que: a materia orgânica da serrapilheira interfere de forma positiva nos atributos fisicos do solo, melhorando sua qualidade estrutural; a presenca das arvores interfere no valor nutritivo do capim-braquiaria, possibilitando aumento dos teores de PB e FDN e reduzindo a DIVMS.

/pdf/influencia-de-pterodon-emarginatus-vogel-sobre-atributos-3vpuj4b4wr.pdf

Influência de Pterodon emarginatus Vogel sobre atributos físicos e químicos do solo e valor nutritivo de Brachiaria decumbens Stapf em sistema silvipastoril

Managing Tephrosia mulch and fertilizer to enhance coffee productivity on smallholder farms in the Eastern African highlands

Keywords: food security, biophysical and socioeconomic conditions, farmer resource groups, productivity, economic evaluation, scenario analysis Smallholder livelihoods in sub-Saharan Africa(SSA) are constrained by a number of factors that limit food production and thereby threaten food security. Soil fertility is one of the major factors explaining the decrease in per capita food production in SSA. Nutrient deficiencies in particular N and P severely limit agricultural production in many regions in the tropics. Supply of adequate amounts of nutrients throughfertiliserapplication is therefore a prerequisite to balance soil fertility budgets and to boost food production. However, mineral fertilisers are not accessible to the large majority of smallholder farmers. Farmyard manure, an important source of organic fertiliser for smallholder farmers, is available at limited quantities due to low livestock densities in many regions, for example Rwanda. Agroforestry, a low-input technology, was shown to contribute to the enhancement of food production while ensuring sustainability in sub-Saharan Africa.Agroforestry may contribute to soil fertility by increasing nutrient availability and providing other various benefits and services. However, to be successful agroforestry technologies need to match the characteristics of different smallholder farming systems, like for example soil fertility status, socioeconomic status and farmer management. These factors are rarely studied in an integrated manner. This thesis aims to understand and characterise different farming systems, evaluate the potential for the most promising agroforestry practices and suggest the most suitable agroforestry recommendations for different farming systems in targeted agro-ecological zones of Rwanda. The approach combined characterization of farming systems, participatory tree testing, farmer’s evaluations of technologies, and scenario and trade-off analyses in two agro-ecological zones: Central Plateau (moderate altitude) and Buberuka (high altitude zone). Two locations, Simbi and Kageyo sectors were selected as representative study sites. Wealth ranking techniques allowed the identification of three farm resource groups (RGs). Though three farmer classes were identified in the two locations and referred as RG 1, RG 2 and RG 3 respectively, farmer classes were unique to each location. Averaged over sampled villages, 76% of all households belong to RG 1 class in Simbi versus 67% in Kageyo. This least resourced group with on average 0.20 ha of land and with 1 goat wasthe most vulnerable farmer groupin terms of food security (20 to 25% protein deficient).RG 2 (9 to 31%) was intermediate between RG 1 and RG 3. RG 3 (2 to 7 %) was the wealthiest (1 to 3 ha, 2 or more cattle) and food-secure for at least 10 months. Soil nutrient balances were negative in most farms due to small amounts of nutrients applied, which did not compensate for nutrient removal during harvest. From an agroforestry perspective, Simbi contrasted with Kageyo in tree diversity and density but tree niches and management were similar between the locations. The main agroforestry species may becategorisedinto three classes including timber, legume and fruit tree species based on the main functions. The results clearly indicated the need to improve soil fertility and food production using integrated soil fertility approaches that promote a combined use of agroforestry resources and other fertiliser sources to replenish the soil nutrients and improve the efficiency and cost effectiveness of inputs use at farm level. Experiments evaluated the potential effects of agroforestry species on production within different farming systems. Tephrosia species were tested as a source of mulch in coffee plantations in the Central Plateau agro-ecological zone. Application of Tephrosia mulch resulted in higher biomass and better economic returns when established in coffee fields, particularly when Tephrosiamulch was combined with NPK. Application of prunings of Calliandra increased maize productivity, net returns and the ratio between gross margin and costs of inputs on all farms except the richest farms. This positive effect of Calliandra was larger in Kageyo than in Simbi. The effect was even more pronounced with P application. The results indicated that fields responded differently within farms, and significant differences between locations were present. The assessment of fodder availability within different farming systems revealed that animal feeds are widely diversified, with Pennisetum being largely used in wealthier farms (RG 3), while RG 1 farmers use larger quantities of marshland-herbs and crop residues.There was a strong variation in seasonal feed availability. Napier and Calliandra were more available during the wet season, while banana pseudo-stems were used more in the dry seasons. Quantification of the year-round fodder availability showed that RG 1 farmers are unable to keep a cow, while RG 2 and RG 3 could keep local or improved cows under specific scenarios. Biophysical (rainfall, field type) and socio-economic conditions (wealth status) as well as farmer preferences were factors influencing the choice and performance of agroforestry technologies. The study recommends revisiting current agroforestry research policies and taking into account farmer’s preferences as priorities in the agroforestry research agenda.

Tailoring Agroforestry Technologies to the Diversity of Rwandan Smallholder Agriculture Charles Bucagu

Improving fallow quality in cassava–fallow rotations in southeastern Nigeria through the use of leguminous cover crops has been shown to sustain the productivity of such systems. We studied the effects of age (1 or 2 years) of Tephrosia candida fallow on biomass and nutrient accumulation, on weed biomass and yield response of cassava/maize intercrop and on changes in soil chemical properties in a 3 yr field trial. Results were compared with those obtained in natural fallow. Total biomass and litter were three times higher in plots fallowed for 2 yr with Tephrosia candida than in those under natural fallow for the same period. Weed biomass was 205% lower in T. candida plots fallowed for 2 yr than in the natural fallow and was 174% smaller in T. candida plots fallow for 1 yr than in the natural fallow. Nutrient (nitrogen, phosphorus, calcium, magnesium and potassium) yields in leaves of T. candida fallow for 2 yr were on average 200–300% higher than in leaves of other fallows. The same trend was observed for cassava and maize yields. Soil chemical changes at soil depth 0 to 5 cm showed significant increases in N and C concentrations after 2 yr fallowing and a year of cropping, particularly in the planted fallow plots. Conversely, soil pH, available P and the exchangeable cations, especially Ca were lower, while Al was higher than the initial values, mainly in plots fallowed under T. candida, indicating a tendency of this fallow species to further exacerbate the soil acidification problem of the acid Ultisol at the study site in southeastern Nigeria.

M.P. Gichuru

Papers

Nutrient recycling potential of Tephrosia candida in cropping systems of southeastern Nigeria