The CIAT’s cassava research took the initiative to contribute to such approach

The potential yield of bioethanol is apparently higher in cassava than for any other plant species, including the traditional bioethanol source crops such as maize, sweet sorghum and sugarcane. However, the gap between the potential experimental yields of cassava and the actual yields on farmers’ fields is more than fivefold . With the exception of India, current farmers’ yields as low as 6 – 8 t/ha exists in Africa and as high as 13 – 18 t/ha occurs in some Asian and Latin American countries. These low yields are normally attained with local, traditional varieties grown on marginal soils without the application of purchased agrochemicals.

The expected higher demands in developing countries for cassava products as food, feed, and industrial uses in the face of climate changes would call for the removal of the many socioeconomic constraints on cassava production, uses and marketing. Moreover, since the cassava plant has inherently high leaf photosynthetic capacity in current air and at high temperature coupled with high solar irradiances , also , and responds positively to elevated CO2, possible future expansion in cassava cultivation may enhance atmospheric carbon sequestration, and hence helps mitigating adverse effects of globally warming climate . Under the predicted CO2 rises in this century , cassava may be one of the few tropical food crops that can adapt to this climatic changes by shifting upward its optimum temperature for photosynthesis, growth and production.

Most crops increase their WUE in elevated CO2 environments, particularly under water deficits,due to both higher carbon uptake and lower stomatal conductance to gas diffusion that lead to less transpiration water losses. Cassava is equipped with a tight stomatal control mechanism over gas exchanges, which is more sensitive to changes in air humidity and soil water status than other crops , also , making it highly efficient in water use . As most cassava production by smallholders occurs in marginal lands with low levels of soil fertility , cassava breeding strategy at CIAT focused on selection for adaptation to farmer’s field conditions . Cassava soil-and-plant nutrition management section , and later cassava physiology section , oriented their research objects toward characterization of CIAT cassava germplasm in response to infertile, low-P, acidic soils in the South American tropics.

From 1982 to 1996, more than 1800 accessions, including land races, common varieties and elite CIAT breeding lines have been evaluated for responses to P, and many clones with high level of adaptation to low P have been identified and included in crop improvement program . Later several dozens of cassava core germplasm have also been tested for their tolerance to low-K soils, with few clones with high level of tolerance have been identified . In the following subsections, data of many tested accessions for their tolerance of low-P and low-K soils, as well as responses to P or K fertilizer application, are presented. Current hydrological and GCMs models predict, within the next decades, the occurrence of extended drought periods across continents, coupled with irregularity in intensity and distribution of rainfall, as well as a possible increase in land area prone to drought in tropical and subtropical regions. This expected shortage in water resources, combined with rises in Earth’s surface temperature, will be significant enough to negatively impacts agricultural productivity and food security for the projected >9 billion world population , particularly in developing countries.

The inherent capacity of cassava to tolerate adverse environments, a comparative advantage over most tropical staple food crops, enhanced the expansion of the crop cultivation in more marginal areas in sub-Saharan Africa, Northeastern Brazil and other areas in Asia . Moreover, in the coming decades when experiencing globally warming climate, cassava will play even more important role, as other less adapted staple food crops will probably fail to produce reasonably.Cassava responds positively to elevated CO2 , and to high temperatures,two crucial atmospheric characteristics of climate change. Adaptation and mitigation measures then become essential approaches to obviate expected adverse effects of climate change,with the development of improved genetic and agronomic technologies being the main elements.The physiological research at CIAT have elucidated and documented the many mechanisms underlying cassava tolerance to abiotic stresses , and was pivotal in enhancing interests for expanding cassava production in semiarid areas in South America and Sub-Saharan Africa, areas where other main staple tropical crops such as cereals and grain legumes probably will fail to produce.

The dispersion test was used as a routine procedure for all samples submitted to SCS Laboratories

In our studies this could not be shown, probably because the organic matter contents and release of N were comparably small and thus system related differences were not visible against the general “noise” of spatial and temporal heterogeneity. Determination of the impact of tillage on WSA did not result in a clear-cut trend suggesting that reduced tillage and residue retention would always increase aggregate stability, as has been proven elsewhere. However, ambiguous results in regard to the influence of tillage and residue retention on WSA were also found by for Western Kenyan cropping systems under integrated soil fertility management.

A higher share of larger aggregates under ZT points towards better soil structure, which in turn positively affects soil water infiltration and retention—witnessed by our results on these properties. Further, more large aggregates in C16 than in B4 was most likely a positive effect of the higher SOM content in C16, as SOM is the glue that holds aggregates together. However, our observations show that WSAs change with soil depth. To reveal the underlying mechanisms further research is required to fully understand the impact of tillage on WSA of the high-clay, montmorillonitic soils of northern Syria, which are typical for the Mediterranean region. It was somewhat surprising that soil water infiltration capacity varied significantly over time, which basically meant, at least for the soils at ICARDA headquarters, that the applied method did not give consistent results complying with what could be considered saturated hydraulic conductivity. Also, quantities were much higher— at least a factor 10—than Ks-values established for the same soil .

Nevertheless, the consistency of results provides evidence about the soil ameliorating impact of ZT and residue management. An increased water infiltration capacity allows water to infiltrate deeper into the soil and diminishes water runoff and thus soil erosion. This has been known for many years, and has been shown in many other comparable studies, such as in Germany , USA , Australia , Poland , Argentina , and Mexico . On the other hand, observed surface crusting and decreased water infiltration under NT. Yet, despite reduced infiltration, their NT treatments still conserved more soil moisture during the dry fallow period than the tilled plots. also could not find any improvement in infiltration rate under ZT in comparison to chisel ploughing in Argentina. We tried to answer the question whether in addition to higher water infiltration capacity by reduced tillage and residue management a surface residue layer would conserve soil moisture.

During the late cropping season, high surface residue levels did not contribute to moisture conservation in the top 15 cm of soil, contradicting what has been reported elsewhere. However, increased crop transpiration—manifesting itself in significantly higher yields compared to the off-site control—could have confounded the results. After harvest, under fallow conditions, residues could in general not prevent the loss of soil moisture from 0 – 15 cm depth within about four weeks although moisture levels were some few per cent higher during the first three weeks under the plots with the two highest residue levels. This means residue retentionimpacted moisture in the top soil for a limited time only. Under fallow conditions the effect was still notable five weeks after application of 30 mm of irrigation water when including 15 – 30 cm depth into the calculation, but only if very high amounts of residue were retained; much more than can be produced on-site under dry rainfed conditions.

A temporary reduction of soil water evaporation during the cropping season when residues are retained should improve the crop-soil water balance by shifting water losses from unproductive evaporation to productive crop transpiration. However, a recent modelling study revealed that the impact is limited, not exceeding on average 10 – 15 mm per season that is transpired instead of evaporated . Corresponding yield data revealed that minimum tillage and residue retention translates into higher yields for all major crops of the region in the majority of years. Our data show that obviously this is due to the effect of an increased soil quality and more favorable soil water relations. Adequate, balanced nutrient management including crop nutrition by chemical fertilizer application is, of course, an underlying necessity. Our results provide evidence that SOM increased in response to N-fertilizer application, but further research is required to consolidate this observation.The lack of success of dams and embankments as a result of the use of dispersive soil has been recognized byengineers and geologists in South Africa and internationally for many years.

Agroforestry production systems decreased incomeinequality in the study area

Notwithstanding this concern the Gini coefficient still remains a popular inequality measure of total inequality and as a decomposable measure. Using the CV approach, we decomposed the total household incomes into three major categories of income namely; income from crops, income from timber products , and income from off-farm activities . We purposefully used CV to pinpoint the contribution of these three categories of income sources to total income inequality. This is useful because conventionally, most studies have often attempted to evaluate the distributional impact of certain types of income by merely comparing the size of distribution of that particular income with that of the total rural income as a whole.

Because it neglects the twin issues of income weights and covariance between income sources, any approach, which solely compares the size distribution of one particular income with that of total income, is likely to arrive at erroneous conclusions regarding the distributional impact of that particular income . Our results , indicate that 50% of the sample households in the study area had incomes of less than the mean income . About 90% of the households had incomes of less than TZS 3,342,022 and only 10% had income higher than this. These results suggest existence of income inequality in the study area. At the 50 percentile, the mean incomes for disaggregated analysis were the highest for farmers with farmland located far from homestead , followed by those of farmers who accessed extension services during the past two years and farmers who were members of community-based financial institutions .

The mean incomes were the lowest for female-headed households , followed by farmers who did not access extension services , and farmers with farmland located close to homestead . Farmlands located far from homestead were mostly found along the footsteps of the mountains or lowland areas where landholdings were relatively larger allowing for more intensification and crop revenues than the farmlands located in the upper gradients. This relationship is common in mountain areas. Mountain areas are considered as less favoured due to difficulties caused by short growing seasons, steep slopes at lower altitudes, or by a combination of the two . Land holdings in high altitudes of mountain areas are limiting the scale of economic activities performed by farmers to increase farm income. Doucha et al. , for example showed that, farmers in in Czech less favoured areas could rarely grow permanent pasture along with extensive cattle breeding or undertake any additional non-agricultural activities on farm . In fact, Kata confirmed decreasing value of income from operational farm activity toward higher altitude. In this circumstance, farm incomes may remain insufficient for smallholder farmers to undertake a profitable agricultural production.

The influence of altitudinal variation on crop production and animal husbandry is also reported by Zhang et al. who investigated the response of altitudinal vegetation belts of the Tianshan Mountains of north-western China. They indicate that residents used the natural advantage of this area to develop animal husbandry. However, the changes in the montane steppe belt were seen to greatly affect the scale of animal husbandry and the income of herdsmen . To address the challenges of agricultural production in mountain areas, farmers who are relatively better-off, tend to move along an altitude gradient—to the lowlands .The results of analysis of income inequality using the Gini index and Lorenz curves for income distribution are shown in Table 4 and Figure 3 respectively. The Gini coefficient for the pooled sample was 0.97. The analysis of income data disaggregated by farmland location, gender of household head, access to extension services, and membership to community-based financial institutions, revealed that the latter had the most equalizing effect on income. The Gini coefficient for farmers who were not members of any community-based was 0.77 implying that nonmembership to these institutions had a more inequalising effect on income.

Importantly, income inequality was the highest among farmers with farmland located far from homestead . Overall, these findings support the argument that the size of households, access to extension service, credit access, and membership to social groups determine income distribution . Unexpectedly however, income inequality among farmers who accessed extension services was higher than that of their counterpart farmers who did not access the services . We attribute this to variations in personal household characteristics , and economic characteristics as indicated in our results of coefficients for the independent multiple linear regression models presented in Appendix 3.