High soil salinity on irrigated land results causes an estimated crop loss of 27.3 billion USD per year globally. Traditional irrigation schemes in Tanzania are often plagued poor infrastructure and inadequate water circulation resulting in soils with high salinity and sodicity. While irrigation schemes have created the ideal conditions in terms of water content for rice crops to flourish, poor infrastructure results in increased salinity as water flows through consecutive fields. The combination renders farmland infertile, incapable of producing even minimal yields for most crops. For rice, this culminated in grains that failed to fill, producing empty husks.
In Northeastern Tanzania where rice is the principal crop, soil salinity is of particular concern. Due to the combination of low yields and increasing consumption, an estimated 10-25% of rice consumed in Tanzania is imported. Roughly 90% of rice production in Tanzania is done by small-scale farmers. In areas with low rainfall, irrigation schemes have doubled rice production. However, a consequence of increased irrigation is often high soil salinity if improperly managed. Traditional irrigation schemes are often sub-optimal due to insufficient outlets and rising salinity due to the re-use of water.
Rice is an increasingly important commodity with rising rates of consumption throughout sub-Saharan Africa. A combination of land degradation and the increased use of poorly-designed irrigation schemes has aggravated existing high soil salinity areas. As rates of irrigation increase sustainable land management is needed to mitigate crop losses caused by salt-affected soils. As a result, the Innovative Agricultural Research Initiative (iAGRI) prioritized the research conducted by Sophia Kashenge-Killenga, Senior Researcher at Chollimo AGRO Scientific Research Center in Dakawa, Tanzania. The research combines the use of the following to mitigate saline and sodic soils.
- Soil treatment combining the use of gypsum and flushing plus farmyard manure to lower sodicity and improve soil structure
- Experimental soil treatment infusing soils with rice husks and sawdust to improve filtration of compacted soils
- Improved Tanzanian rice varieties developed for local markets through hybridization using salt tolerant parents collected from International rice research institute (IRRI)
The research has resulted in the reclamation of some of the fields within 680 hectares of Ndungu irrigation scheme. One field (0.45ha) was previously abandoned for 20 year had produced 15 bags (of 80kg each) after Dr Kashenge intervention. The use of sawdust and rice husks improved soil conditions enough to be able to produce 3.0 t/ha on average. The combination of gypsum application and improved varieties raised rice yields from 0.5 t/ha to 6.0 t/ha. Today, the rehabilitated soils support rice production for 1,774 households in the semi-arid region of Ndungu, Tanzania. The project is applicable to a further 59 irrigation schemes in nine other regions in Tanzania similarly affected by saline and sodic soils.
For more information on the ongoing research on soil salt affected soils in Tanzania, download the following publications:
- S. Kashenge-Killenga. 2010. Breeding investigations for salt tolerance in rice incorporating characterisation of salt affected soils and farmers perceptions and preferences for tolerant cultivars in north-eastern Tanzania, Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg.
- S. Kashenge-Killenga, P. Tongoona, J. Derera. 2013. Morphological and physiological responses of Tanzania rice genotypes under saline condition and evaluation of traits associated with stress toleranceInternational Journal of Development and Sustainability, 2 (2), pp 1457-1475.
- S. Kashenge-Killenga, P. Tongoona, J. Derera, Z. Kanyeka. 2014. Farmers’ perception of salt affected soils and rice varieties preferences in the north-eastern Tanzania and their implications in breeding, International Journal of Development and Sustainability,3 (6), pp 1257-1271.
- S. Kashenge-Killenga, P. Tongoona, J. Derera, Z. Kanyeka, and J. Meliyo. 2012. Soil characterisation for salt problems in selected rice irrigation schemes: A key aspect towards improvement of salt Tolerance Rice Genotypes in North Eastern Tanzania. Journal of Advances in Developmental Research. Volume 3, No.1
- S. Kashenge-Killenga, P. Tongoona, J. Derera, and Z. Kanyeka. 2012. Irrigated rice-based farm characteristics and production constraints in selected salt affected areas of North-eastern Tanzania. Journal of Advances in Developmental Research, 3 (1).