Site and Management Effects on Grain Yield and Yield Variability of Rainfed Lowland Rice in the Kilombero Floodplain of Tanzania

Abstract

In East Africa, smallholder farmers produce rainfed lowland rice mainly in floodplains. Low nitrogen contents of the predominant Fluvisols and highly variable hydrological conditions result in low yields and large yield variations, and hence, result in high production risks for farmers. We investigated crop management strategies aimed at increasing yield and reducing yield variability. The field trials were carried out in the Kilombero floodplain near Ifakara in Tanzania, in three hydrological zones (potentially drought-prone fringe, favorable middle and submergence-prone center positions) over three years. The study compared farmers’ management practices (no field levelling and bunding, no fertilizer input), with the effect of bunding and levelling alone, or in combination with mineral N use at 0 (bunding), 60 (recommended rate) and 120 kg + 60 kg PK ha−1 (attainable yield). Rice mean grain yields (averaged over the four treatments) were higher in the fringe (6.5 t ha−1) and the middle (5.7 t ha−1) than in the center positions (4.6 t ha−1). Farmers’ practice resulted in lowest yield (3.0 t ha−1) and highest yield variability, with an adjusted coefficient of variation (aCV) of up to 91% between fields, years and positions. Simple bunding of the plots and field levelling increased yields by 40% above farmers’ practice, particularly in the fringe and middle positions, while reducing yield variation (aCV of 36–61%). Mineral N application resulted in the highest yields (7.0 t ha−1) and further reduced yield variation (aCV of 14–27%). However, only in bunded fields of the floodplain fringe rice could benefit from N application beyond 60 kg ha−1, while mineral N use efficiency was lower in middle and center positions. Improved crop management options are most beneficial in floodplain fringe positions, where they can increase yields and reduce production risks. Due to low yield, high production risks and poor responsiveness to management interventions, the center may be taken out of rice production and could be considered for future use as protection zones.

Long-Term Land Use/Land Cover Change Assessment of the Kilombero Catchment in Tanzania Using Random Forest Classification and Robust Change Vector Analysis

“…In addition, forest loss would directly translate into further habitat loss, biodiversity loss and negative impacts on local livelihoods that depend on their ecosystem services. Hence, further agricultural development must rely on measures to increase productivity, e.g., moderate irrigation, use of fertilizer, leveling, weeding, bunding [106,107]. Such options must be weighed carefully, as also agricultural intensification without areal extension can have detrimental effects on the environment, if not done in a sustainable manner, causing soil compaction, erosion or pollution through input of chemicals [108].…”

“…Such options must be weighed carefully, as also agricultural intensification without areal extension can have detrimental effects on the environment, if not done in a sustainable manner, causing soil compaction, erosion or pollution through input of chemicals [108]. Nevertheless, good agricultural practices can improve yields but are currently not common practice in the Kilombero area [107]. Intensification, however, requires financial capital, access to fertilizer, and capacities.…”

The Impact of Land Use/Land Cover Change (LULCC) on Water Resources in a Tropical Catchment in Tanzania under Different Climate Change Scenarios

“…The demographic growth accelerated in the 90s and after 2000 due to the migration of mainly pastoralists into the valley [23] and correlates with the growing share of cropland in the valley, which was increasingly converted from grassland and savanna into cropland to feed the growing population. We use these conversions into cropland as a proxy for demographic growth, due to the stagnating trends in rice yields in the area [73,74], although conversions into cropland might also be affected by investors from outside the valley and other factors. Lastly, the influence of politics and the economy is not included, but might change the LULC drastically by setting incentives for agricultural activities e.g., the SAGCOT initiative [22], changing the allocation or status of conservation areas or by developing the infrastructure.…”

“…The cropland scenario for 2030 ( Figure 7b) displays a strong increase in the discharge amount of Q10, which is distributed to the months of March to May (Figure 9d). This might lead to aggravated flooding events, which could either endanger the farmer's harvest [73,74] their lives, critical infrastructure and their livelihood [84]. Especially newly promoted, high yielding, but low growing improved varieties such as like SARO5 (TXD 306) might be negatively affected by these changes.…”

Dynamics of Human–Water Interactions in the Kilombero Valley, Tanzania: Insights from Farmers’ Aspirations and Decisions in an Uncertain Environment

“…It is a very dynamic environment (Leemhuis et al 2016) affected by increasing variability in the onset and intensity of the rainy season (Näschen et al 2019b). Agricultural production needs not only to cope with, but also adapt to the changing availability of water during the course of the year (Gabiri et al 2018;Kwesiga et al 2019;Kwesiga et al 2020). Agricultural development has been prioritized by Tanzania's development vision formulated in the Kilimo Kwanza or Agriculture First initiative and set to be achieved through the more recent SAGCOT initiative.…”