Sustainability of Intensification of Smallholder Maize Production in Tanzania

Abstract

Tanzania’s fast growing population will increase the demand for food crops, particularly maize. Sustainable intensification is needed to meet this demand while, at the same time, preserving the environment and climate. A joint project of Yara, Syngenta, Sokoine University of Agriculture, and the Norwegian University of Life Sciences demonstrated that a balanced supply of crop nutrients together with other improved practices has the potential to increase maize yields and farm profitability. A framework was developed and applied to assess the potential impacts of different cropping intensities on climate, soil, water, and biodiversity in order to evaluate the environmental sustainability of the measures. Maize yields increased by 49–163 % compared to prevailing farmer practice (FP). This in turn may reduce the need for arable land expansion and thus potentially avoid GHG emissions. If GHG emissions from potential arable land expansion into tropical scrubland are considered, GHG emissions from the low-yielding treatments would be 3.6–12 times greater than the CFP of the improved protocol. Low positive soil nutrient balances with the improved cropping protocol indicate sustainable fertilizer use, which can replenish the soil with sufficient nutrients. In contrast, FP often showed negative nutrient balances, signifying unsustainable nutrient mining even at low yield levels. The increased nitrogen rates and crop productivity lead to increased soil acidification, which needs compensation from liming. The improved maize protocol doubled maize stover biomass, which can be used to improve the organic matter and fertility of the soil either through direct incorporation into the soil or through feeding livestock and producing and applying manure. A water footprint calculation at one site revealed that the maize produced according to FP consumed 50 % more water per ton of grain compared to the improved protocol. Biodiversity was assessed in different ways. In-field biodiversity was reduced with the suggested protocol, while on-farm biodiversity was enhanced through the planting of additional trees instead of expanding cropland. About 50 % less land was needed to produce one ton of maize grain, reducing pressure for land expansion that would have potential negative effects on biodiversity on a larger scale.

Appendix

1.1 Welela Site

See Table 7.1.

Table 7.1 Nutrient application rates, productivity, profitability, and environmental parameters for the Welela site (profitability not available for 2014 due to lack of data)

• Nutrient management

  • Increased fertilizer rate in YSS (+20 %) adjusted to high yield in 2013

  • FP treatment with increasing fertilizer use during the project

• Productivity

  • High yield potential (9.3 t/ha in 2013)

  • On average, 2.6 times higher grain yield and three times higher stover yield with YSS protocol

  • FP yield increasing with increasing fertilizer use (1.8–3.8 t/ha)

• Profitability

  • On average, 3.3 times higher profit with YSS

• Environment

  • Average carbon footprint (CFP) with YSS 61 % higher without considering potential land use change (pLUC) needed to compensate for the yield difference between FP and YSS (for more information about the pLUC concept and definition, see Plassmann et al. 2014)

  • Average CFP 12 times higher if pLUC is included

  • Negative N and P balances with FP (i.e., reducing soil reserves)

  • K balance negative in both treatments

  • Decreasing pH in both treatments, indicating a need for lime application

  • On average, FP requires almost three times more land to produce one ton of maize grain.

1.2 Ibumila Site

See Table 7.2.

Table 7.2 Nutrient application rates, productivity, profitability, and environmental parameters for the Ibumila site (profitability not available for 2014 due to lack of data)

• Nutrient management

  • Decreased fertilizer application rate (−20 %) in 2013 and 2014 due to low yield level

  • Farmer applied relatively high nutrient rates from the beginning

  • Farmer applied in addition some manure to FP plot

• Productivity

  • Low yields overall, low NUE, but still on average +48 % grain yield and +68 % stover yield with YSS protocol

  • Profitability

  • Small but still positive financial results with YSS compared to loss with FP

  • Whether a profit or loss is realized depends on maize price; therefore, investing in inputs is high risk for the farmer

• Environment

  • High product carbon footprint in both treatments (>500 kg CO₂e/t grain)

  • Five times higher CFP with FP when including potential land use change effects

  • On average, unsustainably high N surplus in YSS treatment (+72 kg N/ha), negative K balances in both treatments

  • Very low pH from the beginning, even decreasing during the project, Al/Mn toxicity is a possible reason for low yields; liming is required

  • Additional liming experiment was established, but not presented here; some positive effects on soil pH, but not yet on grain yield

  • On average, FP requires 1.7 times more area to produce one ton of maize grain.

1.3 Kichiwa Site

See Table 7.3.

Table 7.3 Nutrient application rates, productivity, profitability, and environmental parameter for the Kichiwa site (profitability not available for 2011 and 2014; no nutrient balances in 2013 due to missing plant samples; no data for 2012 because FP plot was harvested without yield measurements)

• Nutrient management

  • Increased fertilizer rate in YSS (+20 %) adjusted to high yield in 2012 (not shown)

  • Farmer adopted improved system partially (comparably high input rates and same products)

• Productivity

  • Very good crop response to fertilizer application

  • High yield potential (8.7 t/ha in 2014), less fluctuation than in Welela (better soil)

  • On average, 51 % higher yield with YSS protocol, only 14 % more stover yield

  • FP yield much higher than TZ average (5 t/ha)

• Profitability

  • Similar profit with both strategies, but less risk with FP if investment in inputs fails, e.g., due to lack of rain

• Environment

  • Comparably low CFP in both treatments (about 250 kg CO₂e/t grain)

  • On average, 4.3 times higher CFP with FP if potential land use change is considered

  • Negative N and K balances with FP, negative K balance in YSS treatment

  • Higher soil pH compared to other Njombe sites; in acceptable range in both treatments

  • 50 % higher water consumption per ton of grain in FP treatment, more efficient use of available water with YSS protocol

  • On average, 51 % more area required with FP to produce one ton of grain.

1.4 Matingajola Site

See Table 7.4.

Table 7.4 Nutrient application rates, productivity, profitability, and environmental parameters for the Matingajola site (profitability not available for 2014 due to lack of data)

• Nutrient management

  • Very low input/output in FP; no adoption of improved practice

• Productivity

  • Good yield response in first year but declining yields in both treatments during the course of the project (lack of rain but also soil acidification may have contributed)

  • On average, 2.6 times higher grain yield and 2.4 times higher stover yield with YSS protocol

• Profitability

  • On average, more than eight times higher profit with YSS protocol

  • Negative result in 2013 in FP, probably leading to the decision not to invest in fertilizer in 2013

• Environment

  • Very low CFP in FP treatment due to low or zero mineral N fertilizer use; 3.8 times higher CFP with YSS protocol on average

  • Including potential land use change effects, the CFP of the FP treatment is about 10 times higher

  • Consistently negative N and K balances in FP treatment, probably unsustainably low P balance

  • Increasing N balances with YSS due to decreasing N use efficiency, need for N input adjustment

  • Drop in soil pH in particular with YSS; liming is needed

  • 2.5 times more land is needed to produce a ton of grain with FP.

1.5 Site Sokoine University of Agriculture (SUA)

See Table 7.5.

Table 7.5 Nutrient application rates, productivity, profitability, and environmental parameters for the Sokoine University of Agriculture (SUA) site (profitability not available for 2014 due to lack of data)

• Nutrient management

  • No fertilizer input in FP treatment in first season, which is typical for maize cultivation on newly re-established fields; low input in subsequent years

• Productivity

  • Comparably high yields with no or low input in FP due to high soil fertility of the re-established maize field (was left fallow for some years before)

  • Good and consistent grain yield response to fertilizer input in YSS (+49 % compared to FP; +59 % more stover yield)

• Profitability

  • 23 % higher profitability with FP

  • Profitability in FP treatment is based on natural soil fertility not sustainability, as negative nutrient balances indicate

• Environment

  • Very low CFP in FP treatment due relatively high yield with low N input, 75 % higher CFP with YSS

  • Including potential land use change effects changes the result with 3.6 times higher CFP for FP

  • Consistently negative N, P, and K balances in FP treatment clearly indicate mining of natural soil fertility

  • Positive but low N and P balances and negative K balance in YSS treatment

  • Soil pH in recommended range but decreasing over the trial period; liming will become necessary

  • On average, 51 % more land is needed with FP to produce one ton of grain.