**2. Fertilizer use for maximization of the farmer's profit**

Smallholder cropping systems are typically diverse, and each crop or intercrop has some level of profit potential for each nutrient that might be applied [2, 3, 5–13]. Crop-nutrient response functions typically have a diminishing profit-to-cost ratio as the nutrient rate approaches the agronomic optimum. A financially constrained farmer maximizes net returns through optimized choice of crop-nutrient-rate options (**Figure 1**; [4]). In contrast, when fertilizer use is not financially constrained, the profit-oriented farmer targets to apply at the rate at which net returns per hectare are maximized. Fertilizer use decisions can be made by integrating crop-nutrient response functions using linear optimization through computer-based and simple paper decision tools that have been developed for 73 recommendation domains across 15 nations of tropical Africa by the project Optimizing Fertilizer Recommendations in Africa [2, 3, 14].

#### **Figure 1.**

*Net returns in Kenyan shillings (KSh) to investment in nutrient application vary with crop-nutrient-rate choices, exemplified for Central Kenya with fertilizer use costs and on farm commodity values typical in 2016 [4].*

**199**

**Figure 2.**

*Fertilizer Use Issues for Smallholder Agriculture in Tropical Africa*

**3. Management of soil acidification and nitrogen sources**

+

slowed by avoiding excessive application of N and leaching of NO3

economical to use relatively less expensive but more acidifying NH4

. Soil acidification is greater if NO3

Supply of nitrogen to cropland typically contributes to soil acidification whether the N is supplied through fertilizer, organic materials, biological fixation of atmospheric N, or wet and dry deposition of atmospheric NH4-N [15]. Soil

rather than recovered by plants. Soil acidification associated with N sources can be

izers and occasionally amend the soil with lime application rather than using less

Soil acidification concerns are important in Kenya, for example, especially in some high elevation and high yield potential areas (**Figure 2**). The promoted N fertilizer for these areas is calcium ammonium nitrate (CAN) rather than urea. The chemical composition of CAN varies, but CAN of 27% N contains about

N. Therefore, urea is about 28% more acidifying per kg of N

carbonate (dolomite) may be added to give the fertilizer about 20% calcium carbonate equivalent (CCE). The acidification effect of ammonium nitrate and urea is 3.65 kg CCE for each kg of N applied. If the CCE of CAN is neutralized in the soil, it reduces the net acidification effect of CAN-N by about 22% to about

compared with CAN. Calcium is supplied by CAN but cannot be credited with

economic value to farmers if the yield response to CA is not profitable.

uptake by plants with subsequent release of

<sup>−</sup>-N, and calcium carbonate or calcium-magnesium

<sup>−</sup>-N is leached from the soil

+

<sup>−</sup>-N fertilizers [16]. Very often, it is most

<sup>−</sup>-N and by the


*DOI: http://dx.doi.org/10.5772/intechopen.89040*

acidification also occurs with NH4

use of less acidifying but more costly NO3

+


*Soil pH distribution across Kenya determined using AfSIS data.*

cations, mostly H<sup>+</sup>

acidifying fertilizers.

13.5% each of NH4

2.85 kg CCE kg<sup>−</sup><sup>1</sup>

*Sustainable Crop Production*

investments. Fertilizer use can have a high probability of high profit with wellinformed crop-nutrient-rate choices but also with efficient input supply, favorable credit terms, subsidies, and efficient marketing of the commodity produced [2–4]. The objective of this chapter was to explore four issues affecting the profit potential of fertilizer use by financially constrained smallholder farmers: (1) the choice of fertilizer use options with the greatest potential return on investment, (2) the choice of N source and management of soil acidification, (3) the use of tailored fertilizer blends as alternatives to common straight fertilizers, and (4) the alternative nontraditional products for managing soil productivity. The implications for farm profitability are fundamental to the discussion of these issues.

Smallholder cropping systems are typically diverse, and each crop or intercrop has some level of profit potential for each nutrient that might be applied [2, 3, 5–13]. Crop-nutrient response functions typically have a diminishing profit-to-cost ratio as the nutrient rate approaches the agronomic optimum. A financially constrained farmer maximizes net returns through optimized choice of crop-nutrient-rate options (**Figure 1**; [4]). In contrast, when fertilizer use is not financially constrained, the profit-oriented farmer targets to apply at the rate at which net returns per hectare are maximized. Fertilizer use decisions can be made by integrating crop-nutrient response functions using linear optimization through computer-based and simple paper decision tools that have been developed for 73 recommendation domains across 15 nations of tropical Africa by the project

*Net returns in Kenyan shillings (KSh) to investment in nutrient application vary with crop-nutrient-rate choices, exemplified for Central Kenya with fertilizer use costs and on farm commodity values typical in* 

**2. Fertilizer use for maximization of the farmer's profit**

Optimizing Fertilizer Recommendations in Africa [2, 3, 14].

**198**

**Figure 1.**

*2016 [4].*
