**1. Introduction**

Kenya is the world's fourth largest producer of pigeonpea after India, Myanmar and Malawi, of which 99% is produced in semi-arid eastern Kenya, especially Machakos, Kitui, Makueni, Meru, Lower Embu, and Tharaka-Nithi Counties. It is also grown in the drier parts of Kirinyaga, Murang'a, and Kiambu Counties in Central Kenya; and some parts of Lamu, Kilifi, Kwale, Tana River, and Taita-Taveta Counties at the Coast; mainly by small-scale resource-poor farmers [1–6]. Most farmers intercrop pigeonpea with maize or sorghum on the same land, either in alternate or multiple rows, as a form of security against total crop failure [7].

Pigeonpea provides multiple benefits to the rural poor. Firstly, its protein-rich grain can be consumed both fresh and dry and provides a cheap source of protein for the poor farmers in the drylands. Secondly, its leaves and hulls are used as

livestock feeds and the stem as fuelwood. Thirdly, it has the ability to enrich the soil through di-nitrogen fixation [8], litter fall and being a deep-rooted crop, to mobilize nutrients, particularly phosphorus, from the deep soil horizons [9–11]. Fourthly, intercropping pigeonpea with cereals enhances soil coverage, reduces soil erosion, and boosts cereal yields [9, 10]. Finally, the crop provides an assured source of income for farm families and foreign exchange for Kenya. About 7000 ton of dhal (dehulled pigeonpea) and 15,000 ton of whole grain are exported annually to Europe, North America, the Middle East, and India, but this figure represents just 30% of Kenya's export potential [1, 4–6, 12]. Thus, pigeonpea has immense untapped potential which if fully exploited could transform the lives of many communities and economies of many countries in the East African region. Maize on the other hand is the staple food for over 90% of Kenya's population and accounts for 56% of cultivated land in Kenya [13].

Despite the importance of maize-pigeonpea intercropping system in semi-arid Kenya and elsewhere in the region, their productivity has continued to decline. Maize and pigeonpea yields on farmers' fields are low, averaging 300–500 kg ha−1 against a yield potential of 2.5 t ha−1, mainly due to non-use of improved varieties and poor farming practices, low soil fertility and climate variability [2, 6, 14]. The situation is bound to worsen in future with the expected change in climate. Temperatures and rainfall in Kenya and the rest of East Africa are expected to increase by about 2°C and 11%, respectively, by 2050 due to climate change [15–18]. However, the rise in temperature may cause a substantial increase in evaporation rates, which are likely to balance and exceed any benefit from the predicted increase in precipitation [19]. Thus, if not checked, climate change will undermine agricultural productivity and expose millions of people to hunger and poverty, especially in semi-arid areas where temperatures are already high and rainfall low and unreliable, agriculture is predominantly rain-fed and adoption of modern technologies is low [20, 21].

A lot of work has been done to quantify some of the agricultural impacts associated with projected changes in future climate using a variety of simulation models, but most of it has been carried out at global, regional and country levels hence not applicable to community-based adaptation planning [20, 22–24]. Similarly, despite the importance of pigeonpea in Kenya and elsewhere in the region, few studies have assessed the impact of climate change on its performance. Most studies have focused on staple and commercial crops such as maize, tea, wheat, rice, beans and groundnuts [20, 21, 25–27], and tomatoes [28]. There is a need for more detailed information on the impacts of climate change on pigeonpea-maize intercropping systems to guide in formulating appropriate adaptation measures that will increase their productivity, ensure food security in future, and safeguard pigeonpea's niche markets. Therefore, the objective of this study was to assess the impact of climate change under a range of scenarios on intercrops of maize and improved pigeonpea varieties developed and released in Kenya in recent times.

## **2. Materials and methods**

#### **2.1 Study area**

The study was conducted at the Kenya Agricultural and Livestock Research Organization (KALRO) Katumani Research Centre in Machakos County, 80 km south-east of Nairobi (37°14′E and 1°35′S). Katumani has bimodal rainfall pattern and receives an average of 711 mm annually. The long rains (LR) occur from March to May and the short rains (SR) from October to December with peaks in April

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*Impact of Climate Change on Maize and Pigeonpea Yields in Semi-Arid Kenya*

and November, respectively [7, 29]. Inter-seasonal rainfall variation is large with coefficient of variation ranging between 45 and 58% [30]. Temperatures range between 17 and 24°C with February and September being the hottest months. The mean annual temperature is 20°C. Evaporation rates are high and exceed the amount of rainfall, most of the year, except in the month of November. The mean potential evaporation is in the range of 1820–1840 mm per year whilst evapotranspiration is estimated at 1239 mm [31] giving an r/ETo ratio of 0.57. Katumani is 1600 m asl and the terrain ranges from flat to hilly with slopes varying from 2 to 20% [32]. It falls under agro-climatic zone IV which has a low potential for rain-fed agriculture [29]. The dominant soils are chromic Luvisols [33, 34], which are low in organic C, highly deficient in N and P and to some extent Zinc and generally have

Mixed farming systems involving food crops and livestock are characteristic of the region. Crops grown are predominantly drought-escaping or early maturing varieties of pigeonpea, maize, beans, sorghum, and millet [29]. Due to the erratic nature of rainfall, most farmers around Katumani and the larger semi-arid Eastern Kenya prefer to intercrop maize with at least a legume (pigeonpea, beans, or cowpeas) on the same land. This is often done either in alternate or multiple rows and is seen by many farmers as a form of security against total crop failure [7]. Long duration pigeonpea is normally planted during SR in October–November and harvested in August–September the following year. Medium and short duration varieties can be planted and harvested in one season. Crop combinations, planting patterns, and plant populations of pigeonpea and other crops vary considerably, depending on the soil type, climate, and farmer's preferences. However, dominant pigeonpea cropping systems practiced in the region include: pigeonpea intercropped with maize, sorghum, millets, cowpea and green gram; pigeonpea and cowpea intercrops; and

Agricultural Production Systems Simulator (APSIM) version 7.3 was used to predict the impact of climate change on maize and pigeonpea yields in Katumani and similar areas in eastern Kenya. APSIM was preferred due to its user-friendliness, widespread application in the region and ability to make highly precise simulations/predictions once properly initialized [16, 36–40]. The APSIM has the capacity to predict the outcome of diverse range of farming systems and management practices under variable climatic conditions, both short and long term [39, 41–44]. It also simulates growth and yield of a range of crops in response to a variety of management practices, crop mixtures, and rotation sequences, including pastures and livestock [44]. The model runs with a daily time step and has four key components: (1) a set of biophysical modules that simulate biological and physical processes in farming systems, (2) a set of management modules that allow the user to specify the intended management rules that characterize the scenario being simulated and controls the conduct of the simulation, (3) various modules that facilitate data input and output to and from the simulation, and (4) a simulation engine that drives the simulation process and controls all messages passing between the independent modules [44, 45]. It has a user interface which allows selection of input data (climate, soil, crop, and management), output data from modules of interest (e.g., water balance, carbon, nitrogen and phosphorus balances, and crop growth and yield) management of simulation scenarios (saving, running, retrieving, and deleting), error checking (summary of scenario set-up inputs and run time operations), and output analysis via software

links for viewing output data in text file, Excel, or graphs [44].

*DOI: http://dx.doi.org/10.5772/intechopen.93321*

maize/bean/pigeonpea intercrops [1, 4–6].

**2.2 Long-term simulation**

poor structure [35].

#### *Impact of Climate Change on Maize and Pigeonpea Yields in Semi-Arid Kenya DOI: http://dx.doi.org/10.5772/intechopen.93321*

and November, respectively [7, 29]. Inter-seasonal rainfall variation is large with coefficient of variation ranging between 45 and 58% [30]. Temperatures range between 17 and 24°C with February and September being the hottest months. The mean annual temperature is 20°C. Evaporation rates are high and exceed the amount of rainfall, most of the year, except in the month of November. The mean potential evaporation is in the range of 1820–1840 mm per year whilst evapotranspiration is estimated at 1239 mm [31] giving an r/ETo ratio of 0.57. Katumani is 1600 m asl and the terrain ranges from flat to hilly with slopes varying from 2 to 20% [32]. It falls under agro-climatic zone IV which has a low potential for rain-fed agriculture [29]. The dominant soils are chromic Luvisols [33, 34], which are low in organic C, highly deficient in N and P and to some extent Zinc and generally have poor structure [35].

Mixed farming systems involving food crops and livestock are characteristic of the region. Crops grown are predominantly drought-escaping or early maturing varieties of pigeonpea, maize, beans, sorghum, and millet [29]. Due to the erratic nature of rainfall, most farmers around Katumani and the larger semi-arid Eastern Kenya prefer to intercrop maize with at least a legume (pigeonpea, beans, or cowpeas) on the same land. This is often done either in alternate or multiple rows and is seen by many farmers as a form of security against total crop failure [7]. Long duration pigeonpea is normally planted during SR in October–November and harvested in August–September the following year. Medium and short duration varieties can be planted and harvested in one season. Crop combinations, planting patterns, and plant populations of pigeonpea and other crops vary considerably, depending on the soil type, climate, and farmer's preferences. However, dominant pigeonpea cropping systems practiced in the region include: pigeonpea intercropped with maize, sorghum, millets, cowpea and green gram; pigeonpea and cowpea intercrops; and maize/bean/pigeonpea intercrops [1, 4–6].
