(a) Fig. 1.1 shows a layout of a furrow irrigation system on a gently sloping field of maize. Fig. 1.1 (i) Describe how water moves through the furrows to r...

Labelled answer diagram:

(a)(i) In a furrow irrigation system on a sloping maize field, water enters at the upper (supply) end of each furrow and flows downhill by gravity along the channel between the crop rows. [1] As it moves along, the water soaks laterally (sideways) through the soil into the raised ridges where the maize roots are growing, wetting the root zone from below and from the sides. [1]

(a)(ii) Two factors that affect how far water travels along a furrow before soaking in:

1. Soil texture - sandy soils have large pores and absorb water rapidly, so the wetting front advances only a short distance along the furrow before all the water has infiltrated. Clay soils absorb more slowly, allowing water to travel further. [1]
2. Flow rate - a higher volume of water entering the furrow per unit time pushes the wetting front further along before infiltration absorbs it all. A low flow rate means the water soaks in close to the inlet. [1]

(Also acceptable: gradient/slope of the furrow, furrow length, or initial soil moisture content.)

(b)(i)

• Advantage of sprinkler irrigation: sprinklers distribute water from above, giving more uniform coverage across the field, including on uneven terrain where furrows would cause water to pool in low spots and miss high spots. [1]
• Disadvantage of sprinkler irrigation: sprinklers require a pump and pressurised pipe system, which involves significantly higher capital investment and ongoing energy costs than gravity-fed furrow irrigation. [1]

(b)(ii) The choice of irrigation method affects foliar disease spread because of how each system interacts with the crop canopy:

1. Sprinkler irrigation wets the leaves, creating a humid microclimate on the leaf surface that favours the germination and spread of fungal spores (e.g. leaf blight, rust). Prolonged leaf wetness is a key trigger for many foliar pathogens. [1]
2. Furrow irrigation keeps the foliage dry because water is delivered only at ground level in the channels between rows. With dry leaves, fungal spore germination is inhibited, substantially reducing the risk of foliar disease. [1]

(c) Irrigation scheduling is the planned determination of when to irrigate and how much water to apply at each irrigation event. It is based on the crop's water requirement at its current growth stage, the soil moisture status, and weather conditions (especially evapotranspiration rate), and its purpose is to supply enough water for optimal growth without waste or waterlogging. [1]