Property Field A Field B pH 6.5 4.8 Organic matter / % 3.2 1.4 Nitrogen / mg per kg 45 28 Phosphorus / mg per kg 18 6 (a) Define the term soil fertility. [2...

(a) Soil fertility is the ability of the soil to provide the essential nutrients, water, and physical conditions needed to support healthy plant growth. [2] A fertile soil has adequate levels of macro- and micronutrients, good structure for root penetration, appropriate pH, and sufficient organic matter to sustain biological activity.

(b)(i) Field A would be more suitable for growing cabbages. [1] Its pH of 6.5 falls within the preferred range of 6.0 to 7.0 for cabbage growth, whereas Field B has a pH of 4.8, which is too acidic. [1]

(b)(ii) The farmer should add lime (calcium carbonate / ground limestone / dolomite) to Field B. [1]

(b)(iii) Lime raises the soil pH from acidic towards neutral. [1] At a higher pH, essential nutrients such as phosphorus and nitrogen become more available to plant roots because they are no longer locked up in insoluble chemical forms. Liming also reduces aluminium toxicity, which inhibits root growth in very acidic soils. [1]

(c) How crop rotation maintains soil fertility: [2]

1. Different crops have different nutrient demands, so alternating crops prevents the progressive depletion of any single nutrient that monoculture would cause. [1]
2. Including a legume (e.g. beans, groundnuts) in the rotation adds nitrogen to the soil through biological nitrogen fixation: Rhizobium bacteria in the legume's root nodules convert atmospheric nitrogen gas into plant-available forms, enriching the soil for the following crop. [1]