Soil productivity is the capacity of the soil, in its normal environment to support plant growth. Soil fertile greatly affects soil productivity. A fertile soil always leads to high soil productivity. The following are the factors that affects the fertility and productivity of the soil;-
(a) Leaching: This is common with nutrients that are highly soluble such as nitrogen, these nutrients are carried to lower far from beyond the reach of many plants roots, soil with many leached nutrients are infertility.
(b) Soil capping: This is when the soil is covered (capped) with an impervious material which prevents the penetration of rainwater into the soil, this leads to surface run – off. This denies the soil adequate moisture and exposes the soil to erosion.
(c) Soil erosion: This is the carrying away of the top fertile soil by moving water and wind. Erosion leads to loss of the fertile top soil and plant nutrients, this makes the soil infertility.
(d) Monocropping: Monocropping is the practice of growing one type of gropes on a piece of land for a long time. The gropes grown uses only those nutrients it needs while other nutrients remain unused, this leads to exhaustion of some nutrient.
(e) Accumulation of salt: Soil water contains dissolved minerals salts from the parent rock; some of the salt comes from decomposition of organic matter. Under normal condition, the salts are washed away by rain water, thereby keeping their concentration in the soil low. However in arid and semi-arid areas the rainfall is irregular and is not enough to remove the salt from the soil.
(f) Change in the pH: Inappropriate use of fertilizers may change the soil pH, for example, the use of acidic fertilizer over a long period of time can make the soil acidic. Change in pH affects the activity of the soil microorganisms and the availability of some nutrients. This, in run, affects the fertility of the soil.
(g) Burning of vegetation: When vegetation is burned, organic matter is destroyed; this affects the activities of microorganisms such as nitrogen fixation and decomposition of organic matter.