**1. Introduction**

Tillage is part and parcel of crop production systems since inception of agricultural practice. The process of soil preparation was greatly refined with the invention of the first plow and since then, various types of tillage equipment and modalities for preparation and cultivation of seedbed have been designed and implemented. Development and application of modern equipment for tillage practices were introduced in the last one decade throughout the world, giving way to the essence of precision manipulation of soil [1]. Modern tillage systems make efforts to minimize the quantity of tillage operations, the amount of energy used in terms of human, materials and machineries [2], the quantity of dust that is created [3] and the bulk of soil disturbance [4].

Tillage practices greatly affect crop growth and yield [5]. It is one of the fundamental agrotechnical operations in agriculture as recorded by [4, 6–10]. It is a known fact that passes of tractor wheels during tillage result in stiffness of the soil that is capable of affecting both the soil properties and subsequent effects on crop development to maturity and fruiting. Odey et al. [11] and Odey [12] revealed that soil compaction has adverse effects on crop production, affecting agricultural produce in the entire globe.

A number of researchers have studied how soil manipulation affects agricultural output generally. Adekiya et al. [13] reiterated that tillage is important for sustainable okra production on arable soil of southwest Nigeria. According to Ozpinar and Isik [14], tillage systems affecting soil properties are conventional, conservative, reduced, zero or direct seeding, mulch, ridge, stale seedbed, minimum and strip [1, 15, 16]. The state of the earth for agricultural practice should have enough water and plant food, including air to enhance development of roots through it [17–25].

Nowadays, concentration of tillage practices has been much on soil conservation as well as on zero tillage method, primarily to limit cone index and erosion of soil, reduce drought and cost of soil manipulation, enhancing biological activities in the soil for increased crop nutrients for abundant crop production, limiting overall carbondioxide release, taming the consequences and depletion of the ozone layer [11, 12, 26]. Generally, okra production is influenced by physiochemical conditions of the lithosphere, including the load-bearing capacity of the soil, density, structure, texture, colloids, nitrogen (N), pH, phosphorus (P), carbon (C) and many more.

The aim of this chapter is to present different field experiments conducted by researchers on different tillage systems and also to propose different models for predicting growth and yield of crops, for enhancement of agricultural production.

### **2. Tillage systems**

Tillage is the physical manipulation of soil using tillage equipment to cut, lift, turn, pulverize and break soil clogs in order to prepare the soil for planting. Tillage is broadly classified into primary and secondary. Primary tillage is the initial manipulation done on the soil using primary tillage equipment such as plows to break the soil. While secondary tillage operations are subsequent manipulations done on the soil to further prepare the soil for planting. Depending on the type of seedbed required by the farmer, the type of crops to be planted, soil condition, cost of tillage and the availability of equipment, farmers can decide to adapt different types of tillage systems, as explained in the following paragraph. Different researchers/authors have revealed their thoughts on different tillage practices, notable among them are Rasmussen [19]; MWPS (MidWest Plan Service) [20]; Owen [21]; ASAE (American Society of Agriculture and Biological Engineers) [22]; Leonard et al. [23]; Hedayatipoor and Alamooti [24] and Odey [25].

#### **2.1 Conventional tillage**

In conventional tillage, operation plowing and harrowing are carried out more than once before planting of crops. This system of tillage has been historically and traditionally used to prepare a seedbed and produce a given crop [20, 22]. Thus, in conventional tillage practice, less than 30% of the soil surface is incorporated by crop remains after cultivation.
