Supplementary reading

I. AGRONOMY

1. Effects of some organic materials on bicarbonate extractable phosphate content of soils having different pH

Organic matter concentration of soils is a dynamic property and affects both soil physical and chemical properties and its overall sustainability. It is known that adding organic matter to soil develop soil physical conditions and regulate chemical conditions. Many studies showed that the amelioration of soil physical and chemical properties largley based on increaments of organic carbon in the soils with using organic wastes. Soil organic matter is an essential but transient component of the soil that controls many physical, chemical and biological properties of the soil. In the formation of fertile soil, organic substances play a direct role as sources of plant nutrients which are liberated in available form during mineralization. The incorporation of agricultural wastes such as; poultry manure and cow dung, with rock phosphate significantly improved the release phosphorus and raised crop yields. Organic matter level of soils is mostly low in Turkey. This is a big problem especially in semi-arid regions. To increase the level of organic material, the most common approach is to apply different organic matter sources to cultivcated soils. The use of waste in agriculture, forestry and land reclamation has been increasingly identified as an important issue for soil fertility, conservation and residual disposal. Using waste in agriculture helps not only dispose these materials economically, but also reduces negative effects on the environment and improve soil quality parameters. Soil quality can be improved with the addition of wastes, which contains appropriate levels of organic matter. Organic conditioner application into soils improves not only the soil structure but also the nutrient quantity and availability in soils. This study was carried out to determine the effects of rice husk compost (RC), town waste compost (TW) and tobacco waste (TB) applications on extractable P content in soils having different pH levels .

2. Spatial variability of soil physical properties in a cultivated field

There are several spatially variable factors influencing crop yields. These are usually soil related, anthropogenic, topographic, biological, and meteorological factors. Knowledge of the spatial variation of soil properties is important for crop production in precision agricultural management systems. It has been known that most soil properties are spatially variable in a field . Iqbal et al. (2005) reported that spatial variability of soil properties in any field position is inherent in nature due to geologic and pedologic soil forming factors, but some of the variability may be induced by tillage and other management practices. Benefits from soil tillage are known as improvement of soil-airwater relations in seedbeds, control of undesired vegetation, and reduction of the mechanical impedance to root growth. Skuodiene et al. (2013) determined that the shallow ploughing and shallow ploughless tillage treatments contained more weed seed species in the soil compared with the deep ploughing treatment. Soil tillage practices causes changes to soil structure and hydraulic properties dynamically in space and time. The ordinary kriging is one of the most common methods in spatial interpolation of soil properties after estimating semivariogram parameters of soil properties using geostatistical tools Castrignanò etstudied the intensive tillage effects on spatial variability of soil physical properties such as; particle size, bulk density, soil strength, mean pore size and saturated hydraulic conductivity. They reported that all soil physical properties, except saturated hydraulic conductivity, were weakly spatially dependent for the 6 to 9 cm depth, and moderately spatially dependent for 27 to 30 cm soil depth. Although the major purposes of tillage are to reduce bulk density and soil strength and to control pests and diseases, soil cultivation may lead to the formation of a hard pan below the plough layer that restricts root penetration and downward movement of water, therefore zero or minimum till practices must be carried out in these areas. (Singh and Singh, 1996) reported that soils, especially having vertic soil properties, must have a good and right soil management for a long term productivity. Inappropriate soil tilling and using unsuitable instruments, firstly cannot manage healthy plant growth and cause soil degradation in long time periods.