China
Africa
Explore chapters and articles related to this topic
Micronutrient R&D in Pakistan
Published in Abdul Rashid, Munir Zia, Waqar Ahmad, Micronutrient Fertilizer Use in Pakistan, 2023
Abdul Rashid, Munir Zia, Waqar Ahmad
Fertilizer use in Pakistan predominantly pertains to nitrogen (N) and phosphorus (P); potassium (K) use is confined to a few high-K requiring crops, like tobacco and potato. Compared with the actual crop requirements, micronutrient fertilizer use in the country is negligible (NFDC, 1998; Rashid, 2006a). Also, many recently introduced high-yield potential crop varieties are more susceptible to micronutrient deficiencies (Chaudhry et al., 1977a; Rashid and Din, 1992; Rashid et al., 2002a, 2002b, 2002c). Hence, soil conditions and agronomic practices in the country are conducive to the incidence of micronutrient deficiencies in crop plants. The soils across much of the cultivated areas were formed from calcareous alluvium and loess deposits and are low in OM, and many essential plant nutrients. The climate, except for some high mountains in the north, is mostly arid to semi-arid. Because of the calcareous nature of parent material and low rainfall, almost all the soils are young on the geological time scale. Hence the soils are alkaline and calcareous in nature due to the presence of alkaline earth cations (Ca2+ and Mg2+). These cations are hardly leached down from the upper soil horizons or beyond the root zone. Some small pockets of moderately acid soils exist in the country, but these are predominantly confined to the high rainfall areas of Mansehra and Swat districts in KP province. The parent material of these soils is predominantly non-calcareous like granite (Rashid, 1993; Nizami et al., 1994). Even a vast majority of these acid soils suffer from deficiencies of Zn (Rashid, 1994).
Soils with Climatic Problems
Published in Manorama K.C. Thampatti, Problem Soils, 2023
Salt accumulation is also high under dry conditions. Gypsiferous and calcareous soils are found in the driest areas on the earth, where the layers of gypsum or calcium carbonate prevent agriculture. The potential productivity of calcareous soils is higher compared to gypsiferous soils, if adequate water and nutrients are supplied. The high calcium saturation tends to keep the calcareous soils in well aggregated form and good physical condition. However, if soil contains an impermeable hardpan either calcareous or gypsiferous that should be broken before cultivation. Soils with gypsic horizon are prone to formation of sink holes when irrigated.
*
Published in A. Monem Balba, in Arid Ecosystems, 2018
The carbonates in calcareous soils consist of calcium and magnesium carbonates. They are usually evaluated and expressed as carbonate equivalent. The CaO/MgO ratio indicates that calcium carbonate predominates. Also, X-ray diffraction patterns indicate that calcite is the major mineral present in the calcareous soils. Dolomite is usually present in a limited proportion. Aragonite usually constitutes a small fraction (Meester3). This may be due to the higher solubility of aragonite than calcite at variable degrees of temperature. Buehrer and Williams4 postulated that calcium carbonate exists in the soil in forms other than calcite and aragonite as the precipitated form resulting from variable reactions in the soil system.
Physical and mechanical properties of calcareous soils: A review
Published in Marine Georesources & Geotechnology, 2022
Liang-Jie Xu, Xin-zhi Wang, Ren Wang, Chang-qi Zhu, Xiao-peng Liu
Calcareous soil is a unique geotechnical medium rich in calcium carbonate and other insoluble carbonate substances caused by marine organisms (coral, algae, shells, etc.), often termed “calcareous soil” due to calcium carbonate being the main mineral composition. The deposition of calcareous soil mainly derives from calcareous bio-skeletons, detritus, and carbonate materials in seawater, deposited in solution due to changes in temperature and pressure. As the sediments are not transported long distances, small pores in the protozoan skeleton are preserved, forming fragile particles due to having an abundance of internal pores. They also have an irregular shape and are quickly cemented, amongst other characteristics. Engineering mechanical properties of calcareous soils are significantly different from those of ordinary continental sediments (Wang et al. 1997; Sun 2000).
Undrained monotonic and cyclic behavior of Qeshm calcareous sand
Published in Marine Georesources & Geotechnology, 2021
Javad Saeidaskari, Mahdi Alibolandi, Alireza Saeedi Azizkandi
Calcareous soils constituted a considerable part of the offshore and coastal earth structures such as wharf, quay walls, breakwaters, and wind turbine foundations that might be subjected to a variety of loads such as waves, winds, floods, and earthquakes. These sands are often the skeletal remains of marine organisms consisting of thin-walled algal and platy shell fragments including some voids inside their bodies and large intra-particle void space calcareous soils lead to higher compressibility in uncemented conditions and greater crushability compare to terrigenous materials. Due to the mentioned characteristics of calcareous soils, several studies were performed to investigates the behavior of these soils (e.g. Golightly and Hyde 1988; Sharma and Ismail 2006; Randolph and Gourvenec 2011; Shahnazari et al. 2016; Kargar, Salehzadeh, and Shahnazari 2016; Shahnazari, Rezvani, and Tutunchian 2017; Fatemiaghda et al. 2017; Kouzegaran, Shahnazari, and Jafarian 2020).
Mechanical properties of calcareous silts in a hydraulic fill island-reef
Published in Marine Georesources & Geotechnology, 2021
Xing Wang, Jie Cui, Yang Wu, Changqi Zhu, Xinzhi Wang
Calcareous soil is a marine biogenic soil with a calcium carbonate content exceeding 95%. It is mainly distributed on coral reefs between 30°N and 30°S (Liu, Shan, and Wang 1999). Calcareous silt is a fine-grained calcium-rich soil with a plasticity index of 10% or less, in which the percentage of the total soil particle mass with a particle size of >0.075 mm is <50% (Ministry of Housing and Urban-Rural Development of the People’s Republic of China 2002). The mechanical properties of silt lie between those of sand and clay. Due to the lack of understanding of the mechanical properties of silt, early researchers once classified it as clay. Later, as our understanding of the mechanical properties of silt improved, it was distinguished from clay. However, silt and clay both fall into the category of fine-grained soil.