Soil Phosphorus and Potassium RNA Chapter 14 1 2 Phosphorus and - PowerPoint PPT Presentation

2018/5/29 Role of P in Plant Nutrient and Soil Fertility • ATP • DNA Soil Phosphorus and Potassium • RNA Chapter 14 1 2 Phosphorus and Plant Growth • Adequate phosphorus nutrition enhances many aspects of plant physiology, including the fundamental processes of photosynthesis, nitrogen fixation, flowering, fruiting (including seed production), and maturation. • Root growth, particularly development of lateral roots and fibrous rootlets, is encouraged by phosphorus. ( 小 根 ) • In cereal crops, good phosphorus nutrition strengthens structural tissues such as those found in straw or stalks. ( 穀類 )( 稻草、麥桿 )(stalk=stem) 3 4 1

2018/5/29 The Phosphorus Problem in Soil Fertility • The total phosphorus level of soil is low, usually no more 腐朽 , 摧毀 than 1/10 to ¼ that of N, and 1/12 that of K. 直立的 • The phosphorus compounds commonly found in soils are unavailable for plant uptake, often because they are highly insoluble. • When soluble sources of phosphorus, such as those in Crushing strength of stalk: 是指要施與多少壓力才能讓植物倒伏之意 fertilizers and manures, are added to soils (changed to unavailable forms) and in time form highly insoluble compounds. • Fixation reactions in soils may allow only a small fraction (10 to 15%) of the phosphorus in fertilizers and manures to be taken up by plants. 5 6 Effects of P on Environmental Quality The Phosphorus Problem in Soil Fertility Some farmers apply two to four • Land degradation times as much phosphorus as is • Accelerated eutrophication removed in the crop harvest. Repeated over many years, such practices have saturated the phosphorus-fixation capacity and built up the levels of available phosphorus in many agricultural soils. 7 8 2

2018/5/29 Land Degradation Land Degradation • Undisturbed natural ecosystem in these regions usually • The remaining inorganic phosphorus in the soil is largely contain enough phosphorus in the biomass and soil unavailable for plant uptake. In this manner, the organic matter to maintain a substantial standing crop of phosphorus-supplying capacity of the disturbed soil trees or grasses. rapidly becomes so low that regrowth of natural vegetation is sparse and, on land cleared for agricultural • Most of the phosphorus taken up by the plants is that use, crops soon fail to produces useful yields. released from the decomposing residues of other plants. Very little is lost as long as the system remains • Leguminous plants that might be expected to replenish undisturbed. soil nitrogen supplies are particularly hard hit by phosphorus deficiency, because low phosphorus supply • Once the land is cleared for agricultural use, the losses of inhibits effective nodulation and retards the biological N- phosphorus in eroded soil particles, in runoff water, and fixation process. ( 補充 ) in biomass removals can be substantial. With in just a few years the system may lose most of the phosphorus that had cycled between the plants and the soils. 9 10 Water Quality Degradation Phosphorus Losses in Runoff • Particulate P • Point sources , such as sewage treatment plant • Dissolved P outflows, industries, and the like, are relatively easy to identify, regulate, and clean up. • Nonpoint sources of P are principally runoff water and eroded sediments from soils scattered throughout the affected watershed. 乳牛場 廣義的豬 11 12 3

2018/5/29 磷施用過量 Phosphorus balance in surface soil (Utisoils) of adjacent and agricultural watersheds Precipitation 含磷的砂塵 自從被耕犛起，農地已 有近一半的有機磷被轉 變為無機磷或流失，其 礦化作用是林地的 4 倍， 因逕流流失的則達 8 倍。 5% Particulate form Particulate form 95% Particulate form 佔 95% Delaware Netherlands 已農耕 >100 年 未被干擾 >40 年 13 14 Phosphorus Losses in Runoff 圓盤犁 pfiesteria 耕犛會增加 particulate P 的流失，但不耕犛會讓 dissolved P ( 通 常來自化學肥或糞肥 ) 較易流失，因此耕犛翻土可讓 dissolved P 被吸附而較不易流失。 15 16 4

2018/5/29 Management of phosphorus 17 18 The Phosphorus Cycle • HPO 4 2- , H 2 PO 4 - 19 20 5

2018/5/29 The Phosphorus Cycle • Organic phosphorus • Calcium-bound inorganic phosphorus • Iron- or aluminum-bound inorganic phosphorus • Phosphorus is not generally lost from the soil in gaseous form. • Because soluble inorganic form of phosphorus are strongly adsorbed by mineral surfaces, leaching losses of inorganic phosphorus are generally very low. • The amount of P that enters the soil from the atmosphere (sorbed on dust particles) is quite small (0.05 to 0.5 kg/ha annually), but may nearly balance the losses from the soil in undisturbed forest and grassland ecosystem. 21 22 Organic Phosphorus in Soils Organic Phosphorus in Soils • Inositol phosphorus or phosphorus esters of a sugarlike • Inositol phosphorus are the most abundant of the known compound. 肌醇 C 6 H 6 (OH) 6 organic P compounds, making up 10 to 50% of the total organic P. They interact with the higher-molecular-weight • Nucleic acids humic compounds. • Phospholipids • Nucleic acids are adsorbed by humic compounds as well • Dissolved organic phosphorus (DOP) as silicate clays. Adsorption on these soil colloids probably helps protect the phosphorus in nucleic acids from microbial attack. • The nucleic acids and phospholipids together probably make up only 1 to 2% of the organic P in most soils. 23 24 6

2018/5/29 Organic Phosphorus in Soils Organic Phosphorus in Soils • The other chemical compounds that contain most of the • The relative amounts in the two forms vary greatly soil organic P have not yet been identified, but much of from soil to soil. The organic fraction generally the organic P appears to be associated with the fulvic constitutes 20 to 80% of the total phosphorus in acid. surface soil horizons. • Dissolved organic phosphorus (DOP) is generally more • The deeper horizons may hold large amounts of mobile than soluble inorganic P, probably because it is not inorganic phosphorus, especially in soils from arid so readily adsorbed by organic clays and by CaCO 3 layers and semiarid regions. in the soil. In the lower horizons of such soils, the DOP commonly makes up more than 50% of the total soil solution P. • In heavily manured areas with sandy soils DOP can leach down to nearly 2 m. 25 26 Adsorption by iron and aluminum oxides Calcium phosphate compounds Calcium phosphate compounds 27 28 7

2018/5/29 Organic Phosphorus in Soils Mineralization of Organic P • Net immobilization of soluble P is most likely to occure if residues added to the soil have a C/P ratio greater than 42 years 300:1, while net mineralization is likely if the ratio is Cow manure 土壤無法完全吸收過多的 below 200:1. 有機磷 僅有機磷可穿透至 1.0 m 以下 29 30 Mineralization of Organic P Contribution of Organic P to Plant Needs • In temperate regions, mineralization of organic P in soils • Recent evidence indicates that the readily decomposable typically releases 5 to 20 kg P/ha/yr, most of which is of easily soluble fractions of soil organic phosphorus are readily adsorbed by growing plants. These values can be often the most important factor in supplying P to plants in compared to the annual uptake of P by most crops, trees, highly weathered soils (e.g., Ultisols and Oxisols), even and grasses, which generally ranges from 5 to 30 kg P/ha. though the total organic matter content of these soils may not be especially high. • When forested soil are first brought under cultivation in tropical climates, the amount of P released by • The inorganic P in the highly weathered soils is far too mineralization may exceed 50 kg/ha/yr, but unless P is insoluble to contribute much to plant nutrition. added from outside sources these high rates of • Apparently plant roots and mycorrhizal hyphae are able to mineralization will soon decline due to the depletion of obtain some of the P released from organic forms before it readily decomposable soil organic matter. forms inorganic compounds that quickly become insoluble. 31 32 8