[
  {
    "start": 0.3,
    "end": 7.56,
    "text": "In today's textbook episode, we will take a closer look at buffer systems which play an important role in soil acidification."
  },
  {
    "start": 8.34,
    "end": 22.18,
    "text": "As you have learned on episode twenty-eight of Soil Acidification pH changes and soils are natural phenomenon but because the sophisticated structure of soils these changes often weakened or delayed compared to pure water."
  },
  {
    "start": 22.9,
    "end": 24.86,
    "text": "this resistance is called buffering."
  },
  {
    "start": 25.62,
    "end": 33.74,
    "text": "Before we take a closer look at the topic, let's start with a few words about pH value and soil acidification to refresh our knowledge."
  },
  {
    "start": 34.54,
    "end": 39.36,
    "text": "The pH value is a parameter that quantifies the amount of hydrogen ions in solution."
  },
  {
    "start": 40.04,
    "end": 44.26,
    "text": "In simple terms it assesses how acidic or alkaline the soil order is."
  },
  {
    "start": 45.56,
    "end": 64.92,
    "text": "The concentration of hydrogen ions is increased, for example through the input of acids via precipitation or through substances secreted by plant roots – the so-called root exodates."
  },
  {
    "start": 65.72,
    "end": 75.12,
    "text": "The pH value is very important as it has a major influence on soil's ecosystem services and is often used as first indicator to assess soil health."
  },
  {
    "start": 75.94,
    "end": 80.86,
    "text": "It is therefore one of most crucial factors for plants & other organisms living in the soil."
  },
  {
    "start": 81.66,
    "end": 88.76,
    "text": "If that was a little too quick for you, I recommend listening to episode twenty-eight again where all this was discussed in more detail."
  },
  {
    "start": 89.64,
    "end": 94.04,
    "text": "So let's move on the buffering capacity of soils – what is its role?"
  },
  {
    "start": 94.74,
    "end": 100.48,
    "text": "Whereas buffering can happen both directions of pH scale acidification and alkalinization."
  },
  {
    "start": 101.12,
    "end": 111.4,
    "text": "soil acidity is the most prevalent process especially for soils in mid latitude regions such as Europe which is why we will focus on acidification today."
  },
  {
    "start": 112.16,
    "end": 119.68,
    "text": "Buffering ensures that although there's an input of hydrogen ions, the concentration in the soil solution does not increase."
  },
  {
    "start": 120.22,
    "end": 129.979,
    "text": "This might sound a bit like magic but these hydrogen ions must go somewhere otherwise their concentration would steadily increase and the pH value it would plummet."
  },
  {
    "start": 130.699,
    "end": 133.3,
    "text": "So what happens to this hydrogen ions?"
  },
  {
    "start": 133.8,
    "end": 138.42,
    "text": "The secret lies in different chemical reactions where hydrogen ions are captured."
  },
  {
    "start": 139.2,
    "end": 146.32,
    "text": "As a result, the hydrogen ions do not affect the pH value of the soil solution and the acid input has been buffered."
  },
  {
    "start": 147.06,
    "end": 155.44,
    "text": "However these buffers are limited and consumed over time –the amount of hydrogen ions that a soil can buffer is called buffering capacity."
  },
  {
    "start": 156.26,
    "end": 163.46,
    "text": "To make it a bit clearer imagine your room or flat you're living And now let's pretend that the hydrogen ions are dust."
  },
  {
    "start": 164.1,
    "end": 169.26,
    "text": "There is a constant input of dust in our rooms, and believe me I know what i'm talking about!"
  },
  {
    "start": 169.9,
    "end": 174.28,
    "text": "But also there are certain buffer systems like a vacuum cleaner or a duster."
  },
  {
    "start": 175.08,
    "end": 184.58,
    "text": "With these tools – or buffers we can clean up the dust or neutralize the hydrogen irons That then are part of the dust bag Or chemical compound."
  },
  {
    "start": 185.18,
    "end": 192.64,
    "text": "But if our vacuum is full or the dust are too dirty, we cannot remove the dust as effectively anymore and it will accumulate."
  },
  {
    "start": 193.48,
    "end": 196.92,
    "text": "Which is exactly what happens of the buffer in our soils I used up."
  },
  {
    "start": 197.86,
    "end": 201.72,
    "text": "The hydrogen ions will accumulate and the pH value will decrease."
  },
  {
    "start": 202.5,
    "end": 212.52,
    "text": "And just as level of dirt and disorder determines tool to use for cleaning different buffer systems come into place based on degree of acidification."
  },
  {
    "start": 213.34,
    "end": 215.38,
    "text": "Okay, enough talk about cleaning."
  },
  {
    "start": 215.54,
    "end": 220.16,
    "text": "Let's bring it back to chemistry and let's take a look at the most important buffers in soils."
  },
  {
    "start": 221.0,
    "end": 226.22,
    "text": "So depending on the pH value of soil The operative buffer system can be assessed."
  },
  {
    "start": 226.88,
    "end": 229.16,
    "text": "Lets start with so-called carbonate buffer."
  },
  {
    "start": 230.0,
    "end": 235.56,
    "text": "It is effective within a pH range from slightly alkaline To slightly acidic."
  },
  {
    "start": 236.2,
    "end": 243.36,
    "text": "You are quite likely familiar With carbonates usually In the form of calcium carbonate or in other words, lime."
  },
  {
    "start": 244.08,
    "end": 252.7,
    "text": "They are present on the soil when geological substrate is pulsarius often in form of marine deposits and generally speaking limestone."
  },
  {
    "start": 253.18,
    "end": 260.72,
    "text": "When hydrogen ions enter the soil solution carbonates react with them to form hydrogen-carbonate and calcium cations."
  },
  {
    "start": 261.36,
    "end": 267.5,
    "text": "These substances then are washed out causing the soil to irreversibly reduce its buffering capacity."
  },
  {
    "start": 268.32,
    "end": 276.22,
    "text": "This happens until the carbonate buffer used up In other words, until there is no more lime in the soil meaning that the soil is decalcified."
  },
  {
    "start": 276.96,
    "end": 282.38,
    "text": "In the field you can find out whether this soil contains carbonates by dripping some hydrochloric acid on it."
  },
  {
    "start": 282.92,
    "end": 286.72,
    "text": "If it contains carbonate this will produce very satisfying bubbles."
  },
  {
    "start": 286.94,
    "end": 290.52,
    "text": "It's quite fun but of course be careful using acid!"
  },
  {
    "start": 291.5,
    "end": 299.32,
    "text": "In order to counteract a decrease in pH caused by depletion of carbonate buffer typically farmers apply lime into their fields."
  },
  {
    "start": 299.8,
    "end": 303.22,
    "text": "Thereby, hydrogen ions are captured and the pH increases."
  },
  {
    "start": 303.46,
    "end": 305.88,
    "text": "And a healthy environment is kept for plants."
  },
  {
    "start": 306.64,
    "end": 314.82,
    "text": "In natural soil formation decalcification as normal process will lead to decrease in pH if not counteracted by human measures."
  },
  {
    "start": 315.66,
    "end": 321.52,
    "text": "It's important know that carbonate buffers only exist in soils with calcerous parent material."
  },
  {
    "start": 322.32,
    "end": 324.8,
    "text": "Soils have developed on carbonate free."
  },
  {
    "start": 324.9,
    "end": 334.0,
    "text": "rocks such as granite usually start off less buffering capacity and at a lower pH, which makes them more susceptible to acidification."
  },
  {
    "start": 334.8,
    "end": 343.7,
    "text": "But the carbonate buffer is not only one and also carbonate-free soils do have other buffering systems – One of those is the so called exchange buffer."
  },
  {
    "start": 344.5,
    "end": 356.88,
    "text": "This buffer offers whole series of exchange reactions during which positively charged hydrogen ions are absorbed onto negatively charged surfaces of clay minerals oxides and hydroxides."
  },
  {
    "start": 359.16,
    "end": 362.72,
    "text": "It is typically active at a pH range from neutral to aesthetic."
  },
  {
    "start": 363.3,
    "end": 366.12,
    "text": "In order to understand the mechanism, let's take a closer look."
  },
  {
    "start": 378.44,
    "end": 390.9,
    "text": "surfaces are negatively charged."
  },
  {
    "start": 391.44,
    "end": 396.98,
    "text": "And when the surfaces are negatively charged, they can bind hydrogen ions and thus act as a buffer."
  },
  {
    "start": 397.78,
    "end": 405.76,
    "text": "It is interesting to know that many important plant nutrients like calcium potassium and magnesium Are cations just like Hydrogen ions."
  },
  {
    "start": 406.32,
    "end": 411.76,
    "text": "This means That They carry A positive charge and also adsorbed onto negatively charged surfaces."
  },
  {
    "start": 412.4,
    "end": 417.84,
    "text": "this leads To a competitive situation between hydrogen ions & cationic plant nutrients."
  },
  {
    "start": 418.54,
    "end": 428.02,
    "text": "When the concentration of hydrogen ions in soils is very high, these hydrogen ions occupy a lot space on surfaces and thus displace the plant nutrients."
  },
  {
    "start": 428.72,
    "end": 437.1,
    "text": "These nutrients then dissolve into soil solution can be washed out if not taken up by plants causing reduced soil fertility in long run."
  },
  {
    "start": 437.96,
    "end": 455.26,
    "text": "Typically clay soils have higher buffering capacity than sandy soils as they offer more exchange sites And thus better ability to capture hydrogen ions whereas sandy soils are prone to acidification and thereby often show a lower nutrient availability, which makes them last for time."
  },
  {
    "start": 456.14,
    "end": 464.26,
    "text": "Another buffer system is silicate weathering – which becomes relevant from pH values slightly acidic and below as the name suggests."
  },
  {
    "start": 464.34,
    "end": 467.92,
    "text": "silicates undergo a chemical alteration during this process."
  },
  {
    "start": 468.62,
    "end": 469.88,
    "text": "But what are silicates?"
  },
  {
    "start": 470.3,
    "end": 476.04,
    "text": "Silicates are minerals more precisely a mineral group whose building blocks of silicon an oxygen ions."
  },
  {
    "start": 476.56,
    "end": 480.52,
    "text": "This includes, for example quartz and feldspar as well as clay minerals."
  },
  {
    "start": 480.92,
    "end": 489.18,
    "text": "In general silicates are the most diverse mineral group And they're used to produce a variety of products such as glass ceramics porcelain and cement."
  },
  {
    "start": 490.04,
    "end": 497.36,
    "text": "Unlike exchange buffers however The minerals in this buffer system weather... ...and therefore destroy or alter it into process."
  },
  {
    "start": 497.98,
    "end": 501.54,
    "text": "New minerals conform which I then call secondary minerals."
  },
  {
    "start": 502.08,
    "end": 507.9,
    "text": "During the process, plant nutrients such as calcium and magnesium are released from these altered silicate minerals."
  },
  {
    "start": 508.66,
    "end": 512.039,
    "text": "The silicate buffer system takes longer than the exchange buffer."
  },
  {
    "start": 512.659,
    "end": 515.74,
    "text": "This is why the pH-buffer effect is much slower."
  },
  {
    "start": 516.46,
    "end": 521.6,
    "text": "However, silicate weathering accelerates as a concentration of hydrogen ions increases."
  },
  {
    "start": 522.38,
    "end": 526.82,
    "text": "Consequently, the more acidic the soil ,the faster Silicate Weathering occurs."
  },
  {
    "start": 527.26,
    "end": 533.04,
    "text": "At an acidic pH around four point five or below, silicate weathering produces aluminium ions."
  },
  {
    "start": 533.64,
    "end": 542.7,
    "text": "This plays a crucial role in terms of the toxic effect of aluminium on plants as both aluminum-containing silicates and aluminium oxides decay."
  },
  {
    "start": 542.86,
    "end": 549.12,
    "text": "at this pH value The concentration of aluminium ion then the soil solution increases sharply."
  },
  {
    "start": 549.98,
    "end": 556.18,
    "text": "In this acidic milieu, the soil suitability for plant growth is therefore permanently at risk."
  },
  {
    "start": 556.84,
    "end": 564.48,
    "text": "Highly weathered soils of the tropics usually have a low pH value and aluminium toxicity makes managing these soils a big challenge."
  },
  {
    "start": 565.3,
    "end": 570.98,
    "text": "We can conclude that various buffer systems in soil slow down or temporarily stop acidification."
  },
  {
    "start": 571.76,
    "end": 583.7,
    "text": "The main buffer system are carbonate buffers, exchange buffers & silicate buffers It is important to note this pre-dominate at different pH values and elicit from higher to lower pH."
  },
  {
    "start": 584.24,
    "end": 592.18,
    "text": "However, the buffering capacity of a soil is always limited and buffers are consumed at some point under humid climatic conditions."
  },
  {
    "start": 592.82,
    "end": 598.92,
    "text": "I hope you can now make sense of the soil's buffer capacity and appreciate its significance in soils a little better!"
  },
  {
    "start": 599.7,
    "end": 603.8,
    "text": "This will be important for our next episode on soil formation factors."
  },
  {
    "start": 604.34,
    "end": 608.12,
    "text": "Until then have great time and stay buffered."
  }
]