Plant Nutrition : Macronutrients (N, P, K, S, Mg and Ca)

Tanah, dan bukan air, merupakan materi yang menyusun tanaman

Law of the Minimum: Nutrient in least supply limits growthBiodiversity Heritage Library

Lawes & Gilbert began investigating plant nutrition at Rothamsted 1843Images used by permission of Rothamsted Research

Plants assimilate mineral nutrients from their surroundings

Plants assimilate mineral nutrients mainly as cations or anionsMACRONUTRIENTSMICRONUTRIENTSCharged ions require transport proteins to cross membranes

mol / g (dry wt)ElementAssimilated form250Potassium (K)K+1000Nitrogen (N)NO3-, NH4+60Phosphorus (P)HPO42-, H2PO4-30Sulfur (S)SO42-80Magnesium (Mg) Mg2+125Calcium (Ca) Ca2+

mol / g (dry wt)ElementAssimilated form2Iron (Fe) Fe3+, Fe2+0.002Nickel (Ni) Ni+1Manganese (Mn) Mn2+0.1Copper (Cu) Cu2+0.001Molybdenum (Mo)MoO42+2Boron (B)H3BO33Chlorine (Cl) Cl-0.3Zinc (Zn)Zn2+

However, larger and more complex nutrients also can be taken upSchmidt, S., Raven, J.A. and Paungfoo-Lonhienne, C. (2013). The mixotrophic nature of photosynthetic plants. Funct. Plant Biol. 40: 425-438 by permission of CSIRO Publishing; Adlassnig, W., Koller-Peroutka, M., Bauer, S., Koshkin, E., Lendl, T. and Lichtscheidl, I.K. (2012). Endocytotic uptake of nutrients in carnivorous plants. Plant J. 71: 303-313. Hill, P.W., Marsden, K.A. and Jones, D.L. (2013). How significant to plant N nutrition is the direct consumption of soil microbes by roots? New Phytol. 199: 948-955.

Vascular plants assimilate mineral nutrients mostly via rootsBarberon, M. and Geldner, N. (2014). Radial transport of nutrients: the plant root as a polarized epithelium. Plant Physiol. 166: 528-537.

Roots have several adaptations to enhance nutrient captureSchmidt, S., Raven, J.A. and Paungfoo-Lonhienne, C. (2013). The mixotrophic nature of photosynthetic plants. Funct. Plant Biol. 40: 425-438 by permission of CSIRO publishing.

Elemen EssentialKlasifikasi elemen essential;Ketiadaan elemen tersebut menyebabkan tumbuhan tidak mampu menyelesaikan daur hidupnya_ Tidak dapat digantikan oleh elemen lain_ Efek yang ditimbulkan adalah secara langsung_ Dibedakan menjadi :* makronutrient (10 -3 to 10 -2 mol/L)* mikronutrient (10-7 mol/L)

1. Essential Nutriens of Plants

ChemicalAtomicIonic formsApproximate dry Element symbolweightAbsorbed by plants____concentration_____ Mccronutrients NitrogenN14.01NO3-, NH4+4.0 %PhosphorusP30.98PO43-, HPO42-, H2PO4-0.5 %PotassiumK39.10K+4.0 %MagnesiumMg24.32Mg2+0.5 %SulfurS32.07SO42-0.5 %CalciumCa40.08Ca2+1.0 %MicronutrientsIronFe55.85Fe2+, Fe3+ 200 ppmManganeseMn54.94Mn2+ 200 ppmZincZn65.38Zn2+ 30 ppmCopperCu63.54Cu2+ 10 ppmBoronB10.82BO32-, B4O72- 60 ppmMolybdenumMo95.95MoO42- 2 ppmChlorineCl35.46Cl-3000 ppmEssential But Not AppliedCarbonC12.01CO2 40 %HydrogenH 1.01H2O 6 %OxygenO16.00O2, H2O 40 %________________________________________________________________ Plant tissues also contain other elements (Na, Se, Co, Si, Rb, Sr, F, I) which are not needed for the normal growth and development.

Beneficial elementsTidak diperlukan secara absolut untuk survival tetapi dapat memacu pertumbuhan dan vigorContoh : Selenium (SeO42-)Rubidium (Rb+)Strontium (Sr2+)Aluminium (Al3+)

Klasifikasi nutrien berdasarkan fungsi biokimiawi

Klasifikasi nutrien berdasarkan fungsi biokimiawi

Klasifikasi nutrien berdasarkan fungsi biokimiawi

Senyawa organik yg mengandung N yang diperlukan untuk metabolisme sel : Vitamin, cofactors, hormones, chlorophyll, fitokromSenyawa metabolit sekunder yang mengandung N : alkaloids (morphine, nicotine, quinine)Non photosynthetic pigmen contain N : betacyanin

Nitrogen: The most abundant mineral element in a plantBlank, L.M. (2012). The cell and P: From cellular function to biotechnological application. Curr. Opin. Biotech. 23: 846 851.From: Buchanan, B.B., Gruissem, W. and Jones, R.L. (2000) Biochemistry and Molecular Biology of Plants. American Society of Plant Physiologists.

Nitrogen can be found in many inorganic formsAdapted from Robertson, G.P. and Vitousek, P.M. (2009). Nitrogen in agriculture: Balancing the cost of an essential resource. Annu. Rev. Environ. Res. 34: 97-125.

SpeciesNameOxidation StateR-NH2Organic nitrogen, urea -3NH3, NH4+Ammonia, ammonium ion-3N2Nitrogen0N2ONitrous oxide+1NONitric oxide+2HNO2, NO2-Nitrous acid, nitrite ion+3NO2Nitrogen dioxide+4HNO3, NO3-Nitric acid, nitrate ion+5

A.Nitrogen (N)1) Soil Nitrogen Cycle Fiksasi Nitrogen : transformasi N dari atmosfir menjadi N tersedia bagi tumbuhan perlu bakteri yg mampu memfiksasi N :Rhizobium (symbiotic) found in legumes (bean, soybean) Azotobacter (non-symbiotic bacteria) Nitrifikasi di tanah : dekomposisi bahan organik menjadi amonium dan nitrat, diperantarai oleh bakteri yang mampu melakukan amonifikasi dan nitrifikasi Ammonifying bacteria : (Actinomycetes) Nitrifying bacteria : (Nitrosomonas) (Nitrobacter)Plant residue NH4+ NO2 NO3-(Protein, aa, etc) Ammonium Nitrite Nitrate

*Fungsi N bagi tumbuhan :Komponen protein, enzim, asam amino, asam nukleat, klorofilC/N rasio ( karbohidrat : nitrogen rasio)C/N rasio tinggi : tanaman cenderung dalam fase reproduktifC/N rasio rendah : tanaman cenderung dalam fase vegetatifTransaminasi : NO3 ---- NH2 ----- asam glutamat------ asam amino lain ------- protein / enzim

*Gejala defisiensi dan toksisitas N Defisiensi : pertumbuhan terhambat, daun tua menjadi kuning

Kelebihan N : pemanjangan tunas / batang daun hijau gelap, sukulen

Pupuk N- Ammonium nitrate (NH4NO3)Calcium nitrate [Ca(NO3)2]Potassium nitrate (KNO3)Urea [CO(NH2)2]

- Kebanyakan tumbuhan menyukai 50:50 NH4+ : NO3- NH4+-form of N lowers soil pH NO3--form of N raises soil pH

- Pupuk organik (manure, plant residue) :* slow acting* dapat diaplikasikan lewat daun

*

Defisiensi NitrogenCorn Symptoms- kerdil- Daun tua hijau kekuningan Kadang semua daun menjadi hijau muda dan mengalami klorosis di ujungnya Daun mati jika sangat kekurangan N

Daun menjadi sempit, pendek, tegak, hijau kekuningan Seluruh tanaman dapat menjadi kekuningan- Mengurangi anakan- Mengurangi jumlah bulirTomato

Gejala kekurangan Nitrogen (N)Daun tua menjadi kuning- nitrogen mudah tertransport didalam sel tumbuhan

B. Phosphorus (P)1) keberadaan dalam tanah- Mineral apatite [Ca5F(PO4)3]- Relative stabil- Sulit terserap2) Fungsi bagi tumbuhan- Komponen asam nukleat (DNA, RNA), phospholipids, coenzymes, high-energy phosphate bonds (ADP, ATP)- Biji memiliki kandungan P tinggi3)Defisiensi dan toksisitas- P bersifat mobile / mudah tertransport (Deficiency occurs in older leaves)- Defisiensi : dark, purplish color on older leaves- kelebihan P: causes deficiency symptoms of Zn, Cu, Fe, Mn4) Pupuk- Superphosphates (may contain F)Single superphosphate (8.6% P): CaH4(PO4)2Triple superphosphate (20% P): CaH4(PO4)2- Ammonium phosphate:(NH4)2PO4, NH4HPO4- Bone meal- Available forms:PO43-, HPO42-, H2PO4-P absorption influenced by pH

Defisiensi PhosphorCorn Cabernet sauvignon grapes, CA Symptoms- Tanaman kerdil- Perkembangan tanaman lambat Beberapa spesies seperti tomat, selada, jagung menunjukkan warna keunguan pada daun, tangkai daun atau batang- under severe deficiency conditions, there is also a tendency for leaves to develop a blue-gray luster Pada daun yang tua jika defisiensi P sangat besar akan terbentuk jaring warna coklat pada tulang daun- Terbentuk spot nekrosis

C. Potassium (K)1) Keberadaan di tanah- terdapat cukup banyak pada mineral tanah- konsentrasi rendah pada tanah organik/humus2) Fungsi bagi tummbuhan- Activator banyak enzim-enzim- pengatur pergerakan air melewati membran dan stomata3) Deficiency and Toxicity- Deficiency:Leaf margin necrosis and browningOlder leaves are more affected- Toxicity:Leaf tip and marginal necrosis4) Fertilizers- Potassium chloride (KCl)- murate of potash- Potassium sulfate (K2SO4)- Potassium nitrate (KNO3)

Necrosis pada tepi daun Poinsettiaakibat defisiensi Potassium (K)

Potassium deficiencyCorn Soybean Symptoms- mottled or marginal chlorosis, which then develops into necrosis on tips, margins and between veins- symptoms initially on more mature (older) leaves- leaves may curl and crinkle- stems may be slender and weak, with abnormally short internodal regions- in K-deficient corn, nodes may have increased susceptibility to root-rotting fungus present in the soil- this together with stem weakness results in bending of stems to the ground (lodging)

Defisiensi Macronutrients N, P, pada daun seladaControl

Defisiensi Macronutrient pada tanaman kacang-kacangan

D. Calcium (Ca)1) Soil Relations- Present in large quantities in earths surface (~1% in US top soils)- Influences availability of other ions from soil2) Plant Functions- Component of cell wall- Involved in cell membrane function- Largely present as calcium pectate in meddle lamelaCalcium pectate is immobile in plant tissues3) Deficiency and Toxicity- Deficiency symptoms in young leaves and new shoots (Ca is immobile) Stunted growth, leaf distortion, necrotic spots, shoot tip death Blossom-end rot in tomato- No Ca toxicity symptoms have been observed4) Fertilizers- Agricultural meal (finely ground CaCO3MgCO3)- Lime (CaCO3), Gypsum (CaSO4)- Superphosphate- Bone meal-organic P source

Blossom End Rot of TomatoCalcium DeficiencyRight-Hydroponic tomatoes grown in the greenhouse, Left-Blossom end rot of tomato fruits induced by calcium (Ca++) deficiency

SulfurDisulphite bridge (-S-S-) stabilize tertiary protein structureSulphydryl groups (-SH) ada di bagian aktif enzymeIron-sulphur protein (ferredoxin) involved in electron transferFlavour (Brassicaceae, onions, garlic)

E. Sulfur (S)1) Soil Relations- Present in mineral pyrite (FeS2, fools gold), sulfides (S-mineral complex), sulfates (involving SO4-2)- Mostly contained in organic matter - Acid rain provides sulfur2) Plant Functions- Component of amino acids (methionine, cysteine)- Constituent of coenzymes and vitamins- Responsible for pungency and flavbor (onion, garlic, mustard)3) Deficiency and Toxicity- Deficiency: light green or yellowing on new growth (S is immobile)- Toxicity: not commonly seen4) Fertilizers- Gypsum (CaSO4)- Magnesium sulfate (MgSO4)- Ammonium sulfate [(NH4)2SO4]- Elemental sulfur (S)

F. Magnesium (Mg)1) Soil Relations- Present in soil as an exchangeable cation (Mg2+)- Similar to Ca2+ as a cation2) Plant Functions- Core component of chlorophyll molecule- Catalyst for certain enzyme activity

3) Deficiency and Toxicity- Deficiency: Interveinal chlorosis on mature leaves (Mg is highly mobile)- Excess: Causes deficiency symptoms of Ca, K4) Fertilizers- Dolomite (mixture of CaCO3MgCO3)- Epsom salt (MgSO4)- Magnesium nitrate [Mg(NO3)2]- Magnesium sulfate (MgSO4)

Defisiensi Magnesium (Mg) pada PoinsettiaInterveinal Chlorosis on Mature Leaves

MicronutrientsMicronutrient elementsIron (Fe)Manganese (Mn)Boron (B)Zinc (Zn)Molybdenum (Mo)Copper (Cu)Chlorine (Cl) Usually supplied by irrigation water and soilDeficiency and toxicity occur at pH extremes

Influence of pH on Nutrient Availability

3. MicronutrientsA. Iron (Fe) - Komponen of cytochromes (needed for photosynthesis)- Essential for N fixation (nitrate reductase) and respiration- DeficiencySymptom: Interveinal chlorosis on new growthFe is immobileIron chlorosis develops when soil pH is high

Remedy for iron chlorosis: 1) Use iron chelatesFeEDTA (Fe 330) Stable at pH < 7.0FeEDDHA (Fe 138) Stable even when pH > 7.02) Lower soil pHIron is in more useful form (Fe2+)

Gejala defisiensi Iron (Fe)

12431-Piggyback Plant, 2- Petunia, 3-Silver Maple, 4-Rose (A-normal, B-Fe-deficient)AB

B. Manganese (Mn) - Required for chlorophyll synthesis, O2 evolution during photoshynthesis- Activates some enzyme systems- Deficiency: Mottled chlorsis between main veins of new leaves(Mn is immobile), similar to Fe chlorosis- Toxicity: Chlorosis on new growth with small, numerous dark spots Deficiency occurs at high pH Toxicity occurs at low pH- Fertilizers: Manganese sulfate (MnSO4)Mn EDTA (chelate) for high pH soilsC. Boron (B)- Involved in carbohydrate metabolism- Essential for flowering, pollen germination, N metabolism- Deficiency: New growth distorted and malformed, flowering and fruitset depressed, roots tubers distorted - Toxicity: Twig die back, fruit splitting, leaf edge burns- Fertilizers: Borax (Na2B4O710H2O), calcium borate (NaB4O7 4H2O)D. Zinc (Zn)- Involved in protein synthesis, IAA synthesis- Deficiency: (occurs in calcarious soil and high pH) Growth suppression, reduced internode lengths, rosetting, interveinal chlorosis on young leaves (Zn is immobile in tissues)- Toxicity: (occurs at low pH) Growth reduction, leaf chlorosis

Micronutrient Toxicity on Seed GeraniumBCuFeMnMoZnConcentration (mM)Cont0.250.5123456

E. Molybdenum (Mo) - Required for nitrate reductase activity, vitamin synthesis

Nitrate reductase NO3- NH2 MoRoot-nodule bacteria also requires Mo

- Deficiency: Pale green, cupped young leaves (Mo is immobile)Strap leafe in broad leaf plantsOccurs at low pH- Toxicity: Chlorosis with orange color pigmentation- Fertilizer: Sodium molybdateF. Copper (Cu)- Essential component of several enzymes of chlorophyll synthesis, carbohydrate metabolism- Deficiency: Rosette or witchs broom- Toxicity: Chlorosis- Fertilizers: Copper sulfate (CuSO4)G. Chlorine (Cl)- Involved for photosynthetic oxygen revolution- Deficiency: Normally not existing (Only experimentally induced)- Toxicity: Leaf margin chlorosis, necrosis on all leaves- Fertilizer: Never applied (Cl- is ubiquitous!)

Molybdenum Deficiency on Poinsettia

Iron deficiencyTomato Symptoms- strong chlorosis at the base of the leaves with some green netting- deficiency starts out with interveinal chlorosis of the youngest leaves, evolves into an overall chlorosis, and ends as a totally bleached leaf- bleached areas often develop necrotic spots- because iron has a low mobility, iron deficiency symptoms appear first on the youngest leaves- iron deficiency is strongly associated with calcareous soils and anaerobic conditions, and it is often induced by an excess of heavy metals

Influence of the pH on the availability of nutrient elements in organic soils- main losses of nutrients from agricultural systems due to leaching that carries dissolved ions, especially nitrate, away with drainage water

- in acid soils, leaching may be decreased by the addition of lime a mix of CaO, CaCO3 and Ca(OH)2 to make the soil more alkaline, because many elements form less- soluble compounds when the pH is higher than 6

- width of the shaded areas in the graph indicates the degree of nutrient availability to the plant root

Bagaimana cara senyawa esensial diserap dan didistribusikan dalam tumbuhan?

Bagaimana caranya sel tumbuhan mengontrol pergerakan ion dan air?

Bagaimana caranya tumbuhan bertahan terhadap kelebihan ion atau logam toksik?

Bagaimana caranya sel-sel tumbuhan berkomunikasi satu dengan lainnya?Arabidopsis

Ion uptake and transport in the plantExcept C,H and O, plants acquire all other elements as inorganic ions , even C : carbonat or bicarbonat ionNot all the ions in the soil are totally free in the soil solutionInorganic clay particlesOrganic particles (humus)

The region of most active ion uptake by roots is the young region of roots behind the apical meristem and root hair region

Transportmolecular and ionic movement from one location to another

How are essential nutrients taken up by the plant and distributed in the plant?

Phospholipid bilayer serves as a barrier (semi-permeable membrane)

Transport proteins catalyze transport of nutrients and metabolites as enzymes catalyze chemical reactions; 3 classes of transport proteinsChannelsCarriersPumps3. Transport can be active or passivepassive and active transport of ions results in an electric potential difference across membranes

Biological membranes are barriers to ionsHigh permeability Low permeability GlycerolPermeability [cm s-1]Artificial membraneBiological membraneH2O

Glycerol10-2

10-4

10-6

10-8

10-10K+Cl-K+, Na+, Cl-CO2H2O,CO2O2O2Na+

Adsorption, absorption and accumulationAdsoption of the cations to the cell wall

H+ ions moving out of the cell by action of proton pumps

H+ are then accessible to be exchanged for soil solution cations

Absorbtion through the plasma membrane

Accumulation : when the ions are taken up to a greater concentration inside the plasma membrane than outside

Adsorption : attraction outside the plasma membraneAbsorption : actual entry into the cell to the inside of plasma membrane

Channels, Carriers and Pumps mediate the transport of solutes across membranes

Major Transport Proteins in PlantsIon pumps: H+-pumping ATPases

Channels allow rapid, passive transport of ions and metabolites

Aquaporins (water channels) transport water

H+-coupled co-transport is necessary for the transport of many nutrients and metabolites (active transport; energy from H+-gradient is used to drive uphill movement of nutrients)

Transport proteins catalyze transport like enzymes catalyze chemical reactions

Transport can be active or passivePassive transport: movement down (downhill) an electro-chemical gradient

Active transport: movement against (uphill) an electro-chemical gradient

What is an electrochemical gradient? How is it formed?Passive and active transport of ions result in an electric potential difference across membranes.Movement of an uncharged molecule is dependent on the concentration gradient aloneMovement of an ion depends on the electric gradient and the concentration gradientPrimary vs. Secondary active transport

How do you know if an ion is moving uphill or downhill?Nernst equation predicts passive ion distribution, distinguishes between passive and active transport

What is the driving force for uphill movement?ATP or H+ electrochemical gradient

Diffusion potentials develop when positively and negatively charged ions move across a membrane at different rates

Nernst EquationDifference in electric potential between the two compartments is known as the Nernst Potential Ej, where J is the passive flux (i.e. the amount of solute crossing a unit area of membrane per unit time)

Ej = Einside Eoutside

The difference in electric potential between the two compartments at equilibrium is

Ej = Einside Eoutside = RT (ln Cjoutside) zjF Cjinside

Ej = 2.3RT (log Cjoutside) zjF Cjinside

At 25C for a univalent cation

Ej = 59mV * log Cjoutside Cjinside

Microelectrodes are used to measure membrane potentials across cell membranes

Using the Nernst Equation to predict ion concentration in pea root tissue at equilibrium when the cell membrane potential is -110 mVActive uptakeEnter cell by diffusion down their electro-chemical potential gradients

Special techniques are used in nutritional studies- roots immersed in nutrient solution- large volume of nutrient solution and adjustment required- oxygen supply, bubbling

- roots receive ample supply of oxygen

Special techniques are used in nutritional studies- roots suspended in air while being sprayed continuously with a nutrient solution - easy manipulation of gaseous environment- requires larger amounts of nutrients vs. hydroponics

- roots are periodically immersed in nutrient solution- requires higher levels of nutrients vs. hydroponics

The Role of Chelators in nutrient solutionProblem with nutrient solutions is maintaining the availability of iron due to precipitation of iron out of the solution.

Add chelators that form complexes with cations (Fe, Ca) in which cation is held by ionic forces rather than covalent bonds.

Chelated ions remain physically available for the plant.Diethylenetriaminepentaacetic acid (DTPA) DTPA chelated to an Fe3+ ion that binds through N atoms and three ionized O atoms;Resulting ring structure clamps the Fe

Mineral deficiencies disrupt plant metabolism and functionInadequate supply of an essential element results in nutritional disorder manifested by characteristic deficiency symptoms

Group 1: Deficiencies in mineral nutrients that are part of carbon compounds (N, S)Group 2: Deficiencies in mineral nutrients that are important in energy storage or structural integrity (P, Si, B)Group 3: Deficiencies in mineral nutrients that remain in ionic form (K, Ca, Mg, Cl, Mn, Na)Group 4: Deficiencies in mineral nutrients that are involved in redox reactions (Fe, Zn, Cu, Ni, Mo)

For more examples on nutrient deficiencies, please visithttp://3e.plantphys.net/article.php?ch=t&id=289

Inorganic fertilizerStraight fertilizerSuper phosphate, ammonium nitrateCompound fertilizer (i.e. contain two or more mineral nutrients)

Organic fertilizerResidues of plants and animalsMineralization (organic compounds broken down by microorganisms)Treating nutritional deficiencies

Foliar application of fertilizers

Uptake is fasterDeficiency can be preventedNot tied up in soils (Fe, Mn and Cu)ExpensiveVineyards

Plants develop extensive root systemsWheatFibrous Root SystemTap Root System

Different areas of the root absorb different mineral ions- depends on plant species

- Fe is taken up either at apical region (barley) or over entire root surface (corn)

- K, NO3, NH4+, P absorbed at all locations of root

- root hairs are most active in P absorption

- strong demand of nutrients in apical region (cell elongation)

Root infected with ectotrophic mycorrhizal fungi- fungal hyphae surround the root to produce a dense fungal sheath and pene- trate the intercelluar spaces of the cortex to form the Hartig net- total mass of fungal hyphae may be comparable to the root mass itself

Example: only tree species; gymnosperms and woody angiosperms

Association of vesicular-arbuscular mycorrhizal fungito promote P acquisition- fungal hyphae grow into the intercellular wall spaces of the cortex and penetrate individual cortical cells

- plasma membrane or tonoplast of host cell does not break

- instead, the hypha is surrounded by these membranes and forms arbuscules, which partici- pate in nutrient ion ex- change between the host plant and the fungus

Example: Alfalfa

Nutrition - Summary macro- dan micronutrients essential (penting ) untuk kehidupan tanaman Kekurangan nutrient berakibat fatal karena nutrien berperan dalam penyimpanann energi, struktur tanaman, kofaktor enzim, reaksi transport elektron- mineral nutrition can be studied through the use of solution culture- to prevent development of deficiencies, nutrients may be added back to the soil/plant through fertilizers- size of soil particles and cation exchange capacity determine the reservoir for water and nutrients- soil pH affects availability of mineral elements to plants- plants develop extensive root system to obtain nutrients- plant roots form associations with mycorrhizal fungi- hyphae facilitate the acquisition of mineral elements (P) - in return, plants provide carbohydrates to mycorrhizae

The barrel illustrates the Law of the Minimum. The height of the water is determined by the shortest stave. Above this, it doesnt matter how long the other staves are, they cant substitute for the short one. Similarly, if a plant is deficient in one nutrient, growth with be determined by the limiting nutrient, and the growth rate cannot be accelerated by adding other, non-limiting nutrients. In practice, this means that knowing what nutrients are limiting ensures optimal growth and avoids excessive use of unneeded fertilizers. *http://www.rothamsted.ac.uk/sir-john-bennet-lawes/sir-john-bennet-lawes-timelinehttp://www.era.rothamsted.ac.uk/pix.php?area=home&image=metadata/broad/Broadbalkharvest1880.jpg for permission********************************