MK. KESUBURAN TANAH
K - Ca - Mg TANAH
Prof Dr Ir Soemarno,M.S.
Magnesium is essential to the basic nucleic acid chemistry of life, and thus are essential to all cells of all
known living organisms.
Plants have an additional use for magnesium in that chlorophylls are magnesium-centered porphyrins.
Many enzymes require the presence of magnesium ions for their catalytic action, especially enzymes utilizing
ATP, or those which use other nucleotides to synthesize DNA and RNA.
Magnesium is a vital component of a healthy human diet and has been implicated in a number of human diseases.
Magnesium is readily available in the food that we eat and magnesium deficiency is therefore relatively rare.
It is also difficult to overdose on magnesium. However, both of these conditions do occasionally appear
in humans. The major causes are genetic with the inactivation of
magnesium transporters in the Kidneys. General failure of the Kidneys may also lead to
magnesium imbalance.
KALIUM TANAH
Jumlah K-tanahLithosfer mengandung 2.6% KTanah mengandung <0.1 - > 3%, rata-rata sekitar 1% KTanah lapisan olah (setebal 20 cm) mengandung <3000 - >100.000 kg K/haSekitar 98% K dalam tanah terikat dalam bentuk mineral
Mineral Kalium K-feldspar merupakan mineral utama sumber kalium, 16%K-mika sekitar 5.2%, terdiri atas Biotit sekitar 3.8% dan Muskovit 1.4%
Kekuatan ikatan K dalam mineral Kation K diameternya 2.66 Å, terbesar di antara unsur hara lain; oleh karena itu ikatannya dalam struktur mineral lebih lemah dibandingkan kation lainnya yg lebih kecil dan muatannya lebih besar.Karena ukurannya besar, kation K dapat diselimuti oleh 7-12 ion oksigen, sehingga kekuatan masing-masing ikatan K-O relatif lemah
KALIUM dlm
FELDSPAR
KIMIA & strukturFeldspar adalah aluminosilikat , formulanya KAlSi3O8, kandungan
kaliumnya 14%.Di alam, sebagian kalium digantikan oleh Na dan CaKation pusat Si4+ sebagian digantikan oleh Al3+, satu penggantian
untuk setiap empat tetrahedra, sehingga menjadi AlSi3O8-
Polimorf dari feldspar Ortoklas: monoklinik - prismatik, dlm batuan plutonikSanidin : Monoklinik, dalam batuan vulkanikMicrocline : Triklinik, mengandung magmatit-pegmatitAnortoklas : Substituted feldspar, (K,Na)AlSi3O8Nepheline : Mengandung lebih banyak Na dp KPlagioklas : (Ca, Na feldspar) mengandung sedikit kalium
Pelapukan Mineral Kalium
Proses pelapukan fisik menghancurkan batuan induk, sedangkan pelapukan kimia akan melepaskan ion K+ dari mineralTemperatur penting untuk pelapukan fisika, sedang hidrolisis penting untuk kimiawiAsam-asam yg penting pd hidrolisis mineral kalium adalah H2CO3 dan asam-asam organik hasil dekomposisi Bahan organik tanah
HIDROLISIS Feldspar
KALIUM
Abstraksi proses hidrolisis
KAlSi3O8 + HOH ===== HAlSi3O8 +K+ + OH- (Fase cepat)
HAlSi3O8 + 4HOH ===== Al(OH)3 + 3H2SiO3 (fase lambat)
Penambahan H+ mempercepat pembebasan K+ dan merusak ikatan Al-O; Al yang dibebaskan membentuk gugusan AlOH2 koordinasi-4:
Si-O-Al + H2O + H+ ==== Si-O + Al-OH2 + K+ | | K H
Hancurnya ikatan Si-O-Si mungkin disebabkan oleh melekatnya OH- ke Si sehingga menjadi gugusan Si-OH; dengan cara ini ikatan kovalen rangkap dihancurkan.
Joint reaction H2O dan H+ dlm menghancurkan ortoklas:
3 KAlSi3O8 + 12H2O + 2H+ ===== KAlSi3O6.Al2O4(OH)2 + 2K+ + 6 H4SiO4
Pelapukan ortoklas menjadi kaolinit: H2O 2KAlSi3O8 -------------- Al2Si2O5(OH) + 2K+ + 2OH- + 4H4SiO4
KALIUM TANAH
Sumber K-tanahMineral primer yang mengandung kalium:1. Feldspar kalium : KAlSi3O82. Muskovit : H2KAl3(SiO4)33. Biotit : (H,K)2(Mg,Fe)2Al2(SiO4)3
Mineral sekunder:1. Illit atau hidrous mika2. Vermikulit3. Khlorit4. Mineral tipe campuran
Proses pelapukan mineral
KAlSi3O8 + HOH KOH + HAlSi3O8
K+ + OH-
K
Ca K+, Ca++, H+ (larutan tanah)
Koloid liat H
Pelapukan Mineral
KALIUM
Pelapukan 1. Proses fisika: Penghancuran fisik, ukuran partikel menjadi
lebih halus, luas permukaannya menjadi lebih besar2. Proses kimiawi: Hidrolisis, Protolisis (Asidolisis)
Proses Hidrolisis dan Protolisis
KAlSi3O8 + HOH HAlSi3O8 + K+ + OH- (cepat)
HAlSi3O8 + 4 HOH Al(OH)3 + 3 H2SiO3 (lambat)
Si-O-Al + H2O + H+ Si-O + Al-OH2 + K+
K H
Pelapukan Ortoklas:
3 KAlSi3O8 + 12H2O + 2H+ KAlSi3O6 .Al2O4(OH)2 + 2K+ +6H4SiO4
H2O
2 KAlSi3O8 Al2Si2O5(OH) + 2K+ + 2OH- + 4 H4SiO4
Faktor Pelapukan Feldspar
KALIUM
Faktor Pelapukan 1. Faktor Internal 2. Faktor Eksternal
Faktor internal: 1. Regularity of the crystal lattice. Microcline lebih stabil / sukar lapuk dibanding Ortoklas dan Sanidine2. Na content of crystals. Anortoklas lebih mudah lapuk daripada ortoklas3. Si content. Feldspar-substitusi lebih mudah lapuk dp Feldspar4. Particle size. Semakin kecil ukuran partikel, maka semakin luas permukaannya untuk mengalami reaksi hidrolisis dan asidolisis.5. ………….
Faktor Eksternal:1. Temterature. Proses pelapukan lebih cepat pd kondisi suhu yg lebih tinggi2. Solution volume. Kondisi basah mempercepat proses pelapukan3. Migration of weathering products. Proses pelapukan akan terhambat kalau hasil-hasil pelapukan terakumulasi di tempat4. The formation of difficult soluble products of hydrolysis. Kalau hasil reaksi hidrolisis mengendap maka reaksi akan dipercepat5. pH value. Semakin banyak ion H+, proses protolisis semakin intensif.6. The presence of chelating agents.
MASALAH KALIUM TANAH
Ketersediaan K-tanahTanah mineral umumnya berkadar kalium total tinggi, kisarannya 40 - 60 ribu kg K2O setiap HLOSebagian besar kalium ini terikat kuat dan agak sukar tersedia bagi tanaman
Kehilangan akibat PencucianSejumlah besar kalium hilang karena pencucian :Tercuci dari tnh lempung berdebu 20 kg K2O/ha/thnDiangkut /dipanen oleh tanaman 60 -”-
Konsumsi berlebihan: Luxury consumptionTanaman dpt menyerap kalium jauh lebih banyak dari jumlah yg diperlukanPemupukan kalium harus dilakukan secara bertahap
Masalah Kalium tanah: 1. Pd saat tertentu sebagian besar K-tanah tidak tersedia2. K-tanah peka terhadap pengaruh pencucian3. Kalium dapat diserap tanaman dlm jumlah banyak, melebihi kebutuhan optimalnya
Kadar K-tanaman
(Tinggi)
Kadar K-tanaman
K diperlukan untuk Pemakaian berlebihan pertumbuhan optimum
Kalium yg diperlukan
(Rendah)Rendah K-tersedia dalam tanah Tinggi
BENTUK & KETERSEDIAAN
Relatif tidak tersedia Feldspar, Mika, dll. (90-98% dari K-total)
K segera tersediaK dpt ditukar dan K dlm larutan
tanah( 2 % dari K-total)
K lambat tersedia K tidak dapat ditukar (1 - 10 % dari K-total)
K tidak dapat ditukar K dapat ditukar
K dalam larutan tnh
LOKASI DAN JALUR KALIUM DLM TANAH
K dalam mineral primermis. Muskovit
K dalam tanaman
K dalam mineral sekunder mis. Kaolinit
K dalam larutan tnh
K dalam PUPUK
Pelarutan pupuk
Absorpsi K
Pelepasan Kdd
atau K-terfiksasi
Adsorpsi atau Fiksasi K
Pelepasan K
Fiksasi K pd mineral primer
Transisi mine-ral sekunder menjadi mika akibat fiksasi K
Pelepasan K mengakibatkan pembentukan min. sekunder
Pelepasan K dari mineral primer
Pelepasan K dari mineral primer selama periode pertanaman intensif; media tumbuh mineral dicampur pasir kuarsa. Ukuran partikel mineral primer < 50 ; ukuran partikel illit < 20 .
Pelepasan K-tukar, g / g mineral
2000 -
Biotite
Illite
Muscovite
Ortoklas 400 5 10 15
cropping periode, (0-15) days Sumber: Verma (1963)
Konsentrasi K-larutan tanah vs Kdd
K-larutan tanah (me/l)
5.0
Tanah berpasir4.0
3.0
2.0
Tanah liat1.0
10 50 100
K dapat ditukar, mg K / 100 g tanah
FIKSASI KALIUM TANAH
Faktor yg mempengaruhi fiksasi K-tanah1. Sifat koloid tanah2. Pembasahan dan pengeringan tanah3. Pembekuan dan pencairan tanah4. Adanya kalsium yg berlebihan
Koloid dan Kelembaban Kaolinit sedikit mengikat kalium Montmorilonit dan Ilit mudah dan banyak mengikat kalium, lazim disebut dengan FIKSASI KALIUM:
lapisan liat 2:1
Ion kalium
Ion lainnya
K - tersedia
Terangkut tanaman
Hilang pencucian
Hilang Erosi & Run-off
Fiksasi Kalium
Sisa tanaman & Pupuk kandang
Pupuk buatan
Mineral kalium lambat tersedia
Faktor Ketersediaan K-
tanah
1. MOBILITAS
Mobilitas kalium dalam tanah ditentukan oleh bentuk K+, yaitu bentuk bebas dalam larutan tanah atau bentuk terjerap pada permukaan koloid tanah
2. Interaksi dg ion lain3. Mass flow dan Difusi4. Kapasitas dan Intensitas5. Mineral Tanah: Mineral Primer dan Mineral Liat
a. Kadar K mineral primerb. Kecepatan pelepasan K+ dari mineral primerc. Jumlah mineral liatd. tipe mineral liat
6. Bahan Organik Tanah7. pH tanah8. Aerasi
9. Lengas TanahDifusi K+ dalam tanah terjadi melalui dua cara, yaitu:
1. Ruang pori yang berisi air, dan2. Selaput air di sekeliling partikel tanah.
Pengaruh pH
thd fiksasi K
Pengaruh thd fiksasi K Pengaruh pH terhadap fiksasi K bersifat tidak langsung, yaitu melalui pengaruh pH thd jenis aktion yg dominan pada posisi inter-layer mineral liat.Pd tanah masam Al+++ menempati posisi-posisi jerapan.Pengasaman dapat mengakibatkan akumulasi ion Al-hidroksil pd inter-layer mineral liat, shg KTK lebih rendah
Pada Vermikulit, ion Al+++ dapat mengusir K+ dari kompleks jerapan, sehingga menurunkan kapasitas fiksasi K+.Sehingga pengaruh pengasaman tanah thd fiksasi K tergantung pada adanya vermikulit dan adanya Al+++ yg akan mendominir kompleks jerapan
Pengaruh pengapuran tanah masam thd fiksasi K tgt pada adanya Ca++ yg akan
menggantikan Aldd, shg membuka peluang terjadinya fiksasi K+
Fiksasi K+ K-releasedpH: 3.50
Pupuk 100 kg K/ha 0.0 pH: 4.35
Tanpa pupuk K pH: 7.00 Dosis kapur, CaCO3 K-adsorbed Pencucian
Efek Pupuk K terhadap
K-tanah
Jelaskan pengaruh pH tanah terhadap kelarutan pupuk kalium dalam tanah
(250 kata), seperti gambar ini
K-larutan tanah
pH: 4.1
pH: 5.1
pH: 6.5
pH: 7.0
Dosis pupuk K
Lengas Tanah terhadap
K-tanah
Jelaskan bagaimana kadar air tanah dapat meningkatkan efisiensi pupuk kalium pada
tanaman jagung (250 kata) ……….
Serapan K tanaman jagung
Pupuk Kalium:
49 mg K/100 g tnh
29
9
0
Kadar air tanah (20-40%)Sumber: Grimme (1976)
Serapan K vs
K-larutan tanah
Konsentrasi K+ dlm larutan tanah merupakan indeks ketersediaan kalium, karena difusi K+ ke arah permukaan akar berlangsung dalam larutan tanah dan kecepatan difusi tgt pada gradien konsentrasi dalam larutan tanah di sekitar permukaan akar penyerap.
Serapan K , kg /ha (Tanaman kacang buncis)
300
r2 = 0.79**
0.2 0.4 0.6 0.8K- larutan tanah ( me K / l)
Sumber: Nemeth dan Forster (1976)
Laju Penyerapan K vs
Konsentrasi K+ larutan
Jelaskan pengaruh konsentrasi K+ dalam larutan tanah terhadap laju penyerapan K+
oleh akar tanaman (250 kata) ……….
Laju penyerapan K+ , mole/g/jam (akar tanaman barley)
10.0
0.05 0.10 0.15 0.20 Konsentrasi K+ larutan tanah ( mM)
Sumber: Epstein (1972)
Efek Ca++ thd penyerapan
K+ akar tanaman
Jelaskan bagaimana Ca++ dapat mengganggu penyerapan K+ oleh akar tanaman
(250 kata)………
Penyerapan K , mole/g (akar tanaman Jagung )
6
+ Ca
0
-1 0.5 1.0 1.5 2.0
jam Sumber: Lauchli dan Epstein (1970)
KALSIUM DALAM TANAH
Sumber Ca-tanahMineral primer : Bahan Pupuk:1. Dolomit : ……….. 1. Kalsium nitrat2. Kalsit : ……….. 2. Gipsum3. Apatit : ……….. 3. Batuan fosfat4. Feldspar kalsium: ……….. 4. Superfosfat5. Amfibol : ………… 5. Ca-cyanamide
Kation kalsium dlm larutan tanah dapat mengalami:1. Hilang bersama air drainase: Proses pencucian2. Diserap oleh organisme3. Dijerap pada permukaan koloid tanah4. Diendapkan sebagai senyawa kalsium sekunder
Faktor ketersediaan Kalsium tanah: 1. Jumlah kalsium dapat ditukar (Ca++ yang dijerap oleh koloid tanah)2. Derajat kejenuhan Kalsium dari kompleks pertukaran 3. Tipe koloid tanah4. Sifat ion-ion komplementer yg dijerap oleh koloid tanah5. …………….
MAGNESIUM DALAM TANAH
Sumber Mg-tanahMineral primer: Bahan Pupuk:1. Dolomit : ……….. 1. MgSO4.7H2O 2. Biotit : ……….. 2. MgSO4.H2O3. Klorit : ……….. 3. K-Mg-sulfat4. Serpentin : ……….. 4. Magnesia5. Olivin : ………… 5. Basic slag
Kation magnesium dlm larutan tanah dapat mengalami:1. Hilang bersama air drainase: Proses pencucian2. Diserap oleh organisme3. Dijerap pada permukaan koloid tanah4. Diendapkan sebagai senyawa kalsium sekunder
Faktor ketersediaan Magnesium tanah: 1. Jumlah kalsium dapat ditukar (Mg++ yang dijerap oleh koloid tanah)2. Derajat kejenuhan Mg dari kompleks pertukaran 3. Tipe koloid tanah4. Sifat ion-ion komplementer yg dijerap oleh koloid tanah5. …………….
Serapan K vs
Dry matter production
Buatlah uraian (250 kata) tentang pola penyerapan kalium tanaman jagung selama
pertumbuhannya, seperti gambar ini
Growth & nutrient uptake, %
100 silkingtasseling
Biji
dry matter
Tongkol Kalium
Batang
Daun
25 50 75 100days after emergence
Sumber: Nelson (1968)
Kandungan K-tanah
vs Respon pupuk K
Buatlah uraian (250 kata) tentang hasil penelitian pemupukan kalium pada tanaman
jagung seperti Gambar ini
Tambahan hasil jagung , bu/ac
25Kdd = 50 ppm
Kdd = 100 ppm
Kdd = 150 ppm
Kdd = 200 ppm
25 50 75 100 125 Dosis pupuk K ( lb / ac )
Sumber: Hanway et al. (1962)
Kandungan K-daun
vs Respon pupuk K
Respon jagung thd pupuk kalium dipengaruhi oleh status K tanaman, yaitu kadar K daun pada fase silking
Defisiensi akut : Kadar K daun 0.25 - 0.41 %KDefisien tanpa gejala: 0.62 - 0.91 %KNormal : 0.91 - 1.3% K
Tambahan hasil jagung , bu/ac
25Kdaun = 0.75 %
Kdaun = 1.0 %
Kdaun = 1.5 %
Kdaun = 1.75%
25 50 75 100 125 Dosis pupuk K ( lb / ac )
Sumber: Hanway et al. (1962)
Mulsa jerami sisa panen dapat menambah sejumlah K, Ca dan Mg ke dalam tanah
Pupuk kalium sangat diperlukan
untuk pembentukan
umbi.
Buatlah uraian (250 kata) mengenai
pemupukan kalium tanaman
ubi-ubian…
Pupuk kalium sangat diperlukan
untuk kesempurnaan
pembentukan buah pisang dan tingginya
kandungan karbohidratnya.
Buatlah uraian (250 kata) mengenai
pemupukan kalium tanaman pisang…
Pupuk kalium sangat
diperlukan untuk
pembentukan umbi beet dan
tingginya kandungan pati-
nya
Kualitas buah anggur sangat
ditentukan oleh pemupukan
K dan Mg
Buatlah uraian (250 kata) mengenai
pemupukan kalium dan Magnesium
tanaman anggur…
Produktivitas pohon kopi sangat
ditentukan oleh kecukupannya pupuk
Mg dan K
Buatlah uraian (250 kata) mengenai
pemupukan kalium dan Magnesium
tanaman KOPI …….…
Penyerapan Hara K, Ca dan Mg
• A deficiency of an element makes it difficult or impossible for the plant to complete a vegetative or reproductive stage of development
• A deficiency can be prevented or corrected by supplying the element
Ikisan.com
Soil pH affects availability of K, Ca and Mg
Nutrient Uptake – from soil to plant via root
• Movement to the roots: • 1) Root extension -
exposure to soil and new supplies of nutrients - roots could contact 3% of the soil or nutrients in the soil.
2) Mass Flow – water absorbed by the root
creates a water deficit near the root,
more water moves to the root carrying nutrients with the water.
Important for nutrients in large quantities in the soil solution - N, K & Ca, Mg
Nutrient Uptake
3) Diffusion - movement of nutrients due to an imbalance of concentration ( diffusion gradient)
root random thermal movement
K. Ca, MgKation
Requirements for nutrient K, Ca, Mg uptake by plants
• Actively growing plants - anything that affects the metabolism of the plant will affect nutrient uptake
• Metabolic energy is required. Plant roots must be able to respire. Soils must have oxygen
Conditions required for Nutrient Uptake by plants
3) Root hairs are the most active points of nutrient uptake.
4) Process is selective - a carrier ion moves from plasmalemma across the plasma membrane into the outer space of the walls of the cells of the cortex and picks up a nutrient ion and moves back across the membrane.
Nutrient Uptake
Carrier ion
Plasma Membrane
Inner space
outer space
NO3- NO3-
K+
Free Space Energy Required to move carrieracross the membrane
NO3-
Nutrient Uptake
Root Hair
NO3- HCO3-
Ca ++H+ H+
Nutrient absorption results in increased acidity.
Soil fertilisation•Formulae containing
potassium sulphate are recommended for pre-planting fertilisation.
•Nitrogen dosage should be determined precisely
according to nitrogen remaining in the soil, production type and
potential staggering of applications
Developing Crop P GuidelinesIn order to not over- or under-supply crops with nutrients from
manure and fertilizer, it's important to determine the crop's need for nutrients. Consider a broader case, including and beyond P for a minute. A crop has many basic needs. The factor that is in shortest supply, relative to crop needs, will limit the yield of the crop, leaving the other factors in excess. This is known as the
Limiting Factor Concept.The Limiting Factor Concept can be illustrated by a barrel of water. The staves represent key factors for crop growth. The
shortest stave height limits how much water the barrel can hold (i.e. crop yield).
Produktivitas kacangtanah sangat
ditentukan oleh kecukupannya pupuk
Ca
Buatlah uraian (250 kata) mengenai
pemupukan kalsium (Ca) pada tanaman
Kacangtanah
…………….…
Produktivitas bawangputih sangat
ditentukan oleh keseimbangan pupuk
N dan K
Buatlah uraian (250 kata) mengenai
pemupukan N dan K pada tanaman
usahatani bawangputih
…………….…
Produktivitas dan kualitas umbi
bawangputih sangat ditentukan oleh
kecukupannya pupuk K
Buatlah uraian (250 kata) mengenai
pemupukan kalium (K) pada tanaman bawnagputih
…………….…
Rendemen tebu sangat ditentukan
oleh kecukupannya pupuk K
Buatlah uraian (250 kata) mengenai
pemupukan kalium (K) pada tanaman
TEBU
…………….…
Produktivitas dan kualitas buah
semangka sangat ditentukan oleh
keseimbangan pupuk Mg dan K
Buatlah uraian (250 kata) mengenai
pemupukan Mg dan K pada usahatani
semangka
…………….…
Relationship between pH-dependent cation
exchange capacity and K concentration in soil
solution (Modified from Brady and Weil, 1999).
Soils with the same initial K levels may have very different abilities to supply K to crops over
time
(Hoeft et al., 2000).
What is the difference between ‘fixed’ and ‘exchangeable’ sorbed K?
These two sorbed phases of K exist in a dynamic equilibrium with soil solution but are very different in how readily they respond to changes in solution K+.
Fixed K is bound deep within the soil particles and requires long periods of time, on the order of months to
years, to equilibrate with the soil solution. Exchangeable K can be released quickly because it is
only weakly held to the surfaces of soil particles, where it is in close contact with the soil solution.
Soils with the same initial K levels may have very different abilities to supply K
to crops during a growing season
(Hoeft et al., 2000).
Effective K managementEffective K management in agricultural land
requires not only a thorough understanding of K transformations in the soil, but also an awareness of how climate, aeration, and water can affect the ability of a plant to access the large reserves of soil
K.
Potassium exists in large, albeit finite, amounts in the soil, but the available forms can be depleted
over long-term agricultural utilization as has been the case on many farms in the regions .
Large amounts of K are removed from the soil during harvest, and in most parts of regions
replenishment of the available K pool with fertilizer amendments are minimal.
Proper management and knowledge of K cycling in the soil can help maintain the present K reserve in
agricultural soils and ensure it is utilized efficiently.
AGLIME: KAPUR PERTANIAN
A good liming program is based on a soil test that determinesthe degree of soil acidity and the correct amount of a
liming material needed to neutralize that acidity.
Once this amount is determined, a liming material must be selectedthat will economically satisfy the soil test recommendation
and result in maximum, efficient production.
However, before considering the necessary lime application amounts, an understanding of aglime materials, quality, and
associated laws is helpful.
Kualitas Kapur: Aglime quality
Not all limestone is the same. The quality of aglime varies significantly and should
be an important consideration in aglime management.
Four factors are most important in assessing aglime quality; chemical purity, speed of reaction,
magnesium content, and moisture.
Chemical purity
The chemical purity of aglime determines the amount of soil acidity the material can neutralize.
Chemical purity is indicated by the material’s calcium carbonate equivalent (CCE):
The amount of soil acidity the material can neutralizecompared to pure calcium carbonate (calcitic limestone,
CaCO3). The CCE is given as a percentage: a 100-percent-CCE limestone would be just as
effective as pure calcitic limestone in neutralizing value; 90-percent-CCE limestone would be only 90 percent as effective; and a 109-percent-CCE
limestone such as a dolomitic limestone would be 109 percent as effective.
CCE indicates only the equivalent neutralizing value of an aglime material; it says nothing about the actual calcium carbonate content of the material. For
example, note that pure calcium hydroxide (hydrated or slaked lime) has a CCE of 136 percent but contains no calcium carbonate.
Kecepatan Reaksi
The speed with which an aglime material reacts with the soil to neutralize acidity and thus increases soil pH is determined by the
fineness of the material. The finer the material, the faster it will react because limestone’s
solubility increases as it is ground finer. Also, limestone affects only a very small volume of soil around each particle, so the finer the
material, the greater the total surface area that is available to come into contact with the soil and neutralize it (assuming adequate soil
mixing).Aglime should react with the soil as quickly as possible.
Generally, aglime should react completely within three years. Quicker reaction may be desirable on rented ground or for shorter-
season annual crops.
Aglime fineness is given as the percentage of thematerial that passes through sieves of specified mesh. Sieve
mesh is the number of wires per inch on the sieve. Thehigher the number, the finer the material that will pass
through.
Aglime larger than 20 mesh (about the fineness of tablesalt/sugar) reacts extremely slowly; little will react within
two to three years.
The speed of reaction increases to a practical maximum with 100-mesh material.
The effect of aglime fineness on speed of reaction is shown clearly in Figure 3.
Kadar Ca dan Mg
In addition to acid neutralization capabilities, lime alsoserves as a source of calcium and magnesium.
The magnesium content of aglime is important when a soil testindicates a need for magnesium. Magnesium requirementsare met most economically by applying an aglime material
that contains magnesium.
The magnesium content of aglime varies considerably.Unfortunately, there is no official trade classification of limestone
according to its magnesium content. Local classification schemes often create confusion. Therefore, to select the proper aglime material, you should use the actual magnesium analysis rather than a name (e.g.,
dolomitic lime, high-magnesium lime).
Kadar Ca dan Mg
Magnesium soil-test recommendations are usually givenin one of the three different ways:
As pounds of Mg per acre, or as pounds of MgO per acre, or as pounds of calcium carbonate equivalent per acre with a specific Mg or
MgO content.
Liming materials must be labeled to indicate their percentage of Mg; however, additional information on percentage of MgO may also
appear. When the recommendation and label are in different forms, a simple conversion is required. To convert Mg into MgO, multiply by 1.67;
but to convert MgO into Mg, multiply by 0.602.
Moisture: Kadar Air Tanah
The moisture content of an aglime does not directly affectits effectiveness.
However, since lime is sold and applied by weight, including water weight, a high moisture content means less actual liming material per ton. When moisture content approaches 10 percent or more,
the application rate of aglime per acre should be adjusted to ensure that the required amount of actual liming material is
applied to the soil. Use the following formula to make the adjustment or refer to the example calculations section:
soil test recommendation (CCE/A) x 100----------------------------------------------------------
100 - % moisture
SOIL TEST AGLIME RECOMMENDATIONS
Liming an acid soil to an optimal range is the initial step in creating favorable soil conditions for productive plant growth.
The lime recommendation on the soil test report is based on the amount of exchangeable acidity (or exchangeable H+) measured by the lime requirement soil
test and the optimum soil pH for the crop.
For a desired pH of 7.0, the lime requirement can be estimated as follows:
Lime requirement = exchangeable acidity x 1,000
For a desired pH 6.5, the lime requirement is estimated as follows:
If the exchangeable acidity is greater than 4.0, then:
Lime requirement = exchangeable acidity x 840
If the exchangeable acidity is less than 4.0 and the soil pH is still less than 6.5, then:Lime requirement = 2,000 lb/A.
Otherwise, no lime is required.
Calcium and Magnesium Cycling
Ca and Mg occur in the soil as soluble ‘divalent’ (‘double-charged’) cations (Ca+2 and Mg+2), on cation exchange sites,
and in mineral forms.
The major processes in the Ca/Mg cycle are plant uptake, exchange, precipitation, weathering, and leaching . Ca/Mg
dynamics in the soil are quite similar to K .
Like K, plants absorb the soluble ionic form from soil solution, which is then replenished by exchangeable and mineral Ca/Mg.
The most notable difference between these nutrient cycles is the absence of Ca/Mg clay fixation.
CALCIUM: Ca
Ca plays an important role in cell elongation and maintaining membrane structure in plants. The presence of Ca in roots also regulates plant cation uptake by limiting excessive sodium (Na)
and increasing beneficial K absorption.
Most soils, especially those in Montana and Wyoming, contain abundant Ca in solution (30-300 ppm) relative to most crop
requirements (~15 ppm).
The supply of Ca in soil solution can be ten times larger than K and plants require much less Ca, so deficiencies are rare. Mass flow supplies adequate Ca to plant roots, except in low Ca soils,
where diffusion becomes an important process.
Ca is usually the dominant base cation in exchange reactions, accounting for more than 70% of base saturation. Base saturation
represents the percentage of the CEC occupied by base cations (Ca, Mg, K, and Na) and generally increases with pH.
Exchangeable Ca exists in equilibrium with the soil solution, replenishing soluble Ca losses by plant uptake or leaching. Leaching can be significant in coarse-textured, acidic soils where substantial
water moves through the profile.
In many calcareous soils, some Ca leaches out of the more acidic, organic-rich topsoil and precipitates in a Ca-rich ‘calcic’ horizon in the sub-soil in the form of calcium carbonate (CaCO3) or gypsum
(CaSO4).
In addition to the dissolution of these secondary deposits, Ca is also released through the weathering of primary minerals such as
feldspars, micas, and limestone; all of which are common throughout this region.
Because of its strong divalent charge, Ca acts as an ionic ‘glue’, attracting clay particles and promoting aggregation through a
process called ‘flocculation’.
Soils with high levels of sodium (Na), referred to as ‘sodic’ soils, promote ‘dispersion’ which is the opposite of flocculation. When monovalent (‘single-
charged’) Na ions dominate the clay surfaces in the soil, the weak positive charge of the ion is not strong enough to overcome the negative charges of clay particles,
which then repel each other.
The result of dispersion is a structureless, gel-like soil with insufficient aeration, permeability, and water-holding capacity for optimum plant growth.
Additions of Ca in the form of gypsum are frequently prescribed for reclaiming sodic soils because it counters the effects of Na and
promotes the aggregation critical for soil productivity. Gypsum is preferable to CaCO3 because gypsum is more soluble. Low Na
irrigation water or rainwater can then be used to leach Na out of the soil profile.
MAGNESIUM
Mg plays a critical role in nearly all parts of plant metabolism and protein synthesis, and is an essential constituent of chlorophyll.
Plants require less Mg than Ca, but deficiencies are more common because less Mg exists in the soil solution.
Mineral forms of Mg are relatively resistant to weathering and represent a large fraction of total soil Mg. Mineral forms of Mg include biotite, horneblende,
olivene, dolomite, and most 2:1 clay minerals. Soluble Mg can also precipitate out of solution as MgCO3 or MgSO4, frequently
along with CaCO3 in the sub-surface. Although Ca and Mg share the same exchange processes, Mg sorbs less strongly to soil colloids and therefore is more prone to leaching, particularly in sandy soils. As a cation, Mg competes with Ca+2, K+, and NH4+ for plant absorption and cation
exchange sites. Mg deficiencies occur when these other cations dominate soils with low Mg
concentrations (<10% of base saturation). A common Mg deficiency problem in cattle is ‘grass tetany’, or ‘hypomagnesaemia’, due to insufficient Mg in forage.
EFFECT OF LIME ON NUTRIENT CONTENT OF SOILS, YIELD AND NUTRIENT CONTENT OF
POTATO AND INFESTATION BY LEAFMINERS
B Lalljee and S FacknathFaculty of Agriculture, University of Mauritius
ABSTRACTThe effects of lime application on micronutrient content of soil
and yield and nutrient of two varieties of potato, Solanum tuberosum, were studied. Lime addition at various rates, 0, 4,
8 and 12 t ha-1 increased pH of soil from 5.12 to 7.22 in a period of 12 weeks. Available soil zinc, copper, iron and
manganese decreased with increasing levels of lime, whereas available boron increased. Liming had positive effects on the
yield, protein content, ash, starch, and calcium of both varieties of potato tubers.
However, Zn, Cu, Fe and P decreased with increased application of lime. All results were significant at 5% level.
Leaf miner infestation was not significant in terms of numbers of adults, but showed a slight significance with respect to
punctures on treated leaves
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