MK. MANAJEMEN KESUBURAN
TANAH
MANAJEMEN PEMUPUKAN
YANG
RAMAH-LINGKUNGAN
Smno.jurtnh.fpub.2013
PENGELOLAAN HARA TANAH..
Tujuan pengelolaan hara tanah adalah menghasilkan tanaman yang
menguntungkan secara berkelanjutan. Hal ini berarti bahwa faktor-faktor
seperti biaya (amandemen, bahan bakar, dan peralatan) harus dievaluasi
kontribusinya terhadap peningkatan hasil tanaman. Misalnya,
penambahan dua kali jumlah pupuk mungkin tidak meningkatkan hasil
panen dua kali lipat. Dengan demikian, petani harus menentukan apakah
biaya tambahan pupuk dapat dilunasi oleh tambahan hasil panen.
Selain itu, petani harus selalu berpikir “bahwa praktik pengelolaan yang
tidak memadai atau berlebihan dapat mempengaruhi kualitas tanah dari
waktu ke waktu”. Salah satu penyebab utama erosi atau kehilangan tanah
adalah karena kerusakan struktur tanah, yang dapat disebabkan oleh
praktek-praktek seperti pengolahan intensif (pengolahan tanah), lalu
lintas kendaraan di atas permukaan tanah secara berlebihan, pengambilan
secara berlebihan residu tanaman, dan pengurasan hara tanah, terutama
nitrogen.
..
UNSUR
HARA
Ada sekitar 14 unsur esensial yg diperoleh tanaman dari tanah
Ca dan Mg diberikan ke tanah berbentuk kapur.
Unsur hara makro yg paling sering bermasalah adalah N, P, K
Ketiga unsur hara ini lazim disebut sebagai UNSUR PUPUK
KESEIMBANGAN HARA
Unsur hara N, P, K bila dipakai secara tepat, akan mampu
mengendalikan, mengimbangi, mendukung dan mengisi satu-samalain, serta berpengaruh baik thd unsur hara lainnya.
Unsur hara pupuk yg diberikan seyogyanya merupakan tambahan
bagi unsur yg sudah ada dalam tanah, sehingga keseimbangan hara
tanah dapat menunjang pertumbuhan tanaman yg baik.
TIGA KELOMPOK BAHAN PUPUK
1. Pembawa nitrogen
2. Pembawa fosfat tersedia
3. Pembawa kalium larut air.
PEMBAWA
NITROGEN
Pupuk N juga disebut dengan istilah AMONIAT, ada dua
kelompok, yaitu:
1. ORGANIK
2. ANORGANIK
PEMBAWA NITROGEN ORGANIK
Pupuk organik harus mengalami aminisasi, amonifikasi, dan nitrifikasi sebelum
nitrogennya tersedia bagi tanaman.
Pupuk organik secara lambat dan berangsur-angsur membebaskan nitrogen
sepanjang musim tanaman.
Pupuk organik
Sumber
Darah kering
Sisa daging
Tepung daging
Sisa ikan kering
Tepung biji kapas
Batang tembakau
Tepung tembakau
Tepung coklat
Sekam padi
Rumah Potong Hewan
RPH
RPH
Pengolahan ikan
Ampas
Sisa
Ampas
Ampas
Ampas
Sumber: Nelson, 1965
Persentase N
8 - 12
5 -10 (3-13% P2O5)
10-11 (1-5% P2O5)
6 - 10 (4-8% P2O5)
6-9 (2-3% P2O5; 1-2% K2O)
1.5 - 3.5 (4-9% K2O)
5 - 7 (2% P2O5, 1% K2O)
3.5 - 4.5
1.0
PEMBAWA
NITROGEN
ANORGANIK
Pertimbangan Umum:
Pupuk N anorganik dapat dibuat dari N2 atmosfer
dengan teknologi sintetik yang semakin maju.
Pupuk
Natrium nitrat
Ammonium sulfat
Amonium nitrat
Amonium nitrat gamping
Urea
Kalsium sianamida
Amonia cair
Larutan amonia
Amofos
Diamonium fosfat
Rumus Kimia
NaNO3
(NH4)2SO4
NH4NO3
NH4NO3 dan dolomit
CO(NH2)2
CaCN2
NH3 cair
NH4OH encer
NH4H2PO4
(NH4)2HPO4
Persentase Nitrogen
16
21
33
20
42 - 45
22
82
20-25
11 (48% P2O5)
21(53% P2O5)
AMONIA
Gas amonia dibuat dari unsur-unsurnya, Hidrogen dan nitrogen:
N2 + 3H2 ------------------------ 2 NH3
NH3
Penggunaannya:
1. Dg menggunakan tekanan tinggi dapat dicairkan menjadi
amonia cair
2. Dapat dilarutkan dlm air menjadi NH4OH
3. Gas amonia dipakai untuk pembuatan pupuk lain
Bagan pembuatan pupuk Nitrogen:
+ NH3
HNO3
Am. Nitrat
33% N
Na-nitrat
Nitrofosfat
16% N
12- 20% N
+ H2SO4
Am. Sulfat
21% N
+ H3PO4
Am. Fosfat
11-21% N
+ CO2
Urea
45% N
Larutan N
27-53% N
Larutan amonia
20% N
Na2CO3
+ Batu fosfat
+O2
NH3
+NH4NO3, +Urea, + H2O
+ H2O
PUPUK
NITROGEN
AMONIUM SULFAT
Banyak digunakan oleh petani di Indoensia
Dapat digunakan untuk membuat pupuk majemuk
Ion NH4+ dalam kondisi aerobik dapat mengalami nitrifikasi
Pada sawah NH4+ bereaksi dengan koloid tanah, shg tdk tercuci
Pada tanah alkalis memberikan hasil yang memuaskan
Natrium & AMONIUM NITRAT
Amonium nitrat mengandung ion NH4+ dan NO3Pemberiannya sebaiknya dlm bentuk pelet, unt mengurangi sifat higroskopis
MUDAH MELEDAK BILA TERJADI KEBAKARAN
UREA
Reaksi pembuatannya:
2NH3 + CO2
NH2COONH4
NH2CONH2 + H2O
SUPERFOSFAT
Kandungan fosfatnya 16-21%, dibuat dengan jalan menambahkan
asam sulfat kepada batu fosfat.
PUPUK
FOSFAT
Ca3(PO4)2 + 2H2SO4
Ca(H2PO4)2 + 2CaSO4 + kotoran
CaHPO4
Superfosfat biasa
( 20% P2O5)
+ H2SO4
Batu
Fosfat
+H2SO4 or
tanur listrik
Pupuk majemuk
H3PO4
54% P2O5
+NH3
NH4-fosfat (20-54% P2O5)
TSP (42-50% P2O5)
+ HNO3 + NH3
Nitrofosfat (11-35% P2O5)
PUPUK
FOSFAT
SP : Super Phosphate
TSP : Triple Super Phosphate
Pupuk
Bentuk Kimiawi
Kadar P2O5 tersedia (%)
Superfosfat
Ca(H2PO4)2 + CaHPO4
Superfosfat
amoniat
NH4H2PO4
CaHPO4
Ca3(PO4)2
(NH4)2SO4
Persen P
15-50
7 - 22
16-18 (3-4%N)
7-8
Amofos
NH4H2PO4
48 (11% N)
21
Amonium-polifosfat
(NH4)4P2O7 & lainnya
58-60 (12-15%N)
26-27
Diamonium fosfat
(NH4)2HPO4
53 (21% N)
23
Sampah tanur baja
(CaO)5.P2O5.SiO2
15-25
7-11
Batu fosfat
Ca-metafosfat
Asam superfosfat
Fluor atau Klor Apatit
Ca(PO4)2
H3PO4 dan H4P2O7
25-30
62-63
76
11 - 13
27-28
33
Klasifikasi
Pupuk Fosfat
Pupuk fosfat dapat diklasifikasikan berdasarkan ketersediaan
fosfatnya.
FOSFAT TERSEDIA: Fosfat yang segera dapat diserap tanaman
dan merangsang pertumbuhan tanaman
KLASIFIKASI PUPUK FOSFAT
1. Larut dalam air
2. Larut dlm sitrat:
15% amonium sitrat
atau 2% asam sitrat
3. Tidak larut
Ca(H2PO4)2
NH4 H2PO4
K H2PO4
Fosfat tersedia
CaHPO4
Tepung tulang
Batuan fosfat
Fosfat tidak tersedia
PUPUK
KALIUM
Bahan dasar pupuk kalium adalah hasil
tambang garam kalium (klorida dan sulfat)
yang terdapat di Jerman, Perancis dan USA.
BAHAN PUPUK KALIUM
Pupuk
Rumus Kimia
Persentase
Kalium klorida
KCl
Kalium Sulfat
K2SO4
Kalium-magnesium sulfat K dan Mg sulfat
(25% MgSO4 )
Kainit
KCl sebagian besar
Kalium Nitrat
KNO3
Abu kayu
K2CO3 sebagian besar
Abu ampas tebu
An-organik
Abu sabut kelapa
An-organik
Sekam padi
Organik
Kalium
48-60
48-50
20-30
12-16
44( 13% N)
3-7 (1-2% P)
30
30
2
PUPUK
MIKRO
Garam-garam unsur mikro yg lazim untuk pupuk
Tembaga sulfat
Tembaga sulfat basa
Tembaga karbonat (basa)
Seng sulfat
Seng sulfat basa
Mangan sulfat
Mangan sulfat basa
Natrium Borat
Fero sulfat
Feri sulfat
Natrium molibdat
.
CuSO4
CuSO4. 3Cu(OH)2
CuCO3. Cu(OH)2
ZnSO4
ZnSO4.4 Zn(OH)2
MnSO4
MnSO4. MnO
Na2B4O7
FeSO4
Fe2(SO4)3
Na2MoO4
25-35% Cu
13-53% Cu
57 % Cu
23 - 35% Zn
55% Zn
23 % Mn
40-49 % Mn
34-44% B2O3
20% Fe
17% Fe
37-39% Mo
PUPUK
MAJEMUK
PUPUK CAMPURAN = PUPUK MAJEMUK = pupuk yang
mengandung lebihdari satu macam unsur hara esensial N, P, K
PUPUK LENGKAP = pupuk yang mengandung unsur hara N, P, K
PENAMPILAN FISIK PUPUK
Umumnya bersifat lepas, sehingga mudah ditabur ke tanah
Pupuk tidak mudah menggumpal dan mengeras
Cara menghindarkan penggumpalan:
1. Pupuk disimpan dalam kantong kedap air
2. Pupuk dicampur dengan bahan yang dapat menyerap air
3. Membuat pupuk berbentuk pelet
PENGARUH PUPUK thd pH TANAH
Kebanyakan pupuk majemuk cenderung mengasamkan tanah
Pengaruh utama adalah karena NH4+ mengalami nitrifikasi:
NH4+ + 2 O2
2H+ + NO3- + H2O
Yield response curve:
The curve below describes the
crop response to fertilizers
application
Zone A - Too low fertilizers
application which results in
nutrient deficiencies and lower
yields
Zone B - Adequate fertilizers
application results in maximum
efficiency and the highest
profitability.
Zone C - Over fertilization
where yield is not affected but
fertilizers are wasted.
Zone D - Excessive fertilizers
application which results in
decreased yields, toxicities and
salinity damages
Sumber: www.smartfertilizer.com/tips-and-info
Careful adjustment of fertilizer application to plant needs and timing
for maximum growth benefit.
www.kalkaskacounty.net/planninge...0020.asp
Fertilizer application in this manner is called "banding," as opposed to
"broadcasting" over entire field.
Sumber: cals.arizona.edu/extension/susta...sic.html
FERTILIZER
PLACEMENT
Potassium fertilizers have
been recently used as much
as nitrogen and phosphorus
fertilizers and therefore
much research work has
been done concerning their
placement. Placement of
potassium fertilizer with the
seed has appeared to be the
most effective method of
application provided the rate
of application is not greater
than the seed can tolerate.
Sumber:
159.226.205.16/curriculum
/3w/02/...dex.html
.kapan memupuk padi?........
.. http://ezt.com.my/apply_status/integrated-nutrient-management
Recommended fertilizer application for transplanted Japonica
rice with growth duration of 150−155 days.
Sumber: www.irri.org/irrc/SSNM/country%2...rice.htm
.MANAJEMEN HARA TANAMAN JAGUNG.
. http://www.soils4teachers.org/fertility.
Site-Specific Nutrient Management (SSNM)
for Manual Transplanted Rice in Jiangsu Province, China
Single Japonica rice: 150−155 days growth duration (from seed to harvest)
SSNM is a plant-based approach for ‘feeding’ a rice crop with nutrients as
needed. SSNM includes the following features:
1.
2.
3.
4.
5.
Applying sufficient P and K within 14 days after transplanting (DAT) to
meet crop needs.
Applying only a moderate amount of fertilizer N before active tillering.
Applying fertilizer N at tillering and later growth stages based on the
needs of the crop for supplemental N as determined with a leaf color chart
(LCC).
Applying fertilizer K at panicle initiation based on crop needs.
Using micronutrients based on local recommendations.
The Scientific Basis for Making Fertilizer
Recommendations
Yield response as influenced by soil test level and soil test recommendation
approach. (Hergert, 1997)
Konsep Kesuburan Tanaman
Three main interpretations have developed as a basis for making
fertilizer recommendations. These have developed slowly, but became
important during the 1950s and 1960s when soil testing research was
conducted.
Because our research database is limited, general principles are
developed so that decisions can be made in areas where all the
desired information is not known. Since agricultural production always
includes unknowns, crop fertilization recommendations are based on
interpretation of data and experience.
Reasonable scientists have come to different conclusions on what
these general fertility principles are. Some of the differences are due to
geographic location; some are due to the specific nutrient in question;
and other differences are due to the value placed on the many possible
objectives.
These three crop nutrition concepts are called: the
deficiency correction approach, the maintenance
approach, and nutrient removal.
These approaches recognize that:
1) Only a fraction of a given plant nutrient in the soil is
measured by a soil test.
2) It is impossible to measure how much of a nutrient will
be readily available to plants. This means that a soil test
value is an index of the soil’s fertility status, not a
quantitative measure of the total amount of nutrient in the
soil or its availability.
3) Early researchers recognized that the level of available
nutrients measured may range from low to high in a given
field. Early recommendations were intended to be applied
on a field basis.
Deficiency Correction Approach
The deficiency correction concept states that a nutrient should be applied
only if there is a reasonable expectation of a crop response. The idea of a
limiting factor resulted (Bray, 1944, 1945). This approach is the basis for the
correlation and calibration process discussed in Soils - Part 9. A soil test is
developed that indicates when a specific nutrient is yield-limiting in a field.
Research is conducted to determine crop yields at different soil test levels
for a given nutrient (correlation). The next step determines how much
fertilizer is required for optimum yields at different soil test levels
(calibration).
This approach requires the most intensive research because the soil test
needs to be responsive to changes in soil levels and correlated with crop
response. The two essential questions to be answered are:
1) Will the crop respond to fertilizationþ
2) How much fertilizer is neededþ
In addition, the soil test should be broadly applicable to various crops and
across geographic regions. The database should be large enough that a
probability statement can be made with each fertilizer recommendation. For
example, “When soil tests for phosphorus are at 10 ppm (Bray and Kurtz
#1), there is a 0-20 percent probability of a yield response to applied
phosphorus.” (NebGuide G859, Fertilizer Recommendations for Soybeans)
.Manajemen Hara………...
. http://www.midwestmachinery.co.nz/shop/new/effluent.html.
The advantage of this method is that the only fertilizers
applied will be those that increase yields, and these will be
applied at optimum rates.
This has been called “fertilizing the crop,” since emphasis
is placed on achieving crop response.
The University of Nebraska soils faculty prefers this
method because it is based on UNL research and has been
proven over many years. This method is both economical
and environmentally sound.
The deficiency correction approach to fertilizing the crop
only recommends fertilizer to the point of economic
optimum yield.
Experience has shown that fertilizer recommendations to
correct deficiencies increase the soil test level for most
non-mobile nutrients.
The point called “economic maximum yield” is the yield at
which a farmer makes the most profit from fertilizer
If a farmer applies less fertilizer than this, he will save
money on his fertilizer bill, but the money lost from
decreased yields will be larger than the money he saved
on fertilizer.
If a farmer applies more fertilizer than needed to reach the
economic yield, he may increase his yield somewhat, but
his fertilizer costs will increase more than the increase in
crop value.
Yield increase x price of corn > lbs of fertilizer x cost of
fertilizer
EKONOMI PEMUPUKAN
Use of fertilizers is an index of the use of modern agricultural
methods
Faktor lain yg berpengaruh:
1. Water control
2. Seedbed
3. Cultivar
4. Date and rate of seeding
5. Stand of population
6. Fertilizer placement
7. Cultivation
8. Weed, insect and disease
9. Harvesting practices
EKONOMI
PUPUK
Petani melakukan usahataninya
bertujuan mendapatkan keuntungan
yang sebesar-besarnya per satuan
luas lahan yang digarapnya ………..
Profit maximizing
The farmer realize that :
“he must spend money to make money”
This is certainly true of expenditures for:
“lime, fertilizer, and manure”
EKONOMI
PUPUK DAN
KAPUR
Level of management on returns from
farming
Level of Management:
Current
Good Superior
Yield, bu per acre
Price per unit
Value per acre
Cost per acre
Cost per unit
Return over cash
Usahatani kedelai
20.0
2.00
40.00
41.98
2.10
-1.98
34.0
2.00
68.00
53.72
1.56
14.28
50.0
2.00
100.00
55.75
1.11
44.25
RETURNS PER RUPIAH SPENT ON
FERTILIZER.
Effect of rate of nitrogen on net return per added Rp invested
Nitrogen rate
kg/ha
Added input
kg N/ha
20
40
60
80
100
120
140
160
180
200
20
20
20
20
20
20
20
20
20
20
Net return per added Rp
invested
7.25
5.75
5.00
3.87
2.38
1.63
0.88
0.50
0.12
-0.62
PROFIT per LAND-AREA.
Petani umumnya akan berupaya melakukan pemupukan untuk mencapai
keuntungan (profit) yang setinggi-tingginya per hektar lahannya.
Maximum profit tercapai kalau tambahan hasil sama dengan biaya tambahan
terakhir dosis pupuk yang diberikan ( Δ hasil / Δ pupuk).
Aspek ekonomi dari respon hasil jagung terhadap dosis pupuk nitrogen
Dosis N
kg/ha
Yield
kw/ha
Marginal Marginal Marginal Return Gross profit per ha
Yield
Cost
……. (harga jagung Rp 1/ ku) ………..
20
40
60
80
100
120
8
15
21
26
30
32
8
7
6
5
4
2
2.4
2.4
2.4
2.4
2.4
2.4
Catatan: Harga pupuk N sebesar Rp 0.12 per kg
3.33
2.92
2.50
2.08
1.67
0.83
5.60
10.20
13.80
16.40
18.00
17.60
What are the most profitable rates of plant
nutrients?.
Beberapa faktor yang berpengaruh:
1. The expected increase in yield from each increment
2. The level of management
3. The price of fertilizer
4. The price the farmer expects to receive for his crops
5. Additional harvesting and marketing costs
6. Residual effects
7. Levels of other nutrients in the soil or fertilizer
Expected increase in yield from each incement of fertilizer.
Hasil per ha
HA
HB
Lokasi A
Lokasi B
HE
Lokasi E
HC
Lokasi C
HD
Lokasi D
N
Dosis pupuk N
Respon tanaman terhadap pemupukan dipengaruhi oleh kesuburan tanah.
Hasil tanaman
Tanah kaya P dan K
HK
HM
Tanah miskin P dan K
N
Dosis pupuk N
Profit PK
Tanah kaya P dan K
PM’
profit difference
PM
PK’
Tanah Miskin P dan K
Max profit
Weather effects on the fertilizer response.
Hasil tanaman
HG
good weather
HD
dry weather
N
Dosis pupuk
Price of fertilizer vs. Value of crop
Hasil tanaman per ha
kurva hasil tanaman
Y
C
garis biaya pupuk
Y
C
EKONOMI PEMUPUKAN.
Hasil tanaman yang lebih tinggi akan menyediakan peluang yang lebih besar untuk
mencapai maximum net-profit per luasan lahan dan memperkecil biaya produksi
per satuan hasil.
Kesuburan tanah yang baik menjadi faktor utama untuk mendapatkan hasil yang
tinggi.
Biaya tetap dalam usahatani adalah biaya yang dikeluarkan oleh petani, tidak
tergantung pada besarnya hasil tanaman. Dengan demikian praktek usahatani yang
meningkatkan hasil tanaman biasanya akan memperendah biaya produksi per
satuan hasil
.
Kurva respon hasil tanaman terhadap pemupukan biasanya mengikuti The Law of
Diminishing Return (Kurva Asimtotis).
Pendapatan per biaya produksi akan semakin menurun, hal ini menjadi
pertimbangan utama bagi petani yang modal kerjanya terbatas.
Petani yang progresif biasanya menyadari bahwa profit per hektar lahan lebih
penting daripada penghasilan per satuan biaya produksi
Maximum profit dari pemupukan akan tercapai kalau tambahan hasil tanaman
sama dengan tambahan biaya pemupukan (dY/dX = dC/dX)
EKONOMI PEMUPUKAN.
Dosis pupuk yang apling menguntungkan dipengatruhi oleh:
1. Peningkatan hasil akibat tambahan pupuk
2. Level of farm management
3. Harga pupuk
4. Harga hasil tanaman
5. Tambahan biaya panen
6. Biaya pemasaran
7. Residual effects
8. Soil fertility level.
Level of farm management: derajat sampai dimana semua faktor produksi tanaman
dapat berhasil dikendalikan.
Pada dosis pupuk yang tinggi, diperlukan kemampuan manajerial yg lebih tinggi
Harga per satuan hara tanaman, beragam dengan bahan pupuk.
Pupuk yang kandungan haramya lebih tinggi dianggap lebih murah biaya
aplikasinya
Prioritas penggunaan modal kerja sangat penting bagi petani.
Umumnya lebih menguntungkan untuk melakukan pemupukan sesuai
dengan ahsil uji tanah.
EKONOMI PEMUPUKAN
Residual effects pupuk menjadi bagian penting dari ekonomi
pemupukan. Semakin banyak jumlah pupuk yang diaplikasikan
dalam jangka panjang, maka nilai residual pupuk harus
dipertimbangkan.
1.
2.
3.
Why high yields are a necessity in periods of low prices ?
What are fixed cost? Variable costs? In relation to the fertilizer
application
Discuss the factors that determine the most profitable rate of plant
nutrients.
4. How would you evaluate the residual nutrients in
your area?
Maintenance Approach
The maintenance approach sets a soil test level goal, and
recommends fertilizer to build the soil to the specific nutrient
level that has been determined to be ideal. This approach uses
soil test levels, as does the deficiency correction approach, to
determine when to fertilize. Soil tests for this approach still
have to be correlated, as with the deficiency correction
approach. The difference is that emphasis is placed on
maintaining the soil fertility level at or above the point of the
economic maximum yield. This has been called “fertilizing the
soil,” since emphasis is placed on achieving a specific nutrient
level in the soil. Those who recommend this approach have
interpreted the research data to conclude that this approach
benefits the producer over time. Generally, the maintenance
approach uses a higher soil test level than the critical level
used for the deficiency correction approach.
This approach is used by several midwestern
universities. Some soil testing laboratories split
their recommendations into a fertilizer
recommendation and a “build” recommendation.
The “build” recommendation is designed to speed
the increase in soil test level to the chosen
optimum value.
Whether it applies to soils of a given region must
be tested to confirm its validity in terms of crop
response and farm profitability.
A specific example of the maintenance idea is the nutrient
balance concept. This concept states that for optimum
crop growth there is a “best ratio” of basic cations
(positively charged ions) and a best total base saturation
for a given soil. There has been little information published
that confirms that a best cation saturation ratio really
exists for all soils or that it should vary from one soil to
another (Leibhardt, 1981; McLean, et. al. 1983).
Because the balance concept includes only calcium,
magnesium and potassium, using an extrapolation of the
balance concept by applying a ratio approach for making
recommendations of micronutrient elements and sulfur is
not valid.
This has brought about criticism of laboratories using the
balance concept.
The balance concept resulted from research on
soils where cation saturations varied widely.
The initial work (Bear, et al., 1945) was done with
alfalfa on one New Jersey soil having uniform
amounts of exchangeable magnesium and
hydrogen and variable amounts of exchangeable
potassium and calcium.
From this study, a “best ratio” for the cation
composition of the cation exchange capacity
(CEC) was proposed — 65 percent calcium, 10
percent magnesium, 5 percent potassium, and 20
percent hydrogen.
Later work by Graham in Missouri (1959) suggested that
the percentages of calcium, magnesium and potassium be
75, 10 and 2.5, but could vary around these values.
The saturation ranges were: 65-85 percent calcium, 6-12
percent magnesium, and 1-5 percent potassium. There is
general agreement that variation of the cation composition
in these ranges will not likely affect yield appreciably.
While the idea of keeping a soil in “balance” is appealing,
it should not be taken so far as to demand remedial
treatment in most cases. If each nutrient is non-limiting
and extreme excess is not apparent, the relative
relationship between nutrients will be acceptable
Nutrient Removal Approach
A third approach to fertilizer recommendations still widely used is nutrient
removal. Before the advent of soil testing, the nutrient removal approach to
crop fertilization was the best science had to offer. Early agricultural scientists
realized that crops obtained their nutrition from the soil and, to maintain good
production, nutrients had to be returned to the soil. This was accomplished
through crop residues, wood ashes, and manures. As a simple guideline to
adding fertilizers, the nutrient removal approach is a major advance over not
considering crop nutrition at all. The theoretical advantage of returning to the
soil what is removed is that productivity is maintained and depletion avoided.
The disadvantage of this approach is that it does not account for the soil’s
ability to supply many essential nutrients. Nutrient removal does not recognize
that not all nutrients are used at 100 percent efficiency. A producer may underor over-fertilize by following the nutrient removal approach. The most
profitable fertilization approach needs to consider the cost of farm inputs and
environmental concerns. Making fertilizer recommendations by relying on the
crop nutrient removal approach ignores these two issues. In addition, a strict
adherence to the nutrient removal approach makes soil testing unnecessary,
since nutrients are added based on what is harvested.
PRAKTEK TERBAIK
PEMUPUKAN - P
PTP-P
Best Management Practices
(BMP) For Phosphorus
Fertilization
Reagan M. Waskom
Extension Water Quality
Specialist
Colorado State University
Cooperative Extension
August 1994
Bulletin #XCM-175
48
PENDEKATAN PTP-P
Peraturan mengamanatkan kepada semua pihak
pengguna bahan agrokimia untuk dapat
mengaplikasikannya secara tepat pestisida dan pupuk
Adopsi PTP-P oleh petani akan membantu
mengendalikan pencemaran sumber-sumber air ,
memperbaiki persepsi publik atas industri dan
mungkin dapat mengeliminir perlunya regulasi lebih
jauh .
49
. Integrated plant nutrient (IPN) components in the Nepalese farming system.
. http://www.fao.org/docrep/010/ag120e/AG120E10.htm.