Kesuburan tanah Lanjutan Sub Topik: Calsium (Ca) dan Magnesium (Mg) Oleh: Dr. Ir. Hamidah Hanum, MP Sekolah Pascasarjana USU

Mg dlm tanaman Function and mobility of Mg   Magnesium activates several enzymes.   It is a constituent of chlorophyll, and thus is involved in CO 2 assimilation and protein synthesis because it activates several enzymes and is a constituent of chlorophyll.   Mg also regulates cellular pH and the cation-anion balance.   It is very mobile and is retranslocated easily from old leaves to young leaves. Deficiency symptoms therefore tend to occur initially in older leaves. y symptons and effects Mg deficieny symptons and effects on growth   Orange-yellow interveinal chlorosis on older leaves.   Mg-deficient plants are pale-colored with interveinal chlorosis first appearing on older leaves, and later on younger leaves as deficiency becomes more severe. Green coloring appears as a "string of beads" compared with K deficiency, in which green and yellow stripes run parallel to the leaf. In severe cases, chlorosis progresses to yellowing and finally necrosis in older leaves. Leaf number and leaf length are greater in Mg- deficient plants, and Mg-deficient leaves are wavy and droopy due to an expansion in the angle between the leaf sheath and leaf blade.   With moderate deficiency, plant height and tiller number are not affected greatly.   Reduced number of spikelets and reduced 1,000-grain weight.   May reduce grain quality (% milled rice, protein, and starch content).   Fe toxicity may be more pronounced where Mg is part of multiple nutrient deficiency stress involving K, P, Ca, and Mg.

Mg -Plant A Ca:Mg ratio of 1–1.5:1 in rice shoots between tillering and panicle initiation is considered optimal. Mg-Soil A concentration of 3 cmolc Mg kg-1 are generally sufficient for rice. For optimum growth, the ratio of Ca:Mg should be 3–4:1 for exchangeable soil forms and not exceed 1:1 in soil solution. Occurrence of Mg deficiency Mg deficiency is more common in rainfed lowland and upland rice where soil Mg has been depleted because of the continuous removal of Mg in crop products without recycling crop residues or replacing removed Mg with mineral fertilizer. Mg deficiency is more common in rainfed lowland and upland rice where soil Mg has been depleted because of the continuous removal of Mg in crop products without recycling crop residues or replacing removed Mg with mineral fertilizer. Mg deficiency occurs on the following soil types: Mg deficiency occurs on the following soil types: - Acid, low-CEC soils in uplands and lowlands, coarse-textured, highly weathered acid soils Coarse- textured sandy soils with high percolation rates and leaching losses Leached, old acid sulfate soils with low base content. Leached, old acid sulfate soils with low base content. Strongly acid soil, Al saturation % Strongly acid soil, Al saturation % Ratio exchangeable Ca/Mg~ 10/1 - 15/1 Ratio exchangeable Ca/Mg~ 10/1 - 15/1 Causes of Mg deficiency Low available soil Mg. Decreased Mg uptake due to a wide ratio of exchangeable K:Mg (i.e., >1:1).

a) (b) (c) Magnesium deficiency symptoms in rice (a) Orange-yellow interveinal chlorosis usually appears first on older leaves. (b) Chlorosis may also appear on the flag leaf. (c) Mg deficiency may also be induced by large applications of K fertilizer on low Mg status soils. Growth stagePlant partOptimum (%)Critical level for deficiency (%) Tillering-PIY leaf0.15–0.30<0.12 Tillering-PIShoot0.15–0.30<0.13 MaturityStraw0.20–0.30<0.10 Optimal ranges and critical levels of Mg in plant tissue.

Siklus Ca/Mg SOIL ORGANIC MATTER Plant & animal residues SOIL SOLUTION Ca 2+, Mg 2+ Adsorption Desorption Plant uptake MINERAL Ca/Mg CLAY MINERALS Exchangeable Ca 2 + / Mg 2+ Ca 2+ Mg 2+ Exchangeable K + Dissolution Tanaman leaching Presipitation

Sumber Mg tanah Berasal dari pelapukan batuan yg mengandung mineral biotit, dolomit, horblende, olivin,serpentin. Pd mineral liat sekunder : clorit, ilit, montmorilonit, vermikulit Juga berasal dari residu tanaman danhewan Prilaku Mg- tnh  [Mg larutan tnh] berfluktuasi, trgtg pd interaksi bbrp faktor: kadar Mg tanah, tingkat pelapukan, Intensitas leaching, serapan tanaman Desorpsi dan leaching Mg meningkat jk terdapat Cl - dan SO 4 2- Pemupukan K + dan NH 4 + dosis tinggi dpt menurunkan Mg-tersedia [Mg-larutan] sgt rendah jk kejenuhan Al 65-70% [Mg -dd] = 4-20% KTK tanah, Kejenuhan Mg optimum > 10%

Ca dlm tanaman Function and mobility of Ca Calcium is a constituent of Ca pectates, important cell wall constituents also involved in biomembrane maintenance. It helps in cell wall stabilization as an enzyme activator, in osmoregulation, and in the cation-anion balance. Ca is less mobile in rice plants than Mg and K. Because Ca is not retranslocated to new growth, deficiency symptoms usually appear first on young leaves. Ca deficiency also results in impaired root function and may predispose the rice plant to Fe toxicity An adequate supply of Ca increases resistance to diseases such as bacterial leaf blight (caused by Xanthomonas oryzae) or brown spot (caused by Helminthosporium oryzae). The rate of Ca uptake is proportional to the rate of biomass production. y symptons and effects Ca deficieny symptons and effects on growth Chlorotic-necrotic split or rolled tips of younger leaves. Symptoms are usually visible only under severe Ca deficiency (e.g., pot experiments, exhaustion experiments). The tips of the youngest leaves become white or bleached, rolled, and curled. Necrotic tissue may develop along the lateral margins of leaves and old leaves eventually turn brown and die. Ca deficiency may resemble B deficiency (), and plant tissue analysis may be required to distinguish the cause of symptoms. ()

Ca -Plant A Ca:Mg ratio of 1–1.5:1 in rice shoots at tillering to panicle initiation stages is considered optimal. White leaf tips may occur when Ca:Mg is <1. A Ca:Mg ratio of 1–1.5:1 in rice shoots at tillering to panicle initiation stages is considered optimal. White leaf tips may occur when Ca:Mg is <1. Ca-Soil Ca deficiency is likely when soil exchangeable Ca is 20%. Ca deficiency is likely when soil exchangeable Ca is 20%. For optimum growth, the ratio of Ca:Mg should be > 3–4:1 for exchangeable soil forms and 1:1 in soil solution. For optimum growth, the ratio of Ca:Mg should be > 3–4:1 for exchangeable soil forms and 1:1 in soil solution. Causes of Ca deficiency Small amounts of available Ca in soil (degraded, acid, sandy soils) Small amounts of available Ca in soil (degraded, acid, sandy soils) Alkaline pH with a wide exchangeable Na:Ca ratio resulting in reduced Ca uptake. Use of irrigation water rich in NaHCO3. Alkaline pH with a wide exchangeable Na:Ca ratio resulting in reduced Ca uptake. Use of irrigation water rich in NaHCO3. Wide soil Fe:Ca or Mg:Ca ratios resulting in reduced Ca uptake. Long-term irrigated rice cultivation may lead to higher Mg:Ca and Fe:Ca ratios. Wide soil Fe:Ca or Mg:Ca ratios resulting in reduced Ca uptake. Long-term irrigated rice cultivation may lead to higher Mg:Ca and Fe:Ca ratios. Excessive N or K fertilizer application resulting in wide NH4:Ca or K:Ca ratios and reduced Ca uptake. Excessive N or K fertilizer application resulting in wide NH4:Ca or K:Ca ratios and reduced Ca uptake. Excessive P fertilizer application, which may depress the availability of Ca (due to formation of Ca phosphates in alkaline soils). Excessive P fertilizer application, which may depress the availability of Ca (due to formation of Ca phosphates in alkaline soils).

Optimal ranges and critical levels of Ca in plant tissue. Growth stagePlant partOptimum (%)Critical level for deficiency (%) Tillering-PIY leaf, shoot0.2–0.6<0.15 MaturityStraw0.3–0.5<0.15 Calcium deficiency symptons in rice. Symptoms only occur under severe Ca deficiency when the tips of youngest leaves may become chlorotic-white

Ca deficiency is very uncommon in lowland rice soils because there is usually sufficient Ca in the soil, from mineral fertilizers, and irrigation water. Soils particularly prone to Ca deficiency occurs on the following soil types: Acid, strongly leached, low-CEC soils in uplands and lowlands Soils derived from serpentine rocks Coarse-textured sandy soils with high percolation rates and leaching Leached, old acid sulfate soils with low base content Occurrence of Ca deficiency

Sumber Ca tanah Berasal dari bahan kapur CaCO 3, CaMg(CO 3 ) 2, CaSO 4 Prilaku Ca- tnh Kadar Ca dlm tnh sellau lebih tinggi drpd kebutuhan tanaman, ttp Ca-uptake dikendalikan secara genetik. Meskipun kadar Ca-larutan 10 x > K-larutan ttp Ca-uptake < K- uptake Faktor-faktor yang menentukan ketersediaan Ca adalah: 1. Jumlah suplay Ca 2. pH tanah 3. KCK.4 Persen Kejenuhan Ca terhadap KCK 5. TIpe Koloid Tanah 6. Ratio Ca tarhadap Kation lain