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M. YAMINI, V. MUNASWAMY*, K.V. NAGA MADHURI AND Y. REDDI RAMU
Department of Soil Science and Agricultural Chemistry, S.V. Agricultural College, Tirupati-517502, Andhra Pradesh, India.
Status of soil phosphorus fractions under rainfed groundnut monocropping system was studied in a long-term field experiment during Kharif, 2014 being conducted at Regional Agricultural Research Station, Tirupati. The soil of experiment field was slightly acidic, non-saline, low in organic carbon and free CaCO3 contents. The soil was low in available nitrogen, medium in phosphorus and medium to high in potassium. The micronutrients status of the experimental field was above critical levels. Inorganic P fractions like Al-P, Fe-P, O-P, Ca-P, organic P, total P and available P at 0-15 cm depth before sowing of the crop ranged from 20.43 to 37.62, 34.46 to 57.12, 16.97 to 31.31, 14.20 to 22.01, 27.25 to 54.50, 112.87 to 192.78, 27.00 to 45.00 mg kg-1, respectively. At harvest the P fractions like Al-P, Fe-P, O-P, Ca-P, organic P, total P and available P at 0-15 cm depth ranged from 17.06 to 33.20, 31.87 to 53.31, 14.87 to 28.31, 10.62 to 20.25, 30.65 to 56.80, 105.40 to 180.52, 21.00 to 45.00 mg kg-1, respectively. Similarly at 15-30 cm depth the inorganic P fractions like Al-P, Fe-P, O-P, Ca-P, organic P, total P and available P before sowing ranged from 16.91 to 31.90, 32.27 to 49.95, 15.92 to 25.06, 12.57 to 22.72, 25.25 to 51.25, 106.72 to 185.47, 27.00 to 41.00 mg kg-1, respectively and at harvest, these ranged from 15.62 to 29.68, 30.00 to 47.50, 13.75 to 25.25, 14.25 to 20.56, 26.30 to 52.42, 101.97 to 175.77, 23.00 to 36.00 mg kg-1, respectively.
Inorganic P fractions (Al-P, Fe-P, Occluded P and Ca-P), Organic P, Total P
Groundnut, (Arachis hypogaea L.) is the major oilseed cum cash crop for millions of small scale farmers in the semi-arid tropics. It is the world’s 4th most important source of edible oil and 3rd most important source of vegetable proteins. The uses of groundnut are diverse as all parts of the plant could be used. The kernel is a rich source of edible oil, containing 36 to 54 per cent oil and 25 to 32 per cent protein. Groundnut can meet a major portion of its N requirement through biological N fixation. However, phosphorus deficiency has been identified as one of the major constraints in crop production. Phosphorus (P) is an essential major element for plant growth. Therefore, maintenance of an adequate amount of soil P through application of inorganic and/ or organic P is critical for the sustainability of cropping systems (Sharpley et al., 1994). Phosphorus, like any other plant nutrient is present in soil in two major components i.e. organic and inorganic. Organic P, which is mainly confined to the surface layer, is mineralized into inorganic forms but, the plants mainly depend on inorganic P forms like saloid-P, Al-P, Fe-P and Ca-P fractions for their P requirements. The role of P in sustaining the crop growth in relation to its various P fractions has not been studied so far. Hence, the present investigation was taken up.
A long term field experiment has been carried out at Regional Agricultural Research Station, Tirupati since 1981 laid out in Randomized Block Design, replicated four times with eleven treatments. The treatments include:
T1 : Control (no manure and fertilizers), T2 : Farm
yard manure (FYM) @ 5 t ha-1 (once in 3 years), T3 : 20
kg Nitrogen (N) ha-1, T4 : 10 kg Phosphorus (P) ha-1, T5 :
25 kg Potassium (K) ha-1, T6 : 250 kg gypsum ha-1, T7 : 20 kg
N + 10 kg P ha-1, T8 : 20 kg N + 10 kg P + 25 kg K ha-1, T9 :
20 kg N + 10 kg P + 25 kg K + 250 kg gypsum ha-1, T10: 20
kg N + 10 kg P + 25 kg K + 100 kg lime ha-1, T11 : 20 kg N
+ 10 kg P + 25 kg K + 250 kg gypsum + 25 kg ZnSO4 ha-
1 (Once in three years). Hence, treatments with FYM, N, P, K and gypsum either alone or in combination with lime and zinc sulphate were imposed.
During Kharif 2014 the soil samples were collected before sowing and at harvest from 0-15 and 15-30 cm depth. Soil physico-chemical and available nutrients were analysed following the standard procedures laid down by Jackson (1973). Fractions of P were analysed as procedures described by Chang and Jackson (1957).
Organic P by Saunders and Williams (1955) and total P by Olsen and Sommers (1982).
Physico-chemical properties of experimental site
The experimental field was slightly acidic with pH ranging from 5.26 to 5.71, non -saline, low in organic carbon (0.30 to 0.48 %) and free CaCO3 (0.22 to 0.47 %) contents. The available nitrogen was low (148 to 205 kg ha-1), P was medium (27 to 45 kg ha-1) and K was medium to high (218 to 409 kg ha-1). The secondary nutrients viz., Ca, Mg and S ranged from 2.35 to 4.35, 1.85 to 2.67 C mol (P+) kg-1, and 7.5 to 12.2 mg kg-1, respectively. The micronutrients status of the experimental field was above critical levels (Table 1).
Before sowing the highest value of Al-P was recorded in T11 (37.62 mg kg-1) and the lowest value in T1 (20.43 mg kg-1). The highest value of Fe-P was recorded in T11 (57.12 mg kg-1) and the lowest in T1 (34.46 mg kg-1). Similarly, the Occluded-P content was highest in T11 (31.31 mg kg-1) and the lowest in T1 (16.97 mg kg-1). The Ca -P was highest in T9 (22.01 mg kg-1) and the lowest in T1 (14.20 mg kg-1). However, the organic P content was highest in T2 (54.50 mg kg-1) and the lowest in T3 (27.25 mg kg-1). The highest value of total P content was recorded in T11 (192.78 mg kg- 1) and the lowest in T4 (112.87 mg kg-1). The available P content was lowest (27.00 mg kg-1) in T6 and the highest in T11 (45.00 mg kg-1).
At harvest, Al-P content was highest in T10 (33.20 mg kg-1) and the lowest in T1 (17.06 mg kg-1). The highest value of Fe-P was noticed in T10 (53.31 mg kg-1) and the lowest in T4 (31.87 mg kg-1). Occluded P content was noticed highest in T10 (28.31 mg kg-1) and the lowest in T1 (14.87 mg kg-1). The highest Ca-P content was recorded in T9 (20.25 mg kg-1) and the lowest in T6 (10.62 mg kg-1). Whereas, the organic P content was highest in T2 (56.80 mg kg-1) and the lowest in T3 (30.65 mg kg-1). Total P content was highest in T11 (180.52 mg kg-1) and the lowest in T4 (105.40 mg kg-1). However, highest available P content was recorded in T11 (45.00 mg kg-1) and the lowest (21.00 mg kg-1) in T1 (Table 2 and 3).
Before sowing the Al-P and Occluded P content were highest in T11 (31.90 and 27.02 mg kg-1) and the lowest in T1 (16.91 and 15.92 mg kg-1), respectively. Fe-P content was also highest in T11 (49.95 mg kg-1) but lowest in T4 (32.27 mg kg-1). The highest Ca-P content was noticed in T9 (22.72 mg kg-1) and the lowest in T1 (12.57 mg kg-1). Whereas, the organic P content was recorded highest in T2 (51.25 mg kg-1) and the lowest in T3 (25.25 mg kg-1). The highest total P content was recorded in T11 (185.47 mg kg-1) and the lowest in T4 (106.72 mg kg-1). The available P was highest in T11 (41.00 mg kg-1) and the lowest (27.00 mg kg-1) both in T1 and T4 (Table 4 and 5).
Similar trend was observed at harvest stage also. The Al-P and Occluded P content were highest in T10 (29.68 and 25.25 mg kg-1) and lowest in T1 (15.62 and 13.75 mg kg-1), respectively. However, Fe-P content was highest in T10 (47.50 mg kg- 1) and the lowest in T4 (30.00 mg kg-1). Ca-P content was recorded highest in T9 (20.56 mg kg-1) and the lowest in T4 (14.25 mg kg-1). Similarly, organic P content was highest in T2 (52.42 mg kg-1) and the lowest in T3 (26.30 mg kg-1) and total P content was recorded in T11 (175.77 mg kg-1) and the low in T4 (101.97 mg kg-1). Whereas, available P content was recorded high in T6 (36.00 mg kg-1) and the low in T1 (23.00 mg kg-1).
The results revealed that all the P fractions were low in sub-soil (15-30 cm depth) compared to surface soil samples. Such results were reported earlier for Al-P and Fe-P by Kalaivanan and Sudhir (2012) and attributed for lower amounts of Al2O3 content at lower depths. The high Fe-P content in surface soil was attributed to release of organic acids due to decomposition of organic matter, which resulted in precipitation of Fe-P. In this particular experiment, the source of organic matter might be the leaf fall during crop growth except in T2 where FYM was added. More or less, the same trend was observed in case of O-P, total P, available P and Ca-P, but for Ca-P slightly higher value was noticed at harvest in 15-30 cm depth.
Significant variations were noticed with respect to P-fractions among the treatments both before and after harvest of groundnut crop. The lowest values was observed in control plot for Al-P, Fe-P, Occluded P, and Ca-P while the total-P, organic-P and available-P were lowest in treatments T4, T3 and T6, respectively at 0-15 cm depth of soil.
Similarly the P-fractions viz., Al-P, Fe-P, Occluded-P, Ca-P, organic-P and total-P significant among treatments but the available-P was non-significantly influenced by treatment at 15-30 cm depth both at before sowing and after harvest of the crop.
