**3. Phosphorus**

Phosphorus (P) contents in plants are in wide range, mainly from 0.1 to 0.8 % P in dry matter. Reproductive organs, especially of leguminose plants contain high levels of P about 0.6 % P. Uptake of P into plants is intensive in the early stages of growth and in period forming of generative organs (Hrustic et al., 1998). Store of P in plants, especially in grain, are mainly in form of fitine acid. P efficiency is in close connection with water and temperature regimes in soil. Under optimal soil moisture P uptake can be up to three-fold higher than in dry soil. Also, oversupplies of water, cold weather and low pH reducing P uptake in plants.

P removal by plants is mainly from 10 to 45 kg P, while by soybean is from 15 to 30 kg P/ha/year. The end of growth is the first symptom of P deficiency. Leaves are dark green and in the later stage develops chlorosis and violet color as result of increasing antociane synthesis. Necrotic spots, drying and falling of the leaves is the latest stage of P deficiency. Active nodules (dark pink center) of N-fixing bacteria are absent or few in number under conditions of P deficiencies. Also, decreasing of protein and chlorophyll synthesis was found.

Excess of P is rare. Plants reducing growth and dark frowning spots in leaves were observed. Intensity of plant development increasing and as results are the earlier flowering, grain forming and senescence. Oversupplies of P could be reason for some nutritional unbalances, for example Zn, Fe, Mn, Cu and B deficiencies.

P, mainly in combination with N and K as NPK fertilizers, can be applied broadcast and incorporated into the soil before sowing or applied as starter at sowing time. With low soil test P levels band application of fertilizer is more efficient than broadcasting. If applied as a starter, the recommend placement of the fertilizer is in band 2 inches to the side and 2 inches bellow the seed (Dahnke et al., 1992; Barbagelata et al., 2002). P materials such as triple superphosphate or from liquid or dry formulations of ammoniated phosphates are available to improve soil P status. However, organic soybean growing has restriction in P use and it is limited on rock phosphate or manures as sources of P.

Anetor and Akinrinde (2006) found that P deficiency in soil is an important growthlimiting factor in acidic alfisolof Western, Nigeria. Lime application may not be feasible for poor resourced farmers. However, the complementary benefits (liming and nutrient supply) of organic fertilizers and rock phosphates could sufficiently ameliorate acid soil conditions and greatly reduce P fertilizer cost for effective and sustainable soil fertility management.

Win et al. (2010) tested the P effects on three soybean cultivars (CKB1, SJ5 and CM60) based on the seed oil content (SOC) and the seed protein content (SPC) and to assess the physiological responses associated with changes in shoot P-utilization efficiency (SPUE). The experiment was carried out during 2008 and 2009 with a split-plot design at the Agronomy Department, Kasetsart University, Bangkok, Thailand. The main plots were for tested three P levels in a nutrient solution (0.5, 1.0 and 2.0 m*M* P), with subplots for the three soybean cultivars. The results indicated that at maturity, the P levels of 2.0 m*M* P decreased SPUE by 27% compared to that of 0.5 m*M* P (the control). SOC was not significantly affected by the P level. Relative to the control, the P nutrition levels of 1.0 and 2.0 m*M* P significantly decreased SPC by 4% and 5%, respectively. There were no significant differences in SOC between varieties. The SPC of CKB1 was 8% greater than that of SJ5 but showed no significant difference to that of CM60 (Table 2).

Zheng et al., (2010) reported effectiveness of P application in improving regional soybean yields under drought stress of the 2007 growing season in Northern China including Heilongijang, Jilin and Liaoing Provinces. Total soybean acreage of this region was around 4.5 million ha, which accounts for about 5% of the total soybean acreage in the world (FAOSTAT, 2009). Contemporary climate change is characterized by increase in frequency and intensity of drought. Total 118 soybean fields throughout Hailun County of Northern China. Regression trees analysis showed that regional soybean yield variability was mainly induced by soil available phosphorus and the amount of P applied, which explained 16.3 and 15.2% of the yield variation, respectively. The productivity of soybean over the region did not increase when P application rate reached a threshold of 55.67 kg/ha (Zheng et al., 2010).

synthesis. Necrotic spots, drying and falling of the leaves is the latest stage of P deficiency. Active nodules (dark pink center) of N-fixing bacteria are absent or few in number under conditions of P deficiencies. Also, decreasing of protein and chlorophyll synthesis was

Excess of P is rare. Plants reducing growth and dark frowning spots in leaves were observed. Intensity of plant development increasing and as results are the earlier flowering, grain forming and senescence. Oversupplies of P could be reason for some nutritional

P, mainly in combination with N and K as NPK fertilizers, can be applied broadcast and incorporated into the soil before sowing or applied as starter at sowing time. With low soil test P levels band application of fertilizer is more efficient than broadcasting. If applied as a starter, the recommend placement of the fertilizer is in band 2 inches to the side and 2 inches bellow the seed (Dahnke et al., 1992; Barbagelata et al., 2002). P materials such as triple superphosphate or from liquid or dry formulations of ammoniated phosphates are available to improve soil P status. However, organic soybean growing has restriction in P use and it

Anetor and Akinrinde (2006) found that P deficiency in soil is an important growthlimiting factor in acidic alfisolof Western, Nigeria. Lime application may not be feasible for poor resourced farmers. However, the complementary benefits (liming and nutrient supply) of organic fertilizers and rock phosphates could sufficiently ameliorate acid soil conditions and greatly reduce P fertilizer cost for effective and sustainable soil fertility

Win et al. (2010) tested the P effects on three soybean cultivars (CKB1, SJ5 and CM60) based on the seed oil content (SOC) and the seed protein content (SPC) and to assess the physiological responses associated with changes in shoot P-utilization efficiency (SPUE). The experiment was carried out during 2008 and 2009 with a split-plot design at the Agronomy Department, Kasetsart University, Bangkok, Thailand. The main plots were for tested three P levels in a nutrient solution (0.5, 1.0 and 2.0 m*M* P), with subplots for the three soybean cultivars. The results indicated that at maturity, the P levels of 2.0 m*M* P decreased SPUE by 27% compared to that of 0.5 m*M* P (the control). SOC was not significantly affected by the P level. Relative to the control, the P nutrition levels of 1.0 and 2.0 m*M* P significantly decreased SPC by 4% and 5%, respectively. There were no significant differences in SOC between varieties. The SPC of CKB1 was 8% greater than that of SJ5 but showed no

Zheng et al., (2010) reported effectiveness of P application in improving regional soybean yields under drought stress of the 2007 growing season in Northern China including Heilongijang, Jilin and Liaoing Provinces. Total soybean acreage of this region was around 4.5 million ha, which accounts for about 5% of the total soybean acreage in the world (FAOSTAT, 2009). Contemporary climate change is characterized by increase in frequency and intensity of drought. Total 118 soybean fields throughout Hailun County of Northern China. Regression trees analysis showed that regional soybean yield variability was mainly induced by soil available phosphorus and the amount of P applied, which explained 16.3 and 15.2% of the yield variation, respectively. The productivity of soybean over the region did not increase when P application rate reached a threshold of 55.67

unbalances, for example Zn, Fe, Mn, Cu and B deficiencies.

is limited on rock phosphate or manures as sources of P.

significant difference to that of CM60 (Table 2).

kg/ha (Zheng et al., 2010).

found.

management.


Table 2. Effects of P on seed oil and protein contents and P use efficiency in three soybean cultivars (Win et al., 2010)
