Phosphorus (P) Adsorption Behavior and Harvested P by the Sugarcane (Saccharum Officinarum L.) Affected by Inorganic and Organic Fertilizer Applications on an Ultisol

The field and laboratory experimental studies were conducted to determine the phosphorus (P) adsorption behavior employing Langmuir Method and yield of sugarcane as affected by compost and inorganic fertilizer applications, and to determine the correlations between the Langmuir parameters and the availability of P in soil or harvested P by the sugarcane. Both field and lab experiments were arranged in a randomized block design, consisting of five treatments (A= 100% NPK, B=100% compost, C=100% NPK + 50% compost, D= 50% NPK + 100%, compost, and E= no fertilizer). Each treatment was replicated three times. Field and laboratory studies were carried out in the sugarcane field and in the Laboratory of Soil Science, the University of Lampung for Langmuir P studies, respectively. The results showed that the applications of 100% NPK plus 50% organic fertilizer, and 100% NPK resulted in the highest amount of available-P in the soil, the lowest maximum adsorption of P (Xm) and the lowest relative bonding energy of P (km); as well as the highest effect on the increase of sugarcane production. On the other hand, the treatments of no fertilizer and the 100% organic fertilizer resulted in the highest maximum adsorption of P (Xm) and the lowest sugar production. There were very significant negative correlations between the maximum adsorption of P (Xm) and soil P, harvested P by the sugarcane and stem biomass; while similar trend but no significant correlations between the relative bonding energy of P (km) and soil P, harvested P, leaf biomass and stem biomass were detected.

The field and laboratory experimental studies were conducted to determine the phosphorus (P) adsorption behavior employing Langmuir Method and yield of sugarcane as affected by compost and inorganic fertilizer applications, and to determine the correlations between the Langmuir parameters and the availability of P in soil or harvested P by the sugarcane. Both field and lab experiments were arranged in a randomized block design, consisting of five treatments (A= 100% NPK, B=100% compost, C=100% NPK + 50% compost, D= 50% NPK + 100% , compost, and E= no fertilizer). Each treatment was replicated three times. Field and laboratory studies were carried out in the sugarcane field and in the Laboratory of Soil Science, the University of Lampung for Langmuir P studies, respectively. The results showed that the applications of 100% NPK plus 50% organic fertilizer, and 100% NPK resulted in the highest amount of available-P in the soil, the lowest maximum adsorption of P (X m ) and the lowest relative bonding energy of P (k m ); as well as the highest effect on the increase of sugarcane production. On the other hand, the treatments of no fertilizer and the 100% organic fertilizer resulted in the highest maximum adsorption of P (X m ) and the lowest sugar production. There were very significant negative correlations between the maximum adsorption of P (X m ) and soil P, harvested P by the sugarcane and stem biomass; while similar trend but no significant correlations between the relative bonding energy of P (k m ) and soil P, harvested P, leaf biomass and stem biomass were detected.
The availability of phosphorus (P) in soils can directly affect crop production (Williams et al. 2013;Oelkers and Valsami-Jones 2008;Lumbanraja 1995;Lumbanraja et al. 1982). Regardless of P is naturally present at high concentration in some soils, it is often a limiting nutrient factor due to the insoluble nature of most soil P compounds and the rapid formation of poorly available P after phosphorus fertilizer incorporation (Malik et al. 2012;Arai and Sparks 2007;Lumbanraja et al. 1994;Lindsay et al. 1989;Sparks 1989;Lumbanraja et al., 1981). Application of inorganic fertilizers can sufficiently supply P to crops (Reddy et al. 2005;Ayaga et al. 2006) and it is timely dependent (Vetterlein et al. 1999;van der Zee et al. 1988;van der Zee et al. 1986;Lumbanraja et al. 2017). This practice can saturate binding sites of P in soil particles and result in a reduction of the capability of the soil to retain P. In soil with low P retention potential, there is high release of P into soil solution, therefore the P could be available to crops (Manthambala et al. 2016). Such the degree of P saturation is a potential indicator of P release into soil solution, which does not only indicate that P is available for crops but might be also indicate P losses through leaching and erosion through runoff or drainage water (Kang et al. 2011;Allen et al. 2006;Casson et al. 2006).
The dependency on inorganic fertilizers can be reduced by applying organic fertilizers such as animal manure, crop byproducts, and any waste products containing high nutrients (Nugroho et al. 2012;Nugroho et al. 2013;Zhao et al. 2009;Reddy et al. 2005). Moreover, by beneficially utilizing animal manure and any other natural organic byproducts, there is no need to waste the animal manure or burn the rice straw. Therefore, applying a combination of inorganic and organic P fertilizers can be beneficial because of the synergetic effects that cause an increase of the efficient use of applied P fertilizers, thus improving agricultural productivity (Kaur et al. 2008;Kasno 2009). Organic amendments can improve P recovery by crops either through applied organic P and inorganic P fertilizers from the irreversible adsorption complexes in the soils (Delgado et al. 2002;Siddique and Robinson 2003) or it can mobilize native soil P (Mohanty et al. 2006).
Sugarcane (Saccharum officinarum L.) is an important crop in Indonesia that is lately cultivated in the upland area of humid tropical soils. The crop is a high nutrient uptake crop, which can remove about 2 kg N, 0.2 kg P and 2.3 kg K from soil for every one ton of its production (Singh et al. 2007). The removed NPK nutrients are supplied mostly by unbalanced inorganic NPK fertilizers applied to the soil, while the sugarcane also removes the other macro and micronutrients contained in the soil. It has been observed that the yield of sugarcane has decreased due to the imbalanced availability of nutrients in soils (Babu et al. 2007). The loss of organic matter in the soils is the main factor for the declining productivity. Restoration of organic matter is needed for maintaining the soil health and improving soil productivity.
One source of organic materials that can be used to reduce P adsorption on soil colloids is Organonitrophos fertilizer that has been introduced by Nugroho et al. (2012), in which its application can be combined with inorganic fertilizers. The use of both Organonitrophos and inorganic fertilizers in the current study was intended to study their impacts on sugarcane production and phosphorus uptake by the sugarcane. In addition, the same rates of the fertilizers were applied on subsoil samples in the laboratory experiment to study the effect of the fertilization on the maximum adsorption of P and relative P bonding energy on the soil, which were estimated by fitting the empirical Langmuir model.

Study Site
The field experiment was performed in the sugarcane area of Integrated Agricultural Experimental Stations (Laboratorium Lapang Terpadu), the University of Lampung, in September 2015 until September 2016 (one year period). A laboratory experiment of P adsorption on subsoil samples was conducted in the Laboratory of Soil Science, the University of Lampung. The soil characteristics including available-P (Bray 1 Method), total-P (25% HCl Method), total-N (Kjeldahl Method), exchangeable-K (Method 1 N NH 4 OAc pH 7), total-C (Walkley and Black Method), and CEC (1 N NH 4 OAc pH 7) (Thom and Utomo 1991) were measured in the laboratory. The yield of sugarcane and harvested P by the sugarcane were also determined.
The subsoil samples (20-40 cm depth) were taken from the same field as used for the field experiment in order to conduct a laboratory experiment. The soil samples were air-dried and sieved through 2 mm sieve, then applied with similar fertilizer treatments as used in the field experiment. About 2 kg of subsoil sample that had been treated with each treatment was saturated with water with the ratio of soil to water of 1:1 for one week. The use of subsoil samples in the laboratory experiment was aimed to minimize the effects of soil organic matter and the fertilizer treatments applied on the topsoil on the P adsorption estimated using the Langmuir model (Parfitt 1978;Bubba 2003;Yang et al. 2014;Diana et al. 2010;Lumbanraja 2017).

Phosphoprus Adsorption Analysis
The Langmuir Isotherm Model with a modified series solution: 0 ppm P, 10 ppm P, 20 ppm P, 50 ppm P, 100 ppm P, and 200 ppm P (KH 2 PO 4 ) in 5 mmol CaCl 2 solution had been applied to the saturated subsoil samples. The treated subsoil sample of each treatment were weighed 2 g and put into a shaker bottle, then the representing subsoil sample of the treatment was added each with 20 ml of representing of series solutions (0, 10, 20, 50, 100, and 200 ppm P). Then the soil suspension was shaken using shakers during two hours, and then centrifuged at 3,000 rpm for 10 minutes. The clear supernatant was used to measure P in equilibrium solution using a spectrophotometer with 720 nm wavelength (Sari 2015;Carter and Gregorich 2008;Fiantis 2004). The Langmuir equation curve is presented in Figure 1. (Parfitt 1978;Bubba 2003;Mohammad et al. 2012;Diana et al. 2010;Lumbanraja 2017).
In which C = P equilibrium concentration in solution (mg P L -1 ), X = the amount of adsorbed P (mg P kg -1 soil), X m = maximum adsorption (mg P kg -1 soil); k m = relative bond energy; C/X = solution to adsorbed P index.

Data Analysis
The student-t test was performed (Susilo 2013) to see the difference between each maximum phosphorus adsorption (X m ) of each treatment and each relative phosphorus bond energy (k m ) of each treatment using the Langmuir isotherm model. Analysis of variance was performed to analyse the data of vegetative and generative components of the sugarcane. In addition, the Least Significant Difference (LSD) test was futher performed to see the differences among means.

Chemical Properties of the Soil from Field Experiment
The results of the soil analysis showed that the Ultisol that had been used for the field experiment has slightly acidic pH, and the nutrient availability in the soil such as total-N, exchangeable K, and available-P is in moderate, high, and very high amount, respectively (Table 1). The very high available-P content in the soil can be affected by the residual P fertilizer applied in the previous cultivation of crops and by the soil parent material that is formed from the basaltic materials.
Data in Table 1 also indicated the low total C content of the soil. This can be caused by the rapid decomposition process of soil organic matter that occurs in the humid temperate region, which indicated by the low soil C/N ratio and CEC. The CEC of Ultisol that is low to very low has been reported by many researchers due to the organic matter content and the parent materials of the soil Syahputra et al. 2015;Lumbanraja 2012;Helling et al. 1964). The results of soil chemical analysis after sugarcane harvesting showed that the highest available-P was measured in the soil from the treatment A (100% NPK + 50% compost) and the lowest available-P was measured in the soil without fertilization, which might be Figure 1. An ideal Langmuir Curve.
because of the addition of compost in the treament A that could increase the content of available-P in the soil.
The results of analysis of soil samples taken after sugarcane harvesting showed that all the treatments decreased the total C contents in the soil ( Table 2). The decrease in soil organic matter content can be due to the rapid decomposition process of soil organic matter. Rindyastuti and Darmayanti (2010) reported that organic materials with a C/N ratio of 26.15 can be decomposed within 1 up to 3 months, whereas in the current study the average value of soil C/N ratio is 7.85, which is considered as low. The amount of available-P in soil after sugarcane harvesting also decreased in comparison to that in the initial soil. This result can be understood by the high uptake of P by the sugarcane. The decreasing of soil organic matter content could also cause the decrease of available-P in the soil. This result indicates that the amount of available-P in the soil is strongly influenced by the amount of organic matter contained in the soil. If the soil organic matter content is high then the amount of available-P in the soil will be high as well (Sari 2015;Utami and Handayani 2003;Singh 2015). Table 3 shows the production of sugar and dry biomass of leaves and stems obtained from all the treatments. There were similar trends of the significant effects of the treatments on the sugar production and the stem biomass. On the other hand, there was no significant effect of the treatments on the leave biomass. The sugar production and sugarcane stem biomass in the treatment A (100% NPK) were not significantly different from those in the treatment C (100% NPK + 50% compost), but the sugar production and stem biomass in both A and C treatments were significantly higher than those in the treatment B (100% compost) and D (50% NPK + 100% compost). However, there was no significant different effect between treatment B and D on the sugar production and stem biomass. The result also showed that the the highest sugar production and stem biomass were obtained in the Table 2. Chemical properties of the soil after sugarcane harvesting. 8.00 l 7.00 l 8.50 l 7.50 l 7.00 l A= (100% NPK); B= (100% compost); C= (100% NPK + 50% compost); D= (50% NPK + 100% compost); E= (without fertilizer). The numbers followed by the same letters indicate the criteria of soil chemical properties, namely vh= very high; m=moderate; l=low; sa= slightly acid (Balai Penelitian Tanah 2009).

Sugar Production and The Amount of Harvested P by the Sugarcane
Exchangeable-K (cmol kg -1 ) treatment C. This result indicates that the soil needs the combination of inorganic and organic fertilizer application to increase the sugar production to some rates. It has been also reported that the maize crops grown on similar soil without fertilizer application resulted in the lowest yield (Soplanit and Soplanit 2012;Christine 2013;Dermiyati et al. 2016).
The results in Table 4 showed that all the treatments did not significantly affect the amount of harvested P by the sugarcane leaves. In contrast, the amount of harvested P by the sugarcane stems of all the treatments showed a different trend. Similar to that of sugar production, the total harvested P in the treatment C was the highest, but not significantly different from that in the treatment A; while, the effect of the treatment D was not significantly different from that of the treatment A. Furthermore, the lowest amount of harvested P was measured in the treatment E and B, and surprisingly the amount of harvested P in the treatment E was not significantly different from that of the treatment Table 3. The effect of application of organic and inorganic fertilizers on sugarcane production. B. Several studies have reported that the P content in plants showed a significant effect on the dry biomass of stems (Hossain et al. 2010;Grant et al. 2004;Prado 2010). The lower the amount of harvested P, the lower the dry biomass of stems is, and vice versa. Table 5 shows the soil pH, and the amounts of available-P and potential-P measured after treatments and one week incubation of subsoil samples. The results indicate that the highest soil pH was measured in the treatment C (100% NPK + 50% compost) and the lowest pH was measured in the soil without fertilization as it was expected.

Isothermal P Adsorption
The Langmuir curves are presented in Figure  2 and the linear equations are presented in Table 6. Based on the curves presented in Figure 2, it shows that the higher the P index (C/X) in the soil, the higher the availability of P in the soil is and vice versa. Figure 2 shows that the subsoil samples  Table 4. Effect of application organic and inorganic fertilizer on amount of harvested P by the sugarcane.
applied with both treatment A (100% NPK) and treatment C (100% NPK + 50% compost) have the highest equilibrium P (can be interpreted as available-P) in the solutions, and the subsoil applied with treatment E (no fertilizer) has the lowest P in the equilibrium solution. On the other hand, the equilibrium P in the solution of the subsoil applied with both treatment B (100% compost) and D (50% NPK +100% compost) are lower than that of in the treatments A and C but higher than that in the treatment E. The Langmuir equations are represented in Table 6 and the results of t-test to differentiate the values of X m and k m among the treatments are listed in Table 7. The results show that the treatment A (100% NPK) and C (100% NPK + 50% compost) have the lowest maximum P adsorption (X m = 574.789 mg P kg -1 and X m = 549.342 mg P kg -1 , respectively) and both treatments A and C are not significantly different for X m and k m (Table 7). In contrast, the highest maximum P adsorption and the  Figure 2. The relationship between the P (C/X) index of the P concentration in the solution equilibrium (C). A= 100% NPK; B= 100% compost; C= 100% NPK + 50% compost; D= 50% NPK + 100% compost; E= without fertilizer.
relative adsorption energy are obtained in the treatment E (no fertilizer) (X m = 1103.699 mg P kg -1 , k m = 0.218). The maximum P adsorption (X m ) of the treatment E is highly significant different from that of the treatment A and significantly higher than that of the treatment B, C, and D. It is understood that when the soil has been fertilized with full recommended amount of phosphorus such as in the treatment A and C, the soil has less capacity to adsorb P from soil solution. On the other hand, when it is not fertilized, the soil has high capacity to adsorb P from the soil solution. The most interesting results of X m and k m are found for the treatment B (100% compost) and D (50% NPK and 100% compost). Even though the maximum adsorption of P (X m ) of the treatment B is not significantly higher compared to that of the treatment D, but the relative adsorption energy for P binding (k m ) for the treatment B is significantly lower compared to that of the treatment D (Table.7). The addition of 50% NPK and 100% compost in the treatment D has lowered the maximum adsorption of P but increase the relative adsorption energy for P binding on to the soil colloids. Laverdière and Karam (1984) reported that Ultisols that were treated neither with organic nor inorganic fertilizers had maximum adsorption of P up to 1278 m g P k g -1 caused by high Al and Fe oxide content. The same result has been reported by Lumbanraja et al. (2016), which shows that the Al and Fe oxides are the main cause of the maximum pile of P in the soil colloids, and when the soil treated with organic matter, the amount of available-P in the soil indirectly increases by the process of organic matter chelating the Al and Fe ions in the soil solution.
Table 7 also indicates that the relative Padsorption energy in soil (k m ) of the treatment A is significantly lower than that of the treatment B and D. It is assumed that full-rate of NPK fertilizer application is sufficient for P in the soil so that the soil in the treatment A has lower capacity to adsorb P from soil solution. Therefore, when the soil has

The Relationship Between Soil Adsorption Behavior and Crop Analysis
Based on the results of the correlation test (Table 8), there are positive correlations between soil P (available-P and total-P) and the amount of harvested P by the sugarcane. The results suggest that the increase of available-P in the soil can increase the P content of the sugarcane, thus affecting the dry biomass of leaves and stems of the sugarcane. However, the amount of harvested P by the sugarcane has no significant effect on the dry biomass of sugarcane leaves. Similar result has Treatments T-calculated T- Table   Xm Table 6. Langmuir isotherm equations for the soil affected by organic and inorganic fertiler applications.
been reported by Temegne et al. (2015) that shows that the content of P in the plant does not affect the number of leaves of the plant. This is due to the content of N in the plant further affects the leaf biomass of the plant (Nguyen et al. 2003). It has been reported that the phosphorus feeding into the soil and increasingly high amount of available-P in soil solution can increase the phosphorus uptake by plant and increase the growth and production of plant (Kasno 2009;Grant et al. (2004). Table 9 shows that the maximum adsorption of P (Xm) has a significantly negative effect on the amounts of total-P and available-P in the soil, stem biomass, and the amount of harvested P by the sugarcane, but not significantly affect the leaf biomass. The results indicate that the higher maximum adsorption of P in the soil will lower the P uptake by the sugarcane, resulting the low production of the sugarcane (Morel et al., 2014). This is because P is an essential nutrient that plays a role in increasing the dry weight of plants (Babu et al. 2007). The same is true for the relative bonding energy of P (k m ), which has a negative relationship but does not significantly affect the total-P content, available-P, leaf and stem biomass, and harvested P (Table 9). It is also reported in the study of Handayani (1988) that the addition of organic matter to the soil is able to increase the amount of available-P in the soil and increase the uptake of P by the sugarcane. The increasing harvested P by the sugarcane can speed up the process of cell division that can increase crop production (Babu et al. 2007).

CONCLUSIONS
The results showed that the applications of 100% NPK plus 50% organic fertilizer, and 100% NPK resulted in the highest amount of available-P in the soil, the lowest maximum adsorption of P (X m ) and the lowest relative bonding energy of P (k m ); as well as the highest effect on the increase of sugarcane production. On the other hand, the no fertilizer and the 100% organic fertilizer applications resulted in the the highest maximum adsorption of P (X m ) and the lowest sugar production. There were very significant negative correlations between the maximum adsorption of P (X m ) and soil P, harvested P by the sugarcane and stem biomass, while similar Table 9. Correlations between the maximum adsorption of P (X m ), relative adsorption energy of P (k m ) onto soil and soil P, sugarcane biomass and harvested P by the sugarcane. r = correlation coefficient; ** = highly significant at 1% level; * = significant at 5% level; ns = not significant.
leaf biomass leaf biomass leaf biomass trend but no significant correlations between the relative bonding energy of P (k m ) and soil P, harvested P, leaf biomass and stem biomass were detected.