Available P Enhancement in Andisols under Pasture and Rock Phosphate Amended with Poultry Manure ^†

Abstract

Poultry manure (PM) is a great nutrient source for plant growth. PM enhances soil properties and increases the crop yield. As an important strategy to decrease the amount of inorganic phosphorus (P) fertilizers, the combined use of rock phosphate (RP) with PM has been found to be more advantageous for sustainable agriculture than their single use. The objective was to assess the effect of PM on P availability in Andisols and RP dissolution. In the first incubation, an Andisol was mixed with 100, 200, and 300 mg P kg⁻¹ rate using PM, and Olsen P was determined at 1, 3, 5, 7, and 10 days. In the second experiment, four Andisols were incubated with 200 and 300 mg P kg⁻¹ soil for 20 days and acid phosphatase activity (APase) was measured. In the last experiment, PM and rock phosphate (RP) were mixed at two different rates: 50:50 and 70:30 for 30 days and total inorganic P was determined. We found that Andisols amended with PM increased P availability and APase, and the mixture of PM:RP at 70:30 showed the highest inorganic P. We therefore conclude that PM addition may improve P availability in soil as well as in combination with RP.

1. Introduction

Dairy and meat production in Southern Chile are based on the use of permanent pastures established on Andisols as the main source of food for cattle [1]. These soils have andic properties and immobilize highly reactive phosphate anions through sorption and/or precipitation with cations such as Al and Fe [2,3,4]. As a result of this immobilization, phosphorus (P) available for plant uptake in soil solution is very low. In Southern Chile, 91% of the 1.3 million ha of pasture are naturalized, where a total of 48% is under grazing and does not receive any type of fertilizers to compensate for the nutritional losses [5]. Thus, improving pasture production by fertilization management on Andisols is a major concern that must be approached in a sustainable manner [5,6]. Lately, the combined use of low P-available rock phosphate (RP) fertilizers with organic manures has resulted in increased P availability and crop yields [7,8,9,10]. Among organic manures, poultry manure (PM) is a great source of plant macro- and micronutrients and may have an important effect on the soils’ physicochemical properties [7,11,12,13] and some biological properties, such as the activity of acid phosphatases (APase) enzymes [12,14,15]. Is an important issue to consider that PM applied to soil will improve soil properties and increase crop production, while providing a way to reuse waste material from broiler production. The latter represents an important strategy under the context of circular economy by adding value to this waste and, thus, decreasing the amount of inorganic P fertilizer application. The aim of this study was to assess the effect of PM on P availability in Andisols under pastures as well as in the dissolution of RP.

2. Materials and Methods

2.1. Characterization of Poultry Manure

Chemical Characterization

Composted poultry manure (PM) was homogenized, freeze-dried, ground to pass 2 mm, and stored at −20 °C until use. Chemical analyses were performed in accordance with the methodology described by Sadzawka et al. [16]. Total P was determined in extracts by alkaline digestion with sodium hypobromite (NaBrO) in accordance with the methodology of Dick and Tabatabai [17] and determined through a spectrophotometer at 880 nm following the method of Murphy and Riley [18]. Selected poultry manure properties are showed in

Table 1. Selected poultry manure properties.

	Dry Matter	pH	Total OC	Total N	Total P
	%	(H2O)	(g kg−1)
Poultry manure	56.1	8.77	267.8	37.1	25.0

.

2.2. Soil Sampling

One soil sample was collected from Santa Elena farm, located 50 km from Temuco city, in Freire (La Araucanía region, Chile). Soil belonged to the Barros Arana series (BAR), classified as Typic Hapludand (

Table 2. Selected soil physicochemical properties.

Soil	Soil Order	Soil Family	Bulk Density (g cm−3)	pH (H2O)	Available P (mg kg−1)	Total OC (g kg−1)	Total N (g kg−1)
BAR	Andisol	Typic Hapludand	0.85	5.7	10.0	87.0	2.1
CUN	Andisol	Acrudoxic Hapludand	1.05	6.0	11.0	32.9	8.2
VILL1	Andisol	Acrudoxic Fulvudands	0.65	5.2	6.1	130.3	7.7
VILL2	Andisol	Acrudoxic Fulvudands	0.65	5.2	6.9	130.3	6.6
LLA	Andisol	Typic Durundands	0.84	6.1	2.8	82.7	5.3

). Soil was sieved (2 mm), air-dried, and stored at room temperature. In addition, four soil samples were collected from pasture farms belonging to the Cunco (CUN), Villarrica (VILL1 and VILL2), and Los Lagos (LLA) series (Table 2).

2.3. Incubation Assays

2.3.1. Effect of Poultry Manure on Soil P availability

We carried out three incubation experiments. Firstly, we incubated an Andisol belonging to the Barros Arana series (BAR) with poultry manure to assess its effect on available P. Briefly, 1 kg of bulk soil was moistened to field capacity in polyethylene bags. Soil was then thoroughly mixed with PM using three replicates to provide 100 (PM100), 200 (PM200), and 300 (PM300) mg P kg⁻¹ soil (2.5, 5.0, and 7.5 g PM kg⁻¹ dry soil). Additionally, unfertilized soil was used as control. Soil was incubated under controlled conditions at 25 °C. Subsamples were taken at 1, 3, 5, 7, and 10 days after incorporation and soil-available P was measured according to Olsen and Sommers [19] by extracting 2.5 g of soil with 0.5 M of sodium bicarbonate (pH 8.5) for 30 min and measuring, by spectrophotometry at 880 nm, according to the Murphy and Riley [18] method.

2.3.2. Effect of Poultry Manure on Soil P Enzyme Activity

The second incubation experiment was performed in order to test the poultry manure effect on Andisol acid phosphatase activity. The four Andisols corresponding to Cunco (CUN), Villarrica (VILL1 and VILL2), and Los Lagos (LLA) (Table 2) were sieved (2 mm), air-dried, and stored at room temperature. Each soil sample was incubated using 1 kg of soil, in three replicates, and mixed at two PM rates of 200 (PM200) and 300 (PM300) mg P kg⁻¹ soil for 30 days at 25 °C. Acid phosphatase activity (APase) was determined following p-nitrophenol release (p-NP) according to the methodology of Tabatabai and Bremer [19] modified by Rubio et al. [20].

2.3.3. Effect of Poultry Manure on P Availability from Rock Phosphate

In the third incubation, we quantified the available P of rock phosphate mixed with poultry manure. Rock phosphate was highly reactive [21] with a marine sedimentary origin (Bahia inglesa) [22] and its selected properties are listed in

Table 3. Selected properties of rock phosphate.

	pH	Available P	CaO	MgO	CaCO3
	H2O	g kg−1	%
Rock phosphate	8.72	82.8	30	1.2	10

. PM and RP were combined, in three replicates, at 50:50 and 70:30 ratios. Samples were moistened in polyethylene bags and incubated at 25 °C for 30 days. Total inorganic P content was then measured after 0.5 M sodium bicarbonate (pH 8.5) extraction for 16 h and determined using the Murphy and Riley [18] method.

2.4. Statistical Analyses

Data was normality- and homogeneity-checked using the Shapiro–Wilk and Levene tests. Significant differences (p ≤ 0.05) between treatments and sampling days were performed by two-ways ANOVA followed by post hoc Tukey test using the R statistical platform (R foundation for statistical computing version 3.6.3).

3. Results

3.1. Available P in an Andisol Amended with Poultry Manure

PM treatments highly increased the soil-available P in BAR soil from the first day of incubation (Figure 1). In the BAR soil, the available P varied between 10.4–31.8 mg kg⁻¹ for PM100, 36.6–65.9 mg kg⁻¹ for PM200, and 44.5–131.9 mg kg⁻¹ for PM300. Soil-available P was significantly (p ≤ 0.05) improved by increasing PM rate at 200 PM and 300 PM. The highest values were shown in the BAR soil amended with PM300 on the third sampling day. Then, available P decreased for the 200 PM and 300 PM treatments, but maintained higher values than control. For the BAR soil amended with 100 PM treatment, available P did not show any differences compared to the control until the fifth day, while in the seventh and tenth day, available P increased significantly.

3.2. Acid Phosphatase Activity in Andisols Amended with Poultry Manure

The incubation of soil with different rates of PM results in an important increase of acid phosphatase (APase) activity after 10 days (Figure 2). APase activity in the four Andisols ranged from 246 to 743 mg p-NP kg⁻¹ h⁻¹. The 300 PM treatment obtained the highest APase activity in CUN, VILL1, and VILL2 soils, while in the LLA soil, the 200 PM and 300 PM treatments showed similar values. Among unfertilized soils, VILL2 showed the highest APase activity, followed by VILL1, LLA, and CUN.

3.3. Available P in the Mixture of Poultry Manure and Rock Phosphate

The increase of available P was calculated as the difference between the initial values of available P in the PM and RP and values obtained by the mixtures at each sampled day (Figure 3). Initial available P of PM was 2440 mg kg⁻¹, while RP showed the lowest value of 156 mg kg−1. PM and RP mixed at a 50:50 ratio showed the highest increase in P availability at the 1st day, followed similarly by the 20th and 30th day and, finally, by the 10th day. On the other hand, in the 70:30 ratio, the greatest values of available P occurred similarly after the 1st and 30th day, followed by the 10th and, finally, the 20th day. Available P released from the PM:RP mixture was increased at the 30th day. PM and RP mixed at a 70:30 ratio was higher in P availability on all sampling days compared to 50:50 ratio.

4. Discussion

We assessed the poultry manure effect on P availability in Andisols as well as from the dissolution of rock phosphate through investigating three incubation experiments. Our results showed that the greatest values of available P were obtained by amending Andisol with the highest PM rates (200 to 300 mg P kg⁻¹). In practical terms, treatments used in this study represented 4.2, 8.5, and 12.7 Mg of PM ha⁻¹, which is a very high P input. These results are in accordance with the study performed by Waldrip et al. [12], who amended a Typic Haplorthod soil with 42.6 Mg of PM ha⁻¹. In addition, Blair et al. [14] indicated that, in a Typic Fragiudult, a PM amendment corresponding to more than 56 kg P ha⁻¹ was sufficient to increase the soluble P pool. Moreover, they found that acid phosphatase (APase) activity was increased immediately, which was attributed to the organic matter input from PM. We found that the APase activity was also improved in the four assessed soils following PM treatments. APase activity in soils is associated to macromolecular organic P solubilization leading to its utilization by plants which mainly occurs under P-deficient conditions, while lately, this was also reported in P-sufficient soils receiving organic manures [15]. Thus, the improvement effect of PM on the P availability of soil could additionally exert an enhancement of APase activity in Andisols. Accordingly, Poblete-Grant et al. [13] studied the long-term effect of PM applied in Andisols, concluding that increases in the P availability of soil could be associated with a remobilization from P contained in less available pools, direct P input from the amendment, or by decreases of P-sorption sites.

In order to decrease the amount of PM used, we suggested the combined application with rock phosphate (RP) in 50:50 and 70:30 mixtures. We found that, from the first day, available P was highly increased in the mixture of 70:30, which might be attributed to the organic acids released during PM decomposition and microorganisms existing in this amendment [9]. Additionally, Abbasi et al. [7] reported an 80% increase in P release from RP when applied in combination with PM (50:50) compared to its application alone, which might be explained by higher microbial activity due to amendment with organic manures. On the contrary, Mahimairaja et al. [10] reported low levels of RP dissolution mainly attributed to small amounts of protons released during nitrification processes or/and high concentrations of calcium. However, our findings showed that rock phosphate mixed with poultry manure increased the amount of available P considerably, which might enhance its fertilizer efficiency to provide P to plants. Poblete-Grant et al. [8] reported that soil microbial biomass P was greatly increased by combination of RP with PM compared to its single application. We therefore suggest that poultry manure could be a suitable P fertilizer to increase either available P or acid phosphatase activity in Andisols, as well as inorganic P from the low-P amendments such as rock phosphate.

5. Conclusions

The results obtained in the three experiments evidenced the enhanced effect of the organic manure in different aspects. Firstly, the use of this organic material increased the availability of P in an Andisol. Moreover, soil biological activity of phosphatase enzyme was promoted in several Andisols under organic fertilization. Finally, the synergistic effect of poultry manure on P availability released from rock phosphate could decrease the use of this non-renewable source. We therefore concluded that poultry manure addition might be an alternative source to maintain agriculture production in Andisols through the improvement of soil fertility and its biological condition. However, long-term results will be necessary to analyze the combined effect of poultry manure and rock phosphate in field conditions.