Research Article

Effect of Rock Phosphate Augmented with Humic Acid on Phosphorus uptake and Yield of Wheat (Triticum aestivum L.)

Sonia Sumreen1, Muhammad Sharif2, Tariq Sultan1 and Ijaz Ali1*

1Land Resources Research Institute, National Agricultural Research Centre, Islamabad-45500, Pakistan; 2Department of Soil and Environmental Sciences, The University of Agriculture Peshawar, Pakistan.

Received | December 15, 2020; Accepted | January 11, 2022; Published | June 28, 2022

*Correspondence | Ijaz Ali, Land Resources Research Institute, National Agricultural Research Centre, Islamabad-45500, Pakistan; Email: [email protected]

Citation | Sumreen, S., M. Sharif, T. Sultan and I. Ali. 2022. Effect of rock phosphate augmented with humic acid on phosphorus uptake and yield of wheat (Triticum aestivum L.). Pakistan Journal of Agricultural Research, 35(2): 417-424.

DOI | https://dx.doi.org/10.17582/journal.pjar/2021/35.2.417.424

Keywords | Rock phosphate, Humic acid, P uptake, Grain yield, Wheat crop

Copyright: 2022 by the authors. Licensee ResearchersLinks Ltd, England, UK.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Introduction

Nutrient deficiency is considered a main constraint to crop productivity in Pakistan. After nitrogen, phosphorus deficiency is most widely spread in soils (Balemi and Negisho, 2012). About 80 % soils are accounted for phosphorus (P) deficiency in Pakistan (Nasir et al., 1990). Main causes of deficiency of P in these soils are the soils derived from P deficient parent materials or the soils were mined due to the inclusion of exhaustive crops in intensive agriculture without the addition or low application of P from both organic and inorganic fertilizers. To overcome P deficiency in soil, P fertilizers are required for crop production to produce better yield, but P fertilizers are very expensive and has become a big constraint to use P fertilizers as per recommendation. The recent hike up in prices of fertilizers especially that of P fertilizers has further aggravated the problem.

Natural phosphate rocks have been recognized as a valuable alternative for P fertilizer. Rock phosphate is relatively cheap and environmentally friendly as compared to chemical fertilizers. It increases C accumulation, exchangeable Ca, and Mg in soils (Hu et al., 1996). Rock phosphate (RP) contains at least 15 to 20% total P which is in the form of tri-calcium phosphate with only a negligible amount of P available when applied to soil. It is mainly used to produce phosphatic fertilizers for the agriculture sector. In Pakistan, rock phosphate deposits are found in Hazara, which is a raw source for phosphate fertilizer production in Pakistan. P solubility from rock phosphate may be increased by augmenting rock phosphate with different organic sources (Sharif et al., 2015; Hanafi and Selwa, 1998; Martinez et al., 1984). Organic sources contain different types of organic acids which react with the insoluble tri-calcium phosphates and convert it to di and mono-basic phosphates which is soluble in water and available for plant uptake. The amount of P solubilized from RP is strongly affected by using different organic sources because they contain different types and amount of organic acids.

Complex process of chemical and biological transformation of organic matter in soil result in humus formation which contains complex types of organic molecules called humic acids. Humic acids can also be derived from lignite coal (Karaca et al., 2006). Humic acids consists of carboxylic (COOH–), phenolic (OH–), alcoholic and carbonyl fractions which act on phosphate ions and increase its availability from RP thus preventing P precipitation and fixation in alkaline soils (Hua et al., 2008). Therefore, under saline and high lime content of soils, HA enhances nutrient availability making the soil more fertile and productive thus enhancing nutrient uptake resulting in improved plant performance (Osman and Rady, 2012; Asik et al., 2009; Katkat et al., 2009; Çelik et al., 2008). HA application also improve physical condition of calcareous soils by improving aggregate stability which results in improved soil biological condition, ion exchange capacity and water holding capacity. Improved soil physical condition enhances plant root proliferation, nutrient mobility to plant roots and improved uptake (Mahmoud et al., 2011).

Wheat is on top position in major crops of Pakistan. It covers about 40% of the cultivated area of the country and about 80% farmers grow it. Almost all crop rotations of the country contain wheat. in Pakistan, of the total food energy intake, 37% is obtained from wheat. Average wheat yields in Pakistan is 2765 kg ha‒1 which is far below the potential yield and as well as from the yield of other countries having almost the same agroclimatic conditions. The main constraint to cover this yield gap is low organic matter and soil nutrient deficiencies.

Considering RP and HA as an important indigenous and economical source of fertilizer, this study was initiated to determine the effect of RP augmented with different levels of HA on the yield and P availability and uptake of wheat crop.

Materials and Methods

Rock phosphate (RP) with and without the augmentation of different doses of humic acid (HA) were evaluated in a field trial at the research farm of Agriculture Research Institute Tarnab Peshawar in rabi season 2011‒2012. RP was augmented with HA @ 5 and 10 Kg ha‒1 and randomized in complete block design (RCBD). The treatments combinations were Control (No fertilizers); Rock Phosphate (RP); RP+HA‒5 (Rock Phosphate applied with Humic Acid (HA) @ 5 Kg ha‒1); and RP+HA‒10 (Rock Phosphate applied with Humic Acid (HA) @ 10 Kg ha‒1).

In total number of 12 plots, Pir Sabaq-2000 variety of wheat was grown using a seed rate of 100 Kg ha ‒1 with the help of tractor driven drill. Plot size of 6×7.5 m2 was kept with a row to row distance of 30 cm. N, P and K fertilizers were used at the rate of 120‒90‒60 Kg ha‒1, respectively. Before drilling the seed, soil was prepared with cultivator by driving 2 times and after cultivator, rotavator was used to get the soil surface smooth for seed drilling. All the P and K was applied at the time of sowing before seed drilling while N was used in split doses i.e. one half at the time of sowing and other half after 2 months of germination. All other management and plant protection practices were carried out uniformly throughout the season for optimum crop growth.

Soil sampling and analysis

Before sowing of wheat, randomly three samples were collected from the experimental area at 0−20 cm soil depth. All the three samples were mixed properly to get a uniform soil sample. A portion from it in the form of composite soil sample was taken into a plastic bag and taken to the laboratory for analysis. The composite soil sample was analyzed for Soil texture (Koehler et al., 1984), pH and EC (Soltanpour and Workman, 1981), Soil organic matter (Nelson and Sommers, 1996), Lime content (Ryan et al., 2001), Total N (Helrich, 1995), Soil P and K (Soltanpour and Workman, 1979) were determined.

Plant sampling and analysis

At crop maturity, one-meter square area from each treatment was harvested. Dried in oven at 64°C for three days. Total dry biomass/matter was recorded. Grains from biomass were threshed manually and grain weight was recorded. For straw yield, grain weight was subtracted from total biomass. Data on total biomass, grain and straw was converted to Kg ha‒1.

After harvesting of wheat, composite soil samples from the surface soil (0−20 cm soil depth) of each plot were collected. Soil samples were analyzed for NO3−N, P2O5 and K2O contents. Plant samples of straw and grains were also analyzed for total N by Kjeldahl method (Bremner, 1982). P and K concentrations by wet digestion method (Walsh and Beaten, 1977). Nutrient uptake was calculated by multiplying straw and grain yields with their nutrient concentrations and total nutrient uptake was calculated by adding nutrient uptakes of straw and grains.

Statistical analysis

Analysis of variance was applied to the data collected on soil nutrient content, plant nutrient uptake and yield by using MSTATC statistical package. Means of the data were separated using DMR test. Graphs were made in Microsoft Excel 365.

Results and Discussion

Properties of Soil, Rock Phosphate and Humic Acid

Soil under use was calcareous having alkaline pH (7.96) with low EC (0.16 dS m‒1). Texture of the soil was silty clay loam with a low soil organic carbon (0.51%). Soil was deficient in total N (0.08%) and soil available P (5.75 mg kg‒1). Rock Phosphate applied has 22% total P2O5, 0.001% extractable P2O5 having pH of 7.92. Humic acid used was contained 3.15% N, 0.18% P and had pH of 7.75.

Soil P, N and K content

Soil P2O5, NO3−N and K2O contents at post-harvest of wheat are given in Table 1. Soil P2O5 content was significantly (p=0.0061) affected by Rock Phosphate application with and without Humic Acid. RP alone significantly increased soil P content by 87% as compared to control which was further increased significantly by 41% when Rock Phosphate combined with 5 Kg ha−1 of Humic Acid (RP+HA-5) was applied as compared to RP treatment. When the rate of humic acid augmentation of rock phosphate was increased two-fold (RP+HA-10), P availability further increased with statistically non-significant differences. This increase was only 7% in P availability over RP+HA-5 treatment. These finding agree that organic amendments enhance P availability in calcareous soils (Struthers and Sieling, 1950; Awad and Al-Obaidy, 1989). Sharif et al. (2015) also reported significant increase in soil P content when applied with either poultry manure or farmyard manure. Dissociation of H+ and OH− from the molecular structure of humic acid in calcareous soils gives rise to the cation exchange sites on the functional groups resulting in chelation of cations which increase solubility of rock phosphate instead of being precipitated with cations (Martinez et al., 1984; Hanafi and Selwa, 1998).

 

Table 1: Soil P, N and K concentrations under RP with and without different levels of Humic Acid.

Treatments	P2O5	NO3‒N	K2O
	(mg Kg−1)
Control	3.26 c	10.81	123
RP	6.12 b	11.22	122
RP+HA-5	8.63 a	13.33	130
RP+HA-10	9.26 a	15.11	133
LSD (p ≤ 0.05)	1.371	NS	NS

Means with different letter(s) in columns are significantly different at p ≤ 0.05. Where RP, rock phosphate; RP+HA-5, rock phosphate with humic acid @ 5 Kg ha−1; RP+HA-10, rock phosphate with humic acid @ 10 Kg ha−1.

 

Both soil NO3−N and K2O contents were not significantly (p=0.0598 and 0.0713) affected with treatments. Whereas both soil NO3−N and K2O contents were gradually increased with the increasing augmentation of treatments with humic acid. In the treatment where rock phosphate augmented with 5 Kg ha−1 of humic acid (RP+HA-5) was applied, soil NO3−N content was increased by 23% and K2O content by 6% over control. When rock phosphate mixed with 10 Kg ha−1 of humic acid (RP+HA-10) was applied, soil NO3−N content was further increased by 13% and that of soil K2O content by 2% over the treatment RP+HA-5. Therefore, these finding showed that increase in soil NO3−N and K2O contents were due to the application of humic acid. Sharif et al. (2015; 2010) also recorded significantly high soil NO3−N content over control by applying farmyard manure and humic acid to soil. The increase in soil NO3−N content due to the application of Rock Phosphate combined with Humic Acid might be attributed to the N content of humic acid which releases it in soil. Whereas increase in K2O content might be because of the dissociated functional groups of humic acid in calcareous soils which gives rise to the cation exchange sites resulting in chelation of cations which protect the cations from precipitation and slowly release them to increase their availability.

 

Plant P, N and K uptake

Rock phosphate significantly (p=0.0083) increased plant P uptake either applied alone or in combination with humic acid (Figure 1). All the three treatments i.e rock phosphate alone or mixed with two levels of humic acid gradually increased P uptake in wheat in the order RP+HA-10 > RP+HA-5 > RP as compared to control. RP increased P uptake by 193% over control. When humic acid was mixed with RP @ 5 Kg ha‒1 (RP+HA-5), it further significantly increased P uptake by 23% over RP treatment. As the humic acid level mixed with RP was increased to 10 Kg ha‒1 (RP+HA-10), the P uptake was further increased by 10% which was at par with RP+HA-5. Taalab et al. (2008) also reported increased P uptake when rock phosphate was applied combined with organic fertilizers. Enhanced P uptake in plant by applying humic acid and P fertilizers to soil were also observed by Erdal et al. (2000). Belal et al. (2019) also reported increase in P uptake in barley tissue with the application of humic acid. This increase in P uptake by plant may be due to the high availability of P in soil because nutrient uptake in plant tissues depends on soil available nutrients and their ease of mobility towards roots (Belal et al., 2019; Mahmoud et al., 2011). Humic acid improve soil fertility and increases nutrient availability (Osman and Rady, 2012; Rady, 2011) due to the humic acid role in enhancement of processes involved in nutrient uptake and movement within plant tissues (Nardi et al., 2002) thus increasing the uptake of nutrients by wheat plant. Sharif et al. (2015) noted the highest P uptake in experimental plots where Rock Phosphate and farm yard manure were applied.

 

Plant N uptake under different treatments of rock phosphate and humic acid was also significantly (p=0.0221) affected (Figure 2). RP alone significantly increased plant N uptake by 194% as compared to control. Whereas humic acid treated rock phosphate further increased plant N uptake significantly as compared to RP alone treatment. Rock phosphate treated with humic acid @ 5 Kg ha−1 (RP+HA-5) increased plant N concentration by 41% over RP treatment which was further increased by 23% when humic acid was mixed with rock phosphate @10 Kg ha−1 (RP+HA-10). The significant increase of N uptake in wheat tissue under RP treatments might be due to the synergistic effect of high available soil P2O5 content on the N absorption and translocation within plant (Sumner and Farina, 1986; Terman et al., 1977). Mutual synergistic effects of both P and N stimulate plant growth resulting in enhanced uptake of these nutrients (Sumner and Farina, 1986). In the humic acid augmented treatments, further significant increase in plant N uptake is due to the synergistic effect of more and more soil P availability and due to humic acid which releases itself N into soil and also stimulate root absorption capacity for nutrients (Mahmoud et al., 2011). Similar results were observed by Erdal et al. (2000) that nutrients uptake by plants were increased by integrated use of chemical fertilizers with organic materials. Increased accumulation of N in plant was observed when rock phosphate mixed with organic fertilizers was applied (Taalab et al., 2008). N uptake by plants was also increased significantly in a study conducted by Awaad et al. (2009) using rock phosphate mixed with organic fertilizers. Sharif et al. (2015) observed similar results and noted higher N uptake by wheat plants when applied rock phosphate mixed with farmyard manure. This increase in N uptake may be attributed to the increased availability of N in soil because nutrient uptake by plant tissues depends on soil nutrients availability and their ease of mobility towards roots (Belal et al., 2019; Mahmoud et al., 2011).

 

Plant K uptake was also significantly (p=0.0131) affected by different treatments (Figure 3). Rock Phosphate alone (RP treatment) significantly increased plant K uptake by 122% as compared to control. The significant increase in K uptake in wheat under RP treatment might be due to the balanced availability of N and P with K in soil. Balanced nutrition availability to plants enhances nutrients uptake by plant due to the interactive synergistic effect of nutrients (Fageria, 2001). Li et al. (2019) and Wang et al. (2011) also reported similar results that at low or optimum application rates the interaction between P and K is synergistic. Plant K concentration was also significantly increased by rock phosphate applied in combination with humic acid as compared to both RP and control treatments. Rock Phosphate combined with 5 Kg ha−1 of Humic Acid (RP+HA-5) increased plant K uptake by 29% over RP treatment. When Rock Phosphate was applied along with 10 Kg ha−1 of Humic Acid (RP+HA-10), plant K uptake was further increased significantly by 28% as compared to the treatment RP+HA-5. But the increase in plant K uptake among rock phosphate treatments may be attributed to humic acid application which increased soil K2O content due to the dissociation of H+ and OH− from the molecular structure of humic acid in calcareous soils. The dissociation of H+ and OH− from the molecular structure of humic acid in calcareous soils resulting in chelation of cations which protect the cations from precipitation and slowly release them to increase their availability in soil. Therefore, increase in K uptake may be attributed to the increased availability of K in soil because nutrient uptake by plant depends on soil available nutrients and their ease of mobility towards roots (Belal et al., 2019; Mahmoud et al., 2011).

 

 

Grains, Straw and Total Dry matter yield

Application of Rock Phosphate (RP) significantly (p=0.0034; p=0.0113; p=0.0072) increased grain, total dry mater and straw yield of wheat (Figure 4, 5, and 6) over control. RP increased grain, total dry mater, and straw yield of wheat by 17, 35 and 47% over control, respectively. When Rock Phosphate was applied combined with Humic Acid, these yield parameters were further increased significantly. Rock Phosphate with 5 Kg ha−1 of Humic Acid (RP+HA-5) increased grain yield by 19%, total dry matter by 54% and straw yield by 64% over RP treatment. Whereas Rock Phosphate with 10 Kg ha−1 of Humic Acid (RP+HA-10) furthermore increased 5, 4 and 4% in grain, total dry mater and straw yield of wheat respectively as compared to treatment RP+HA-5 which was a statistically non-significant increase. Similar results have been reported by Phiri et al. (2010), Awaad et al. (2008), and Sharif et al. (2015, 2014 and 2013) who found a significant increase in wheat grain yield with the application of rock phosphate mixed with humic acid. A prominent increase in total dry matter of wheat with the application of rock phosphate with humic acid and other organic sources (Amanullah et al., 2010; Awaad et al., 2008). Ibrahim et al. (2008) and Phiri et al. (2010) also reported a significant increase in wheat yield when used Rock Phosphate with various organic materials. This increase in wheat yield is attributed to the enhanced availability of nutrients in soil resulting in increased nutrients uptake.

 

Conclusions and recommnendations

Humic acid increased P availability from rock phosphate in soil which increased N, P and K uptake and yield of wheat. The results of this study proved that rock phosphate can be used as P source when augmented with humic acid and has a potential to enhance crop production. More research work is needed to investigate the degree and extent of P solubility from RP by mixing with different organic material and determine their effect on yield and P uptake of different crops in various agro-ecological zones of Pakistan.

Novelty Statement

Humic acid enhances P release in soil from rock phosphate and has potential to enhance crop production.

Author’s Contribution

Sonia Sumreen: Contributed to the paper.

Muhammad Sharif: Supervised the experimental trial.

Tariq Sultan: Proof read and suggested in manuscript write-up

Ijaz Ali: Analyzed Data and wrote manuscript.

Conflict of interest

The authors have declared no conflict of interest.

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