Long Term Effect of Tillage and Organo-Mineral Fertilizer Application on Phosphorus Dynamics on Ferric Lixisol in Burkina Faso

A Pot experiment was conducted on 30 years long term soils under different soils management to evaluate the effect of organic amendments and soil tillage on phosphorus evolution in Ferric Lixisol. Two (2) levels of incubation with and without sorghum bicolor were used with six (6) treatments: (1) Tillage with animal traction + 10 t manure / ha / year + 100 kg NPK (14-23-14-6S-1B) / ha + 50 kg urea (46 % N); (2) Tillage with animal traction + 100 kg NPK (14-23-14-6S-1B) / ha + 50 kg urea (46 % N); (3) Minimum tillage+ 10 t manure / ha / year + 100 kg NPK (14-23-14-6S-1B)/ ha + 50 kg urea (46% N); (4) Minimum Journal of Agricultural Studies ISSN 2166-0379 2020, Vol. 8, No. 4 http://jas.macrothink.org 241 tillage + 100 kg NPK (14-23-14-6S-1B) / ha + 50 kg urea (46 % N); (5) 30-years-old fallow and (6) control plot (continuous sorghum without fertilizer) from soil fertility sustainability trial. Each treatment was pretreated with carbon plus nitrogen or without nitrogen before the experiment. The results showed that tillage increased P availability by 70 to 273 % compared to fallow in general and the use of organic matter improved only P-NaHCO3 by 83 %. The effect of nutrient (carbon and nitrogen) addition varied according to different fraction of P. P-NaHCO3 with sorghum incubation seems to be more responsive to nutrient addition. Therefore, minimum tillage with organic and mineral fertilizers amendments has beneficial effect on available P fractions.


Introduction
Improper agricultural practices contribute to natural resources and soil degradation (Nasir Ahmad et al., 2020;Ayub et al., 2020). The degradation of natural resources, particularly of soils, remains a major problem for agro-sylvo-pastoral sustainability in the Sudano-Sahelian zones (Lal, 1997). Improper management practices negatively affect soil health (depletion of organic matter and other nutrients) as well as decline in crop productivity (Ramos et al., 2011). This decline in soil fertility results also, in depletion of soils phosphorus. There are three major pathways of P loss from soil: erosion, leaching both non-intended and sometimes mutually interlinked, and the uptake by plants and removal with harvests. Phosphorus (P) is the second most important macronutrient as an essential plant nutrient. It is a key nutrient for sustainable agricultural productivity and which limits plant growth in many soils (Scervino et al., 2011). In fact, when soil phosphorus is removed by plants, bioavailable phosphorus becomes limiting. Therefore, a sustainable agricultural system requires replenishment of this nutrient to increase the levels of bioavailable phosphorus (Compaoré , 1996). Major global problems related to soil phosphorus in Burkina Faso (P) are the limited plant productivity caused by its low availability and high fixation in soils (Sé dogo, 1995). Phosphorus deficiency in tropical Lixisol can be caused by the nature of the geological substratum, the evolution during the formation of soil, and also by the low organic matter content and the rapid soils depletion after cultivation (Sé dogo et al., 1991;Eduah, 2019). Inorganic fertilizer is widely used in agriculture to increase soil nutrient and soil productivity. Soil tillage is among the important factors affecting soil properties and crop yield. Among the crop production factors, tillage contributes up to 20 % (Derpsch et al., 2010). Organic matter has a favourable effect on P dynamics of the soil; in addition to P release by mineralization, the competition of organic ligands for Fe and Al oxides surface can result in a decrease in P fixation of applied and native P. Organic carbon plays a central role in the inherent soil fertility through mineralization of soil organic matter which occurs in tropical areas as Burkina Faso with about 2 % of the carbon stock per year (Pieri, 1989).
Phosphorus mobility in soils has been commonly studied by quantifying P in different extracts to assess its lability. For soils, H2O or resin extractable P are thought to be composed of dissolved inorganic P, whereas NaHCO3 and NaOH extractable fractions may be a mixture of amorphous and crystalline Al and Fe phosphates and some physically and chemically Journal of Agricultural Studies ISSN 2166-0379 2020 protected organic P (Toor et al, 2006). Compared to nitrogen, tillage system and its relationship with phosphorus availability have received less attention. Long-term experiments are useful to assess the evolution in soil quality induced by the adoption of cropping systems, soil management practices, fertilizer application, or organic matter management. This paper aims at studying the effect of organic amendments and soil tillage on phosphorus evolution on a Ferric Lixisol.

Site and Trial Description
The support of this study is a long-term trial "Soil Physical Study Trial" installed since 1990 at the Institute of Environment and Agricultural Research Station of Saria (12˚16'N, 2˚9'W) in Burkina Faso. The trial site is located in a north-Sudanian climate (Fontè s and Guinko, 1995) with an average daily temperature varying from 30 ℃ during the rainy season to 45 ℃ in April and May. The rainfall is confined to the period from May to October with an annual mean of 800 mm. The main species of natural vegetation are Parkia biglobosa, Vitellaria paradoxa, Tamarindus indica, Andropogon gayanus and Pennisetum pedicellatum. The soil is Ferric Lixisol (FAO, 2006). Soil in the study area is mainly poor with low organic carbon (SOC), N and available P contents (Table 1). The Experiment design used in the long-term trial is a Fisher block. It consists of three blocks ISSN 2166-0379 2020 (or repetitions) each incorporating two parameters, namely tillage and organic amendment. Each block is divided into four elementary plots where two types of soil tillage are combined with two levels of organic amendments. The treatments are defined as follow: T1-MO: Tillage with animal traction + 10 t cow dung manure / ha / year + 100 kg NPK (14-23-14-6S-1B)/ ha + 50 kg urea (46% N); T1: Tillage with animal traction + 100 kg NPK (14-23-14-6S-1B)/ ha + 50 kg urea (46% N); T3-MO: Minimum tillage+ 10 t cow dung manure / ha / year + 100 kg NPK (14-23-14-6S-1B)/ ha + 50 kg urea (46% N); T3: Minimum tillage + 100 kg NPK (14-23-14-6S-1B)/ ha + 50 kg urea (46% N).

Journal of Agricultural Studies
Two other treatments were added to the experiment as reference such as: F: 30-years-old fallow that was served as base and C: Control plot (continuous sorghum without fertilizer) of soil fertility sustainability trial.
This experiment was conducted in pot experiment using soil from the long-term trial with the six treatments cited earlier (T1, T1-MO, T3, T3-MO, C and F). It was conducted in 4 repetitions in pots containing 100 g of soil each and before plant sowing three types of pretreatments was applied to each treatment. The pretreatments were carbon (5 g supply in form of glucose); carbon and nitrogen (0.1 g in form of ammonium sulfate) and no nutrient supply. Two levels of incubation with sorghum and without sorghum were used with the different treatments. Sorghum variety Sariasso 14 was used for the experiment. The duration of the incubation was 4-6 weeks depending on the vegetative stage of plant. Fractionation of phosphorus was done on soil samples before incubation, and one, two and six weeks after incubation from pots without sorghum crop and on the plant material. Plant was irrigated with distilled water to avoid any nutrient supply.
Soil chemical analysis: soil pH (ratio of 1: 2.5) was measured according to Afnor standards, 1981). Soil organic carbon content (mg C kg -1 Soil) was assessed using the Walkley and Black, 1934 method. Soil organic matter and carbon contents were determined by the equation: Where, T = 10 / V '(10 = volume of K2Cr2O7 for white and V' = volume of Mohr salt used for determination of white). T = Mohr salt for titration V = Mohr salt volume for the determination of the sample (ml) PE = soil test sample (g) and

Journal of Agricultural Studies
ISSN 2166-0379 2020, Vol. 8,No. 4 To determine the total nitrogen (N) and potassium (K) contents, soil samples were first hot-mineralized with an H2SO4-Se-H2O2 mixture. Total nitrogen was determined using an automatic colorimeter (Skalar SANplus Segmented Flow Analyzer, Model 4000-02, Holland), while total K was determined by flame photometry. Total P levels were determined by mineralizing soil samples, according to the Kjedhal method, using a concentrated H2SO4 acid solution in the presence of selenium catalyst and H2O2. The total phosphorus contents are then determined in the mineralizers using a SKALAR automatic colorimeter (Segmented flow analyzer, model SANplus 4000-02, Skalar Holland).
Fractionation of phosphorus Hedley et al. (1982) method was used for phosphorus fractionation. The Hedley fractionation recognizes plant-available forms (Resin Pi, Bicarbonate Pi, and Bicarbinate Po) and refractory forms (NaOH Pi, NaOH Po, sonic Pi, sonic Po, HCl Pi, and Residual P) of soil phosphorus. The soil samples were weighed to 4 g and are agitated for 16 hours in 20 ml of distilled water with 2 anionic membranes saturated with bicarbonate. The membranes have an area of 2 cm 2 (1 cm × 2 cm). To release the P set by the membranes, they were removed and agitated in 20 ml of 0.5 M HCl for 30 minutes. The obtained solution was sequentially agitated for 16 h in 20 ml of buffered 0.5 M NaHCO3 and 0.5 M NaOH at pH 8.5. After centrifugation and filtration, inorganic P (P-NaHCO3 and P-NaOH) were determined by acid digestion by autoclaving in 10 ml of H2SO4 and 0.5 g of K2S2O8. The same procedure was used for the determination of P-HCl after sharing the solution in 1.0 M HCl. P-resin was extracted by Acid mineralization in 10 ml of H2SO4 and 0.5 g of K2S2O8.

Statistical analysis
The results were subjected to analysis of variance using Genstat 9 th edition. Significant treatment means of each soil were identified by using the least significant differences (LSD) value at 5 % level of probability for P source, time and incubation.

Results
Soil tillage with soil amendment significantly (p<0001) increased P availability compared to fallow and the control (Table 2). Higher amount of P was observed with T1 (tillage with animal traction + 100 kg NPK (14-23-14-6S-1B) / ha + 50 kg urea (46% N)) for all P sources except from P-NaHCO3 (with sorghum) .The values are ranged from 20.26 mg Kg -1 to 35.24 mg Kg -1 with the incubation of sorghum and from 12.77 mg kg -1 to 32.4 mg kg -1 with no incubation of sorghum. The highest P amount was observed with P-NaOH fraction (35.24 mg Kg -1 ). Phosphorus extracted with NaOH was greater in all cropping systems compared to P-HCl, P-resin and P-NaHCO3 in general. It was also observed that soil incubation has a positive effect on P availability. The results showed that soil planted with sorghum has increased P availability compared to non-incubated soil. The used of organic matter significantly increasing only P-NaHCO3 content by 83 % on tillage with animal traction treatment. Addition of mineral fertilizer significantly improved P different fraction in general. ISSN 2166-0379 2020 P-HCl was increased by 57 to 138 % and P-NaOH increased more than 20 % when mineral fertilizer application is combined with soil tillage. Soil phosphorus availability varied significantly (P<0.001) with different soil management (Table 3). Phosphorus content was high with the used of organic matter in all the treatments. Organic matter application increased P-HCl and P-NaHCO3 by 33 % and 16 % over the control and the fallow practice, respectively. The result also showed low P content with the use of mineral fertilizer compared to the other treatments. Phosphorus availability responses to the type of nutrient application were different among the treatments. The supply of carbon and nitrogen or carbon alone did not significantly affect phosphorus availability for P-HCl, P-NaOH and P-NaHCO3 even though the supply of nutrient increased P availability, generally (Table 4). Only P-resin was significantly (p<0.001) affected by nutrient application. Addition of carbon and nitrogen increased both the control and the fallow practice soils P-resin content by 53 % and 51 %, respectively, compared to the ISSN 2166-0379 2020 no nutrient application treatment. Addition of nutrient did not increase soil P-resin content with tillage. Nutrient application did not significantly increased phosphorus availability when sorghum is not inoculated. Significant effect (P<0.001) was observed only with P-resin and P-NaHCO3 content with sorghum. Phosphorus availability increased until two weeks after carbon and nitrogen or carbon application and decreased until the end of the experiment for both P-resin and P-NaHCO3 content (Figure 1 and 2). The P-resin content did not improve when nutrient is added. The highest amount (26.5 mg Kg -1 ) and the lowest amount (21.7 mg Kg -1 ) of P-resin content after two weeks were observed with no nutrient treatment and carbon treatment, respectively. Carbonate P increase with the used of nitrogen and carbon or carbon and the maximum amounts were obtained two weeks after application. The used of carbon alone improved P-NaHCO3 (24.1 mg Kg -1 ) compared to the combination of nitrogen and carbon (21.1 mg Kg -1 ) after 2 weeks.

Journal of Agricultural Studies
Figure1. Evolution of P-Resin after nitrogen and / or carbon application Figure 2. Evolution of P-NaHCO3 after nitrogen and / or carbon application

Discussion
Phosphorus availability increased (P<0.001) with tillage and application of mineral fertilizer, in general. Soil phoughing with sorghum incubation increased P-NaOH, P-resin and P-HCl, by 37%, 70%, and 273 %, compared to fallow, respectively. Tillage has various physical, chemical and biological effects on soil depending on the appropriateness or otherwise of the methods used. Soil tillage can reduce soil drainage and improve soil structure. This condition can develop better condition for microbial activities for the mineralization of phosphorus. Management practices that improve soil aggregation may therefore have benefits for soil P ISSN 2166-0379 2020 availability (Andrew et al, 2017;Barro, 1997). The use of organic matter together with soil phoughing improved P-NaHCO3 by 83 % unlike the other form of P. Phosphorus derived from NaOH, resin and HCl were greater with the use of mineral fertilizer. This can be explained by the fact that P added from manure tends to become less available to plants in long term (Sample et al., 1980, Lemming et al., 2019. Depending of the status of P fertilizer in soil, manure and mineral fertilizer appear to contribute to different P pools (Griffin et al 2003).

Journal of Agricultural Studies
The use of organic matter improved P-HCl and P-NaHCO3 by 33 % and 16 % over the control and fallow, respectively. These results are in agreement with those reported by Sharpley and Smith (1995) and Shafqat and Pierzynski (2010) who found that continuous application of organic matter significantly increased P-NaHCO3 and P-HCl. The application of organic matter increases soil P solubility, decreases P fixation, and thus improves P availability to plants as reported by Khiari and Parent (2005) and Soma et al., (2018). Soil colloids are also essential for the P adsorption and availability (Dhillon, 2004, Pratap, 2015. Manure application increase soil fertility, especially in the Sudano-Sahelian region where nutrient depleted and weathered soils are typically managed with low input (Oué draogo et al., 2001).
Soil incubation with sorghum positively influenced soil P availability. Lal and Steward (2016) reported that plants and their symbionts directly acidify soil environment by the exudation of organic acids and chelating agents, promoting and make P occluded in secondary minerals available.
Pretreatment of soil with nitrogen and carbon associated with soil management significantly affected P-resin, only. Addition of carbon and nitrogen increased both the control and fallow P-resin by 53 % and 51 %, respectively, compared to no nutrient added.

Conclusion
Long term effect of tillage and soil amendments had significant effect on different soil P fraction. Reduced tillage in conjunction with organic and mineral amendment improved soil phosphorus availability by 70 to 273 % compared to fallow and soil under continous cultivation. The increase occurred mainly when soil is incubated with sorghum. Addition of carbon and nitrogen improved soil P availability under soil incubated with sorghum. Reduced tillage with organic and mineral fertilizers amendments can be used to increase P availability under sorghum cropping system.