Effect of Compost and Synthetic Fertilizer on Soil Fertility, Yield and Nitrogen Use Efficiency of Broccoli Crop in Arid Region of Morocco

Broccoli (Brassica oleracea var. italica) is a crucifer family (Yoldas et al., 2008). like other crucifers, broccoli has a potential anticancer property because it’s a rich source of antioxidant, vitamin C, K and E and beta-carotene (Nagraj et al., 2020).      
 
In Morocco, broccoli has become a very popular vegetable for consumers. The main difficulty with broccoli is related to high nitrogen needs. Indeed, for a yield of 10 to 20 t/ha, the crop needs vary from 150-200 to 350-450 kg ha^-1 (Thompson et al., 2002; Silva et al., 2019).
 
Farmers lack data about the performance of organic fertilizers and nitrogen use efficiency (NUE). NUE is defined as the fraction of nitrogen applied which is absorbed and used by plant (Baligar and Fageria, 2015). Improving a plant’s ability to use nitrogen is a key factor in improving yields and chemical soil parameters especially for organic fertilizers where NUE is not available. This parameter was investigated by many researchers (Doberman, 2007; Fageria et al., 2008; Sharma et al., 2017).
 
The need for more research in this area is primary at this time (Singh et al., 2003). Cereals have been extensively investigated (Yimer et al., 2022; Agrama, 2006 ; Mandolino et al., 2018). For vegetable crops, there is a lack of studies on growth and nitrogen uptake for vegetable crops, of which broccoli is one.
 
In order to optimize nitrogen fertilization, the main objective of this work was to study nitrogen use efficiency of compost and synthetic fertilizer at different doses in broccoli crop.
 

The present study was carried out at the horticultural complex of Agadir-Agronomy and Veterinary Institute Hassan II (30°35' N,-9°47' E, 3 m.a.s.l)  in the Souss Massa region in the south of Morocco. The climate was semi-arid. The soil of the plot is sandy-loam type. The initial soil analysis before planting and the irrigation water analysis are presented in Table 1 and 2. The experiment was conducted in a randomized block design with three repetitions per treatment. The treatments studied were as follows: TC₈ t/ha: compost, 8 t/ha (equivalent 200 kgN /ha), TC₁₂ t/ha: compost:12 t/ha (equivalent 300 kg N /ha), T_SYN: Synthetic chemical fertilizer on fertigation (200 kg N/ha), TC_+SYN: 50% compost, 4 t/ha+50% Synthetic fertilizer (equivalent 200kgN/ha) and T0: control 50% of fertilizers quantities were applied before planting and 50% were applied at a flowering period near the roots at 50 days after planting (DAP). The synthetic chemical fertilizer was applied by fertigation at a rate of 200 kg N /ha. The compost used in this experiment was rich in organic matter (55%) with a NPK composition of 2.5-3-2.5 and a C/N ratio of 15. The experimental unit was 8.22 m² each containing 24 plants. The planting was on 20/03/2015 after tillage with a cover crop. The variety used was Italica. The planting was done with a spacing of 40 cm between two plants and 60 cm between ridges. The plants were irrigated by drip irrigation. The cultivation cycle was 75 days. The impact of fertilizer on soil fertility was determined by soil analysis. Three samples were taken: before crop planting, 50 days after planting and 75 days after planting. For each fertilization program, three soil samples were taken at random. Analyses were performed on: Soil pH was determined in a 1:2.5 soil/water suspension (Jackson, 1973). Soil Organic matter: S OM was determined by the method of Walkley and Black (1934), N content by the method of Kjeldahl. Samples of three plants from each experimental plot were taken at 30 days from the date of transplanting to determine main head yield. Total nitrogen uptake was determined by the Kjeldahl method. The yield and nitrogen uptake parameters are used to calculate agronomic efficiency (AE), agro-physiological efficiency (APE) and Apparent recovery efficiency (ARE) according to the formulas mentioned in the table (Table 3) (Baligar et al., 2001; Doberman, 2005).






 
The data were analyzed using STATISTICA software (version 6.0). The statistical model adopted was one-way analysis of variance (ANOVA). Duncan’s test was used to determine significant differences (α=0.05).
 

Main head yield of broccoli
 
The main head yield had the highest significant difference (p value 0.001) values for the treatment TC_+SYN followed by T_SYN (13.50 t/ha) with a high followed by TC₈ t/ha and TC₁₂ t/ha with 12.92 and 12.75 t/ha respectively. There was no significant difference between TC₈ t/ha and TC₁₂ t/ha.  The control recorded the lowest yield with 9.04 t/ha. (Table 4). In our experiment, broccoli produced its maximum yield when the nitrogen fertilizer application rate was 200 kg N ha^-1. The same result was observed in California, it was between 200-250 kg N ha^-1(Kim et al., 2021). Other research in brazil has shown that the optimum content of N ranges from 211 to 373 kg ha^-1 N (Oliveira et al., 2016; Silva et al., 2019).


 
Available soil nutrients
 
pH decreased throughout the crop cycle for all treatments. This decrease was -7.14% for TC₁₂ t/ha (Table 5). The decrease in soil pH with compost may be due to the increase of nitrogen in the soil by microorganisms in the form of NH4+ soil ammonium (Zhu et al., 2016). NH4+ is the form of N taken up by the plant, so the plant releases H+ which leads to a decrease in soil pH (Hammad et al., 2020). Regarding Electrical conductivity, an increase was observed between 50 and 75 DAP for all treatments (Table 5). The highest values at 75 DAP were observed in the compost TC₁₂ t/ha and T_SYN with 2.34 and 2.25 mS/cm respectively. No significant difference was observed between treatments. The possible explanation for the increase in EC may be due to the large amounts of soluble salts and HCO₃ contained in the compost and the decrease of pH in the soil (Abdrabbo et al., 2015).


 
Organic matter increased significantly in all plant’s growth stages. Indeed. It increased by 138% and 105% for TC₁₂ t/ha and TC₈ t/ha respectively. The results are in conformity with (Azuka and Idu., 2021) how found that organic manure improve soil organic matter (Table 5). At 50 DAP, the highest total soil N content was observed for T_SYN and TC_+SYN with 287.6 kg/ha and 267.2 kg/ha respectively (Table 5). Then, the values decreased to 75 DAP. Statistical analysis revealed significant differences between different treatments tested. The evolution of the total nitrogen content of the soil was influenced by the type of fertilizer. The values dropped at the end of broccoli cycle, which was explained by the high nitrogen requirements of broccoli (Purakayastha et al., 2015).
 
N uptake and nitrogen use efficiency
 
Total plant N uptake is presented in Table 6. N content for broccoli was 273 kg/ha for T_SYN followed by TC_+SYN, TC₈t/ha and TC₁₂t/ha with 266 kg/ha, 244 kg/ha and 234 kg/ha respectively. The control had the lowest N content with 90 kg/ha (Table 6).


 
Agronomic efficiency (AE) was significantly affected by fertilizer type (p<0.005). The highest values were recorded by TC_+SYN and T_SYN: about 22 kg/kg (Table 6). The agronomic efficiency for the synthetic fertilizer was higher compared to compost alone which was in agreement with the results of Musyoka et al. (2017) for the cabbage crop, agronomic efficiency of compost 20t/ha gave :14 kg/kg and 20.8kg/kg for the conventional treatment. High nitrogen input in TC₁₂t/ha decreased AE. This result was in agreement with (Ren et al., 2022). A high correlation (r = 0.97; p<0.01) was observed between AE and yield of broccoli (Fig 1) (Ren et al., 2022).


 
Agrophysical efficiency (APE) varied from 24.37 to 25.79 kg/kg for T_SYN and TC_+SYN respectively (Table 6). There was a significant difference between compost doses. This result is in agreement with Fageria et al. (2014) who found that N rate affects significantly APE.
 
For apparent recovery efficiency (ARE), which represents the quantity of N uptake per unit of N applied, the values varied from 48% for T C12t/ha, 77% for TC₈t/ha ,88% for TC_+SYN to 91% for T_SYN. The ANOVA analysis showed significant variations between treatments. The highest value was observed with TC_+SYN et T_SYN (Table 6). The use of compost and synthetic fertilizers significantly increased N use efficiency (Plaza-Bonilla et al., 2021; Widnyana et al., 2021). Which it depends on several parameters: soil type, fertilizer, amount applied and climatic conditions (Fageria et al., 2014). Reduces the amount of mineral nitrogen provided by 50% (Zhang et al., 2021).
 

This study showed the importance of organic fertilization for the organic broccoli production and their impact on soil fertility and nitrogen use efficiency. Using compost with synthetic fertilizer achieved the highest yield and improved growth parameters. The use of 300 kgN/ha dose of compost decreased the main head yield, agronomic efficiency and nitrogen use efficiency. The combination of compost with synthetic fertilizer at 200 kg N/ha achieved satisfactory and efficiently results that are similar or superior to those with synthetic fertilizer alone.