Analysis of variance shows that the cumulative yield responded to all factors in the first year. Table 3 indicates that interaction between compost type and compost rate was also significant (p ≤ 0.01). In this experiment, tomato responded to the interaction of all factors at both the experimental years. Compost is a good resource to release nutrients during growing season (Abbasi et al. 2002), and to ensure a sustainable and healthy production of tomato. Erhart et al. (2005) reported an increase of yield up to 10% for compost treatments as compared to the control in wheat, barley, and potato for 10 years. They also reported that yield response to compost amendment was increased over time. Furthermore, Mehdizadeh et al. (2013) have also illustrated that tomato fruit yield has been increased by 94% in comparison with control.
In 2014, treatments with CM produced significantly (p ≤ 0.01) more tomatoes (103 t ha−1) than the other fertilizers; however, in the second year, the differences were not significant (Table 4). Higher yield production in treatments with CM could be due to higher mineralization of organic matter in CM, which can provide enough nutritional release for the plant (Angin et al. 2017). Table 4 shows that higher compost rates did not produce a higher amount of tomatoes in the first year. Yield productions in treatments with a medium compost rate were significantly higher (98 t ha−1) than treatments with high compost rate (88 t ha−1). Reduction of yield at a higher level of soil conditioner application might be linked to salinity of the soil by compost and organic fertilizer application, while treatments with VC and lower EC showed less reduction compared to other composts (Tables 2, 5). This reduction is higher at SMC with row application and HC with broad application, which can be due to the incorporation of salt into the soil. Similar results were reported by Angin et al. (2017). However, applying nutrients have different effects on soil microbes and plant communities. Studies show that N fertilizers can suppress soil microorganisms (Geisseler and Scow 2014). In the second year, there was no significant difference between treatments with different compost rates.
In the first year of the experiment, treatments with SMC at a medium rate with broadcast application produced the maximum amount of tomato (120 t ha−1), which was not significantly different with treatments of the same compost in low rate and with row placement (Table 6). This could be explained by the availability of compost for root area in row application. Besides, SMC in higher rates produced less tomato in row application, which might be due to high salinity around the root area (Table 2). All soil conditioners showed a high amount of tomato production with the medium rate and broad application with the exception of VC (Table 5). This result is understandable because VC has been applied 14 t ha−1 less than the other composts due to its local consumption by farmers. Table 5 demonstrates that using CM does not necessarily produce higher yield. A study by Mehdizadeh et al. (2013) published a similar result with regard to the application of HC and CM in tomato production. In their experiment, with the application of 20 t ha−1 for HC and CM, 33 and 27 t ha−1 of tomato were produced, respectively.
In the second year of experimentation, the yield was significantly lower, which could be due to transplant or weather conditions in transplanting period. Besides, C:N ratio has decreased in the second year (Table 1) though organic matter decomposition will increase, which might cause a reduction in the supply of soil organic matter (Reicosky et al. 1995).The differences between treatments (Table 5) during the second year were not as large as compared to the first year. This could be a result of the homogeneity of the soil or enhancement of soil quality after 1 year of plantation with organic soil conditioners (Table 1). In the second year, CM treatment with high rate and row placement produced a higher amount of yield (69 t ha−1), which did not differ significantly with any other composts using the same rate and placement method. On the contrary, tomato yield decreased in treatments with CM more than the other soil conditioners. However, the differences between these diminished treatments in the second year are not significant. This indicates that composts have a better effect over time in comparison with CM. Studies showed that we cannot expect a big response on plant growth in a short time because compost is not a rich source for N availability, but there is evidence that compost is a suitable amendment for long-term improvement of soil organic matter (Abbasi et al. 2002; von Fragstein and Schmidt 1999). Mehdizadeh et al. (2013) showed that HC had a significantly better effect as compared to CM, poultry manure, and sheep manure, in cumulative tomato yield and the number of tomato per plant. In the proposed study, there was a reduction on tomato yield in the second year due to warm weather during the transplanting phase. Flowering is an important phase in plant development as the plants are vulnerable to environmental stress. It is the stage of plant development that determines when vegetables are ripe for harvest (Wien 1997). This amount did not show any significant difference with other soil conditioners in different application rates. The analysis of variance between 2 years of experiment was not significantly different (p ≤ 0.05) for yield production (Table 3).
Vermicomposting had less effect on the production compared to other fertilizers in this experiment; however, the amount of VC applied was almost one-third of the amount of other fertilizers, based on the local consumption by farmers. For this reason, VC can be considered as a suitable fertilizer and soil conditioner for tomato production when applied at a relatively higher rate (9 t ha−1), as it could have significantly increased tomato production during the second year. Yang et al. (2015) reported that tomato yield with VC amendment had greater yield in comparison with horse and chicken composts, and also chemical fertilizer under medium irrigation systems. Compared with the traditional composting process, VC has a higher degree of humification (Jeyabal and Kuppuswamy 2001). Special substances in VC, such as plant growth regulators that are biologically active, and also, the existence of functional microorganisms due to higher soil microbial biomass are the reasons that separate VC from other composts (Arancon et al. 2003; Amossé et al. 2013; Yang et al. 2015). Studies indicate that VC had a positive effect on sugar content and vitamin C level in tomato fruits compared with other fertilizers (Yang et al. 2015).
Analysis of variances for plant DM illustrates that different organic fertilizers as well as the methods of application differed markedly between treatments in the first year of production. Whereas in the second year, only different fertilizer type showed significant difference, but compost rate and placement method have no significance. In both the years, the interaction effect between factors shows significant differences between treatments (Table 6).
In the first year, treatments with CM produced more DM (2.4 t ha−1) than treatments with HC and SMC while their differences with VC treatments (2.1 t ha−1) were not significant. However, in the second year, treatments with VC produced markedly lower DM (2.8 t ha−1) than treatments with CM (3.6 t ha−1). Despite that the yield production decreased in the second year, the DM concentration had increased in the same year (Table 7). Studies show that DM content has a direct correlation with the improvement of the nutritional status of soil and the soil structure (Azarmi et al. 2008; Gutiérrez-Miceli et al. 2007).
Table 8 indicates that treatment with CM in high rate and with broad application created the largest DM (3.1 t ha−1) in 2014. This amount did not differ compared with other treatments with CM, different rates, and different application methods. This finding is relevant to that of Pellejero et al. (2017) on lettuce, in which treatments with higher compost dosage showed higher root dry weight as well. This also included treatments with other fertilizers with high rate and broadcast application. Based on these results, treatments with SMC in high rate and row placement, as well as HC in low rate and row placement, showed the lowest DM content (1.2 t ha−1 and 1.2 t ha−1, respectively) in 2014. On the contrary, treatment with CM in low rate and broadcast application had the highest DM (5.8 t ha−1) in the second year, and this amount did not differ significantly with treatments of CM and SMC in medium rate and HC in high rate, all with broadcast application and treatment of SMC in high rate and row placement (3.6, 3.6, 3.9, and 3.5 t ha−1, respectively). As the result indicates in Tables 6 and 8, DM content was significantly higher in the second year of experiment owing to the availability of compost around the plot area. The analysis of variance between 2 years of experiment was not significantly different (p ≤ 0.05) for DM production (Table 6).