Allelopathic effects of plant residues is an important research avenue regarding optimization of rotation systems in agronomy. The aim of this study was to investigate the allelopathic effects of four plant residues, namely, black cumin, dragonhead, dill, and soybean on the germination and growth of wheat (Triticum aestivum) in different cropping systems. Results showed that application of organic manure for previous crops reduced the residue phytotoxicity and consequently alleviated the adverse effect of plant residues on the leaf area, length, and dry weight of the wheat root, affecting chlorophyll a, chlorophyll b, and carotenoids of wheat seedling leaves. In the presence of plant residue, the length and dry weight of the wheat roots were more negatively affected in comparison with shoots. The greatest allelopathic inhibition was observed for the wheat cultivated in the residue of black cumin, but soybean, dill, and dragonhead residues also potentially showed inhibition effects. It can be concluded that agroecosystems in which autumn wheat is in the rotation should be avoided where there are residues of soybean, black cumin, dragonhead, and dill. The tillage system in the same condition may not be agronomically suitable because of the allelopathic effects of previous crops. Manuscript profile

Growers often apply high amounts of chemical fertilizers for vegetable production and this application contributes to concerns about nitrate levels in food. An experiment was conducted to investigate soil N amendment effects for reducing the nitrate accumulation and improving the quality of fresh purslane (Portulaca oleracea L.). Treatments included four levels of animal manure as follows, N-based broiler litter (T1), P-based broiler litter (T2), N-based cattle manure (T3), P-based cattle manure + urea (T4), four levels of chemical fertilizer equivalent to organic treatments, and a T0 (no fertilizer and manure). Results showed that nitrate levels of broiler litter and cattle manure treatments were significantly lower than those of chemical fertilizer treatments. The highest level of nitrate in the first harvest was recorded in the T7 treatment and higher levels were recorded in T5 and T7 treatments in the second harvest. In the first harvest, T1 and T2 treatments had higher appearance quality but in the second harvest, appearance quality of T2 and T5 treatments showed a significant increase compared to the other treatments. It is concluded that organic manure application results in higher quality as compared with the inorganic fertilizer andreduces nitrate accumulation in fresh purslane. Manuscript profile