The effect of integrated soil fertility management on weed population dynamics and corn silage yield

Nowadays, environmental pollution, by herbicides and chemical fertilizer is one of the most important human issues. The application of conventional tillage and herbicide methods is costly and increase the risk of soil erosion and have negative effects on soil structure and crop yield in the long time. The present study was conducted to evaluate the effect of integrated soil fertility management on weed population dynamics and corn silage yield.
This research was performed during growing season 2013-14 at the Agricultural Research Station of Islamic Azad University of Karaj, Iran. The experiment was conducted as a split plot based on a randomized complete block design with four replications. Main factors included non-chemical soil fertility management treatments at 4 levels (Fallow, Manure, Perko PVH and Buko as green manure) and sub factors also included application of nitrogen fertilizer at 3 levels (120 and 240 and 360 kg ha-1, utilized urea source). Perko PVH and Buko belong to Brassicaceae family. Corn Seeds (sc 704) were planted at density of 12 plants m-2. Sampling of weeds after planting corn was conducted in primary stage of the corn canopy closure. The collected plant samples were dried in oven at 70°C for 48 hours and then were weighted. In this experiment, weed species diversity indices including Shannon-Weiner index, Margalef index and Simpson dominance index were investigated. At the end of the season, forage yield was determined. The data analyses were conducted with SAS (Version 9.1.3), and means were compared by LSD test at probability level of 5%.
Variation analyses showed that the effect of non-chemical soil fertility management treatments on total weed biomass and forage yield of maize was significant (P≤0.01). The highest and lowest forage yield were obtained at Perko PVH Pre-sowing treatments (78.23 ton ha-1) and the manure treatment (63.71 ton ha-1), respectively. The highest total weed biomass was observed at manure and fallow Pre-sowing treatments (380.03 and 364.79 g m-2) and the least total biomass was for the Buko and Perko PVH treatment (140.48 and 154.67 g m-2).The effect of nitrogen levels on total weed biomass was non-significant. There was a significant difference (P≤0.01) between nitrogen levels on forage yield. Interaction effect of pre-sowing treatments and nitrogen levels was significant on lambsquarter biomass, pigweed biomass, total weed density, lambsquarter density and pigweed density (P≤0.01 and P≤0.05); The lowest amount of these mentioned traits was obtained from Buko pre-sowing treatment by using 120 kg ha-1 nitrogen. The highest total weed density (39.25 plant m-2) was observed in fallow by using 240 kg N ha-1 and the lowest density (16.5 plant m-2) was obtained from the Buko treatment by using 120 kg N ha-1. The effect of non-chemical soil fertility management on weed species diversity was significant (P≤0.01). The highest weed species diversity were observed at fallow and manure treatments and the least diversity were for the Buko and Perko PVH treatments.
According to the results of this research, the combined usage of organic fertilizer with chemical nitrogen fertilizer enhances the forage yield of silage corn by reduced weed biomass, density and species diversity. Therefore, by application of the organic fertilizers could be reduced the environmental impacts meanwhile considerably reducing the use of chemical nitrogen fertilizer. In general can be said that by cultivation the pre-sowing crops and return their remnants to the soil leads to soil fertility and consequently improve the quantitative traits of corn silage and can be considered as one of the ways to achieve sustainable agriculture