Integrated Soil Fertility Management to Improve Forage Yield of Corn

One of the most limiting factors in livestock development and animal feed production in Iran is the production of poor-quality and low-yielding forages (Keshavarz Afshar et al., 2014). In most of the agricultural soils in the country, particularly in arid and semi-arid regions, yield of forage crops, especially, corn is low due to limited soil organic matter and low soil nitrogen levels. The problem should be resolved by proper utilization of nitrogenous fertilizers. However, these fertilizers are often mismanaged (Jahanzad et al., 2015). In this regard, pre-sowing treatments can be employed to retain and add nitrogen and carbon to agricultural systems, and to control soil erosion. Grasses, legumes and brassicas are three major plant groups that can be used as green manure. The present study was conducted to evaluate the effect of the pre-sowing treatments and nitrogen levels on various characteristics of silage corn.
This research was performed during the 2013-14 growing season at the Agricultural Research Station of Islamic Azad University of Karaj, Iran. The experiment split plot based on a randomized complete block design with four replications. Main factors were four pre-sowing treatments including (Fallow as control, Perko PVH and Buko as green manure and livestock manure) and sub factors were three levels of nitrogen from urea (120 and 240 and 360 kg ha-1). Perko PVH and Buko belong to Brassicaceae family that if incorporated to the soil, they can increase soil organic matter content. Corn (SC 704) was planted by pneumatic machine at 12 plants m-2. At the end of the season, qualitative and quantitative characteristics, including fresh forage yield, dry forage yield, plant height, dry matter digestibility yield, dry matter intake, relative feed value and protein content were determined.
The results of variance analysis indicated that the effect of pre-sowing treatments and different nitrogen levels on fresh forage yield, dry forage yield, plant height, dry matter intake and dry matter digestibility was significant (P≤0.01) (Table 4). The highest digestible dry matter (15.43 ton ha-1) was observed in Perko PVH pre-sowing treatment and the lowest digestible dry matter (8.93 ton ha-1) was detected when the corn plant was treated by the livestock manure. Pre-sowing treatments of Perko PVH and Buko increased digestible dry matter by 46.39 and 26.09 % relative to the control treatment (fallow), respectively. Bahrani et al. (2007) reported that green manure had a significant positive effect on corn dry yield and this yield increase was attributable to a rise in total soil nitrogen content, which resulted from returning the above-ground organs of pre-sown plant to soil and rapid decomposition of its aerial parts. Among nitrogen rates, the maximum digestible dry matter (13.17 and 12.80 ton ha-1) were recorded with the application of 240 and 360 kg N ha-1, respectively. The interaction effect of pre-sowing treatments and nitrogen levels was significant on relative feed value and protein content (P≤0.05). The greatest protein content (2537.6 kg ha-1) was obtained under the pre-sowing treatment of Perko PVH along with nitrogen application rate of 240 kg ha-1. The least protein content (800.6 kg ha-1) was associated with livestock treatment and 120 kg N ha-1 rate. In addition, the results of the interaction effects indicated that pre-sowing treatments of Perko PVH and Buko and nitrogen rate of 120 kg ha-1 fell in the same statistical group with fallow control treatment and 360 kg N ha-1 rate, suggesting that as much as 240 kg ha-1 of nitrogen could be saved using the brassica green manure.
According to the results of this research, the combined use of organic fertilizer and nitrogen fertilizer enhanced the quantitative and qualitative characteristics of silage corn. Hence, using the organic fertilizers led to a considerable reduction in the chemical fertilizer consumption, which can consequently decrease the detrimental environmental impacts of nitrogen fertilizers. Since the highest digestible dry matter was observed in Perko PVH pre-sowing treatment and nitrogen rate of 240 kg urea ha-1, this treatment is recommended and introduced as a superior treatment in this experiment.