Abstract:

At present， there is a shortage of seasonal green feed in Ningxia， despite the excessive application of nitrogen fertilizer. This situation is indicative of an imbalance between grassland and livestock development in this region. To address this issue， we explored the suitability of a multiple cropping model of forage triticale-silage maize for autumn sowing with different levels of nitrogen fertilizer applied annually. The experiment had a single factor randomized block design. Triticale and silage maize were sown in autumn and subjected to five different fertilization treatments， namely N₁ （0 kg?ha^-1， CK）， N₂ （150 kg?ha^-1）， N₃ （300 kg?ha^-1）， N₄ （450 kg?ha^-1）， and N₅ （600 kg?ha^-1）. The effects of these fertilization treatments on the performance， nutrient quality， and nitrogen-use efficiency of the multiple cropping system were determined. The results showed that the annual nitrogen application rate had significant effects on the plant height， stem diameter， chlorophyll content （measured as SPAD value）， dry matter accumulation， yield， and quality of triticale and maize in the multiple cropping system. The growth indexes and dry matter accumulation of both triticale and maize gradually increased during the growth period， reaching peak values in triticale at the flowering stage， and in maize at the filling stage. As the nitrogen application rate increased， the growth indexes and dry matter accumulation showed a trend of first increasing and then decreasing. The highest values of growth indexes and dry matter were in the N₄ treatment. In terms of overall performance， the treatments were ranked as follows： N₄>N₅>N₃>N₂>N₁. The yield of fresh grass in the multiple cropping system increased gradually as the annual nitrogen application rate increased. The maximum yield in the N₅ treatment was 156.8 t?ha^-1， which was 61.3% higher than that in the control. The hay yield in the N₄ treatment was 39.1 t?ha^-1， which was 45.9% higher than that in the control. The recovery of applied N in forage was 31.9%， 30.2%， 27.3% and 18.5% for N₂， N₃， N₄ and N₅ treatments， respectively. The nitrogen application rate significantly affected the nutritional quality of forage， with the highest values in the N₄ treatment. The contents of crude protein （CP） and crude fat in the triticale forage， corn silage， and the whole cropping system were significantly higher in the N₄ treatment than in the other treatments. The CP contents in triticale forage， corn silage， and the whole cropping system were 33.7%， 11.2%， and 31.8% higher， respectively， in the N₄ treatment than in the control， but the acid detergent fiber and neutral detergent fiber contents were significantly reduced. The nutrient indexes had optimal values in the N₄ treatment. Fertilizer yield response and economic response equations were derived and from these the maximum yield response was predicted to occur at an N application rate of 560 kg?ha^-1 and the maximum economic response at 584 kg?ha^-1. These results provide data for the theoretical optimization of forage yield in multiple cropping cultivation systems.

Key words: annual optimization of nitrogen fertilizer, irrigation area, forage grass, multiple cropping system, productivity