The field experiment conducted with the fixed plots tested in Dongyang Agricultural Experiment Station of Shanxi Academy of Agricultural Sciences in 2011 and 2012 was carried out to investigate the effects of nitrogen, phosphorus, potassium on nutrient uptake, yield and quality of grain sorghum [Sorghum bicolor (L.) Moench] cv. Jinza 23 under the sorghum-maize rotation cropping system in 2013. The experiment included five treatments with fertilizers NPK, PK, NK, NP, and CK (without fertilization) with three replicates in a completely randomized block design. The experimental results showed that at 76 days after emergence, the sorghum maximum leaf area of NPK, PK, NP, and NK treatments increased by 18.7%, 4.1%, 17.9%, and 16.6%，respectively; and the total functional leaf area per plant increased by 54.1%, 18.4%, 47.4%, and 48.2% respectively compared with CK treatment. Fertilization treatment had significantly influences on leaf biomass throughout growth period. Since 121 days after emergence, there were significant effects of different fertilization treatments on the stem biomass. Comparison with CK treatment, the sorghum grain yield of NPK, PK, NK, and NP treatments increased by 93.8%, 35.5%, 91.2%, and 78.1% respectively. The N contents in leaves of CK and PK treatments were significantly lower than those of NPK, NK, and NP treatments at 100 days after emergence. The P contents in leaves of CK and NK treatments decreased significantly as well. At 149 days after emergence, CK significantly reduced the N content in grains. The treatments of CK, PK, and NP increased the amylose contents in grains, while decreased the amylopectin content, resulting in an increased amylose/amylopectin ratio accordingly. The protein content in applying N fertilizer treatments of NPK, NP and NK was significantly higher than that of CK and PK. The grain protein content in NPK treatment was 73.9% and 40.3%, more than that in CK and PK treatments respectively. The grain tannin content of NPK treatment was the highest among treatments. The tannin content of NPK treatment increased by 15.6% and 22.7% respectively, compared with that of CK and PK treatments. These results demonstrated that no N application or no fertilization significantly reduces the growth, dry matte accumulation, grain yield, N and P uptake, and the concentrations of amylase, protein and tannin in grains of grain sorghum. The effect of no N application or no fertilization on sorghum is significantly greater than that of no P or K application. Balanced fertilization with N, P and K is beneficial to increase grain yield and improve grain quality of grain sorghum.
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