| This research was aimed at the problems in citrus nutrition management, implemented a systematic study on soil and plant nutrients status of citrus orchards in Hubei Province which is one of the main citrus produce region in China. The problems include: citrus nutrition management, nutrients diagnose technology and balanced fertilization for high yield, quality and benefit through orchards investigation, field trials and lab analysis. The main results were summarized as follows:1. The study made an investigation on fertilization situation on citrus in the provincial main citrus produce regions and found out the main problems in citrus nutrition management. The orchards with nitrogen (N), phosphorus (P) and potassium (K) fertilization in both inorganic (chemical) fertilizer and organic manure were 91.9 per cent, 86.5 per cent and 68.5 per cent, respectively. The average N, P2O5 and K2O application rates on citrus were 0.38 kg tree-1, 0.18 kg tree-1 and 0.13 kg tree-1 yearly, respectively. Most of the total fertilizer amount was from chemical fertilizer. The ratio of N: P2O5: K2O was 1: 0.47: 0.34 and the chemical fertilizer N: P2O5: K2O was 1: 0.43: 0.27. The main problems of citrus nutrition management are: (1) Difference of fertilizer application rate was very large among the different regions and orchards and different years, which led to big yield change in different orchards and years. (2) Generally, fertilizer applied rates are too low which can't meet citrus growth and fruiting demand. (3) The ratio of N: P2O5: K2O was unbalanced, especially K rate was too low. (4) Both of organic manure application rate and its proportion in total nutrients are too low. (5) The summer fertilizer rate is relative low which can't satisfy citrus mass demand in the fruit enlarge period.2. The research raveled the status of soil and plant macro-/secondary/micro-nutrients content in the citrus orchards. There were 59.4 per cent of the orchards showed that soil organic matter content in low level. And the orchards with available soil N, P, K, Ca, Mg, Fe, Mn, Cu, Zn, Mo and B deficient were accounted by 78.3%, 44.1%, 77.6%, 39.1%, 37.1%, 34.3%, 20.3%, 16.8%, 63.6%, 35.5% and 77.4%, respectively. By contraries, some orchards showed Ca, Mg, Fe, Mn, Cu or Mo content excessive problems. The proportion of citrus leaf nutrients deficiency orchards occupied 42.7% for N, 38.3% for P, 65.5% for K, 24.2% for Ca, 44.5 % for Mg, 36.7% for S, 33.9% for Fe, 33.6% for Mn, 6.6% for Cu, 83.6% for Zn, 44.6% for Mo and 9.4% for B, respectively.3. The research revealed the law of citrus orchards diversification. There was significant change for soil nutrients among regions and in different soil layers.4. This research studied the leaf and fruit nutrients content status for different citrus varieties and established a nutrients content database for Hubei citrus. The average nutrients content of citrus leaf order from high to low was Ca-3.28%, N-2.77%, K-0.82%, Mg-0.44%, P-0.15%, S-0.126%, Fe-109.1 mg/kg, B-50.9 mg/kg, Mn-34.0 mg/kg, Zn-18.6 mg/kg, Cu-5.7 mg/kg, Mo-0.586 mg/kg. Compared the leaf nutrients content in different citrus varieties, the highest content of N, K, Ca, Fe, Mn and Znwas found in navel orange leaf, the highest content of Mg and S was found in 'Ponkan' mandarin leaf, and the highest content of P, Cu, Mo and B was found in Satsuma mandarin. The difference of fruit mineral nutrients content of the main citrus varieties was also big. The highest fruit nutrient content of P, K, Ca, Mn, Zn and Mo was found in navel orange, the highest content of Mg, Fe and B was found in 'Ponkan' mandarin, and the highest of S and Cu content was found in Satsuma mandarin. Some fruit quality indexes of the main citrus varieties in Hubei were: for single fruit weight-navel orange > satsuma mandarin > 'ponkan' mandarin, for edible percentage-satsuma mandarin > 'ponkan' mandarin > navel orange, for sugar content-navel orange > 'ponkan' mandarin > satsuma mandarin, for ratio of sugar to acid-'ponkan' mandarin > navel orange > sats...
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