China is the largest regional tea grower occupying almost 900'000 ha or about 38 % of the global area but producing only 620'000 t or 23 % of the world harvest (mean of 1995-97; FAO PYB 1997). The mean yield of 697 kg/ha is considerably below the global average of 1156 kg/ha and less than half of what is yielded on the Indian subcontinent (1614 kg/ha)(figure 1).

Figure 1: Regional tea production mean 1995-1997
area '000 ha	production '000t
China Indian SC EAsia EAfrica others

Imbalance in fertilization seems to be one of the reasons for the rather low yield. Dr. R. Härdter, IPI Coordinator for China and his colleagues showed with their studies on "Nutrient cycling in tea" that for instance farmers in Xingchang apply 573 kg/ha N but only 64 kg/ha K₂O, a NK ratio of 1:0.11 (figure 2). The NK ratio in Hangzhou improved slightly to 1:0.20 because K use increased to 105 kg/ha K₂O together with 529 kg/ha N. In Anqi farmers apply 116 kg/ha K₂O with 439 kg/ha N, which results in a NK ratio of 1:0.26. P use in all cases is almost similar to K. In context with the NK ratio in fertilizer use, it should be reminded that for each kg of N the equivalent of 0.47 kg/ha K₂O is removed by the harvested leaves, i.e. a NK ratio of 1:0.47 in crop removal. Soil K mining can be assumed under these conditions.

Figure 2: Source of nutrients in tea fertilization selected provinces in China
N:P2O5:K2O 1:0.13:0.11	N:P2O5:K2O 1:0.20:0.20	N:P2O5:K2O 1:0.25:0.26

The major source of K in Xingchang is organic manure. Farmers in Hangzhou use primarily compound fertilizers and in Anqi straight potash to apply potassium. It is interesting to note, that the NK ratio in fertilizer use improves with the use of mineral fertilizers, especially of straight potash. Obviously the K content of organic manure is too low to counterbalance N, the resulting NK ratio is comparably wide (figure 2).

The working group also conducted a range of studies in yield physiology on the following subjects:

• The interaction between soil water regime and potassium availability on the growth of tea by Jianyun Ruan, Xun Wu and R. Härdter, published in Commun. Soil Sci. Plant Anal., 28 (1&2), 89-98 (1997)

  The abstract says: "… tea grown in China often suffers from severe seasonal drought in the summer causing drastic effects on productivity. In a field trial, …summer tea yields of 1994 (dry year) increased significantly at K2 (300 kg/ha K₂O) compared to K1 (150 kg/ha K₂O). In contrast, only marginal effects were observed … in years with adequate water availability … achieving maximum tea yields already at K1. In an additional pot experiment … the study indicates that under moisture stress, increased survival, improved dry matter production and yields of tea plants were due to improved K bioavailability following K application …".

• Effect of potassium, magnesium and sulphur applied in different forms of fertilisers on free amino acid content in leaves of tea (Camellia sinensi L) by Jianyun Ruan, Xun Wu, Yong Ye and R. Härdter, published in J Sci Food Agric, 76, 389-396 (1998)

  "…Free amino acids in tea leaves are important constituents that considerably influence the quality of tea, especially green tea. … Biomass production and the free amino acid contents in tea leaves increased considerably following the application of K and Mg. … A comparison between K₂CO₃ vs K₂SO₄ and MgO vs MgSO₄ revealed significantly higher amino acid contents in tea leaves when both K and Mg were applied in sulphate form. … A pot experiment using KCl and K₂SO₄ … to compare the two commercially available K fertilisers … showed no difference on biomass production … , however KCl tentatively depressed nitrate reductase activity and hence the accumulation of free amino acids, K₂SO₄ significantly increased the contents of these quality promoting constituents of tea leaves …".

• Effects of potassium and magnesium nutrition on the quality components of different types of tea by Jianyun Ruan, Xun Wu and R. Härdter, published in J Sci Food Agric 79, 47-52 (1999).

  "… In field experiments, the effects of K and Mg nutrition on the quality components of … black tea, oolong tea and green tea were studied. The results show that K and Mg … increased the contents of free amino acids and caffeine of the various tea types .… The content of polyphenols … theaflavins and thearubigins in black tea were also increased by K application. Flavour compounds in brewed oolong tea … improved with K and Mg …".

As important as to inform the scientific world on the effect of balanced nutrition on yield and quality of tea is to inform the growers. Keeping this in mind, IPI together with the Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou, 310008 PR China published a bilingual booklet in Chinese/English to this subject under the following title

• Potassium and Magnesium for better tea production by Wu Xun, Ruan Jianyun and Wu Binghua, 1997 (32 pages)

The booklet is available with R. Härdter, IPI Coordinator China, c/o K+S/VMA, POB 102029, D-34111 Kassel, Germany, fax +49 561 301 1416; Email rolf.haerdter@kalisalz.de

Extracts from Potassium and Magnesium for better tea production available on-line
1) Status of K and Mg content in China's tea soils
2) K and Mg in tea physiology
3) K and disease resistance in tea
4) Recognition of K and Mg deficiency symptoms in tea plants
5) Effect of K and Mg in balanced nutrition on the growth of tea plants and the yield of different types of tea
6) Effect of K and Mg in balanced nutrition on the quality of different types of tea
7) Fertilizer recommendation for K and Mg in tea production

	In this context, it is opportune to remind readers interested in tea on the Proceedings of the International Seminar on "Integrated crop management in tea: towards higher productivity", conducted by the International Potash Institute together with the Tea Research Institute, Talawakele, Sri Lanka, on April 26-27, 1994 in Colombo, Sri Lanka. The workshop discussed in 4 sessions tea production in various regions, integrated management practices, balanced fertilization and nutritional aspects of tea production and physiology. The Proceedings contain on 247 pages 18 technical papers presented by specialists from Bangladesh, China, India, Indonesia, Kenya, Sri Lanka and Vietnam. It is available for US$ 16 at the International Potash Institute, PO Box 1609, CH-4001 Basel, Switzerland, tel +41 61 261 2522; fax +41 61 261 2925; Email: ipi@ipipotash.org web site http://www.ipipotash.org
Order Proceedings of the International Seminar on "Integrated crop management in tea: towards higher productivity"