The Response Of Water-melon To Nitrogen And The Changing Characters Of Soil Active Nitrogen On Gravel-sand-mulched Field

Gravel-sand-mulched field is a special farming in the northwest of China..And the Gravel-sand field is more and more in recent years in NingXia of China.Gravel-sand field not only brings economic benefits but also driving development of the third industry for location.Nitrogen is an essential nutrient to plant growth.the plant absorbs nutrients from soil.Nmin and SSON are important nitrogen in soil,it not only keeping nitrogen balance in soil,but applying nitrogen for plant..For the Gravel-sand field,due to the sand making the nutrient transformation is different from the common field,so it is very necessary to study the response of water-melon on gravel-sand field to Nitrogen rates and to explore the distribution,transformation and the influencing factors of reactive nitrogen in order to rational supplying nitrogen fertilizer,improving yield and quality of water-melon,and sustainable using and managing Gravel-sand field.The field experiment with five nitrogen rates was carried out in Xingren County of Ningxia Hui Autonomous Region.Study the growth and development,nitrogen absorb,nutrient diagnosis on gravel-sand-mulched watermelon.And study the effect of nitrogens on active nitrogen.So that clear the effect of nitrogens on gravel-sand-mulched watermelon and active nitrogen.The results showed that:1.A proper amount of nitrogen application was benefit for improving and coordinating with the vegetative growth and the reproductive growth of gravel-sand watermelon,meanwhile the growth,yield and quality of gravel-sand watermelon are optimum at 75.00-112.50 kg hm'2 nitrogen rates.2.The order of N content in different organs was root<stem<base leave<middle leave<top leave,and during watermelon growing stage,the changing tendency of N content was "W" and it was most in fruiting stage.The notrogen content were varied with the growth stages and N rates.The nitrogen content was most in the rational N rates from seeding stage to fruiting stage,meanwhile the growth,yield and quality of gravel-sand watermelon are optimum at 75.00-112.50 kg hm-2 nitrogen rates.But it was increase with the increase of N rates from expanding stage to maturing stage.3.The SPAD value was higher from stretching stage to expanding stage,and the suitable nitrogen application can enhance chlorophyll,but excess nitrogen makes the SPAD lower.Meanwhile,during the whole growing period of watermelon,the SPAD in middle leaves is higher and stable and the changes with the increase of nitrogen rate followed the law of diminishing returns,so the middle leaves can be as the diagnosis organ of nitrogen for watermelon on gravel-sand field.However,there was a close relationship between SPAD value in base leaves and the yield of watermelon from stretching stage to expanding stage.4.With the growth of Gravel-sand watermelon and the depth of sandy soil,the nitrogen content increased with the increase of water content and active nitrogen.When nitrogen rate was 37.5-75 kg hm-2,Water content in 60-100 cm soil layer was increased steadily.Nitrogen fertilizer and soil organic nitrogen content in different soil layers at different growth stages were increased.While the contents of nitrogen and ammonium nitrogen in the soil were increased or decreased in different degrees and the content of ammonium nitrogen in 40-100 cm soil layer increased at the ripening stage and was most at 150kghm-2 N rate.