| A field experiment was carried out in Dingxi City in Gansu Province in 2014 in order to optimize N fertilizer in potato production management and efficient use of nitrogen fertilizer. We design two field experiment(in irrigated land N0-N5 pure N 0mg/kg 75mg/kg, 150mg/kg, 225mg/kg, 300mg/kg, 375mg/kg, and in dry land N0-N5 pure N 0mg/kg, 50mg/kg, 100mg/kg, 150mg/kg, 200mg/kg, 250mg/kg)Through the research on the region of different amount of nitrogen fertilizer agronomic traits of potato, dry matter accumulation, accumulation and distribution of nitrogen, yield and soil mineral nitrogen content influence,aimed at the demonstration and promotion of the best local potato nitrogen fertilizer application techniques, guiding the reasonable application of nitrogen fertilizer in potato production, and reduce the harm on the environment caused by the unreasonable application of nitrogen fertilizer. The results shown that: 1.The effects of different nitrogen levels on potato agronomic traitsWith the increasing of nitrogen fertilizer, the potato number of branches, stem weight, leaf weight and root weight were increased, that shows that adequate supply of nitrogen fertilizer, is conducive to the formation and growth of potato overground part and the roots of potato. However, with the increasing of nitrogen fertilizer, tuber weight first increased and then decreased, tuber weight per plant is not increased with N fertilizer, excessive application of N fertilizer were adversely affected the growth and development of potato. In the whole growth period, the potato plant height increased first, after reaching a stage of maturity decreased slightly. At maturity, the potato stems and leaves stop growing gradually, along with the dry aging, resulting in the plant height decreased.With the increasing of nitrogen fertilizer, the plant height increased, nitrogen fertilizer can delay the senescence of plant. 2. The effects of different nitrogen levels on dry matter accumulation and distribution in potatoIn the whole growth period of potato, the whole plant dry matter accumulation is a gradual increase in the process, with in the tubers were consistent, but the accumulation of dry matter in roots, stems, leaves, showed increased first, then decreased slightly. At the starch accumulation stage, in the root, stem, leaf dry matter accumulation reached the maximum, at mature stage were decreased. In the mature stage,the dry matter content of potato tuber in percentage of whole plant with the increase of nitrogen application amount showed first increased and then decreased trend. With the increasing of nitrogen fertilizer, in the irrigated conditions, the percentage of dry matter accumulation in the tubers in the whole plant did not increase, in the mature period, showed the decline trend after the first increase, reached the highest at the N3 level, accounting for 66.57% of the whole plant. In dry conditions, potato tuber growth period, starch accumulation period and mature period, with the amount of nitrogen fertilizer increased, tuber total strain ratio first increased and then decreased, both at the level of N3 reached the highest, reaching 69.37% in the mature period, and with the amount of nitrogen fertilizer continues to improve, the percentage of potato in tuber gradually decreased. 3. The effects of different nitrogen levels on nitrogen accumulation and distribution of nutrient in potatoIn the whole growth period, the potato root nitrogen varies between 1%~3% and nitrogen content in the stem between 1%~4%, nitrogen content in leaf between2%~6% and nitrogen contents in tubers between 1%~3%. With the increase of nitrogen, nitrogen content in various organs of potato has an increasing tendency. Nitrogen content in potato roots throughout their reproductive performance at first increased and then decreased again ascending and then descending trend, early tuber growth reached the lowest in starch accumulation period percentage of nitrogen in the root and the emergence of a peak. Within potato whole fertility period, the nitrogen pigment in content ground stems, leaves and tubers are performance for gradually declined of trend.In the early growth of potato, because the part on the ground gradually completed, the demand for nitrogen is large relatively. In the tuber growth period, ground and underground part requires a large amount of nitrogen, After the tuber starch accumulation period, potato tubers gradually stop growing, and the nitrogen content gradually decreased. With the increasing of nitrogen fertilizer, whole plants during the whole growth period, nitrogen accumulation in the whole potato showed increasing trend, but with the increasing of nitrogen fertilizer, nitrogen accumulation in potato tubers were increased first and then decreased. Under the conditions of this experiment, the agronomic N use efficiency and physiological efficiency of potato increase with the amount of nitrogen increased and then decreased,the recovery N use efficiency with the increasing of nitrogen application amount showed a downward trend. 4. The effects of different nitrogen levels on soil mineral nitrogen contentUnder the conditions of this experiment, with the potato growth period in advance, the NH4+-N content in different levels of nitrogen fertilization in the soil showed a first decreased and then increased trend. After a period of growth, with the increasing of nitrogen fertilizer the content of NH4+-N in soil had no significant change; NO3--N in farmland was extremely unstable, with the potato growth period in advance, the content of NO3--N accumulation increased gradually, with the increasing of nitrogen fertilizer, nitrogen accumulation was almost linear growth. Under irrigated conditions NO3--N content in 0-20 cm soil layer of N1、N2、N3、N4and N5 at the harvest period reached to the higher levels of 57.53mg/kg, 88.53mg/kg, 149.86mg/kg, 185.10mg/kg and 240.43mg/kg, which in 20-40 cm soil layer were 63.90mg/kg, 88.11mg/kg, 156.70mg/kg, 192.13mg/kg and 244.51mg/kg, under the condition of dry land NO3--N content in 0-20 cm soil layer of N1、N2、N3、N4and N5 at the harvest period reached to the higher levels of 70.62mg/kg, 109.96mg/kg, 141.50mg/kg, 179.33mg/kg and 228.39mg/kg, which in 20-40 cm soil layer were 105.38mg/kg, 101.08mg/kg, 150.46mg/kg, 173.47mg/kg and 200.36mg/kg, much higher than that in the same soil layers before the sowing period. In the two experimental field, the content of nitrate nitrogen in soil was stable in N3 conditions, with the amount of nitrogen fertilizer increased,the content of nitrate nitrogen in soil increased sharply. 5. The effects of different nitrogen levels on yield of potatoBoth N deficiency and excessive application of N fertilizer led to decline in potato tuber yield. Under the condition of this experiment, under irrigated conditions the N rates for highest yield and largest economic benefit are 180.99kg/hm2 and 231.07/hm2 respectively. Under dry land conditions the N rates for highest yield and largest economic benefit are 182.75kg/hm2 and 197.93/hm2 respectively. The yield component factor analysis result showed that, the average fresh-weight was the major factors affecting the potato tuber yield under the different N rates. |
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