环渤海低平原农田生态系统养分循环与平衡研究

了解农田养分输入、输出和平衡状况,以及土壤肥力现状与变化特征,对实现养分资源优化管理、地力的持续提升、肥料利用率提高和农业可持续发展具有重要意义。基于1985年、2000年和2014年河北省南皮县国民经济统计资料,分析了从1985年到2014年县域农田生态系统养分循环与平衡状况；利用1981年第2次土壤普查和2015年实测南皮县域土壤耕层养分含量数据,探讨了耕层土壤养分变化及空间分布格局特征。结果表明,1985—2014年南皮县农田养分输入输出均呈持续上升趋势, NPK养分输入由10701 t增加至23386 t,年递增率2.33%； NPK养分来源结构略有不同, NP来源以化肥为主,其次是人畜粪尿和作物秸秆有机肥源；而K素来源主要是有机肥源。农田养分输出以作物吸收为主,占养分总输出的80%以上, NPK总输出由1985年的9093 t增加到2014年的18846 t,年均增速2.17%。从养分表观平衡的角度看,从1985年到2014年NP始终有大量盈余, P素盈余大于N素, N和P表观平衡率分别为16.8%~34.2%和26.9%~65.5%；若考虑有机氮的有效性问题,1985—2000—2014年3个时段有效氮盈亏率依次为18.1%、6.5%和-7.8%,有效氮平衡由盈余转向亏缺；而K素经历了由赤字逐渐向盈余的转变过程,由1985年的-33.5%赤字发展至2014年的33.6%盈余。受农田养分平衡状况的影响,南皮县土壤有机质、全氮、有效磷发生了显著变化,1981—2015年有机质由8.62 g·kg-1增至14.0 g·kg-1,增幅62.4%；全氮由0.542 g·kg-1增至0.908 g·kg-1,增幅67.5%；有效磷由2.0 mg·kg-1增加到20.8 mg·kg-1,增加了9.4倍。而碱解氮和有效钾变化不明显,分别由70.5 mg·kg-1和141 mg·kg-1增加到71.8 mg·kg-1和147 mg·kg-1,相对增幅仅为1.8%和4.2%。建议今后南皮县在农业生产中大力推广科学施肥技术,重视有机肥和化肥配施,推广秸秆还田,通过改进施肥方法提高肥料利用效率；养分管理中应提倡“稳氮、控磷、补钾”的施肥对策,避免过多的盈余养分进入环境。

Nutrient cycling and balance in farmland ecosystem in Bohai Lowland Plain

It is important to optimize nutrient management and improve soil fertility and fertilizer use efficiency for sustainable development of agriculture. This can help to understand nutrient input/output and balance in farmland and the state of soil fertility and its change. Based on national economic statistics for Nanpi County for 1985, 2000 and 2014, the state of nutrient cycle and balance in agro-ecosystems was analyzed for the period 1985–2014. The study also explored the state and change characteristics of soil nutrients by comparing data on nutrients in the topsoil in 1981 (when the second national soil survey was conducted) with that in 2015. The results indicated a significant change in nutrient input/output and balance for 1985 through 2014. There was a significant increase in NPK input. Total inputs of N, P and K increased from 10 701 t in 1985 to 23 386 t in 2014, which represented an annual increase of 2.33%. The sources of N, P and K were different, with N and P mainly coming from chemical fertilizers, followed by organic fertilizers such as manure and crop straw. However, K was mainly from organic fertilizers. Nutrient absorption by crops was the main component of nutrient output, accounting for 80% of total nutrient output. NPK output increased from 18 846 t in 1985 to 90 093 t in 2014, with an annual increase of 2.17%. Taking into account apparent nutrient balance, there were huge N and P budget surpluses since 1985. For the period 1985–2014, P surplus (26.9%–65.5%) exceeded N surplus (16.8%–34.2%). Based on the availability of organic N, available N budgets were respectively 18.1%, 6.5% and-7.8% in 1985, 2000 and 2014, which shifted from surplus to deficit conditions. K balance changed from deficit to surplus condition, improving from a deficit of-33.5% in 1985 to a surplus of 33.6% in 2014. Due to the effect of nutrient balance, the contents of soil organic matter, total N and available P significantly changed, respectively increasing from 8.62 g·kg-1, 0.542 g·kg-1 and 2.0 mg·kg-1 in 1981 to 14.0 g·kg-1, 0.908 g·kg-1 and 20.8 mg·kg-1 in 2015. The total increases in 2015 over those in 1981 were 62.4%, 67.5% and 9.4 times, respectively. The changes of available N and available K were not very noticeable, increasing from 70.5 mg·kg-1 and 141 mg·kg-1 in 1985 to 71.8 mg·kg-1 and 147 mg·kg-1 in 2015, representing total increases of 1.8% and 4.2%, respectively. The measures of increasing soil fertility and fertilizer use efficiency included scientific and rational fertilization, combined application of organic fertilizer and inorganic fertilizer, straw return to soils and improved fertilization methods. Under the current soil fertility and crop planting structure, nutrient management countermeasures was to optimize N dose, to control application of P and to increase application rate of K to limit nutrient surplus in the environment.