深松与包膜尿素对玉米田土壤氮素转化及利用的影响

耕作方式和氮肥施用是影响土壤中氮肥转化、利用效率和作物产量的重要因素。通过夏玉米田的2a(2011—2012)定位试验,研究了两种耕作方式(深松、旋耕)配合不同尿素类型(包膜尿素、普通尿素)的施用对玉米田土壤硝态氮和铵态氮含量、脲酶活性、硝化细菌和反硝化细菌数量、玉米产量以及氮肥农学效率的影响。研究结果表明:相同耕作方式下,包膜尿素处理土壤中脲酶活性较稳定,且增加了旱田土壤亚硝酸细菌数量而降低了反硝化细菌数量,有利于土壤硝态氮含量的提高,尤其是作物生长的中后期;包膜尿素处理的产量比普通尿素提高7.25%—10.82%,同时提高氮肥农学效率。深松处理增加了土壤中的反硝化细菌数量,配合施用包膜尿素进一步提高了土壤脲酶活性,增加了亚硝酸细菌数量;旋耕与包膜尿素配合施用在一段时期内能显著增加土壤硝态氮含量,减少反硝化细菌数量。深松配合包膜尿素处理能够显著的增加玉米产量,2a分别比旋耕配合包膜尿素增加1.41%和10.62%。因此,深松措施配合施用包膜尿素能够增强土壤脲酶活性,增加亚硝酸细菌数量,提高氮素转化速率,增加作物产量和氮肥农学效率,其稳产效果在干旱年份尤为显著。

Effects of polycoated urea and subsoiling on nitrogen transformation and utilization in a maize field

Tillage practices and fertilizer application play important roles in nitrogen transformation and utilization and grain yield. The objective of this study was to determine the effects of urea types and tillage modes on soil nitrate and ammonium N content, urease activity, abundance of denitrifying bacteria and nitrite bacteria, and grain yield and nitrogen use efficiency in a maize (Zea mays L.) field. The treatments included two urea types (conventional urea and polycoated urea) applied at a rate of 225 kg N/hm² as a basal fertilizer; additionally, zero N treatments were set as the control under subsoiling and rotary tillage modes. Throughout the experiments in 2011 and 2012, the results showed that both the numbers of nitrite bacteria and denitrifying bacteria increased with the application of urea but then later would decrease to even fewer than in the zero N treatment. Compared with conventional urea, polycoated urea could stabilize soil urease activity and increase upland soil nitrite bacteria numbers but decrease the abundance of denitrifying bacteria. Also, polycoated urea was beneficial for accelerating nitrogen transformation into nitrate and reducing nitrogen losses from denitrification while keeping soil ammonium and nitrate N concentrations in the 0-40 cm layers at a high level for a long time, especially in the middle and later periods of maize growing season. Polycoated urea generally increased grain yield and agronomic efficiency of applied N by 7.25%-10.82% and 56.37%-84.54%, respectively, compared to those with conventional urea regardless of tillage practices. Rotary and subsoiling tillage could temporarily stimulate soil nitrate N concentration. Compared with rotary tillage, subsoiling tillage increased the numbers of denitrifying bacteria. Moreover, the interaction of polycoated urea and subsoiling tillage could not only increase the urease activity but also the abundance of nitrite bacteria. It would keep the nitrate N concentration at a high level in the later maize growing stage. However, nitrogen loss through denitrification and leaching in the early stage of the maize growing season may increase. Polycoated urea in rotary soils could significantly increase soil nitrate nitrogen concentration while reducing the number of denitrifying bacteria within a period of time. The application of polycoated urea in subsoil produced higher grain yield, with increases of approximately 1.41% and 10.62%, compared to those in rotary soil, in 2011 and 2012, respectively. So in a drought year, the effect of subsoiling tillage combined with polycoated urea may be more significant in increasing grain yield. In conclusion, subsoiling tillage coupled with polycoated urea increases urease activity and nitrous bacteria abundance, and stimulates nitrogen transformation, grain yield, and nitrogen use efficiency.