Conservation tillage technology for water-deficit areas in the North China Plain

The intensive exploitation of groundwater for farmland irrigation has led to the decline of groundwater level and the development of eco-environmental problems in the North China Plain (NCP). In order to establish water saving, high yield, carbon sequestration and conservation tillage integration technology system in NCP, a long-term conservation tillage experimental platform was established from Oct. 2001 in the Luancheng Agro-Ecosystem Experiment Station, Chinese Academy of Sciences, which included six treatments, CK (deep plowing and wheat row seeding without maize straw return), CT (deep plowing and wheat row seeding with smashed maize straw incorporation), TR (rotary tillage and wheat row seeding with smashed maize straw incorporation), NT1 (non-tillage and wheat furrow seeding with maize straw incorporation), NT2 (non-tillage and wheat furrow seeding with smashed maize straw incorporation) and NT3 (non-tillage and wheat row seeding with maize straw mulching). Studies on conservation tillage theory and key technologies of winter wheat-summer maize double cropping system integrated with agricultural machinery were conducted at the platform. The agronomic water-saving conservation tillage techniques of high yield systems were widely demonstrated in NCP. The results showed that 1) conservation tillage had obvious effects on carbon sequestration, emission reduction, water saving and soil quality improvement. Long-term conservation tillage induced soil nutrient accumulation at the soil surface. Also C, N, P, K and organic matter contents were higher in the 0-5 cm soil layer than in the 5-10 cm soil layer. Soil organic carbon (SOC) stratification ratio under RT and NT1, NT2 and NT3 treatments was in the range of 1.74-2.04, which was significantly higher than that of CK and CT (1.37-1.45). After 9 years of conservation tillage, soil carbon sequestrations (0-30 cm) were 840 kg·hm^-2·a^-1, 780 kg·hm^-2·a^-1 and 600 kg·hm^-2·a^-1 under NT2, RT and CT treatments, respectively. Then after 14 years of conservation tillage, soil carbon sequestrations were respectively 540 kg·hm^-2·a^-1, 720 kg·hm^-2·a^-1 and 710 kg·hm^-2·a^-1. Long-term non-tillage reduced soil disturbance and consequently decreased the mineralization rate of soil carbon. Soil carbon was mainly fixed in organic carbon particles of soil aggregates. The fixed carbon first changed into readily decomposable organic carbon and then slowly turned into stable carbon. Calculations of global warming potential under different tillage systems showed that farmland ecosystems under non-tillage with straw return served as carbon sink, with annual carbon retention of 947-1 070 kg(C)·hm^-2 after subtracting directly or indirectly carbon emitted equivalent. Other treatments were carbon resource, with CK, CT and RT treatments annually discharging equivalent carbon of 3 364 kg(C)·hm^-2, 989 kg(C)·hm^-2 and 343 kg(C)·hm^-2 respectively into the atmosphere. The mechanism of soil microbial diversity under conservation tillage was as follows:conservation tillage significantly improved the diversity indexes of soil fungi communities, bacteria communities, ammonia-oxidizing bacteria communities and denitrifying micro-organism communities with nirK gene. However, it had little effect on the diversity index of ammonia-oxidized bacteria communities and denitrifying micro-organisms communities with nirS gene. Conservation tillage showed significant water-saving effect, which resulted from improvements in soil structure, water-reservoir porosity and saturated hydraulic conductivity. Straw mulching also effectively reduced soil evaporation. 2) Non-tillage plus straw mulching with minimum soil evaporation model was established in winter-wheat/summer-maize double cropping system area. The unit of 4JS-2 straw combing press machine and 2BMF-6 non-tillage sowing machine with zero evaporation were developed, which reduced the operating rate by 45.2% and operation cost by 33.3%, compared with 2BMF-6/12 non-tillage sowing machine currently promoted. 3) A new soil rotation tillage model of deep plowing and deep sub-soiling every 3 years in non-tillage soil was established and integrated with water-saving, high-yielding and protective tillage technology system. A series of technical regulations of Hebei local standards in terms of conservation tillage of winter wheat/summer maize double cropping system were suggested. Cooperated with the Agricultural Bureau and Agricultural Machinery Bureau of Hebei Province, we demonstrated and promoted conservation tillage technologies in Hebei Province with remarkable social and ecological benefits. The main results won the first prize of Hebei Science and Technology Progress Award in 2013.