Effects of straw and manure management on soil and crop performance in North China Plain

1、Experiment site and time：This study was conducted from October 2010 to June 2016 at theLuancheng Agro-Eco-experimental Station (37°53′ N, 114°40′ E; elevation 50 m) of the Chinese Academy of Sciences.2、Experimental design and field management：Four straw management practices were tested: (1) all the straw from the double-cropping system was left in the field after each harvest (as control, WMs); (2) maize straw was removed as yellow silage and winter wheat straw was left in the field (a practice to increase feed for the local dairy industry, abbreviated as Ws); (3) some manure produced from dairy farms was added to Ws (abbreviated as Ws + M); (4) extra manure was added to WMs (abbreviated as WMs + M).3.Parameter monitoring（1）Weather data：Daily weather data were obtained from a standard weather station approximately 100 m away from the experimental site and included the daily temperature, rainfall, radiation, humidity and wind speed.（2）Soil chemical and physical characteristics：Before and at the end of the test, soil chemical properties were sampled to determine available phosphorus, available potassium, total nitrogen and organic matter. The sampling depth was 0-20cm and 20-40cm.（3）Crop development, biomass and grain yield：Phenological developments were recorded based on the appearance date of 20%, 50% and 80% for the major growing stages of winter wheat and summer maize. Before harvesting winter wheat and summer maize, the spike numbers per unit area (SN) were counted in the field. Then, 80 plants (for winter wheat) and 4 plants (for summer maize) were collected from each plot to determine the kernel number per spike (KNS), kernel weight, thousand grain weight (TGW), total dry matter and harvest index (HI). For yield measurement, 10 m2 from each plot was harvested manually for winter wheat. All plants were anuallythreshed with a thresher. After obtaining the grains, the straw harvested from each plot was returned to the field. For maize, the ears from the plants were manually harvested and threshed to obtain the grains.Grains were air-dried to a constant moisture content (13%), and the weight was recorded to obtain the final grain yield. For the Ws treatment, all the above-ground biomass for maize was removed from the field after harvesting maize。（4）Soil water content, crop water use and use efficiency：Soil water content was regularly monitored using a neutron probe (503 DR, CPN International Inc., USA) down to 2 m by 20 cm increment. An access tube was installed in the center of each plot. The surface soil layer (0–20 cm) was regularly monitored by a portable TDRsensor (MP-160, Meridian).Seasonal crop water use, or evapotranspiration (ET), was calculated based on the water balance equation:WUE=y/ET，ET=P+I+SWD+R-D+CRwhere ET is seasonal evapotranspiration or crop water use (mm), P is precipitation (mm), I is irrigation (mm), SWD is soil water depletion for the top 2 m soil profile (mm), R is surface runoff (mm), D is drainage from the root zone (mm), and CR is capillary rise to the root zone (mm). Surface runoff was not observed due to the low rainfall, and the capillary rise was negligible due to the groundwater table being 40 m below the soil surface. D was calculated following the method used by Liu et al. (2013). Water use efficiency (WUE) in grain production (WUEg) was defined as grain yield divided by crop water use, and WUE in biomass production (WUEb) was defined as biomass divided by cropwater use.（5）. Element contents in straw and manure：The contents of C, N, P and K in the straw were estimated for each season separately by using the biomass production that was measured every year for both winter wheat and summer maize. The total C and N of the straw was measured by the elementary analysis system GmbH(vario MACRO cube, Germany). The method used to measure the P and K contents was the same as used for the soil P and K. The same methods were used to measure the contents of C, N, P and K in the manure.