Producing optimal grain yields while reducing adverse environmental impacts of over-fertilization is essential in intensive, but sustainable, farming systems. We investigated the effects of long-term (1982–2005) application of chemical nitrogen (N), N + chemical phosphorus (P) and N + P + chemical potassium (K) on grain yield, nitrogen recovery efficiency (NRE) and N losses in two rice–wheat sites in subtropical China where pig manure was applied (Suining and Wuchang). Four (Suining) or five (Wuchang) treatments were examined: no-fertilizer, chemical N plus manure (NM), chemical NP plus manure (NPM), chemical NPK plus manure (NPKM) or chemical NPK plus 1.6 times manure (NPKhM, Wuchang only). Fertilizers resulted in 1.5–2.5 times higher grain yields than no-fertilizer, which led to a NRE in the range from 21.0 to 58.3%. Grain yields of rice and wheat were significantly increased by 22.6–25.9 and 34.4–37.5%, respectively, under NPM and NPKM (similar to each other) compared to NM at Suining. Yields were similar for NM, NPK, NPKM and NPKhM at Wuchang. The N accumulation and NRE among fertilizers were in the order NM \u3c NPM = NPKM at the low amount of manure-applied site (Suining), but NM = NPM = NPKM at the high amount of manure-applied site (Wuchang). The ratio of N losses to total N input was 21.4–49.1% at the studied sites. Soil total N accumulated at a rate of 0.01–0.04 g/kg/yr during 1982–2005 with fertilizers and decreased or was constant in soil without fertilizer. Application of chemical P and K fertilizers could be reduced or eliminated after long-term manure application at these two sites, while maintaining optimal grain yields and enhancing soil N accumulation

HighlightsUsing leaching fraction to schedule irrigation is recommended yet no automated measurement system exists.Sensors were developed to automatically measure leachate and irrigation within a sensor network.There was no difference between sensor measured and manually captured volume for sensors deployed in a nursery.After deployment in commercial nurseries, sensors accurately measured leachate and irrigation within 10% margin.Abstract. Nursery crops are often over-irrigated, resulting in wasted water and agrochemical inputs. Irrigating based on leaching fraction is recommended, yet an automated system for measuring and recording nursery container effluent (leachate) does not exist. The objective of this research was to develop and test a sensor-based system for real-time leachate and irrigation measurement in outdoor commercial nurseries. Sensors were developed to automatically measure irrigation and leachate volume in container nurseries that use overhead irrigation with the goal of facilitating the development of an automated leaching fraction-based irrigation system. Sensors were built using readily available components, including tipping bucket mechanisms calibrated to either 4.7 or 8.2 mL per tip, and were designed and constructed to function with commonly used 3.8-, 11.4-, and 14.5-L nursery containers. Sensor networks were developed in order to collect data from the sensors. Sensors were deployed at three commercial nurseries and tested using closed- and open-loop tests. Initially, a closed-loop test was performed on a subset of the sensors to test the integrity of the sensor-container system when subjected to an overhead irrigation delivery system. Following closed-loop tests, sensors were subjected to tests utilizing directed applications of water to compare sensor measurements with the volume of water applied and to compare sensor measurements over time (pre- and post-season). There was no difference between leachate measured by sensors and leachate captured and measured manually in closed-loop tests (p = 0.0570). In directed applications, sensors measured water flow with less than 3% margin at the beginning of the season (p = 0.0485) and less than 10% margin at the end of the season (p = 0.0390) regardless of container size. Pre- and post-season comparisons showed equivalence at the 10% margin for the 4.7-mL tipping bucket size (p = 0.0043) and at 5% for those calibrated to 8.2 mL per tip (p = 0.0198). Sensors deployed in commercial nurseries accurately measured leachate and irrigation within a 10% margin in real-time, on an individual plant scale, making them a viable option for a leaching fraction-based irrigation schedule. Keywords: Container effluent, Container-grown plants, Leaching fraction, Irrigation schedule, Sensor network.

Soil amendments with high carbon (C) content can be effective in semi‐arid regions where soils are characterized by low C. A field study was conducted in 2016–2018 to evaluate the effect of char on soil chemical properties and irrigated maize (Zea mays L.) yields in sandy loam fertilized with urea or composted manure. Carbon‐rich char used was a product of coal combustion residue from a local factory in western Nebraska. The experiment was arranged in a split‐plot randomized complete block design in four replications with char (0, 6.7, 13.4, 20.1, and 26.8 Mg C ha−1) as main and N treatment (0, 90, 180, and 270 kg urea‐N ha−1 and 33.6 and 67.2 Mg ha−1 of composted manure) as subplot factors. A handheld spectral sensor was used to determine normalized difference red edge (NDRE) at growth stages (V6, V8, V10, and R1) in 2017 and 2018. After 2 yr, char increased Fe, reduced pH at lower rates, and increased K and Mg at higher rates in top 20 cm soil but did not affect crop yields. Char applied at ≥13.4 Mg C ha−1 increased soil organic C by ≥8% and composted manure increased soil P and K compared to the control. There was a strong correlation of NDRE with N rates and grain yields at V8 and V10. This study found no adverse effect of char on soil properties. However, more site‐specific research is needed before char can be used as a regular soil amendment in semi‐arid regions.