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Food and energy security are important issues that threaten human survival and development. The rice–wheat rotation system provides a stable source of food for more than 20% of the world's population, but there have been no reports on the energy balance of different rice–wheat rotation systems. This study evaluates the energy inputs and outputs of three rice–wheat rotation systems and their energy production efficiency through the study of dry direct‐seeded, wet direct‐seeded, and transplanted rice–wheat rotation systems. The results of the study showed that the average total energy inputs in the dry direct‐seeded, wet direct‐seeded, and transplanted rice–wheat rotation systems were 58,677, 74,083, and 69,022 MJ ha−1, respectively. The production resources with more energy input in rice–wheat rotation system were all related to water and fertilizer. The energy input in the rice season accounts for more than 50.69% of the total energy input in the rice–wheat rotation system. At the same time, rice–wheat rotation production is highly dependent on nonrenewable energy. Among the three rice–wheat rotation systems, the transplanted rice–wheat rotation system had the highest total energy output and net energy, while the dry direct‐seeded rice–wheat rotation had the highest energy use efficiency, energy productivity, energy profitability, and human energy profitability. The results showed that the key to reducing the energy input in the rice–wheat rotation system is to reduce the amount of water and fertilizer. The transplanted rice–wheat rotation system is more suitable for promotion in rice–wheat rotation production areas with good irrigation conditions, while the dry direct‐seeded rice–wheat rotation system is highly compatible with the current development direction of low energy consumption and high energy efficiency in agricultural production and is suitable for promotion in rice–wheat production areas with poor irrigation conditions.

The effects of global warming on crop production have received great attention in recent years. However, inconsistent results have been obtained with regard to major crops such as rice and wheat in rice–wheat rotation systems of China. Therefore, we undertook a comprehensive meta‐analysis of literature data. The yield response to warming differed for rice and wheat in the rice–wheat rotation system. Overall, warming significantly increased wheat yield (by 4.8%) but significantly reduced rice yield (by 14.8%). A number of factors were responsible for these observations. For example, rice yield responses varied with the temperature increase, variety and nitrogen (N) rate. Of these, N was the most important variable influencing yield responses to warming. The yield loss for rice was lower at temperature increases of 0.40–1.40°C and at a high N rate than that at temperature increases of 1.60–2.49°C and at a low N rate, respectively. The yield loss of indica rice was lower than that of japonica rice. For wheat, however, yield responses to warming varied with the warming regime, ambient temperature, temperature increases, and CO2 concentrations. Of these factors, ambient temperature was the most important variable influencing yield in response to warming. Warming increased wheat yield at a mean growth season temperature ≤10°C, temperature increases of 0.80–1.50°C, and at ambient CO2 concentrations. In addition, either daytime warming or nighttime warming significantly increased wheat yield. However, all‐day warming had no effect on wheat yields. We conclude that global warming will benefit wheat production but result in a serious loss of rice yield in rice–wheat rotations in China.

The rice–wheat rotation model of crop planting is widely used globally, and worldwide, straw returning is the main method of crop straw treatment. However, the straw return method commonly used in the modern rice–wheat rotation system has many adverse effects on the levels and improvement of soil fertility and crop yield, and there is no systematic theory of rice and wheat straw returning to use as a guide. In this paper, we concluded that: in the rice–wheat rotation system, returning 1,500–4,500 kg/ha of rice straw and 2,250–6,750 kg/ha of wheat straw to the field helps increase the organic carbon content and quality of the soil and promotes high annual yields; conventional mixing of straw into the field can increase the organic carbon content of the soil in a short time; long‐term use of concentrated ditch‐buried straw return has obvious advantages over other straw returning methods in increasing the accumulation of soil organic carbon; the combination of little or no tillage plus straw returning helps increase the content and quality of organic carbon in soil; and when the soil water content is 15%–22.5%, it is the most conducive to the accumulation of soil organic carbon. In addition, we also provide relevant suggestions for future research directions on straw returning via systematic analyses and thought processes.

A simple and rapid multi-plug filtration cleanup method based on multi-walled carbon nanotubes was developed to determine 124 pesticide residues in rice, wheat, and corn, which could be done in a few seconds without conditioning and elution steps. Various combinations of sorbents were optimized for each matrix with a dispersive solid-phase extraction procedure to get a satisfactory recovery and clean-up performance. Good linearity was obtained for all pesticides with calibration curve coefficients larger than 0.9958. Most recoveries for the majority pesticides were between 70 and 120% (n = 5) with relative standard deviations below 20%. The limit of detection was 0.1–1.3 μg/kg, and the limit of quantification was 0.2–4.3 μg/kg for the pesticides in all matrices. The work suggests that the multi-plug filtration cleanup method is better than the dispersive solid-phase extraction method and it could be applied to routinely monitor pesticide residues in market samples. This article is protected by copyright. All rights reserved

Soil Sci. Soc. Am. J. 76:1068–1078 doi:10.2136/sssaj 2011.0236 Received 23 Jun 2011. *Corresponding author (sqwang@issas.ac.cn). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Nitrogen Balance in a Highly Fertilized Rice–Wheat Double-Cropping System in Southern China Nutrient Management & Soil & Plant Analysis

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

Phosphorous deficiency limits productivity of rice (Oryza sativa L.)-wheat (Triticum aestivum L.) systems in the Indo-Gangetic Plains. Deterioration of soil and air quality due to straw burning is also a concern. Field experiments were conducted to determine the effects of straw and P management strategies on yield, P balance, and P transformations in soil in a rice-wheat system. Four treatments composed of different combinations of rice and wheat straw removal, burning, and incorporation were the main plots. Subplot treatments were P fertilization to wheat or to both rice and wheat and a no-P control. Wheat yield was similar where straw was burned in situ or removed. Incorporation of straw increased the wheat yield in Year 4. Significant straw x P management interactions, observed after 4 yr, suggested that residues can enhance yield under limited P supply situations. Application of 26 kg P ha -1 to wheat increased grain yield by 6 to 15% compared with no P Rice yield did not respond to incorporation of residues or P fertilization. The P balance was negative with removal or burning of rice straw, but when both wheat and rice straw were incorporated, the balance was positive at the recommended P level (26 kg P ha -1 to wheat only). Changes in total soil P suggested that the two crops remove significant P from below 15 cm. Incorporation of residues increased soil Olsen, inorganic, and organic P; reduced P sorption; and increased P release. Data show that continuous incorporation of residues substituted for 13 kg inorganic P ha yr -1 and improved system yield.

Rice–wheat cropping system to which graded levels of NPK fertilizers had been applied for 20 years were compared for yield trends, and changes in response function, soil organic-C and available N, P, K and S status. This study of system in which only chemical fertilizers had been used over a long period enabled long-term yield declines of rice and wheat at different levels and combinations of NPK fertilizers to be evaluated. The highest rate of yield decline in both rice and wheat was found when 120 kg ha−1 N was applied alone. The lowest rate of decline was observed when all three nutrients (N, P and K) were applied, at 40, 35 and 33 kg ha−1 for N, P and K, respectively, followed by 120, 35 and 33 kg ha−1 (currently recommended levels). The yield response of rice and wheat to N fertilizer declined over the 20 years, with a higher rate of decline in wheat. In contrast, the response to applied P and K increased with time in both crops, with a higher response rate in wheat. With continuous application of N and P fertilizers, there was a marginal change in available N and K in the soil over time, but an approximately 3-fold increase in available P and an approximately 2-fold increase in available S were obtained by regular dressing of P fertilizer (SSP: 7 % P, 12 % S) over 20 years. The results revealed that balanced, high doses of NPK fertilizers are required to maintain soil fertility and raise grain yields. Langzeitwirkungen von Dunger auf die Bodenfrucht-barkeit und die Produktivitat von Reis-Weizen-Anbausystemen Die Ergebnisse unterschiedlicher Konzentrationen von NPK-Dungern in einem 20 Jahre wahrenden Reis-Weizenanbausystem hinsichtlich der Ertragstrends, Anderungen in der Reaktionsfunktion, bodenorganischem C und verfugbaren N, P, K, S wurden untersucht. Die Anwendung auf Dauer von nur einem chemischen Dunger weist Ertragsruckgange von Reis und Weizen in unterschiedlichem Ausmas im Zusammenhang mit NPK-Dungern auf. Die hochste Ertragsabnahme von Reis und Weizen wurde gefunden, wenn mit 120 kg N ha−1 allein gedungt wurde. Die geringste Abnahme wurde beobachtet, wenn alle drei Nahrstoffe (N, P, K) angewendet in Mengen von 40-35-33 kg ha−1 wurden, gefolgt von 120-35-33 kg N-P-K ha−1 (z. Zt. empfohlene Mengen). Die Ertragsreaktionen von Reis und Weizen gegenuber N-Dunger nahm uber die zwanzig Jahre ab, wobei der Ruckgang in Weizen starker war. Die Reaktion auf P und K verstarkte sich im Laufe der Jahre in den Bestanden beider Arten, wobei die Reaktion bei Weizen starker war. Bei einer anhaltenden Anwendung von N- und P-Dungern war nur eine marginale Anderung im verfugbaren N und K im Boden im Laufe der Jahre festzustellen; es wurde aber eine dreifache Zunahme im verfugbaren P und etwa eine zweifache Zunahme im verfugbaren S bei einer regularen Anwendung von P-Dunger (SSP: 7 % P, 12 % S) im Verlauf von zwanzig Jahren beobachtet. Die Ergebnisse weisen darauf hin, dass Ausgeglichenheit und hohere Anwendungsmengen von NPK-Dungern benotigt werden, um die Bodenfruchtbarkeit zu erhalten und die Kornertrage zu steigern.

The frequency and intensity of meteorological droughts over the Indo-Gangetic Region (IGR) of India pertaining to the rice crop during kharif season (June to July to October to November) and the wheat crop during the rabi season (November to December to March) were assessed using the standardized precipitation index (SPI). The monthly distribution of rainfall is more crucial than the cumulative seasonal rainfall on rice–wheat (RW) productivity. Consequently, an attempt was made to measure the effectiveness of using monthly SPI from June to September to assess drought on RW productivity over five major RW growing states of IGR in India. An attempt is also made to test the use of monthly SPI for the early kharif rice and rabi wheat forecasts for these states. The long-term (1906–2005) mean annual rainfall of IGR is 1099.1 mm with a standard deviation of 115.7 mm and a coefficient of variation of 10.5%. It was observed that the kharif rice productivity index and monthly SPI from June to September have a significant (R2 = 0.44) multiple regression at 0.001 level over IGR. It was also observed that in the Indo-Gangetic Region, the wheat productivity index and monthly SPI (June to September) have an insignificant (R2 = 0.21) multiple regression. It indicated that the monthly distribution of monsoon rainfall in terms of the SPI accounted for 44% yield variability in rice and 21% yield variability in wheat. Thus, these indices may be used for forecasting the productivity of the RW system over IGR states in India. Copyright © 2010 Royal Meteorological Society