Crop rotation-dependent yield responses to fertilization in winter oilseed rape (Brassica napus L.)

Differences in soil physical, chemical and biological properties between paddy–upland and continuous upland rotations will influence nutrient relations and crop growth. With the aim of estimating rapeseed yield performance in response to fertilization in rice–rapeseed (RR) and cotton–rapeseed (CR) rotations, on-farm experiments were conducted at 70 sites across Hubei province, central China. The economically optimal fertilizer rates of winter oilseed rape in different rotations were determined. Field experiments showed that previous crops significantly influenced seed yields. Without N fertilization, seed yields were significantly lower for the RR rotation than for the CR rotation. The average yield increase ratio and agronomic efficiency associated with nitrogen (N) fertilization in the RR rotation were 96.6% and 6.56 kg kg− 1, significantly higher than those in the CR rotation. No seed yield differences were detected between the two rotations under phosphorus (P) and potassium (K) fertilization. In contrast to the CR rotation, N fertilizer played a more vital role in maintaining high seed yields in the RR rotation owing to the lower indigenous soil N supply. Compared with local N fertilizer recommendation rates for the RR rotation, on average an additional 18 kg N ha− 1 was recommended according to the economically optimal N fertilizer rate (EONFR). In contrast, the EONFR was 14 kg N ha− 1 lower than the locally recommended N fertilizer rate for the CR rotation. There were no differences between the two rotations for the average economically optimal P and K fertilization rates. Consequently, the average EONFR of winter oilseed rape could be reduced if cotton rather than rice preceded the winter oilseed rape

Establishing grading indices of available soil potassium on paddy soils in Hubei province, China

Abstract Soil testing is an important diagnostic tool for assessing crop-available soil potassium (K) and hence making appropriate fertilizer recommendation. This study was aimed at correlating grain yield response data to soil-test K extracted with ammonium acetate (NH4OAc), cold nitric acid (HNO3), sodium tetraphenylboron (NaTPB) and boiling HNO3 solution, based on 54 field trials conducted during 2011 to 2015 across 15 counties in Hubei province, China. The specific objectives were to establish abundance and deficiency indices of available soil-K (ASK) for rice (Oryza sativa L.) and make accurate K fertilizer recommendations. Potassium extracted with NaTPB and boiling HNO3 was 1.47 times and 3.61 times higher respectively than that extracted with cold HNO3, while K extracted with cold HNO3 was 1.32 times higher than that extracted with NH4OAc. There were significant logarithmic relationships between crop response and soil-test K. The R2 values for cold HNO3-K and NaTPB-K methods were much higher than for NH4OAc-K method. In order to calibrate the application, the abundance and deficiency indices of ASK categorized by cold HNO3-K in low, medium, high and very high ranges were 200 mg kg−1 respectively, and that defined by NaTPB-K were 330 mg kg−1, respectively. These values could be used to evaluate soil K supplying capacity and make appropriate K fertilizer recommendations for rice

Photosynthetic plasticity aggravates the susceptibility of magnesium-deficient leaf to high light in rapeseed plants: the importance of Rubisco and mesophyll conductance

Plants grown under low magnesium (Mg) soils are highly susceptible to encountering light intensities that exceed the capacity of photosynthesis (A), leading to a depression of photosynthetic efficiency and eventually to photooxidation (i.e., leaf chlorosis). Yet, it remains unclear which processes play a key role in limiting the photosynthetic energy utilization of Mg-deficient leaves, and whether the plasticity of A in acclimation to irradiance could have cross-talk with Mg, hence accelerating or mitigating the photodamage. We investigated the light acclimation responses of rapeseed (Brassica napus) grown under low- and adequate-Mg conditions. Magnesium deficiency considerably decreased rapeseed growth and leaf A, to a greater extent under high than under low light, which is associated with higher level of superoxide anion radical and more severe leaf chlorosis. This difference was mainly attributable to a greater depression in dark reaction under high light, with a higher Rubisco fallover and a more limited mesophyll conductance to CO2 (gm). Plants grown under high irradiance enhanced the content and activity of Rubisco and gm to optimally utilize more light energy absorbed. However, Mg deficiency could not fulfill the need to activate the higher level of Rubisco and Rubisco activase in leaves of high-light-grown plants, leading to lower Rubisco activation and carboxylation rate. Additionally, Mg-deficient leaves under high light invested more carbon per leaf area to construct a compact leaf structure with smaller intercellular airspaces, lower surface area of chloroplast exposed to intercellular airspaces, and CO2 diffusion conductance through cytosol. These caused a more severe decrease in within-leaf CO2 diffusion rate and substrate availability. Taken together, plant plasticity helps to improve photosynthetic energy utilization under high light but aggravates the photooxidative damage once the Mg nutrition becomes insufficient

Additional file 1: of The photosynthetic and structural differences between leaves and siliques of Brassica napus exposed to potassium deficiency

Illustration showing development progress of Brassica napus L. (PDF 434 kb

Particulate Organic Matter Affects Soil Nitrogen Mineralization under Two Crop Rotation Systems

<div><p>Changes in the quantity and/or quality of soil labile organic matter between and after different types of cultivation system could play a dominant role in soil nitrogen (N) mineralization. The quantity and quality of particulate organic matter (POM) and potentially mineralizable-N (PMN) contents were measured in soils from 16 paired rice-rapeseed (RR)/cotton-rapeseed (CR) rotations sites in Hubei province, central China. Then four paired soils encompassing low (10th percentile), intermediate (25th and 75th percentiles), and high (90th percentile) levels of soil PMN were selected to further study the effects of POM on soil N mineralization by quantifying the net N mineralization in original soils and soils from which POM was removed. Both soil POM carbon (POM-C) and N (POM-N) contents were 45.8% and 55.8% higher under the RR rotation compared to the CR rotation, respectively. The PMN contents were highly correlated with the POM contents. The PMN and microbial biomass N (MBN) contents concurrently and significantly decreased when POM was removed. The reduction rate of PMN was positively correlated with changes in MBN after the removal of POM. The reduction rates of PMN and MBN after POM removal are lower under RR rotations (38.0% and 16.3%, respectively) than CR rotations (45.6% and 19.5%, respectively). Furthermore, infrared spectroscopy indicated that compounds with low-bioavailability accumulated (<i>e</i>.<i>g</i>., aromatic recalcitrant materials) in the soil POM fraction under the RR rotation but not under the CR rotation. The results of the present study demonstrated that POM plays a vital role in soil N mineralization under different rotation systems. The discrepancy between POM content and composition resulting from different crop rotation systems caused differences in N mineralization in soils.</p></div

Dynamics of Potassium Release and Adsorption on Rice Straw Residue

<div><p>Straw application can not only increase crop yields, improve soil structure and enrich soil fertility, but can also enhance water and nutrient retention. The aim of this study was to ascertain the relationships between straw decomposition and the release-adsorption processes of K⁺. This study increases the understanding of the roles played by agricultural crop residues in the soil environment, informs more effective straw recycling and provides a method for reducing potassium loss. The influence of straw decomposition on the K⁺ release rate in paddy soil under flooded condition was studied using incubation experiments, which indicated the decomposition process of rice straw could be divided into two main stages: (a) a rapid decomposition stage from 0 to 60 d and (b) a slow decomposition stage from 60 to 110 d. However, the characteristics of the straw potassium release were different from those of the overall straw decomposition, as 90% of total K was released by the third day of the study. The batches of the K sorption experiments showed that crop residues could adsorb K⁺ from the ambient environment, which was subject to decomposition periods and extra K⁺ concentration. In addition, a number of materials or binding sites were observed on straw residues using IR analysis, indicating possible coupling sites for K⁺ ions. The aqueous solution experiments indicated that raw straw could absorb water at 3.88 g g⁻¹, and this rate rose to its maximum 15 d after incubation. All of the experiments demonstrated that crop residues could absorb large amount of aqueous solution to preserve K⁺ indirectly during the initial decomposition period. These crop residues could also directly adsorb K⁺ via physical and chemical adsorption in the later period, allowing part of this K⁺ to be absorbed by plants for the next growing season.</p></div

The relationships between the reduction rate of the contribution of MBN to PMN and the reduction rate of PMN content after POM-removal.

<p>Note: the open symbols represent the soils from the rice-rapeseed rotation and the solid symbols represent the soils from the cotton-rapeseed rotation. The contribution of soil MBN to PMN = MBN / PMN; decrease in the rate of contribution of MBN to PMN = (Contribution _{original soil}—Contribution _{POM-removal soil}) / Contribution _{original soil} × 100; Reduction rate of PMN = (PMN_{original soil}—PMN_{POM-removal soil}) / PMN_{original soil} × 100.</p

The kinetics of water absorption for rice straw.

<p>Panel A shows the changes of water absorption in dried rice straw. Panel B shows the changes of water absorption of straw residue for different decomposition periods. The values are the means of 3 replicates (±standard deviation).</p