Higher Crop Yields Research Articles

Development and testing of a motor drive and control unit based on the field-oriented control algorithm for the seed-metering device

Good planting quality is the basis for high and stable crop yield. The performance of the seed-metering device is an essential factor affecting the planting quality. For the drive system of the seed-metering device with the motor as the power source, the working performance of the motor directly affects the seed-metering quality. A high-performance electric drive system should be able to provide stable torque and precise speed for the seed-metering device. However, it is not clear whether the motor can always maintain good speed control performance and torque stability under different working parameters (speed, load) of the seed-metering device. And the working performance of the motor is affected by the control algorithm. It is also unknown whether the motor control algorithm will affect the working performance of the motor, resulting in changes in the seed-metering quality of the seed-metering device. Aiming at the above problems, a motor drive and control unit based on the field-oriented control (FOC) algorithm was developed in this study. The variation law of the motor speed control performance and torque stability with the target speed and load under different control algorithms (square-wave control (SWC) and FOC) were explored. A comparison test of the seed-metering quality between the SWC algorithm and the FOC algorithm was carried out to determine the influence of the motor control algorithm on the seed-metering quality. The research shows that with the increase in target speed of the seed-metering device, the rise time and settling time tend to increase gradually. The motor speed response performance decreases with the increase in target speed of the seed-metering device. The average overshoot, average rise time, and average settling time of the five motor speeds under the FOC algorithm (10.43%, 0.44 s, 0.43 s) were less than the SWC algorithm (15.68%, 0.67 s, 0.95 s). The torque stability of the motor increases with the target speed and load. Torque ripple decreases with the increase in target speed and load level. The torque ripple of the FOC algorithm was always smaller than that of the SWC algorithm. With the increase in target speed and load level, the difference in torque ripple between the two control algorithms is gradually reduced. Compared with the SWC algorithm, the FOC algorithm had better speed control performance and torque stability. The motor control algorithm has a significant impact on the seed-metering quality. The average quality of feed index (QFI), average miss index (MI), and average coefficient of variation (CV) of the SWC algorithm were 98.58%, 1.05%, and 16.29%, respectively. The average QFI, average MI, and average CV of the FOC algorithm were 98.85%, 0.83%, and 14.59%, respectively. The seed-metering quality under the FOC algorithm was better than the SWC algorithm. The seed-metering quality of the electric drive seed-metering system can be improved by optimizing the motor control algorithm.

Residue Management and Nutrient Dynamics in Conservation Agriculture: A Review

Conservation tillage significantly influence the physico-chemical properties of soil that makes microclimate conducive for crop growth and productivity. The use of chemical fertilizers alone to sustain high crop yield has not been successful due to its effects on soil acidity, nutrient leaching, degradation of soil’s physical properties and organic matter. Higher levels of soil organic carbon, microbial biomass of carbon and nitrogen, nitrogen mineralization, total nitrogen and extractable phosphorus are directly related to crop residues under conservation tillage management. Conservation agriculture (minimum or no tillage with residue retention and crop rotation) practices has potential for increasing the nutrient supply to crops through changes in the mineralization and immobilization of nutrients by microbial biomass and provide an eco-protective environment for sustainable production. Conservation agriculture reduces nutrient percolation/leaching from the soil profile, can redistribute the soil profiles thus affects nutrient supply, and its storage. Entire soil-plant continuum changes after the conversion from conventional agriculture to conservation agriculture. The review therefore highlights the nutrient dynamics under crop residue management with no or minimum tillage.

Improving Wheat Yield and Water-Use Efficiency by Optimizing Irrigations in Northern China

Achieving the goal of increasing both crop yield and water-use efficiency with a better irrigation regime is a major challenge in semi-arid areas. In this study, we presented a two-season field experiment (October 2018–June 2019 and October 2019–June 2020) that considered drought stresses, i.e., no irrigation (W0), irrigated in jointing (W1), both in jointing and flowering (W2) after re-greening, and wheat varieties (S086; J22). The results showed that a 45.5% excess of irrigation water input did not promote wheat yield (W1 vs. W2). S086 was beneficial for the usage of soil water consumption under a low amount of irrigation water in both seasons. In addition, irrigation positively affected the activities of superoxide dismutase and catalase in flag leaves (p < 0.05). A decrease in irrigation helped to increase the concentrations of soluble sugar and proline and decrease the amount of malondialdehyde content for S086. For the water- and irrigation-water-use efficiency, W1 was significantly increased by 20.6–21.7% and 38.3–39.3% in 2018–2019 and 23.4–24.4% and 43.8–44.7% in 2019–2020, respectively, as compared to W2. Additionally, a higher yield for S086 than J22 was found under deficit irrigation. Consequently, our study suggested that the S086 variety combined with a total amount of irrigation water of 165 mm might be recommended to meet the win–win goal of high crop yields and water-use efficiency for reducing ground water depletion in the future.

Integrating stay-green and PIN-FORMED genes: PIN-FORMED genes as potential targets for designing climate-resilient cereal ideotypes.

Plant architecture modification (e.g. short-stature crops) is one of the key outcomes of modern crop breeding for high-yielding crop varieties. In cereals, delayed senescence, or stay-green, is an important trait that enables post-anthesis drought stress adaptation. Stay-green crops can prolong photosynthetic capacity during grain-filling period under post-anthesis drought stress, which is essential to ensure grain yield is not impacted under drought stress conditions. Although various stay-green quantitative trait loci have been identified in cereals, the underlying molecular mechanisms regulating stay-green remain elusive. Recent advances in various gene-editing technologies have provided avenues to fast-track crop improvement, such as the breeding of climate-resilient crops in the face of climate change. We present in this viewpoint the focus on using sorghum as the model cereal crop, to study PIN-FORMED (PIN) auxin efflux carriers as means to modulate plant architecture, and the potential to employ it as an adaptive strategy to address the environmental challenges posed by climate uncertainties.

Biochar for Improving crop Production in Nepal

Improving soil fertility and crop productivity is crucial to reduce food insecurity and poverty in Nepal. Biochar as a soil amendment has been found effective in increasing crop production. Here, we reviewed various biochar studies carried out in Nepal by different organizations and assessed future potential of biochar as an effective soil amendment. In this review, we have included the biochar pretreated (enriched) with nutrient or added separately in soil. We found that good quality biochar could be produced using the novel flame curtain metal and soil pit “Kontik” kiln with slow pyrolysis technology. Biochar produced from Kontiki found having high pH (9.8), organic carbon (OC, 72%), surface area (215 m2g-1) and cation exchange capacity (CEC, 72 cmol kg-1). Further, biochar application improved soil chemical properties (pH, OC, CEC, base cations) and nutrient availability such as available phosphorous (P) and potassium (K). Similarly, biochar addition increased crop yield significantly compared with non-biochar plots. Higher crop yield was achieved when biochar was enriched or charged with cattle urine. Thus, from this study, we suggest that biochar should be prioritized in government programs as a potential soil amendment and scale up or increase its use at farm level. SAARC J. Agric., 21(1): 227-238 (2023)

Plants’ Response to Abiotic Stress: Mechanisms and Strategies

Abiotic stress is the adverse effect of any abiotic factor on a plant in a given environment, impacting plants’ growth and development. These stress factors, such as drought, salinity, and extreme temperatures, are often interrelated or in conjunction with each other. Plants have evolved mechanisms to sense these environmental challenges and make adjustments to their growth in order to survive and reproduce. In this review, we summarized recent studies on plant stress sensing and its regulatory mechanism, emphasizing signal transduction and regulation at multiple levels. Then we presented several strategies to improve plant growth under stress based on current progress. Finally, we discussed the implications of research on plant response to abiotic stresses for high-yielding crops and agricultural sustainability. Studying stress signaling and regulation is critical to understand abiotic stress responses in plants to generate stress-resistant crops and improve agricultural sustainability.

Effect of Nutrient Management and Weeds on Incidence of Fungal Diseases in Rice

High-input, modern agriculture uses large amounts of energy, water, fertilizers, and pesticides to produce high crop yields. One of the major bottlenecks of the modern agriculture in the tropics is substantial yield losses due to fungal diseases including rice blast, leaf spots and leaf scald. The aim of this study was to compare the incidence of fungal diseases in judicious nutrient management systems, including organic, integrated, and conventional, under different weed categories during dry season (May to September 2020) and wet season (November 2020 to March 2021). Rice disease incidence were collected for both seasons from 48-84 days after sowing. Additionally, disease incidences on grasses and sedges weeds were also calculated. Brown spot, narrow brown leaf spot, leaf scald, and rice blast incidences were substantial in wet season, while the disease incidences during dry season in 2020 were negligible. The disease incidences were significantly higher (P<0.05) in organic and conventional input systems compared to the integrated input system. Disease incidences of brown spot and leaf scald were found in the dry season. Higher disease incidences were recorded in the wet season than in the dry season. The incidences of the brown spot were higher on sedges than in grasses and vice versa were observed for narrow brown leaf spot disease. Leaf scald incidences were positively correlated with the significant nitrogen status of the rice crop. Disease incidence was low in integrated input system compared to conventional and organic input systems, while weeds were reported as alternative hosts. It can be concluded that the integrated nutrient management with recommended dosage of nitrogen application with proper weed management can lead to low disease incidents, hence is ecologically more sustainable.

Effect of Nitrogen Management on Wheat Yield, Water and Nitrogen Utilization, and Economic Benefits under Ridge-Furrow Cropping System with Supplementary Irrigation

Supplemental irrigation under a ridge-furrow (RF) cropping system is a valuable cropping practice that balances resource efficiency and high crop yield. However, the effects of nitrogen management on crop growth, yield formation, and economic benefits under RF systems have not been clearly investigated. In this study, the experiment was designed with three experimental factorials, including three cropping systems (RF, RF cropping with 80 mm irrigation; TF1, traditional flat cropping with 200 mm irrigation; and TF2, traditional flat cropping with 80 mm irrigation), two nitrogen application rates (NL, 180 kg N ha−1; NH, 240 kg N ha−1), and two fertilizer application models (B, all nitrogen fertilizers were applied basally at the pre-sowing stage; BT, nitrogen fertilizer was applied at both the pre-sowing and jointing stages at a ratio of 1:1). A two-year field experiment was conducted to investigate the effects of nitrogen fertilizer management on wheat yield, water and nitrogen utilization, and economic benefits under the RF cropping system. The results showed that the RF system significantly increased the soil moisture content and improved the water productivity (WP) and grain yield of wheat. Nitrogen reduction (NL) under the RF system did not affect the water use of the wheat compared with traditional high nitrogen application (NH) but increased the nitrogen uptake and fertilizer productivity of the wheat. Although NL led to a reduction in aboveground dry matter accumulation, it did not significantly affect the yield of wheat but increased the net income of wheat cultivation. Under NL conditions, the BT nitrogen application model promoted nitrogen uptake in wheat and ameliorated the reduction in grain protein content due to plastic film mulching, and this model is an integrated planting practice that trades off wheat yield and quality. These findings suggest that NLBT is a promising and recommendable cropping practice under RF systems considering resource utilization, high yield and quality, and economic efficiency.

Smart Farming Revolution: Portable and Real-Time Soil Nitrogen and Phosphorus Monitoring for Sustainable Agriculture.

Precision agriculture is crucial for ensuring food security in a growing global population. Nutrients, their presence, concentration, and effectiveness, are key components in data-driven agriculture. Assessing macro and micro-nutrients, as well as factors such as water and pH, helps determine soil fertility, which is vital for supporting healthy plant growth and high crop yields. Insufficient soil nutrient assessment during continuous cropping can threaten long-term agricultural viability. Soil nutrients need to be measured and replenished after each harvest for optimal yield. However, existing soil testing procedures are expensive and time-consuming. The proposed research aims to assess soil nutrient levels, specifically nitrogen and phosphorus concentrations, to provide critical information and guidance on restoring optimal soil fertility. In this research, a novel chip-level colorimeter is fabricated to detect the N and P elements of soil onto a handheld colorimeter or spectrophotometer. Chemical reaction with soil solution generates color in the presence of nutrients, which are then quantitatively measured using sensors. The test samples are collected from various farmlands, and the results are validated with laboratory analysis of samples using spectrophotometers used in laboratories. ANOVA test has been performed in which F value > 1 in our study indicates statistically significant differences between the group means. The alternate hypothesis, which proposes the presence of significant differences between the groups, is supported by the data. The device created in this paper has crucial potential in terms of environmental and biological applications.

Microbiome transplant can effectively manage root-knot nematode infectivity in tomato

A critical factor in alleviating nematode menace in horticultural crops is discerning the nature of microbial communities associated with roots and rhizosphere. Root-knot nematodes (Meloidogyne spp.) are one of the major constraints for obtaining high yields of vegetable crops. Root-knot nematode-infected and uninfected plants occur in agricultural fields. Most biocontrol strategies used for nematode management focus on introducing a single bioagent. Recently, microbiome transplant has been found effective in curing human diseases and is also used to cure animals. Here we evaluated the role played by the microbial communities in managing M. incognita infection on tomatoes grown in protected cultivation by transplanting the microbial slurry extracted from the rhizosphere soil of the healthy plants and those infected with the root-knot nematode. The relative abundance of Gram-negative bacteria (11.11 % and 16.08 %) and anaerobes (39.58 % and 16.59 %) phospholipid fatty acids (PLFA) was significantly higher in healthy roots and rhizosphere soil. In contrast, Gram-positive bacteria (21.52 % and 37.61 %) were comparatively higher in nematode-infected roots and rhizosphere soil. Nematode penetration and reproduction indices were significantly reduced (34–43 %) by inoculating the healthy plant's unfiltered microbial slurry. However, inoculation with unfiltered microbial slurry from the rhizosphere soil of infected plants increased (8–26 %) nematode penetration and reproduction. Plant growth and fruit yield (13.1 %) of tomatoes were positively influenced by unfiltered microbial slurry from the rhizosphere soil of healthy plants. The significant role of the healthy microbiome transplant in reducing nematode invasion and reproduction and increasing the crop yield of tomatoes grown in protected cultivation suggests that microbial transplants could be an approach to managing plant nematodes.

Research Progress in Crop Root Biology and Nitrogen Uptake and Use, with Emphasis on Cereal Crops

The biological characteristics of crop roots are closely related to the efficient utilization of nitrogen and have become a research hotspot in agricultural cultivation and breeding in recent years. The root system and root microbiota play a crucial role in both the basic and the plastic growth and development of plants in response to external environmental changes. Nitrogen is an indispensable nutrient element for crop growth, and the efficient utilization of nitrogen is the key to achieving the high yield and quality of crops and establishing environmentally friendly agricultural production. The nitrogen absorbed and utilized by rice mainly enters the aboveground part of the plant through the root system from within the soil. This process is explored from the perspective of root biology (root morphology, physiological and biochemical characteristics, root growth and development process and regulation, rhizosphere microorganisms, and their symbiotic systems), which is in line with the directions of “less investment, increased production, environmental protection, and sustainable development” in China. Based on the research status in this field at present, this article explored the interaction mechanism between crop root biology and nitrogen absorption and utilization, and looks forward to the future research directions for root biology. This study provides a theoretical basis for reducing nitrogen fertilizer application, optimizing nitrogen-efficient cultivation management techniques, and selecting nitrogen-efficient varieties.

Serine protease NAL1 exerts pleiotropic functions through degradation of TOPLESS-related corepressor in rice.

NARROW LEAF 1 (NAL1) is a breeding-valuable pleiotropic gene that affects multiple agronomic traits in rice, although the molecular mechanism is largely unclear. Here, we report that NAL1 is a serine protease and displays a novel hexameric structure consisting of two ATP-mediated doughnut-shaped trimeric complexes. Moreover, we identified TOPLESS-related corepressor OsTPR2 involved in multiple growth and development processes as the substrate of NAL1. We found that NAL1 degraded OsTPR2, thus modulating the expression of downstream genes related to hormone signalling pathways, eventually achieving its pleiotropic physiological function. An elite allele, NAL1A, which may have originated from wild rice, could increase grain yield. Furthermore, the NAL1 homologues in different crops have a similar pleiotropic function to NAL1. Our study uncovers a NAL1-OsTPR2 regulatory module and provides gene resources for the design of high-yield crops.

Climate-smart management for increasing crop yield and reducing greenhouse gas emission in Beijing-Tianjin-Hebei region, China

Ensuring stable and high yields of crops and reducing greenhouse gas (GHG) emissions from farmland through climate-smart managements in China are of great significance for mitigating global warming. In this study, the effects of climate-smart managements on crop yields and GHG emissions during 1981–2020 in Beijing-Tianjin-Hebei region of China were explored based on the APSIM crop model. Four cropping patterns and four fertilization measures were set according to the local planting experiences and existing research results. The results showed that proper fertilization management and effective cropping pattern were conducive to the improvement of total crop yield and reduction of GHG emissions in Beijing-Tianjin-Hebei region of China. The total yield of winter wheatsummer maize (W-E) cropping pattern under F4 fertilization measure (400 kg·ha−1) was the highest, ranging from 26,088.82 kg·hm−2 to 31,430.62 kg·hm−2. Among the four fertilization measures, the GHG emission intensity of W-E cropping pattern was the highest, followed by winter wheatsummer maizeearly maize (10 days earlier) (W-M-ME10) and winter wheatsummer maizeearly maize (20 days earlier) (W-M-ME20) cropping patterns. However, the GHG emission intensity of summer maize (ME) cropping pattern was the lowest. As a whole, although the GHG emissions of ME cropping pattern were low, and the yields of summer maize were also low, which was difficult to ensure the local food security needs. As the traditional cropping pattern in Beijing-Tianjin-Hebei region, W-E cropping pattern could ensure the need for high yield, but it also caused excessive GHG emissions in the soil. Comprehensively estimating the environmental effects and crop total yields, the W-M-ME20 cropping pattern was considered an optimal cropping pattern in Beijing-Tianjin-Hebei region of China at present or in the future. Our results have significant ramifications for local agriculture to adapt to continuous global warming as well as for enhancing studies on climate change's effect.

ВЛИЯНИЕ СРЕДСТВ ХИМИЗАЦИИ НА ФОРМИРОВАНИЕ УРОЖАЯ ЗЕЛЕНОЙ МАССЫ КУКУРУЗЫ С ПОЧАТКАМИ МОЛОЧНО-ВОСКОВОЙ СПЕЛОСТИ

Corn is a valuable food and technical crop and almost all its parts are used in different branches of industry which cannot do without corn grains and pulp and paper mills use its leaves and stems. In addition, the crop has important agronomic importance in controlling field weeds. It is one of the most important cereal crops in world agriculture. As a high-yielding crop, it plays an important role in fodder production. A powerful reserve for increasing corn yields is mineral fertilizers, as well as the widespread introduction of new zoned varieties and hybrids of corn into production. This article presents the influence of organic and mineral fertilizers with macro-, micro-, complex fertilizers and growth regulators on corn yield and production. Sufficient nutrients are necessary to obtain high yields. Various growth-promoting substances are also used in modern agricultural practice. They improve seed germination and germination energy, accelerate plant growth, plant development and increase yield. Using special mixtures of fertilizers for corn concentrates all the necessary complexes of nutrients. The necessary complex of nutrients is applied in one step, which reduces the unevenness of fertilization. Spraying of combined fertilizers containing microelements and growth regulators before sowing increases plant resistance to adverse weather conditions. The use of combined compositions of NPK fertilizers allows the development of resource-saving systems and reduces the cost of fertilizers.

The effectiveness of applying various doses of nitrogen fertilizer on spring triticale in the conditions of the Moscow region

Nitrogen is a key element in achieving high yields of grain crops. The study of the reaction of new varieties to the use of nitrogen fertilizers in eld experiments allows us to identify the most e ective techniques for realizing potential yields in speci c soil and climatic conditions. The research was carried out in 2020-2021 in the conditions of the Moscow region on sod-podzolic heavy loamy soils with a low humus content (1.3…1.7 %), high phosphorus content, average potassium content. The scheme of the experiment involved studying the e ect of increasing and fractional doses of nitrogen fertilizer from 30 to 150 kg of active substance per hectare, introduced in the form of ammonium nitrate (NH4NO3). Fertilization was carried out manually by seedlings, in variants with fractional application, the second dose was introduced into the exit phase into the tube. The objects of research were the varieties of spring triticale Timiryazevskaya 42 and Botanicheskaya 4, registered in the State Register of Breeding Achievements in 2022. Nitrogen fertilizers increase the height of plants of the Timiryazevskaya 42 variety by 4.7…10.2 cm, and the Botanicheskaya 4 variety by 8.7…10.1 cm. At the same time, the lodging of crops in the prevailing meteorological conditions was not noted in all variants of the experiment. When applying nitrogen fertilizers in doses from 90 to 120 kg / ha, the increase in grain yield on the Timiryazevskaya 42 variety was 3.61…5.10 t/ha to control (without fertilizers), on the Botanicheskaya 4 variety - 2.71…2.42 t/ha. The highest yield in the experiment was obtained when applying nitrogen fertilizers on the Timiryazevskaya 42 variety at a dose of 120 kg/ha - 9.99 t/ha, on the Botanicheskaya variety at a dose of 90 kg/ha - 7.16 t/ ha. The removal of batteries without fertilizers and high yields, when applying high doses of nitrogen fertilizers, indicate a higher yield potential of the Timiryazevskaya 42 variety, compared with the Botanicheskaya 4 variety.

Analyzing the drivers of smallholder farmer’s market participation in the Sahelian region of Niger

Many sub-Saharan farmers rely on agricultural production for home consumption and sell crops to meet their other needs. Farmers’ market intervention enhances economic expansion and helps to improve household food security. In our current study, we strive to explore the determinants of farmers’ decisions and the intensity of market participation in the Sahelian region of Niger, where little has been published, thereby filling the gap in the literature. A double hurdle approach was employed to achieve this objective using a sample collected from 1784 farm households in Niger.Our findings reveal that the total quantity of crops produced, gender, credit access, farming experience, training, drought, and assets positively impact household market participation significantly. Based on these results, as the quantity of crop sales is driven positively and significantly by the amount of crop produced, finding ways to increase crop production will increase household market participation. This can only be achieved by encouraging farmers to adopt high-yield crop varieties, such as climate-resilient ones, to boost productivity. Furthermore, considering the positive association between credit availability and smallholder market participation, any initiative in the agricultural sector that will bring efforts to supply credit and farm inputs to farmers will surely help to improve agricultural production and household market participation.

Optimal cooperative application solutions of irrigation and nitrogen fertilization for high crop yield and friendly environment in the semi-arid region of North China

Optimal cooperative application solutions of irrigation and nitrogen fertilization for high crop yield and friendly environment in the semi-arid region of North China

Improving field establishment and yield in seed propagated Miscanthus through manipulating plug size, sowing date and seedling age.

Biomass crops provide significant potential to substitute for fossil fuels and mitigate against climate change. It is widely acknowledged that significant scale up of biomass crops is required to help reach net zero targets. Miscanthus is a leading biomass crop embodying many characteristics that make it a highly sustainable source of biomass but planted area remains low. Miscanthus is commonly propagated via rhizome, but efficient alternatives may increase uptake and help diversify the cultivated crop. Using seed-propagate plug plants of Miscanthus has several potential benefits such as improving propagation rates and scale up of plantations. Plugs also provide an opportunity to vary the time and conditions under protected growth, to achieve optimal plantlets before planting. We varied combinations of glasshouse growth period and field planting dates under UK temperate conditions, which demonstrated the special importance of planting date on yield, stem number and establishment rates of Miscanthus. We also propagated Miscanthus in four different commercial plug designs that contained different volumes of substrate, the resulting seedlings were planted at three different dates into field trials. In the glasshouse, plug design had significant effects on above and belowground biomass accumulation and at a later time point belowground growth was restricted in some plug designs. After subsequent growth in the field, plug design and planting date had a significant effect on yield. The effects of plug design on yield were no longer significant after a second growth season but planting date continued to have a significant effect. After the second growth year, it was found that planting date had a significant effect on surviving plants, with the mid-season planting producing higher survival rates over all plug types.Establishment was positively correlated with DM biomass produced in the first growth season. Sowing date had a significant effect on establishment but the impacts of plug design were more nuanced and were significant at later planting dates. We discuss the potential to use the flexibility afforded by seed propagation of plug plants to deliver significant impacts in achieving high yield and establishment of biomass crops during the critical first two years of growth.

Effects of turning rainforest into oil-palm plantations on silicon pools in soils within the first 20 years after the transformation

Potential effects of land-use/land-cover (LULC) transformation from lowland rainforest into oil-palm plantations on silicon (Si) pools in tropical soils remain poorly understood, although appropriate levels of plant-available Si in soils may contribute to maintain high crop yields and increase the vitality and drought resistance of oil palms. Therefore, the aim of our study was to identify possible effects of such LULC change on soil Si pools. For this purpose, we compared soil Si pools under lowland rainforest and ca. 20 year-old oil-palm plantations in Jambi Province, Indonesia. The investigated soils were Acrisols and Stagnosols, in which we quantified six different soil Si pools following a sequential extraction procedure to evaluate, whether 20 years of oil-palm cultivation has led to a depletion of these soil Si pools. The considered pools included mobile Si, adsorbed Si, Si bound in soil organic matter (SOM), Si included in pedogenic oxides and hydroxides, and Si in amorphous silica of biogenic and pedogenic origin. Finally, we also determined total Si. All oil-palm plantations established on sloping terrain and Acrisols only showed decreased Si stocks of mobile Si, adsorbed Si and SOM-bound Si; those established in floodplains and Stagnosols had decreased stocks of SOM-bound Si and biogenic-amorphous silica. Lower Si stocks were mostly attributed to a missing “stable” phytolith pool in the subsoil and less organic matter in topsoils under oil-palm plantations. When comparing well-drained and riparian areas, flooding seemed to increase phytolith dissolution. We conclude that 20 years of oil-palm cultivation has not yet led to a significant depletion of soil Si pools. As topsoils comprise the highest concentrations of SOM-bound Si and Si in amorphous silica of biogenic origin but are susceptible to erosion and surface runoff under managed oil-palm plantations, it would be advisable to instate specific management practices that maintain organic-rich and well-aired topsoils on oil-palm plantations.

Long-Term Organic Manure Substitution Increases Yield and Phosphorus Use Efficiency in a Double-Rice System by Altering Soil Phosphorus Uptake and Apparent Balance

The excessive use of chemical phosphorus (P) fertilizer can lower grain yield and P use efficiency (PUE) by aggravating soil acidity. Substituting organic manure for chemical fertilizer can alleviate the problem, although the long-term effect of organic manure incorporation is unknown. We conceptualized that substituting organic manure for chemical fertilizer may result in higher crop yields and PUE. Therefore, the impact of long-term fertilizer treatments: (i) CK (control), (ii) PK (phosphorus and potassium fertilizer), (iii) NP (nitrogen and P fertilizer), (iv) NK fertilizer, (v) NPK fertilizer, and (vi) NPKM (30% NPK fertilizer plus 70% manure) on rice yield, PUE, P uptake, and apparent balance (APB) was investigated. The results showed that rice yield under different fertilizer treatments ranged from 6.2 to 11.8 t ha−1 (1984–1995), 7.9 to 12.7 t ha−1 (1996–2007), and 6.6 to 12.8 t ha−1 (2008–2018). The rice yield under NPKM was greatly improved compared to other treatments, except with that of NPK (1984–1995). Soil organic carbon (SOC), available P and phosphorus activation coefficient (PAC) under NPKM were significantly higher than other treatments during 1984–2018. Soil pH (1984–2018) was greatly higher under CK and NPKM than under other treatments. Soil total P under PK, NP, NPK, and NPKM was significantly higher than under CK and NK (1984–2018). Compared to other treatments, P uptake was significantly higher under NPKM, except with that of NPK (1984–1995 and 2008–2018). The average PUE (1984–2018) was 10.7, 20.2, 36.1, and 44.2 kg kg−1 under PK, NP, NPK, and NPKM, respectively. The APB under NPKM was significantly lower as compared to PK, NP, and NPK treatments. Therefore, we conclude that in addition to improving soil organic carbon, cations inputs from organic manure can be a factor for the increase in soil pH, making organic manure substitution for chemical fertilizer a more efficient strategy for increasing PUE and crop yield.