Increasing Plant Density Research Articles

Quantifying contributions of leaf area and longevity to leaf area duration under increased planting density and nitrogen input regimens during maize yield improvement

Leaf area and its longevity are the key factors driving dry matter accumulation and yield formation in maize (Zea mays. L). Both factors are influenced by cultivation management measures. The objective of this study was to utilize a quantitative framework to better understand the contribution of leaf area and longevity to leaf area duration (LAD) and yield in maize plants at varying plant densities and nitrogen application rates. A two-year field experiment was conducted using a factorial combination of two plant densities and four nitrogen levels. Leaf area and longevity were measured at each leaf position in two different maize cultivars. We calculated the LAD at the single-leaf, individual-plant, and whole-population scales and quantitatively analyzed the contribution of leaf area and longevity to LAD. The results showed that in the upper leaves, leaf area had a larger proportional contribution to LAD (54.1–95.7%), whereas in the lower leaves, leaf longevity contributed more to LAD (51.8–74.1%). Both were greatly affected by variations in plant density and nitrogen application. At the individual-plant scale, the proportional contribution of leaf area to LAD (57.3%) was similar to that of leaf longevity (57.2%); at the whole-population scale, leaf area accounted for a larger contribution to LAD (87.0%). The increase in LAD (which integrating increases in leaf area and longevity) was positively associated with an increase in dry matter at maturity and grain yield. Yield gain was achieved by reasonable increases in density and nitrogen fertilizer application to promote LAD. The quantitative evaluation of leaf area and longevity described in this study provides a theoretical basis for increasing maize yield under increased plant density and nitrogen input conditions.

Seed fixed oil content, oil yield, and fatty acids profile of Nigella sativa L. in response to fertilization and plant density

The current study aimed to assess the impacts of fertilization and plant density on fixed oil content, oil yield, and fatty acids profile of Nigella sativa L. under Mediterranean environment. The 3-year experiment was set up in a split-plot design with three replications, two main plots (plant densities: 200 and 300 plants m-2) and four sub-plots (fertilization treatments: control, seaweed compost, farmyard manure and inorganic fertilizer). The seed yield, fixed oil content, as well as the fixed oil yield were positively affected by the increase of available nitrogen and negatively by the increase of plant density, with their highest values recorded in the low-density and inorganic fertilization. Regarding the composition in fatty acids, it was found that with the increase of plant density there was a decrease in saturated (SAFA: myristic, palmitic and stearic acid) and polyunsaturated (PUFA: linoleic, α-linolenic and eicosadenoic acid) fatty acids, while there was an increase in oleic acid which was the only monounsaturated fatty acid detected in fixed oil. In terms of fertilization, the organic fertilizers were the ones that contributed positively to the content of the respective fatty acid. As a conclusion, plant densities greater than 200 plants m-2 result in lower seed yield, fixed oil content and yield, whereas the effect of inorganic fertilization was equally important in seed and fixed oil yield; however, when the seed and/or its fixed oil are utilized for their high medicinal and nutritional value, the application of compost is indicated, resulting in a significant increase in the content of PUFAs, characterized for their beneficial effects on human health.

Efficient Need Based Nitrogen Management in Rabi Maize (Zea mays L.) using Leaf Colour Chart Under Varied Planting Density

The field experiments were conducted for two consecutive rabi seasons (November –March) of 2017–18 and 2018–19 at the Wet land farm of S.V. Agricultural College, Tirupati to calibrate leaf colour chart (LCC) for increasing growth yield, nitrogen uptake under varied plant density to establish and evaluate threshold leaf colour greenness as a guide for in-season need based fertilizer N in maize. Research results indicated that the planting density, nitrogen levels and LCC threshold values significantly influenced all the growth and yield attributes, yield and nitrogen uptake. Plant height, days required to 50% tasselling and silking, cob yield, harvest index and nitrogen uptake increased significantly with increase in plant density i.e., 1,11,111 plants ha-1 with application of fertilizer nitrogen at higher dose i.e. 40 kg ha-1 and by using higher LCC threshold value (LCC 5) in different splits. Whereas, leaf area planr-1, cob girth, number of kernels rows cob-1 and number of kernels cob-1 was lessened significantly with increase in planting density, however it was increased with application of nitrogen at higher rate i.e., 40 kg ha-1 by using higher LCC threshold value (LCC 5) at various splits. Eventually, experimental results manifested that, fine-tuning of N dose and time of application by number of splits which synchronize the crop demand was the best management strategy for sustainable crop growth, production and productivity of maize.

Different Responses in Root Water Uptake of Summer Maize to Planting Density and Nitrogen Fertilization.

Modifying farming practices combined with breeding has the potential to improve water and nutrient use efficiency by regulating root growth, but achieving this goal requires phenotyping the roots, including their architecture and ability to take up water and nutrients from different soil layers. This is challenging due to the difficulty of in situ root measurement and opaqueness of the soil. Using stable isotopes and soil coring, we calculated the change in root water uptake of summer maize in response to planting density and nitrogen fertilization in a 2-year field experiment. We periodically measured root-length density, soil moisture content, and stable isotopes δ18O and δD in the plant stem, soil water, and precipitation concurrently and calculated the root water uptake based on the mass balance of the isotopes and the Bayesian inference method coupled with the Markov Chain Monte Carlo simulation. The results show that the root water uptake increased asymptotically with root-length density and that nitrogen application affected the locations in soil from which the roots acquired water more significantly than planting density. In particular, we find that reducing nitrogen application promoted root penetration to access subsoil nutrients and consequently enhanced their water uptake from the subsoil, while increasing planting density benefited water uptake of the roots in the topsoil. These findings reveal that it is possible to manipulate plant density and fertilization to improve water and nutrient use efficiency of the summer maize and the results thus have imperative implications for agricultural production.

Optimum Plant Density for Increased Groundnut Pod Yield and Economic Benefits in the Semi-Arid Tropics of West Africa

Groundnut is a very important crop in the West and Central Africa (WCA) region, accounting for almost 70% of Africa’s groundnut production in 2019. Despite its economic importance, the crop’s yield is still low. For a high yield and profitable economic returns, optimal plant density is a fundamental crop management practice. Plant density experiments were conducted at the ICRISAT-Mali research station between 2016 and 2021 over the main rainy and dry seasons to determine the optimum density for maximum groundnut yield and economic benefits. The treatments contained row spacing of 20 cm, 30 cm, 40 cm, 50 cm, 60 cm, 70 cm, 80 cm, 90 cm, and 100 cm, with intra-row spacing of 10 cm, 15 cm, and 20 cm. Results showed that when plant density was increased, dry pod yield, production value, and net economic benefit per hectare increased in a no moisture stress scenario. During the rainy season, the 40 cm × 10 cm spacing gave the highest dry pod yield (1693 kg), production value ($891.6), and net benefit ($403.5) per hectare. The highest dry pod yield (3703 kg), production value ($2173), and net benefit ($1510.2) per hectare were obtained from 30 cm × 10 cm spacing during the dry season. The number of pods per plant and 100 SW increased with lower plant densities. Therefore, it is recommended to increase plant density to at least 222,000 plants per hectare in the Sudan Savannah agroecology of WCA.

Nutrient Utilization and Double Cropping Rice Yield Response to Dense Planting with a Decreased Nitrogen Rate in Two Different Ecological Regions of South China

An increased planting density and decreased nitrogen (N) rate combination may obtain a stable yield and enhance N utilization. However, the effects of an increased planting density and decreased N rate combination on the yield and nutrient utilization in different ecological regions are unclear. The aim of this research was to assess the interactive impacts of the N rates and planting densities on double cropping rice yields and nutrient utilization in two ecological regions in field experiments during 2018 and 2019. The results showed that, at Shanggao, increased planting densities of 67% and 200% compensated for the biomass, nutrient uptake and yield losses from N application reductions of 20% and 27% and increased the nutrient utilization of the early and late seasons. However, at Xingguo, compared with the N2D1 treatment (165 kg ha−1 with 57 plants per m2), the late rice yield under the N1D2 treatment (120 kg ha−1 with 114 plants per m2) decreased by 6.71% and 5.02% in 2018 and 2019, respectively. The photosynthetic rate and nutrient uptake were likely related to the positive interaction on the double cropping rice yield in the two ecological regions. Our results indicate that dense planting is a feasible cultivation strategy to decrease N inputs for double cropping rice, but the low soil nutrient supplies negatively affect stable yields in different ecological regions.

Response of Common Bean (Phaseolus vulgaris L.) to NP Fertilizer Rates and Plant Population Density at Jimma Zone, Southwest Ethiopia

F Field experiments were carried out for 2018-2020 main cropping seasons at kersa and Omonada Jimma on farmers’ fields. The treatments consisted of factorial combinations of 23/23, 23/46, 46/46 and 69/69 NP kg ha-1 levels with inter and intra (333333, 250000, 200000 and 166667 plant density ha-1) respectively laid down in a randomized complete block design (RCBD) with three replications using (Nassir) common bean variety. Across season and location data analysis of ANNOVA showed that all parameters were significantly affected by different densities and NP fertilizer rates including above ground biomass, harvest index and grain yield except harvest index was not affected by NP fertilizer rates. The highest plant height (72.51cm) was recorded from the highest (69/69 kg ha-1) NP fertilizer rate. The highest above ground biomass and grain yield of 6.40 and 2.45 t ha-1 were obtained from the highest (333333) plant density ha-1. Also, it showed still there was an increase in plant density increases with 26.29 and 6.52% grain yield advantage over the lowest density and control recommendation respectively. Also from economic and sensitivity analysis results treatments (333333) ha-1 plant population density, (23/23) and (46/46) kg/ha NP fertilizer rates gave the highest yield response and net benefit with MMR 1035, 111 and 224% respectively. In conclusion, intra and inter row spacing 3*10cm or equivalent (333333) ha-1 plant population density with applications of one of the two (23-23) or (46/46) kg/ha NP fertilizer rates based on their resource was recommended to farmers of study areas and similar agro ecology.

Effects of irrigation on stem lignin and breaking strength of winter wheat with different planting densities

Increasing planting density is an important cultivation approach to improve wheat single yield. In field production, over irrigation under densified population conditions can easily cause lodging. Therefore, the lodging resistant wheat cultivar JM22 and the lodging sensitive wheat cultivar SN16 was used as experimental materials. Two irrigation treatments [rain-fed and spring irrigation (at jointing and anthesis stage)] were set with five planting densities (150 × 104 plants ha−1, 225 × 104 plants ha−1, 300 × 104 plants ha−1, 375 × 104 plants ha−1 and 450 × 104 plants ha−1). Lignin accumulation and its monomers (guaiacyl, syringyl and p-hydroxyphenyl) in combination with the apparent and microanatomic characteristics of the basal second stems, were determined to elucidate effects of irrigation on the formation of breaking strength in wheat stems at different planting densities. The results showed that the most important factors affecting the breaking strength of stems were different in different stages and different treatments. Through multiple stepwise regression analysis, it was found that under low density (150 × 104 plants ha−1) conditions, irrigation decreased breaking strength of stem mainly by affecting lignin accumulation and its subunits. However, at medium and high density (225 × 104 plants ha−1-375 × 104 plants ha−1), the decrease of stem breaking strength caused by irrigation was the result of the co-regulation of lignin metabolism, stem microscopic and morphological characteristics. At anthesis stage, when irrigated under the condition of low density (150 × 104 plants ha−1), the content of G subunit increased by 100 μg g−1, the stem breaking strength increased by 0.4 N. At medium density (225 × 104 plants ha−1-300 × 104 plants ha−1), irrigation increased S subunit content by 100 μg g−1, which resulting in high stem breaking strength by 0.5 N. However, at high density (375 × 104 plants ha−1-450 × 104 plants ha−1), along with H subunit content was increased by 10 μg g−1, the stem breaking strength was decreased by 0.14 N. Under irrigated and densified populations conditions, the decreasing range of wall thickness (−13.53%), stem filling degree (−16.65%) and the increasing range of H monomer ratio (15.77%) of high lodging resistance varieties were lower than those of SN16. Therefore, it held better ability to resist adverse environment and maintain lodging resistance. In this experiment, on the basis of irrigation (at jointing and anthesis stage) and 25 × 104 plants ha−1 planting density resulted in the highest yield (10,325.03 kg ha−1) and moderate stem.

Planting Arrangement and Effects of Planting Density on Tropical Fruit Crops—A Review

With the growing importance of fruits as valuable food resources, attention has been paid in recent years to enhance productivity and quality. Increasing productivity per unit area through agronomic management is one of the important strategies to increase the production of fruit crops. Keeping this view, this review was undertaken to improve understanding of the planting arrangement and the effect of planting density on productivity and quality of fruit crops. This review will thus provide updated and in-depth information about the influence of planting density on yield and fruit quality, which will also be useful for the growers, consumers, exporters, and processing industry. In fruit crops, the effect of plant density and planting arrangement is well documented. From the review, it is understood that yield per unit area is the product of fruit yield plant−1 and the number of plants per unit area. Fruit size increases with a decreasing planting density, while total yield increases with an increasing density at a certain level. However, fruit quality decreases with an increasing planting density.

Density Alters Impacts of Genotypic Evenness on Productivity in an Experimental Plant Population.

Genetic diversity plays important roles in maintaining population productivity. While the impact of genotypic richness on productivity has been extensively tested, the role of genotypic evenness has not been considered. Plant density can also affect population productivity, but its interaction with genotypic diversity has not been tested. We constructed experimental populations of the clonal plant Hydrocotyle vulgaris with either low or high richness (consisting of four vs. eight genotypes), either low or high evenness (each genotype had a different number vs. the same number of ramets), and either low or high density (consisting of 16 vs. 32 ramets) in a full factorial design. Total biomass of plant populations did not differ between four- and eight-genotype mixtures. When the initial plant density was low, total biomass of populations with high genotypic evenness was significantly greater than total biomass of those with low genotypic evenness. However, this difference disappeared when the initial plant density was high. Moreover, total biomass increased linearly with increasing plant density at harvest, but was negatively correlated to variation in leaf area. We conclude that genotypic evenness but not genotypic richness can benefit population productivity, and that plant density can alter the impact of genotypic evenness on population productivity.

Nitrogen Application and Dense Planting to Obtain High Yields from Maize

The rational application of nitrogen fertilizer and close planting are two important ways to obtain high yields and efficient growth from maize (Zea mays L.). This study utilized the maize varieties DengHai 618 and XianYu 335 as test materials from 2019 to 2020 and the maize variety XianYu 335 as the test material in 2021. The planting densities were 7.5 × 104 plants ha−1 and 12.0 × 104 plants ha−1, respectively. Application rates of nitrogen within the range of 0–765 kg ha−1 per 45 kg ha−1 were considered the nitrogen application gradient. The results showed that as the nitrogen application rate increased, the yield of the maize increased at first and then tended to remain flat. Under conditions of 7.5 × 104 plants ha−1 density, the best yield was 17.6–20.2 t ha−1, and the required nitrogen application rate was 219–337 kg ha−1. Under conditions of 12.0 × 104 plants ha−1 density, the best yield was 18.7–21.9 t ha−1, and the required nitrogen application rate was 243–378 kg ha−1. With the increase in the nitrogen application rate, the dry matter weight showed a linear/platform relationship in each growth period. The best nitrogen application rate was obtained for dry matter accumulation in various stages by fitting the nitrogen application rate and dry matter accumulation in different stages. It is concluded that when the planting density was 7.5 × 104 plants ha−1, the recommended nitrogen application rate was 340 kg ha−1, and the distribution ratio of the nitrogen application rates before and after silking were 61.2% and 38.8%, respectively. When the planting density was 12.0 × 104 plants ha−1, the recommended nitrogen application rate was 380 kg ha−1, and the distribution rates before and after flowering were 65.8% and 34.2%, respectively. In summary, increasing planting density can improve maize yield, and the amount of nitrogen applied should be increased before flowering.

Effects of N fertilizer rate and planting density on short-season cotton yield, N agronomic efficiency and soil N using 15N tracing technique

Straw returning has been widely used as a nitrogen (N) reduction measure in the North China Plain in recent years. However, little is known of the optimal planting density and N application rate of cotton under straw returning. In order to study the effect of the planting density and N application rate on cotton yield, nitrogen agronomic efficiency (NAE), fertilizer N recovery efficiency (FNRE), N balance and soil N under straw returning, a split-plot design in randomized complete blocks was used in the experiment. The main plots were assigned to plant densities (4.50 × 104, 6.75 × 104 and 9.00 × 104 plants hm−2), and the subplots to N application rates (0, 180, 225 and 270 kg N hm−2). The results showed that the biological yield increased as the planting density and the N application rate increase, but the harvest index decreased. Therefore, the highest biological yield was found under D9.00N270, but the highest cotton yield was found under D6.75N225. Excessive N (N270) application rate was not conducive to the improvement of NAE and FNRE. The amounts of plant N derived from fertilizer (Ndff) was reduced with the increase of planting density. Therefore, soil N would be consumed because the N balance was a negative value when N application rate was decreased at N180, especially at high density. The N balance was closest to zero at D6.75N225. In summary, with the yield, NAE, FNRE, N balance and the stability of soil N taken into consideration, the optimal combination of planting density and N application rate in the North China Plain was D6.75N225, because this treatment had the highest cotton yield, and most importantly, it maintained sustainable cotton production in the field.

How to enhance the agronomic performance of cactus-sorghum intercropped system: planting configurations, density and orientation

Clarifying cultivation techniques and making production systems more efficient are practices that have been much sought after in agricultural systems in recent decades. In this context, the forage yield, biological efficiency, and competitive ability, of different cultivation strategies for intercropping forage cactus and sorghum were determined in biosaline production systems from 2018 to 2020 in Brazil. Four experiments were carried out, comprising: 1) cropping configurations for the forage cactus-sorghum intercropping system; 2 and 3) planting densities for the forage cactus intercropped with sorghum with an east-west and north-south row orientation, respectively; and 4) planting densities for the forage cactus and sorghum. Each experiment used a randomised block design with four replications. The intercropped forage cactus and sorghum showed higher productivity than the monocropped systems. The indices of biological efficiency (LER, ATER, LEC and SPI with mean values equal to 1.6, 1.8, 0.6 and 29.0, respectively) and competitive ability (ALGY in average 870.6) show better performance under the intercropped system compared to the single crops. The increased planting density resulted in an increase in productivity under the intercropped forage cactus-sorghum system (on average an increase of 69.4% dry matter). In turn, the orientation had no influence on the productivity of the intercropping system but offered better conditions for the forage cactus when cultivation was in an east-west direction (21.7 Mg ha−1 of dry matter) compared to north-south (17.5 Mg ha−1 of dry matter). Intercropping forage cactus and sorghum using biosaline agriculture is an excellent alternative for a production system in semi-arid environments, especially at higher planting densities (50,000 and 100,000 plants ha−1).

Whether Increasing Maize Planting Density Increases the Total Water Use Depends on Soil Water in the 0–60 cm Soil Layer in the North China Plain

Increasing planting density generally increases total water use by maize (Zea mays L.), but there are contrasting conclusions as well. To determine whether increasing planting density would increase total water use by maize, a 3-year field experiment was conducted in the North China Plain. In 2018, maize was planted at the four densities of 57,100, 66,700, 80,000, and 100,000 plants ha−1. In 2019 and 2020, another four planting densities of 27,800, 41,700, 66,700, and 111,100 plants ha−1 were selected. The results showed that increasing planting density increased leaf area index but decreased leaf stomatal conductance; maize grain yield reached the maximum at about 80,000 plants ha−1. At the VE-V6 and R3-R6 stage, soil water use occurred mainly in the 0–60 cm soil layer, and planting density showed no effect on total soil water use by maize. At the V6-R3 stage, when soil water in the 0–60 cm soil layer was sufficient to meet the evapotranspiration demand, soil water use occurred mainly in the 0–60 cm soil layer; increasing planting density did not increase total soil water use. When soil water in the 0–60 cm soil layer was insufficient and could not meet the demand of evapotranspiration, soil water use in the 60–100 cm soil layer increased greatly and kept rising with increased planting density, resulting in elevated total soil water use. Therefore, we conclude that the effect of planting density on water use by maize varies with soil water content in the 0–60 cm soil layer in the North China Plain.

Yield and Profitability of Organic Radish Cultivation with Different between-Row Spacings

This study aimed to evaluate the yield and profitability of organic radish cultivation using different between-row spacings. The experiment was conducted at the Seridó Ecological Station in Rio Branco – AC in a randomized block design with five between-row spacings (0.05, 0.10, 0.15, 0.20, and 0.25 m) and four replications. Each plot consisted of four rows transverse to the plant bed at a density of 16.7 plants m-¹, spaced 0,06 m from one another, with the planting densities of 316.7, 255.7, 216.7, 166.7, 116.7, and 66.7 plants m-2, respectively. The following agronomic variables were evaluated 35 days after sowing: shoot biomass, root yield, harvest index, root diameter, mean root mass, dry shoot mass, and the economic variables of mean total cost, cost-to-benefit ratio, yield to cover total costs, profitability, total income, net income, total cost, family labor remuneration, and profitability index. The smallest between-row spacing, increasing the planting density, increased the yield and reduced the root diameter without changing the mean root mass and the dry shoot mass. The increase in planting density increased the total cost and reduced the mean total cost, increasing the economic indicators of B/C ratio, profit rate, net and total income, profitability index, and family labor remuneration.

Optimization of nitrogen fertilization improves rice quality by affecting the structure and physicochemical properties of starch at high yield levels

A major challenge in modern rice production is to achieve the dual goals of high yield and good quality with low environmental costs. This study was designed to determine whether optimized nitrogen (N) fertilization could fulfill these multiple goals. In two-year experiments, two high yielding ‘super’ rice cultivars were grown with different N fertilization management regimes, including zero N input, local farmers’ practice (LFP) with heavy N inputs, and optimized N fertilization (ONF). In ONF, by reducing N input, increasing planting density, and optimizing the ratio of urea application at different stages, N use efficiency and the physicochemical and textural properties of milled rice were improved at higher yield levels. Compared with LFP, yield and partial factor productivity of applied N (PFP) under ONF were increased (on average) by 1.70 and 13.06%, respectively. ONF increased starch and amylose content, and significantly decreased protein content. The contents of the short chains of A chain (degree of polymerization (DP) 6–12) and B1 chain (DP 13–25) of amylopectin were significantly increased under ONF, which resulted in a decrease in the stability of rice starch crystals. ONF increased viscosity values and improved the thermodynamic properties of starch, which resulted in better eating and cooking quality of the rice. Thus, ONF could substantially compensate the negative effects caused by N fertilizer and achieve the multiple goals of higher grain quality and nitrogen use efficiency (NUE) at high yield levels. These results will be useful for applications of high quality rice production at high yield levels.

Effects of plant density, nitrogen rate and supplemental irrigation on photosynthesis, root growth, seed yield and water-nitrogen use efficiency of soybean under ridge-furrow plastic mulching

The ridge-furrow plastic mulching system has been reported to increase crop yield and water-nitrogen use efficiency in semi-arid and semi-humid regions, but the effects of plant density, nitrogen (N) rate and supplemental irrigation on chlorophyll, photosynthesis, root growth and seed yield of soybean under ridge-furrow plastic mulching are poorly understood. A two-year field experiment (2019 and 2020) was conducted on soybean in a split-split plot design, with two plant densities (D16: 160,000 plants ha−1; D32: 320,000 plants ha−1) as main plots, two N rates (N30: 30 kg N ha−1; N60: 60 kg N ha−1) as sub plots, and two irrigation levels (W0: rainfed; W30: supplemental irrigation of 30 mm at the flowering-podding stage) as sub-sub plots. The results showed that plant density, N rate and supplemental irrigation had significant effects on leaf chlorophyll content, chlorophyll fluorescence parameters, photosynthesis, aboveground/root growth and seed yield. Increasing plant density enhanced leaf area index (LAI) by 31.9% and aboveground biomass (AGB) by 59.4%, seed yield by 27.4%, water use efficiency of seed yield (WUEs) by 27.9% and nitrogen partial factor productivity (NPFP) by 26.6%. Increasing N rate increased leaf chlorophyll content by 11.9% and photosynthetic rate by 5.5%, thereby increasing LAI by 11.5%, AGB by 10.3%, seed yield by 8.9% and WUEs by 8.2%. Supplemental irrigation increased chlorophyll content by 7.6% and photosynthetic rate by 3.7%, thereby increasing LAI by 4.7%, AGB by 11.0%, seed yield by 4.7% and NPFP by 4.0%, while supplemental irrigation only increased WUEs under D32. Compared with D16N30W0, D32N60W30 enhanced seed yield by 44.0% and WUEs by 37.0%, but reduced NPFP by 28.8%. Compared with D32N30W30, D32N60W30 increased both seed yield and WUEs by 8.5%, but it reduced NPFP by 45.5% with 100% higher N input. LAI, AGB, WUEs, NPFP and some leaf physiological (EXC, Chla/Chlb, EWTleaf and Ls) and root (TRLD, TRVD and TRSD) indexes were closely related to soybean yield. This study provides a better understanding how plant density, N rate and supplemental irrigation improved soybean productivity and water-nitrogen use efficiency by regulating chlorophyll, photosynthesis and aboveground/root growth.

Dense Planting with Reducing Nitrogen Rate Increased Nitrogen Use Efficiency and Translocated Nitrogen in Grains in Double-Cropped Rice

Nitrogen fertilization and planting density are two key factors that influence the yield of rice. Reducing nitrogen fertilizer input and increasing planting density will help to improve nitrogen use efficiency and stabilize yield. Field and 15N tracer method in plot experiments were conducted to study the trends of yield, nitrogen use efficiency (NUE) and nitrogen transfer of hybrid rice and conventional rice under dense planting with a reduced nitrogen rate (DPRN) and sparse planting with a high nitrogen rate (SPHN). Among the nitrogen in rice plants, the proportion of nitrogen from fertilizer under the DPRN was reduced by 1.8–13%. The late-season rice (LSR) had a higher rate of decrease compared with the early-season rice (ESR). The uptake efficiency of nitrogen fertilizer was significantly higher under the DPRN than that under the SPHN, with an increase of 7.7–21.9%. The accumulated nitrogen and translocated ratio under the DPRN before the heading stage were 6.1–10.8% and 2.0–9.6% higher than those under the SPHN, respectively. The yield did not change under different treatments. Those findings suggest that the DPRN could guarantee a stabilized yield while increasing the NUE and the amount of translocated nitrogen in the double-cropped rice system.

Root characteristics and yield of rice as affected by the cultivation pattern of strong seedlings with increased planting density and reduced nitrogen application

To address the relationships between the amount of nitrogen fertilizer application and the yield of double cropping rice systems, we investigated the effects of a cultivation pattern of strong seedlings with increased planting density and reduced nitrogen application (SDN) on the morphological and physiological characteristics of double cropping rice. Our results indicated that the effects of SDN on the morphological characteristics of the single plant roots of double cropping rice were not significant, but the morphological characteristics of the population roots were largely different. Specifically, SDN significantly increased the morphological indexes of the root population such as root fresh weight, root volume, root number, root length and root dry weight. The effects of SDN on the total root absorption areas and root active absorption areas of the single plants were non-significant, but it dramatically enhanced the total root absorption areas and root active absorption areas of the plant population during the tillering, heading and mature stages. In addition, SDN significantly increased the root bleeding intensity and elevated the soluble sugar and free amino acid contents of root bleeding sap. Compared to the traditional cultivation pattern (CK), SDN significantly increased root bleeding intensity at the heading stage by 4.37 and 8.90% for early and late rice, respectively. Meanwhile, SDN profoundly enhanced the soluble sugar contents of root bleeding sap by 12.85 and 10.41% for early and late rice, respectively. In addition, SDN also significantly enhanced free amino acid content of root bleeding sap by 43.25% for early rice and by 37.50% for late rice systems compared to CK. Furthermore, SDN increased the actual yield of double cropping rice mainly due to the higher effective panicle number and the larger seed-setting rate. The actual yields of early rice under SDN were higher than CK by 9.37 and 5.98% in 2016 and 2017, and the actual yields of late rice under SDN were higher than CK by 0.20 and 1.41% in 2016 and 2017, respectively. Correlation analysis indicated that the significant positive correlations were observed between the majority of the root indexes and the actual yield across the four different growth stages.

Horizontal transport of macro- and microplastics on soil surface by rainfall induced surface runoff as affected by vegetations

Surface runoff is considered as an important pathway that transport of plastic waste from terrestrial environment into the aquatic environment but the process is still poorly understood. In this work, runoff plot experiment was carried out to study the horizontal transport of macro- and microplastics between 50 mm and 0.25 mm in size on the soil surface by rain induced runoff. The influences of vegetation cover, characteristics of plastics, and rainfall scenarios were investigated. Results showed that the presence of vegetation significantly enhance the retention of plastics by about 20% under the experimental conditions. Lower density and smaller (<1 mm) plastics were found to have higher mobility. The herb plant (Photinia×fraseri Dress) showed a better interception efficiency on plastics than the shrub plant (Ophiopogon japonicus (Linn. f.) Ker-Gawl.) at the same planting density, while increasing plant density contributed litter to the interception of microplastics. Increase rainfall amount from 20 mm to 60 mm enhanced the transport of plastics while repeating 20 mm rainfall every 3 days did not affect the transport of plastics significantly. The same processes may involve in the transport of plastics and soil particles by rainfall induced surface runoff. Strategies controlling soil erosion could also be used to prevent plastics in soil from entering the aquatic environment. However, effects and risks of plastics retained in the soil are still unclear, which need to be investigated in future.