Agronomy and Physiology of Tropical Cover Crops

Cover crops are important components of a sustainable crop production system. They can be planted with plantation crops such as cacao, coffee, banana, rubber, and oil palm or in rotation with cash crops. Their use in a cropping system is mainly beneficial for soil and water conservation, recycling of nutrients, control of pests and improved microbiological activities. However, beneficial effects depend on the selection of appropriate cover crops and their management. Hence, understanding their agronomy and physiology is fundamental for their use in sustainable cropping systems. Growth and development of a crop (physiological aspects) is determined genetically as well as influenced by environmental variables. This information can be useful in improving production of these crops and, consequently, their incorporation in farming systems, wherever it is possible. There are hundreds of tropical cover crops and, therefore, it is not possible to include all of them in one article. Hence, selected cereals and legumes are included.     

Enhancing Corn Production Through the Use of Starter Fertilizer in the Northern Great Plains

Abstract

The northern portion of the Great Plains has environmental conditions that require unique management practices to ensure optimum corn (Zea mays L.) yield and quality. The objective was to investigate the effect of starter fertilizer on corn yield and quality under different soil management. A field experiment was established within a 2‐year corn/soybean [Glycine max (L.) Merrill] rotation. Whole‐plot treatments were tillage with split‐plot treatments of starter fertilizer. Starter fertilizer treatments consisted of two nitrogen (N) sources, each at four rates, all contained phosphorus (P) and potassium (K). An additional treatment of no starter fertilizer was also incorporated into the experiment. There was a significant increase in yield with application of starter‐N for all years except 2002. The most dramatic yield increase was obtained with the comparison between the no starter (no N, P, or K) treatment and the P and K treatment (no N+P and K). Starter fertilizer with only P and K also increased yield, oil production, and N removal in all years compared with no starter fertilizer treatment. Application of starter fertilizer can have a significant positive impact on yield and quality of corn grown in the northern Great Plains.     

Soybean Growth Response to Low Rates of Nitrogen Applied at Planting in the Northern Great Plains

ABSTRACT

Cool and wet soils at the time of soybean [Glycine max (L.) Merrill] planting in the northern Great Plains may reduce early crop growth and retard nitrogen (N) fixation. Application of N as starter fertilizer may increase initial growth of soybean, but may also negatively impact N fixation when environmental conditions improve. The objective of this study was to evaluate the impact of low rates of N applied at planting on soybean N fixation and crop growth in the northern Great Plains. A field experiment (2000–2002) was established within a two-year corn [Zea mays (L.)] soybean rotation using a split-plot design with four replications. Whole plots were no-tillage (NT) and conventional tillage (CT) and the split plots were starter fertilizer (two sources × four rates) treatments. Nitrogen sources were either ammonium nitrate (AN) or urea (UR) each applied at 0, 8, 16, and 24 kg N ha^?1. Biomass in both 2000 and 2001 growing seasons increased significantly with increasing N rate at both growth stages (R1 and R7) and at the R1 stage in 2002. Ureide concentration and relative ureide decreased with increasing N rate at the R1 stage in all years, indicating a decrease in N fixation up to that point in crop development. This decrease in N fixation was not present at the R7 stage, but the significant increase in plant growth including yield was still present, indicating possibly that starter fertilizer can positively impact soybean production in the cool environmental conditions of the northern Great Plains. However, the positive impact on plant growth and yield is dependent on in-season environmental conditions and time of planting.     

Cover crop and tillage effects on soil enzyme activities following tomato

Increasing numbers of vegetable growers are adopting conservation tillage practices and including cover crops into crop rotations. The practice helps to increase or maintain an adequate level of soil organic matter and improves vegetable yields. The effects of the practices, however, on enzyme activities in southeastern soils of the United States have not been well documented. Thus, the objectives of the study were to investigate the effects of cover crops and two tillage systems on soil enzyme activity profiles following tomato and to establish relationships between enzyme activities and soil organic carbon (C) and nitrogen (N). The cover crops planted late in fall 2005 included black oat (Avena strigosa), crimson clover (Trifolium incarnatum L.), or crimson clover–black oat mixed. A weed control (no cover crop) was also included. Early in spring 2006, the plots were disk plowed and incorporated into soil (conventional tillage) or mowed and left on the soil surface (no-till). Broiler litter as source of N fertilizer was applied at a rate of 4.6 Mg ha⁻¹, triple super phosphate at 79.0 kg P ha⁻¹, and potassium chloride at 100 kg K ha⁻¹ were also applied according to soil testing recommendations. Tomato seedlings were transplanted and grown for 60 days on a Marvyn sandy loam soil (fine-loamy, kaolinitic, thermic Typic Kanhapludults). Ninety-six core soil samples were collected at incremental depths (0–5, 5–10, and 10–15 cm) and passed through a 2-mm sieve and kept moist to study arylamidase (EC 3.4.11.2), l-asparaginase (EC 3.5.1.1), l-glutaminase (EC 3.5.1.2), and urease (EC 3.5.1.5) activities. Tillage systems affected only l-glutaminase activity in soil while cover crops affected activities of all the enzymes studied with the exception of urease. The research clearly demonstrated that in till and no-till systems, l-asparaginase activity is greater (P ≤ 0.05) in plots preceded by crimson clover than in those preceded by black oat or their mixture. Activity of the enzyme decreased from 11.7 mg NH₄⁺–N kg⁻¹ 2 h⁻¹ at 0–5 cm depth to 8.73 mg NH₄⁺–N kg⁻¹ 2 h⁻¹ at 5–10 cm and 10–15 cm depths in the no-till crimson clover plots. Arylamidase activity significantly correlated with soil organic C (r = 0.699**) and soil organic N (r = 0.764***). Amidohydrolases activities significantly correlated with soil organic N but only urease significantly correlated with soil organic C (r = 0.481*). These results indicated that incorporation of cover crops into rotations may increase enzyme activities in soils.     

Soil respiration from winter wheat-based cropping systems in the US Southern Great Plains as influenced by tillage managements

This study compared soil respiration (SR) fluxes from winter wheat-based cropping systems in the US Southern Great Plains (SGP) under reduced and conventional tillage. The study consisted of four sets of paired paddocks assigned to conventional or reduced tillage with a four-year crop rotation applied over time. During the 2016–2017 study year, four sets of paired paddocks were planted to: winter wheat managed for grazing, dual-purpose (grazing and grain production), and grain-only systems of production, and winter canola. Heterotrophic SR fluxes were measured using a plant and root exclusion method on eight permanently deployed PVC cores per paddock. Fluxes from the cores were measured manually using a closed chamber connected to an infrared gas analyser on 12–13 dates during the winter wheat growing season (October through May). There were strong seasonal patterns of SR flux, with lower rates during dry and cold periods, and higher rates during warm and wet periods. Large rainfall induced pulses of SR flux were observed for both tillage systems. There was no consistent large-scale difference in SR flux between tillage treatments applied to paired paddocks. Results from this study indicate SR fluxes from winter wheat-based cropping systems are controlled more by soil environmental conditions than form of tillage.     

玉米豆科覆盖作物间作对潮土酶活性和真菌群落特征的影响

黄淮海地区土地复种指数高,不具备休闲条件,致使土壤养分消耗严重,土壤微生物群落多样性下降.为改善土壤状况,本研究基于两年的玉米豆科覆盖作物(紫花苜蓿、大豆、花生)间作试验,探讨玉米豆科覆盖作物间作对土壤养分、酶活性以及真菌群落特征的影响,同时分析黄淮海平原潮土区玉米豆科覆盖作物间作的可行性.结果表明:间作条件下土壤碱解...     

Changes of Soil Microbial Biomass Carbon and Nitrogen with Cover Crops and Irrigation in a Tomato Field

ABSTRACT

In order to understand how soil microbial biomass was influenced by incorporated residues of summer cover crops and by water regimes, soil microbial biomass carbon (C) and nitrogen (N) were investigated in tomato field plots in which three leguminous and a non-leguminous cover crop had been grown and incorporated into the soil. The cover crops were sunn hemp (Crotalaria juncea L., cv ‘Tropic Sun’), cowpea (Vigna unguiculata L. Walp, cv ‘Iron clay’), velvetbean (Mucuna deeringiana (Bort) Merr.), and sorghum sudangrass (Sorghum bicolor × S. bicolor var. sudanense (Piper) Stapf) vs. a fallow (bare soil). The tomato crop was irrigated at four different rates, i.e., irrigation initiated only when the water tension had reached ?5, ?10, ?20, or ?30 kPa, respectively. The results showed that sorghum sudangrass, cowpea, sunn hemp, and velvetbean increased microbial biomass C by 68.9%, 89.8%, 116.8%, and 137.7%, and microbial N by 58.3%, 100.0%, 297.3%, and 261.3%, respectively. A legume cover crop, cowpea, had no statistically significant greater effect on soil microbial C and N than the non-legume cover crop, sorghum sudangrass. The tropical legumes, velvetbean and sunn hemp, increased the microbial biomass N markedly. However, the various irrigation rates did not cause significant changes in either microbial N or microbial C. Soil microbial biomass was strongly related to the N concentration and/or the inverse of the C:N ratio of the cover crops and in the soil. Tomato plant biomass and tomato fruit yields correlated well with the level of soil microbial N and inversely with the soil C:N ratio. These results suggest that cover crops increase soil microbiological biomass through the decomposition of organic C. Legumes are more effective than non-legumes, because they contain larger quantities of N and lower C:N ratios than non-legumes.     

The erosion threshold for a sustainable agriculture in cultures of bean (Phaseolus vulgaris L.) under conventional tillage and no‐tillage in Northern Nicaragua

Soil erosion by water is one of the main environmental problems of the tropical mountains of Central America. The fragility of these areas, the significant degree of human population pressure exerted and changes in traditional farming systems all contribute to the current state of degradation. In this study, we compare two types of agricultural management (conventional tillage with traditional ploughing and no‐tillage with a digging stick) and analyse the influence of land slope, the management of vegetation cover, and various soil features and properties related to erosion in fields dedicated to the cultivation of beans (Phaseolus vulgaris L.) to determine the erosion thresholds. The study area was located in the hills around El Cuá, in northern Nicaragua. The results showed the system of no‐tillage (NT) to be more effective at controlling erosion than conventional tillage (CT), such that 28.7% less land was affected by erosion. Erosion in plots under CT did not present any statistically significant relationship with the factors analysed. Conversely, the erosion in the plots under NT was significantly related to the coverage of vegetation residues, and we calculated an erosion threshold of 40% of the level of vegetation coverage, which significantly reduces erosion.     

华北平原一年两熟保护性耕作体系试验研究

冬小麦-夏玉米一年两熟的种植方式在华北地区的农业生产中具有极为重要的地位。但是传统耕作方式使该地区的农业生产不可持续。保护性耕作技术是一种先进的保水保土的生产技术。该文在田间试验的基础上，研究了保护性耕作体系对作物产量、土壤容重、土壤含水率、土壤温度的影响，结果表明：保护性耕作能够提高作物的产量，增加土壤的含水率。其对土壤容重和土壤温度的影响并未对作物的生长产生不利影响。但是，从长远来看，对保护性耕作引起的土壤容重增加、温度降低的问题必须引起足够的重视。结果初步表明：以免耕加覆盖为主的保护性耕作体系可以在华北平原一年两熟地区试验推广。     

中国灌溉农田粮食作物水分利用效率的研究

以1980年至1986年、22个省(市、自治区)、10种作物、共计4422个站的年实测作物耗水量和产量数据为基础,用加权平均法计算得到全国灌溉农田上粮食作物平均水分利用效率值约为1.1kg/m³。并根据典型试验站作物产量、总耗水量及水分利用效率之间的相互关系,以及全国粮食作物单产随年分的变化趋势,经分析认为这一数值可以作为衡量全国灌溉农田上粮食作物平均水分利用效率的现状值     

Roller-Crimper Termination for Legume Cover Crops in North Carolina: Impacts on Nutrient Availability to a Succeeding Corn Crop

Nitrogen (N) release from roll-killed legume cover crops was determined for hairy vetch (Vicia villosa Roth), crimson clover (Trifolium incarnatum L.), and a hairy vetch + rye (Secale cereale L.) biculture in an organic corn production system in North Carolina, USA. Cover crops were planted at two locations in fall 2008 and 2009, roll-killed in May, and no-till planted with corn (Zea mays L.). Inorganic soil N and mineral N flux were determined using potassium chloride (KCl) extractions and ion-exchange resin (Plant Root Simulator, PRS) probes at 2-week intervals for 12 weeks and compared to fertilized controls of 0 and 168 kg N ha^?1. In 2009, greater plant available N under hairy vetch than under either 0 N control or crimson clover was found, with peak soil N occurring between 4 and 6 weeks after roll kill. Available soil N under crimson clover mulches was less than or equal to 0 N, suggesting net immobilization.     

中国北方主要旱地作物需水量的计算与分析

论述了作物需水量的概念及其计算模式,根据作物,土壤和气候资料,计算了中国北方主要旱地作物小麦、玉米、谷子、甘薯和马铃薯的作物需水量,并对这些作物的需水规律与作物生长关系进行分析。     

耕作方式与地表覆盖量对苜蓿及小麦地水蚀过程的影响

通过模拟降雨对定西苜蓿-春小麦轮作土壤的水蚀过程进行了研究，试验结果表明：苜蓿翻耕（T1）处理的地面积水产生时间最长，苜蓿不翻耕处理（T2）径流产生时间最长，显著高于其它3个处理。在整个模拟降雨过程中，不翻耕处理的径流产生速率总是低于翻耕处理的径流产生速率，其中以苜蓿不翻耕处理（T2）的径流速率最小，而两个翻耕处理的径流速率之间无显著性差异。T2处理的入渗速率始终高于其他3个处理；秸秆覆盖可有效地降低累积径流量和总侵蚀量，增加累积入渗量；在不同处理中，以苜蓿不翻耕处理加100％秸秆覆盖抗水蚀的效果比较明显。     

Role of Cover Crops in Improving Soil and Row Crop Productivity

Abstract

Cover crops play an important role in improving productivity of subsequent row crops by improving soil physical, chemical, and biological properties. The objective of this article is to review recent advances in cover crops practice, in the context of potential benefits and drawbacks for annual crop production and sustained soil quality. Desirable attributes of a cover crop are the ability to establish rapidly under less than ideal conditions, provide sufficient dry matter or soil cover, fix atmospheric nitrogen (N), establish a deep root system to facilitate nutrient uptake from lower soil depths, produce organic matter with low‐residue carbon/nitrogen (C/N) ratio, and absence of phytoxic or allelopathic effects on subsequent crops. Cover crops can be leguminous or nonleguminous. Leguminous cover crops provide a substantial amount of biologically fixed N to the primary crop, as well as ease of decomposition due to their low C/N ratio. Legume cover crops also possess a strong ability to absorb low available nutrients in the soil profile and can help in increasing concentration of plant nutrients in the surface layers of soil. Some nonleguminous cover crops having high N scavenger capacity compared with leguminous crops and sometimes, the growth of these scavenging grass cover crops is limited by N deficiency, growing grass/legume mixtures appears to be the best strategy in obtaining maximum benefits from cover crops.     

耕作模式对坡耕地土壤水分和大豆产量的影响

为了探讨北方土石低山地区不同耕作模式对坡耕地的土壤水分特征及其对作物产量的影响,以10°坡耕地大豆田为研究对象,监测了传统耕作(CT)、免耕(ZT)、免耕秸秆覆盖(NT)和横垄(CR)4种不同处理下0～100cm土壤水分垂直变化和水平变化,测定了大豆产量和水分利用效率。结果表明:1)在大豆不同生育期中,各处理在0～40cm土壤水分含量均表现为:NTZTCRCT,当土层深度大于40 cm时,各处理间土壤水分含量的大小关系发生波动变化,其中ZT和NT能明显改善0～50cm土层土壤水分含量,较CT处理保墒效果提高25.34%～35.57%。2)CT和ZT处理坡位间土壤水分含量的大小关系,受大豆生育期内总降雨量的影响较小,分别表现为:下坡位中坡位上坡位和下坡位≈中坡位上坡位,而NT和CR处理坡位间土壤水分含量的大小关系,会随着大豆生育期内降雨总量的不同而产生微变。3)各处理剖面土壤水分空间分布格局均表现出下湿上干的特点,CT和CR湿润土层(体积含水率≥11.6%)分别位于坡底40～100 cm和坡顶40～100 cm处,而干燥土层(体积含水率≤8.6%)则分别位于坡顶10～30 cm和坡底10～20 cm处。ZT湿润土层(体积含水率≥12%)分布集中性较差,NT湿润土层分布集中性最好,且范围最大,占据了整个坡面40～100cm深度范围。4)所考虑的3个因素对土壤水分含量影响作用的大小表现为:耕作模式剖面深度坡位。5)在2a试验中,与CT相比CR、ZT和NT处理产量分别平均增加8.77%、15.68%和26.74%,水分利用效率分别平均提高6.32%、11.6%和20.61%,因此建议在研究区种植大豆时,优先采用NT耕作模式。     

基于MODIS/EVI的中国北方地区耕地复种指数提取

复种是区域粮食增产的重要途径之一,也是中国粮食生产中一种重要的耕作模式。该文通过深入分析农作物的农时历和耕地的时间序列植被指数曲线的对应关系,提取了反映作物种植模式的特征时相,并以特征时相的EVI（enhanced vegetation index）值作为特征参量,构建了提取耕地复种指数的决策树方法。该方法仅用了作物生长季中7个时相来提取复种指数,减少了数据使用量,缩短了提取时间,提高了提取效率。最终,采用MODIS（moderate-resolution imaging spectroradiometer）/EVI数据,提取了2005年中国北方15个省市区的耕地复种指数,与之前的研究结果进行比较验证发现该方法具有较高的提取效率和精度。     

Effects of tillage systems in dryland farming on near-surface water content during the late winter period

Tillage systems modify, at least temporarily, some of the physical properties of soil, such as soil porosity. Tillage also has an indirect effect on soil water content throughout the growth cycle, particularly in areas with a Mediterranean climate. This paper presents the results of monitoring the water content in the topsoil (0–0.20 m) of three adjacent plots during February to May cycles starting in 1994–1995 and ending in 1998–1999. Each of the plots had a surface area of 2700 m², an 8% slope and Calcic Cambisol soil. Starting in 1994, three different tillage systems were applied: conventional tillage, which is typical of the area (CT); minimum tillage (MT); and no-tillage (NT). Two vertical 200 mm TDR probes were permanently installed in each plot and measurements were taken every week. The results show that, under an NT system, the soil had significantly higher water content than the other two soil plots. However, this increased quantity of water did not denote increased crop production; on the contrary, these preliminary data point to a decrease in crop production.     

环京津冀北贫困带土地利用/覆被变化研究

运用地理信息系统空间分析技术、数理统计分析方法及景观生态学方法分析了环京津冀北贫困带1985—2000年土地利用变化的时空格局和演进态势,以期为冀北贫困带实现土地资源可持续利用和社会经济可持续发展科学决策提供依据。结果表明:1985—2000年,冀北贫困带林地和城乡工矿居民用地面积大幅度增加,耕地、草地、水域、未利用地大面积减少。增加的林地主要来源于草地和耕地,新增城乡工矿居民用地主要来源于耕地,未利用地主要转化为草地和耕地。土地利用多样性程度和破碎度降低,聚集度增加。耕地破碎程度增加,但形状趋于规整。其它土地类型均向规则、连片方向发展。     

Conservation Tillage,Rotations, and Cover Crop Affecting Soil Quality in the Tennessee Valley: Particulate Organic Matter,Organic Matter,and Microbial Biomass

Abstract

The impact of conservation tillage, crop rotation, and cover cropping on soil‐quality indicators was evaluated in a long‐term experiment for cotton. Compared to conventional‐tillage cotton, other treatments had 3.4 to 7.7 Mg ha^?1 more carbon (C) over all soil depths. The particulate organic matter C (POMc) accounts for 29 to 48 and 16 to 22% of soil organic C (SOC) for the 0‐ to 3‐and 3‐ to 6‐cm depths, respectively. Tillage had a strongth influence on POMc within the 0‐ to 3‐cm depth, but cropping intensity and cover crop did not affect POMc. A large stratification for microbial biomass was observed varing from 221 to 434 and 63 to 110 mg kg^?1 within depth of 0–3 and 12–24 cm respectively. The microbial biomass is a more sensitive indicator (compared to SOC) of management impacts, showing clear effect of tillage, rotation, and cropping intensity. The no‐tillage cotton double‐cropped wheat/soybean system that combined high cropping intensity and crop rotation provided the best soil quality.