Effect of various mulches on soil microarthropods under a maize crop

Soil microarthropod populations in maize plots mulched with the prunings of three woody agroforestry plant residues (Acioa barteri, Gliricidia sepium and Leucaena leucocephala) and two crop residues [maize (Zea mays) stover (leaves and stems) and rice (Oryza sativa) straw] were monitored throughout the 1991 growing season and compared with those in fallow, bare fallow and unmulched control plots with three rates of nitrogen application. The mean densities of detritivore and phytophage microarthropods in the experimental plots decreased in the following order: rice straw > Gliricidia prunings > Leucaena prunings > maize stover > Acioa prunings > control 2 (90 kg N ha^-1 year^-1) > fallow > control 3 (135 N) > control 1 (45N) > bare fallow. Mulching also affected the population dynamics of predatory microarthropods and omnivorous ants. The chemical composition of plant residues probably influenced the densities of detritivore and phytophage microarthropods, which in addition were also greatly influenced by microclimatic conditons imposed by vegetation cover. Extremely low densities of microarthropods were recorded in the bare fallow plots probably as a result of the combined effects of absence of plant residues and vegetation cover. The potential of mulching as a component of farming practice for increasing the density of microarthropods and for influencing their species composition and population dynamics in agroecosystems is discussed.     

Nitrogen and phosphorus uptake by maize as affected by particulate organic matter quality, soil characteristics, and land-use history for soils from the West African moist savanna zone

 The impact of land use (unfertilized continuous maize cropping, unfertilized and fertilized alley cropping with maize, Gliricidia sepium tree fallow, natural fallow) on the soil organic matter (SOM) status and general soil fertility characteristics were investigated for a series of soils representative for the West African moist savanna zone. Three soils from the humid forest zone were also included. In an associated pot experiment, relationships between maize N and P uptake and SOM and general soil characteristics were developed. Soils under natural fallow contained the highest amount of organic C (1.72%), total N (0.158%), and had the highest effective cation exchange capacity (ECEC) [8.9 mEq 100 g^–1 dry soil], while the Olsen P content was highest in the fertilized alley cropping plots (13.7 mg kg^–1) and lowest under natural fallow (6.3 mg kg^–1). The N concentration of the particulate organic matter (POM) was highest in the unfertilized alley cropping plots (2.4%), while the total POM N content was highest under natural fallow (370 mg N kg^–1) and lowest in continuously cropped plots (107 mg N kg^–1). After addition of all nutrients except N, a highly significant linear relationship (R ²=0.91) was observed between the total N uptake in the shoots and roots of 7-week-old maize and the POM N content for the savanna soils. POM in the humid forest soils was presumably protected from decomposition due to its higher silt and clay content. After addition of all nutrients except P, the total maize P uptake was linearly related to the Olsen P content. R ² increased from 0.56 to 0.67 in a multiple linear regression analysis including the Olsen P content and clay content (which explained 11% of the variation in P uptake). Both the SOM status and N availability were shown to be improved in land-use systems with organic matter additions, while only the addition of P fertilizer could improve P availability. Received: 9 April 1999     

Evaporation Reduction with Paper-Pellet Mulch

Crop residue mulch reduces evaporation, but residue production by dryland crops may be inadequate to reduce evaporation effectively. An alternative material is waste paper for which disposal on agricultural land is being considered. A laboratory study compared evaporation from soil with paper-pellet or crop-residue mulch in two trials, each conducted for 21 days. In Trial I, small (4.8-mm diameter) and large (9.5-mm diameter) waste-paper pellets provided full cover or half that amount (on a weight basis). Large pellets at full cover reduced evaporation more than other treatments during most of the trial. Evaporation was reduced most on Day 4 when it was 0.52 of that with bare soil. Both half-cover treatments resulted in similar evaporation. At full cover, evaporation tended to be greater with small than with large pellets. In Trial II, evaporation with small and large pellets at full cover, wheat (Triticum aestivum L.) straw at 0.60 kg m^?2, grain sorghum [Sorghum bicolor (L.) Moench] stover at 1.20 kg m^?2, and bare soil were compared. Except with small pellets after Day 11, evaporation was significantly lower with mulch than with bare soil. Evaporation tended to be greater with small than with large pellets, similar for large pellets and wheat straw, and lower with sorghum than with other treatments on most days. Maximum evaporation reduction occurred on Day 1 with sorghum stover when it was 0.28 of that with bare soil. Use of paper-pellet mulch can reduce evaporation and thus increase water conservation. Technology improvements underway should make paper-pellet use on cropland practical. Waste paper use on cropland will require close attention to soil nutrient relations.     

Film fully-mulched ridge-furrow cropping affects soil biochemical properties and maize nutrient uptake in a rainfed semi-arid environment

Abstract

This study evaluated the effects of plastic mulched ridge-furrow cropping on soil biochemical properties and maize (Zea mays L.) nutrient uptake in a semi-arid environment. Three treatments were evaluated from 2008 to 2010: no mulch (narrow ridges with crop seeded next to ridges), half mulch (as per no mulch, except narrow ridges were mulched), and full mulch (alternate narrow and wide ridges, all mulched with maize seeded in furrows). Compared to the no mulch treatment, full mulch increased maize grain yield by 50% in 2008 and 25% in 2010, but reduced yield by 21% in 2009 after low precipitation in early growth. Half mulch had a similar grain yield to no mulch in the three cropping years, suggesting half mulch is not an effective pattern for maize cropping in the area. Mulch treatments increased aboveground nitrogen (N) uptake by 21?34% and phosphorus (P) uptake by 21?42% in 2008, and by 16?32% and 14?29%, respectively, in 2010; but in 2009 mulching did not affect N uptake and decreased P uptake. Soil microbial biomass and activities of urease, β-glucosidase and phosphatase at the 0?15 cm depth were generally higher during vegetative growth but lower during reproductive growth under mulch treatments than no mulch. Mulching treatments increased carbon (C) loss of buried maize residues (marginally by 5?9%), and decreased light soil organic C (15?27%) and carbohydrate C (12?23%) concentrations and mineralizable C and N (8?36%) at harvest in the 0?20 cm depth compared with no mulch, indicating that mulching promotes mineralization and nutrient release in soil during cropping seasons. As a result of these biological changes, mineral N concentration under mulch was markedly increased after sowing in upper soil layers compared with no mulch. Therefore, our results suggest that mulched cropping stimulated soil microbial activity and N availability, and thus contributed to increasing maize grain yield and nutrient uptake compared with no mulch.     

Priming effect and C storage in semi-arid no-till spring crop rotations

Adoption of less invasive management practices, such as no-till (NT) and continuous cropping, could reduce CO₂ emissions from agricultural soils by retaining soil organic matter (SOM). We hypothesized that C storage increases as cropping intensity increases and tillage decreases. We also hypothesized that pulsed addition of C increases the mineralization of native SOM. We evaluated C storage at the 0- to 5-cm depth in soils from four crop rotations: winter wheat-fallow, spring wheat-chemical fallow, continuous hard red spring wheat, and spring wheat-spring barley on a Ritzville silt loam (Calcidic Haploxeroll). In two incubation studies using ¹⁴C-labeled wheat straw, we traced the decomposition of added residue as influenced by (1) cropping frequency, (2) tillage, and (3) pulsed additions of C. Differences in ¹⁴C mineralization did not exist among the four rotations at any time throughout the incubations. However, differences in total CO₂ production between the continuous wheat rotations and the fallow rotations point to a priming of native SOM, the degree of which appears to be related to the relative contributions of fungi and bacteria to the decomposition of added residue. Addition of non-labeled wheat straw to select samples in the second incubation resulted in a flush of ¹⁴C-CO₂ not seen in the controls. This priming effect suggests C inputs have a greater effect on mineralization of residual C compared to disturbance and endogenous metabolism appears to be the source of primed C, with priming becoming more pronounced as the fungal:bacterial ratio in the soil increases.     

Bean seedling damage by root-feeding grubs (Schizonycha spp.) in Kenya as influenced by planting time,variety, and crop residue management

Use of legume cover crops to improve soil productivity has had unexpected effects on cropping system components in a maize (Zea mays L.) and bean (Phaseolus vulgaris L.) cropping system in Trans Nzoia district, Kenya. Smallholder farmers who recently adopted relay cropping of lablab (Lablab purpureus L.) observed a decline in bean yields where lablab residues had been incorporated prior to maize and bean planting. We investigated chafer grub (Schizonycha spp.) damage to beans and studied the impact of lablab and maize stover residue management strategy, planting time, and bean cultivar selection on seedling damage. Seedling assays (germination to flower initiation), involving four different bean varieties (GLP2, KK15, KK22, and KTL3), were carried out in three consecutive planting periods. The assays were superimposed on a long-term, factorial experiment where soils had been subjected to differential lablab and maize stover residue management strategies for 7 years. Factors were (1) lablab residues removed (L0) or retained (L1); (2) maize stover removed (S0) or retained (S1) and (3) residues left on the soil surface (I0) or incorporated (I1). Planting time significantly affected the degree of chafer grub damage, with later planted beans sustaining substantially more damage. Of the four bean varieties, KK15 and GLP2 were more grub tolerant than KK22 and KTL3. Grub damage was most severe in plots where lablab residues had been retained and maize stovers had been removed (L1S0). This factor combination had the highest seedling mortality, the poorest stand establishment, and the largest proportion of plants with severed roots systems. The results of this study show that the current farmer practice (lablab residue retention and maize stover removal) is conducive to increased grub-induced bean seedling damage and suggest that early planting, retention of maize stover, and selection of grub-tolerant varieties are important management strategies to reduce damage and subsequent productivity decline.     

Transformations and recovery of residue and fertilizer nitrogen-15 in a sandy Lixisol of West Africa

 The fate of ¹⁵N-labeled plant residues from different cover-cropping systems and labeled inorganic N fertilizer in the organic, soil mineral, microbial biomass and soil organic matter (SOM) particle-size fractions was investigated in a sandy Lixisol. Plant residues were from mucuna (legume), lablab (legume), imperata (grass), maize (cereal) and mixtures of mucuna or lablab with imperata or maize, applied as a surface mulch. Inorganic N fertilizer was applied as ¹⁵N-(NH₄)₂SO₄ at two rates (21 and 42 mg N kg^–1 soil). Total N release from mucuna or lablab residues was 2–3 times higher than from the other residues, whereas imperata immobilized N throughout the study period. In contrast, ¹⁵N was mineralized from all the plant residues irrespective of the mineralization–immobilization pattern observed for total N. After 168 days, 69% of soil mineral N in mucuna- or lablab-mulched soils was derived from the added residues, representing 4–8% of residue N, whereas 9–30% of inorganic N was derived from imperata, maize and the mixed residues. At the end of the study, 4–19% of microbial biomass N was derived from the added residue/fertilizer-N, accounting for 1–3% of added residue-N. Averaged across treatments, particulate SOM fractions accounted for less than 1% of the total soil by weight but contained 20% of total soil C and 8% of soil N. Soils amended with mucuna or lablab incorporated more N in the 250–2000 μm SOM pool, whereas soil amended with imperata or the mixed residues incorporated similar proportions of labeled N in the 250–2000 μm and 53–250 μm fractions. In contrast, in soils receiving the maize or inorganic fertilizer-N treatments, higher proportions of labeled N were incorporated into the 53–250 μm than the 250–2000 μm fractions. The relationship between these differences in residue/fertilizer-N partitioning into different SOM particle-size fractions and soil productivity is discussed. Received: 12 March 1999     

Mulching effects on soil physical quality of an alfisol in western Nigeria

Degradation of soil physical quality, following deforestation and cultivation, is a major soil‐related constraint to an intensive use of soil for crop production in subhumid regions of subSaharan Africa. Use of crop residue mulch is an important strategy to minimize the risks of soil degradation. Therefore, a three‐year experiment was conducted to study the effects of five rates of mulch application (0, 2, 4, 6 and 8 Mg ha⁻¹ season⁻¹) on soil physical properties and growth and yield of maize (Zea mays). Mulch rate of rice straw significantly increased maize grain and stover yields during the first season, and the stover yield during the second season. In comparison with the control, the grain yield increased by 20 per cent at 2 Mg ha⁻¹ of mulch rate and by 33 per cent at 8 Mg ha⁻¹ of mulch rate. The rate of increase was 0·16 Mg ha⁻¹ for grain yield and 0·38 Mg ha⁻¹ for stover yield for every Mg of mulch applied. The increase in stover yield during the second season was 67 per cent for 8 Mg ha⁻¹ mulch rate compared with the unmulched control. Effects of mulch rate on soil physical properties were confined mostly to the surface 0–5 cm depth. For this depth, mulching decreased bulk density from 1·17 Mg m⁻³ for control to 0·98 Mg m⁻³, and penetration resistance from 1·54 kg cm⁻² to 1·07 kg cm⁻² for 8 Mg ha⁻¹ of mulch rate. Application of mulch up to 16 Mg ha⁻¹ yr⁻¹ for three consecutive years had no effect on soil physical properties below 5 cm depth. Experiments were probably not conducted for a long enough period. For mulch farming to be adopted by farmers of West Africa, it must be an integral part of the improved farming system. Copyright © 2000 John Wiley & Sons, Ltd.     

Soil organic matter status of Chernozem soil in North Kazakhstan: effects of summer fallow

In North Kazakhstan there is concern about the degradation of Chernozem soil and agricultural sustainability by the inclusion and frequency of summer fallows in crop rotations in terms of their influence on the changes of soil organic matter (SOM) quality and quantity. We examined five fallow-wheat (Triticum aestivum L.) cropping systems with different frequencies of the fallow phase in Chernozem soil of North Kazakhstan; continuous wheat (CW), 6-y rotation (6R), 4-y rotation (4R), 2-y rotation (2R) and continuous fallow (CF). Soil samples were collected from the two phases of each rotation, pre- and post-fallow, and analyzed for potentially mineralizable C (PMC) and N (PMN), ‘light fraction’ organic matter (LF-OM), C (LF-C) and N (LF-N). Potentially mineralizable C was inversely proportional to the frequency of fallow and was highest in CW. Mineral N (min-N) and PMN were more responsive to rotation phase than other indices of SOM. Mineral N was higher in the post-fallow phase while PMN was higher in the pre-fallow phase. Light fraction organic matter was negatively correlated to the frequency of fallow and was higher in the pre-fallow than in the post-fallow phase in a rotation. The results suggested that the yearly input of plant residue in a less frequently fallowed system built up more PMC, whereas PMN was closely correlated to recent inputs of substrate added with plant residues. We conclude that a frequent fallow system may deplete SOM via accelerated mineralization. Also that LF-OM, PMC and PMN are more sensitive to detect subtle changes in SOM quality than total SOM. Our results may provide prediction of SOM response to fallow frequency in wheat-based rotation systems in Chernozem soils of semi-arid regions.     

Intercropping and Crop Residue Incorporation: Effects on Soil Nutrient Status

ABSTRACT

A maize-melon mixture relayed into a cassava-soybean intercrop was established at Ibadan, Nigeria, between 1995 and 1997 in order to study the changes in soil-nutrient status, that occurred due to soybean intercropping and residue incorporation. The experiment was conducted on a Kanhaplic Haplustalf soil. Soybean was planted in drills between cassava rows after harvesting maize and melon. Soybean stover was recycled into half of the soybean plots. Cassava yield was reduced by about 16% with soybean intercropping without the residue incorporation and by about 11% with incorporation of the crop residue. Soil pH was significantly reduced from an initial 6.0 to 5.7 with soybean intercropping. Organic matter was drastically reduced from an initial 31.0 g kg^?1 to 5.3 g kg^?1 with sole cassava cropping, and to 10.1 g kg^?1 with soybean intercropping and incorporation of crop residue. Total nitrogen (N) was also significantly reduced to about 0.4 g kg^?1from an initial content of 1.8 g kg^?1, while the available phosphorus (P) was increased from 1.8 to an average of 4.0 mg kg^?1. The exchangeable potassium (K) and effective cation-exchange capacity (ECEC) were not significantly affected.     

Crop and water productivity,profitability and energy consumption pattern of a maize-based crop sequence in the North Eastern Himalayan Region,India

Mono-cropping is the most common farming practice followed in the North Eastern Hilly Region (NEHR) of India and farmers leave the land fallow after harvesting the main crop. The identification of suitable sequential crops is essential to increase the cropping intensity, land-use efficiency and overall productivity of the land. Therefore, a study was carried out during 2008–09, 2009–10 and 2010–11 on maize (rainy season) followed by table pea, mustard, French bean and groundnut (post rainy season). Sequence crops were imposed with paddy straw mulch at 5.0 t ha^?1 and without mulch. The availability of water and moisture retention was higher (p < 0.05) on mulched plots, yield was also higher. However, recorded soil temperature was higher on mulched plots at 08.00 hours and lower at 12.00 and 16.00 hours compared with the no-mulch plots. Recorded maize equivalent yield, production efficiency, economics and total energy use and output (MJ ha^?1) were higher for maize–French bean.     

Decadal Nitrogen Fertilization Decreases Mineral‐Associated and Subsoil Carbon: A 32‐Year Study

Crop residues and manure are important sources of carbon (C) for soil organic matter (SOM) formation. Crop residue return increases by nitrogen (N) fertilization because of higher plant productivity, but this often results only in minor increases of SOM. In our study, we show how N fertilization and organic C additions affected SOM and its fractions within a 32‐year‐long field‐experiment at Puch, Germany. Five organic additions, no‐addition (control), manure, slurry, straw and straw + slurry, were combined with three mineral N fertilization rates (no, medium and high fertilization), which resulted in 1·17–4·86 Mg C‐input ha^‐1 y^‐1. Topsoil (0–25 cm) SOM content increased with N fertilization, mainly because of the C in free light fraction (f‐LF). In contrast, subsoil (25–60 cm) SOM decreased with N fertilization, probably because of roots' relocation in Ap horizon with N fertilization at the surface. Despite high inputs, straw contributed little to f‐LF but prevented C losses from the mineral‐associated SOM fraction (ρ > 1·6 g cm^‐3) with N fertilization, which was observed without straw addition. Above (straw) and belowground (roots) residues had opposite effects on SOM fractions. Root C retained longer in the light‐fractions and was responsible for SOM increase with N fertilization. Straw decomposed rapidly (from f‐LF) and fueled the mineral‐associated SOM fraction. We conclude that SOM content and composition depended not only on residue quantity, which can be managed by the additions and N fertilization, but also on the quality of organics. This should be considered for maintaining the SOM level, C sequestration, and soil fertility. Copyright © 2016 John Wiley & Sons, Ltd.     

免耕覆盖还田下玉米秸秆氮素的去向研究

采用田间微区试验,以15N标记的玉米秸秆为研究对象,研究了免耕覆盖还田下玉米秸秆氮素经过4个生长季后的作物累积利用率、在土壤(0~60 cm)的残留率以及损失情况。试验共设2个处理:TS1为第1年15N标记秸秆覆盖还田,此后秸秆不还田;TS2为第1年15N标记秸秆覆盖还田,此后每年以非标记秸秆还田。结果表明:经过4个生长季后,两个处理间的玉米籽粒、秸秆的累积产量及总氮素吸收量的差异均不显著。在TS1处理中,秸秆氮素在籽粒和秸秆中的累积回收率分别为14.2%和6.7%,并分别高于TS2处理的12.4%和5.8%。与作物的累积回收率相比,更多的秸秆氮素被保持在土壤中。在TS1和TS2处理中,秸秆氮素在土壤中的残留率分别为40.9%和73.8%,而损失率分别为38.6%和8.1%。与TS1处理相比,TS2处理中较高的土壤微生物生物量碳和氮以及较低的矿质态秸秆氮的含量,说明连续秸秆还田在一定程度上提高了最初还田秸秆氮素在土壤中的微生物固持并降低了秸秆氮素的淋失风险,从而显著提高秸秆氮素在土壤-植物系统中的总回收率。因此,在温带农田生态系统中,长期的免耕结合秸秆覆盖还田可促进秸秆氮素的积累,这对提高和保持土壤氮素含量和稳定性具有重要的意义。     

Carbon and nitrogen forms in soil organic matter influenced by incorporated wheat and corn residues

We have investigated molecular-scale changes in soil organic matter (SOM) as incorporated wheat and corn residues decompose and whether those changes are correlated with soil nitrogen forms. The ‘initial litter quality hypothesis’ that compositional variations in plant residues may persist during decomposition of these residues as they are transformed to SOM was tested. We studied soils in 6-year field experiments of a double-cropped corn–wheat rotation system designed with the following treatments: no crop residue and no chemical fertilizer, chemical fertilizer alone, wheat straw + chemical fertilizer, corn stover + chemical fertilizer, and corn plus wheat residue + chemical fertilizer. Organic carbon and nitrogen forms were assessed, and SOM chemical structures were examined by Fourier transform infrared and solid-state nuclear magnetic resonance spectroscopy. We found that concentrations of organic-N in corn residues plus fertilizer treatment were significantly larger than those in wheat straw plus fertilizer treatment. In addition, concentrations of amide groups and NCH in SOM with corn residue treatment were larger than those in SOM with wheat residue treatment. Incorporation of both corn and wheat residues led to an increase in carbohydrate-derived components of SOM. Compared with the check treatment, aromaticity, alkyl C/O-alkyl C, and hydrophobicity/hydrophilicity indices of the SOM were lower with addition of residue. Aromaticity was greater in corn residue treatment than in wheat residue treatment. This study provides support for the hypothesis that the variation in chemical composition of SOM reflected the incorporation of distinct chemical structures in wheat and corn straw residues.     

Influence of crop residue management, cropping system and N fertilizer on soil N and C dynamics and sustainable wheat (Triticum aestivum L.) production

Management of N is the key for sustainable and profitable wheat production in a low N soil. We report results of irrigated crop rotation experiment, conducted in the North West Frontier Province (NWFP), Pakistan, during 1999–2002 to evaluate effects of residue retention, fertilizer N application and mung bean (Vigna radiata) on crop and N yields of wheat and soil organic fertility in a mung bean–wheat sequence. Treatments were (a) crop residue retained (+residue) or (b) removed (−residue), (c) 120 kg N ha⁻¹ applied to wheat, (d) 160 kg N ha⁻¹ to maize or (e) no nitrogen applied. The cropping system was rotation of wheat with maize or wheat with mung bean. The experiment was laid out in a spit plot design. Postharvest incorporation of crop residues significantly (p < 0.05) increased the grain and straw yields of wheat during both years. On average, crop residues incorporation increased the wheat grain yield by 1.31 times and straw yield by 1.39 times. The wheat crop also responded strongly to the previous legume (mung bean) in terms of enhanced grain yield by 2.09 times and straw yield by 2.16 times over the previous cereal (maize) treatment. Application of fertilizer N to previous maize exerted strong carry over effect on grain (1.32 times) and straw yield (1.38 times) of the following wheat. Application of N fertilizer to current wheat produced on average 1.59 times more grain and 1.77 times more straw yield over the 0 N kg ha⁻¹ treatment. The N uptake in wheat grain and straw was increased 1.31 and 1.64 times by residues treatment, 2.08 and 2.49 times by mung bean and 1.71 and 1.86 times by fertilizer N applied to wheat, respectively. The soil mineral N was increased 1.23 times by residues, 1.34 times by mung bean and 2.49 times by the application of fertilizer N to wheat. Similarly, the soil organic C was increased 1.04-fold by residues, 1.08 times by mung bean and 1.00 times by the application of fertilizer N. We concluded that retention of residues, application of fertilizer N and involvement of legumes in crop rotation greatly improves the N economy of the cropping system and enhances crop productivity in low N soils.     

Climatic Gradient,Cropping System,and Crop Residue Impacts on Carbon and Nitrogen Mineralization in No‐Till Soils

Abstract

In the West Central Great Plains of the United States, no‐till management has allowed for increased cropping intensity under dryland conditions. This, in turn, has affected the carbon (C) and nitrogen (N) mineralization dynamics of these systems. In this region, moisture stress increases from north to south due to an increase in evapotranspiration (ET), resulting in a climatic gradient that affects cropping system management. The objectives of this study were to determine the interaction of cropping system intensification and climatic gradient (ET) on C and N mineralization and to determine if the presence or absence of crop residue on the soil surface affects C and net N mineralization. Two cropping systems, winter wheat‐fallow (WF) (Triticum aestivium L.) and winter wheat‐corn (sorghum)‐millet‐fallow (WCMF) [Zea mays (L.), Sorghum bicolor (L.) Moench, Panicum milaceum (L.)] were studied at three locations across this aforementioned ET gradient. The treatments had been in place for 8 yrs prior to sampling in the study. These results showed that the more intense cropping system (WCMF) had a higher laboratory C mineralization rate at two of the three locations, which the study concluded resulted from larger residue biomass additions and larger quantities of surface residue and soil residue at these locations (Soil residue is defined as recognizable crop residue in the soil that is retained on a 0.6 mm screen). However, no differences in N mineralization occurred. This is most likely due to more N immobilization under WCMF as compared to WF. Presence or absence of crop residue on the surface of undisturbed soil cores during incubation affected potential C and net N mineralization more than either cropping system or location. Soil cores with the surface residue intact mineralized as much as 270% more C than the same soils where the surface crop residue had been removed. In laboratory studies evaluating the relative differences in cropping systems effects on C and N mineralization, the retention of crop residue on the soil surface may more accurately access the cropping system effects.     

Response of soil properties and yam yield to Chromolaena odorata (Asteraceae) and Tithonia diversifolia (Asteraceae) mulches

Plant materials differ in their chemical composition, rate of decomposition and suitability as mulch materials. Experiments were conducted during 2006–2007 and 2007–2008 cropping seasons for early yam cultivation at Owo in the forest–savanna transition zone of southwest Nigeria to study the effect of Chromolaena odorata and Tithonia diversifolia mulches applied at 0.0, 5.0, 7.5, 10.0 and 12.5 t ha^?1 on soil chemical properties, leaf nutrient composition, growth and tuber yield of white yam (Dioscorea rotundata Poir). Both C. odorata and T. diversifolia mulches reduced soil bulk density and temperature; increased concentrations of soil organic matter (SOM), total N, available P, exchangeable K, Ca and Mg, leaf N, P, K, Ca and Mg; enhanced growth and yield of yam compared with control. The values of SOM, total N and available P and leaf N and P concentrations increased with increasing mulch rate. C. odorata mulch and T. diversifolia mulch applied at 10.0 and 7.5 t ha^?1, respectively, was found to be suitable for yam production. T. diversifolia mulch compared with C. odorata mulch produced higher values of soil chemical properties, leaf nutrient concentrations, growth and yield of yam. T. diversifolia mulch produced 19% and 18% higher tuber yield compared with C. odorata mulch during 2006–2007 and 2007–2008 cropping seasons, respectively.     

Effects of Phosphorus Fertilizer Source and Plant Density on Growth and Yield of Maize in Northwestern Pakistan

ABSTRACT

Phosphorus (P) fertilizer source and plant density are considered some of the most important factors affecting crop growth and yield. A field experiment was conducted to determine the impact of P source [zero-P control, DAP (diammonium phosphate), SSP (single super phosphate), and NP (nitrphos)] and plant density (D₁ = 40,000, D₂ = 60,000, D₃ = 80,000, and D₄ = 100,000 plants ha^?1) on growth and yield of maize (Zea mays L cv. Azam) on a P-deficient soil (6.6 mg P kg^?1) at New Developmental Agricultural Research Farm, North-West Frontier Province (NWFP) Agricultural University, Peshawar, Pakistan, during summer 2006 in wheat-maize cropping system. Physiological maturity was delayed, plant height was increased and leaf area was decreased significantly when maize was planted at highest (D₄) than at lowest plant density (D₁). Application of SSP resulted in earlier physiological maturity of maize than other P fertilizers. Grain and stover yield, harvest index, shelling percentage, thousand grain weight and grains ear^?1 were maximized at D₃ (80,000 plants ha^?1) and with application of P fertilizer. Highest benefit in growth and grain yield was obtained with application of DAP to maize planted at D₃. Application of DAP at D₃ gave 15, 29, and 19% higher grain yield than its application at D₁, D₂, and D₄, respectively. In conclusion, the findings suggest that growing maize at 80,000 plants ha^?1 applied with DAP can maximize productivity of maize in the wheat-maize cropping system on P-deficient soils.     

华北平原秸秆覆盖冬小麦减产原因分析

秸秆覆盖是减少农田棵间蒸发和提高水分利用效率的措施之一。冬小麦/夏玉米一年两作种植中, 秸秆资源非常丰富, 随着机械化作业的发展, 小麦秸秆覆盖夏玉米技术在同类地区得到成功应用和推广。但夏玉米秸秆覆盖冬小麦后对冬小麦的生长发育产生了一些不利影响, 造成了冬小麦不增产或减产, 限制了该项技术的推广。秸秆覆盖造成冬小麦穗数的降低是冬小麦产量降低的主要原因, 其次是千粒重的降低。大部分研究表明秸秆覆盖小麦地表后, 使根区土壤温度白天最高温度低于不覆盖处理, 夜间的最低温度高于不覆盖处理, 土壤温度的日较差减小。秸秆覆盖下根区温度的变化可能是引起小麦生长发育滞后和产量降低的主导因素。本文综述了华北平原秸秆覆盖冬小麦减产原因, 为实现两熟区冬小麦秸秆覆盖提供理论依据。     

Faster anaerobic decomposition of a brittle straw rice mutant: Implications for residue management

Rice (Oryza sativa) in Asia is typically grown on submerged soils in intensive cropping systems with only a brief interval between harvest of one crop and planting of the next. Incorporation of crop residues can be challenging because the fallow period between crops is often too short to allow sufficient decomposition. During early stages of anaerobic residue decomposition in flooded soils, plant growth may be inhibited by nutrient immobilization or by the production of potentially toxic organic acids. Straw from a brittle stem mutant of rice (Oryza sativa L. var. IR68) was tested in a 30-d incubation experiment under continuously flooded conditions in a greenhouse to determine if it would decompose more rapidly than the non-brittle phenotype, thereby allowing shorter fallow time between crops. Brittle straw decomposed faster, as indicated by 51% total C loss as CO₂ or CH₄ within 3 weeks of incorporation, compared with 28% for non-brittle straw. However, brittle straw also produced a significantly higher (P<0.0001) amount of formic, acetic, aconitic, propionic, and butyric acids than non-brittle straw. There was no difference in soil N immobilization pattern between the two straw types, or in P or K availability in the soil, perhaps due to the short duration of the experiment. To maximize the potential advantage of faster decomposition of brittle straw in intensive rice cropping systems, it may be helpful to manage water for sufficient soil aeration to mitigate the negative organic acid and methane production effects.