Phosphorus efficiency in long-term (15 years) wheat–maize cropping systems with various soil and climate conditions

Long-term (over 15 years) winter wheat (Triticum aestivum L.)–maize (Zea mays L.) crop rotation experiments were conducted to investigate phosphorus (P) fertilizer utilization efficiency, including the physiological efficiency, recovery efficiency and the mass (the input–output) balance, at five sites across different soil types and climate zones in China. The five treatments used were control, N, NP, NK and NPK, representing various combinations of N, P and K fertilizer applications. Phosphorus fertilization increased average crop yield over 15 years and the increases were greater with wheat (206%) than maize (85%) across all five sites. The wheat yield also significantly increased over time for the NPK treatments at two sites (Xinjiang and Shanxi), but decreased at one site (Hunan). The P content in wheat was less than 3.00 g kg⁻¹ (and 2.10 g kg⁻¹ for maize) for the N and NK treatments with higher values for the Control, NP and NPK treatments. To produce 1 t of grain, crops require 4.2 kg P for wheat and 3.1 kg P for maize. The P physiological use efficiency was 214 kg grain kg⁻¹ P for wheat and 240 kg grain kg⁻¹ P for maize with over 62% of the P from P fertilizer. Applying P fertilizer at 60–80 kg P ha⁻¹ year⁻¹ could maintain 3–4 t ha⁻¹ yields for wheat and 5–6 t ha⁻¹ yields for maize for the five study sites across China. The P recovery efficiency and fertilizer use efficiency averaged 47% and 29%, respectively. For every 100 kg P ha⁻¹ year⁻¹ P surplus (amount of fertilizer applied in excess of crop removal), Olsen-P in soil was increased by 3.4 mg P kg⁻¹. Our study suggests that in order to achieve higher crop yields, the long-term P input–output balance, soil P supplying capacity and yield targets should be considered when making P fertilizer recommendations and developing strategies for intensively managed wheat–maize cropping systems.     

Will nutrient-efficient genotypes mine the soil? Effects of genetic differences in root architecture in common bean (Phaseolus vulgaris L.) on soil phosphorus depletion in a low-input agro-ecosystem in Central America

Crop genotypes with root traits permitting increased nutrient acquisition would increase yields in low fertility soils but have uncertain effects on soil fertility in the long term because of competing effects on nutrient removal vs. the soil conserving effects of greater crop biomass. This study evaluated the relative importance of phosphorus loss in crop extraction vs. phosphorus loss in soil erosion as influenced by genetic differences in root shallowness and therefore phosphorus uptake in common bean (Phaseolus vulgaris L.). Six recombinant inbred lines of varying root architecture and two commercial genotypes of bean were grown in unfertilized, steeply sloped (32%), low phosphorus (5.8 mg kg^?1, Fe-strip) Udults in Costa Rica. Fertilized (60 kg total phosphorus ha^?1) plots of commercial genotypes were also included in the study. Runoff was monitored throughout the bean growing season in 2005 and 2006, and in 2006, monitoring continued through the maize growing season. Phosphorus removed in plant biomass at harvest through the 2006 bean–maize crop cycle averaged 7.3 kg ha^?1 year^?1, greatly exceeding phosphorus loss due to erosion (0.15–0.53 kg ha^?1 year^?1) in unfertilized plots. In fertilized bean plots, total biomass phosphorus averaged 6.32 kg ha^?1 year^?1 and total eroded phosphorus averaged 0.038 kg ha^?1 year^?1, indicating rapid sorption of fertilizer phosphorus. Shoot growth of several recombinant inbred lines under low phosphorus was comparable to that of fertilized commercial genotypes, illustrating the effectiveness of selection for root traits for improving plant growth in low-phosphorus soils. Genotypic differences in root architecture of recombinant inbred lines led to 20–50% variation in groundcover by shoots, which was associated with 50–80% reduction in sediment loss. This study demonstrates that root architecture traits can affect nutrient cycling at the agro-ecosystem level, and that integrated nutrient management strategies are necessary to avoid soil nutrient depletion.     

Accumulation of arsenic and its distribution in rice plant (Oryza sativa L.) in Gangetic West Bengal, India

The presence of arsenic in irrigation water and in paddy field soil were investigated to assess the accumulation of arsenic and its distribution in the various parts (root, straw, husk, and grain) of rice plant from an arsenic effected area of West Bengal. Results showed that the level of arsenic in irrigation water (0.05–0.70 mg l⁻¹) was much above the WHO recommended arsenic limit of 0.01 mg l⁻¹ for drinking water. The paddy soil gets contaminated from the irrigation water and thus enhancing the bioaccumulation of arsenic in rice plants. The total soil arsenic concentrations ranged from 1.34 to 14.09 mg kg⁻¹. Soil organic carbon showed positive correlation with arsenic accumulation in rice plant, while soil pH showed strong negative correlation. Higher accumulation of arsenic was noticed in the root (6.92 ± 0.241–28.63 ± 0.225 mg kg⁻¹) as compared to the straw (1.18 ± 0.002–2.13 ± 0.009 mg kg⁻¹), husk (0.40 ± 0.004–1.05 ± 0.006 mg kg⁻¹), and grain (0.16 ± 0.001–0.58 ± 0.003 mg kg⁻¹) parts of the rice plant. However, the accumulation of arsenic in the rice grain of all the studied samples was found to be between 0.16 ± 0.001 and 0.58 ± 0.003 mg kg⁻¹ dry weights of arsenic, which did not exceed the permissible limit in rice (1.0 mg kg⁻¹ according to WHO recommendation). Two rice plant varieties, one high yielding (Red Minikit) and another local (Megi) had been chosen for the study of arsenic translocation. Higher translocation of arsenic was seen in the high yielding variety (0.194–0.393) compared to that by the local rice variety (0.099–0.161). An appreciable high efficiency in translocation of arsenic from shoot to grain (0.099–0.393) was observed in both the rice varieties compared to the translocation from root to shoot (0.040–0.108).     

Grain concentrations of protein and mineral nutrients in a large collection of spelt wheat grown under different environments

A large number of spelt wheat genotypes (ranging from 373 to 772) were evaluated for grain concentrations of protein and mineral nutrients under 6 different environments. There was a substantial genotypic variation for the concentration of mineral nutrients in grain and also for the total amount of nutrients per grain (e.g., content). Zinc (Zn) showed the largest genotypic variation both in concentration (ranging from 19 to 145 mg kg⁻¹) and content (ranging from 0.4 to 4.1 μg per grain). The environment effect was the most important source of variation for grain protein concentration (GPC) and for many mineral nutrients, explaining between 37 and 69% of the total sums of squares. Genotype by environment (G × E) interaction accounted for between 17 and 58% of the total variation across the minerals. GPC and sulfur correlated very significantly with iron (Fe) and Zn. Various spelt genotypes have been identified containing very high grain concentrations of Zn (up to 70 mg kg⁻¹), Fe (up to 60 mg kg⁻¹) and protein (up to 30%) and showing high stability across various environments. The results indicated that spelt is a highly promising source of genetic diversity for grain protein and mineral nutrients, particularly for Zn and Fe.     

Long-term effects of poultry litter and conservation tillage on crop yields and soil phosphorus in cotton–cotton–corn rotation

Long-term field experiments are needed to fully realize positive and negative impacts of conservation tillage and poultry litter application. A study was initiated on a Decatur silt loam soil at the Tennessee Valley Research and Extension Center, Belle Mina, AL, USA in 1996 to evaluate cotton (Gossypium hirsutum L.) performance with long-term poultry litter (PL) application under different tillages and to study the build up of phosphorus (P) with application of PL. Treatments include incomplete factorial combinations of three tillage systems [conventional till (CT), mulch till (MT), and no-till (NT)], two cropping systems [cotton-fallow and cotton-winter rye (Secale cereale L.)], and two nitrogen sources and rates [100 kg N ha⁻¹ from ammonium nitrate (AN), and 100 and 200 kg N ha⁻¹ from poultry litter (PL)]. Cotton was rotated with corn (Zea mays L.) every third year. Results from 2003 to 2008 showed that all tillages gave similar cotton lint yields with AN at 100 kg N ha⁻¹. Application of PL at 100 kg N ha⁻¹ in NT plots resulted in 12 and 11% yield reductions compared to that of CT and MT, respectively. However, NT plots with higher quantity of PL (200 kg N ha⁻¹) gave similar yields to CT and MT at 100 kg N ha⁻¹. During corn years, higher residual fertility of PL, in terms of grain yields, was observed in NT plots compared to CT and MT. Long-term PL application (100 kg N ha⁻¹ year⁻¹) helped to maintain original soil pH in CT and MT while AN application decreased soil pH. In NT plots, PL at 100 kg N ha⁻¹ was not sufficient to maintain original soil pH, but 200 kg N ha⁻¹ maintained original pH. Although not-significant, elevated P levels were observed in all tillages compared to original P levels which indicates possibility of P build up in future with further application of PL. Application of PL at double rate (200 kg N ha⁻¹) in NT plots resulted in significant build up of P. Results indicate that NT gives similar yields to CT when received AN, but needs higher rate of PL application to achieve similar yields to CT.     

Growth, yield and mineral content of Miscanthus × giganteus grown as a biofuel for 14 successive harvests

Miscanthus × giganteus, a perennial rhizomatous grass commercially used as a biofuel crop was grown in a field experiment on a silty clay loam soil for 14 years. There were 3 rates of fertilizer nitrogen (N), none (control), 60 kg N ha⁻¹ yr⁻¹ and 120 kg N ha⁻¹ yr⁻¹ as cumulative applications. The crop was harvested in winter and dry matter yield measured. N did not influence yield. Yield, which increased for the first 6 years, decreased in years 7 and 8, but then increased again and was highest in the 10th year averaging 17.7 t ha⁻¹ across all treatments. Differences in total production over the14 years were only 5% between the highest and lowest yielding treatments and averaged 178.9 t ha⁻¹ equivalent to 12.8 t ha⁻¹ yr⁻¹. In the first 10 harvests, 92% of dry matter was stem. Although the study showed N fertilizer was not required, it is considered that an application of 7 kg P ha⁻¹ yr⁻¹ and 100 kg K ha⁻¹ yr⁻¹ would avoid soil reserve depletion. Pesticides were not required every year and the crop can be considered as low input with a high level of sustainability for at least 14 years.     

Effects of N application on agronomic and environmental parameters in silage maize production on sandy soils

The current nitrogen (N) use in silage maize production can lead to considerable N losses to the environment. Maize growers fear that a reduction of N inputs needed to minimize N losses might depress yields. The objective of this study was therefore to quantify: (1) the response of silage maize dry matter (DM) yields to N, (2) the economically optimal N reserve, and (3) the trade-off between silage maize DM yield and N losses. The indicators of N losses used in this study were the difference between N input and N uptake and the post-harvest residual soil mineral N. Regression models were used to fit DM yields and N uptakes of silage maize measured in 25 experiments on sandy soils in the Netherlands to the sum (SUMN) of the soil mineral N reserve (SMN_early) in March–April, plus mineral N in fertilizer, plus ammonium N in spring-applied slurry. The values obtained for the economically optimal SUMN in the upper 30 and 60 cm of soil were, respectively, 173 and 195 kg N ha⁻¹, when we assumed that the value of 1 kg fertilizer N equals the value of 5 kg silage DM. The economically optimal SUMN was not significantly related to the attainable DM yield. The apparent N recovery (ANR) of maize averaged 53% at the economically optimal SUMN. The ANR rose considerably, however, when N was applied at lower rates, indicating that N losses may be considerably smaller in less intensive maize cropping. When maize was fertilized at 100 kg N ha⁻¹ below the economic optimum, the ANR was 73%, the difference between the mineral N input and the N crop uptake decreased by 57 kg N ha⁻¹ and the soil mineral N residue at the end of the growing season (0–60 cm) decreased by 24 kg N ha⁻¹. The associated reduction in DM yield averaged 16%. Fertilizer prices would have to be as much as four times higher to make maize growers spontaneously reduce the application rates by a 100 kg N ha⁻¹, however. It is concluded that adjusting the N input to a level below the economically optimal rate can reduce the risks for N losses to the environment associated with conventional maize production, with a limited effect on silage yields.     

Simulation of soil drying induced phosphorus deficiency and phosphorus mobilization as determinants of maize growth near tree lines on a Ferralsol

Understanding the effect trees have on the growth of crops requires an understanding of the multiple interacting processes that determine resource uptake by the crops. On a Ferralsol in sub-humid western Kenya maize (Zea mays L.) growth was primarily limited by phosphorus availability. We observed that maize growth near grevillea (Grevillea robusta A. Cunn.) tree lines was strongly reduced, while maize growth was slightly increased near cassia (Cassia spectabilis DC (syn. Senna spectabilis, DC, H.S. Irwin and R.C. Barneby). This was contrary to expectations because grevillea has a relatively low nutrient demand while Cassia has a relatively high nutrient demand.We compared maize growth in an experiment with simulations using the mechanistic tree–crop interaction model WaNuLCAS. The model simulations showed that the measured 30–40% decrease in maize growth near the Grevillea tree line was due to 0.025 m³ m⁻³ lower soil water contents (at mean levels of 0.35 m³ m⁻³ and high pF). This was not due to direct water limitation. The lower soil water content caused decreased P diffusion to roots and a cumulative decrease in crop root-growth and a concomitant decrease in crop growth over time.Measured maize yield near Cassia was 115%, unaffected by trees. Model simulations predicted it should be reduced to 80% due to direct competition for P between tree and crop. This suggests that rhizosphere modifications measured near Cassia roots probably supplied P to the tree itself and also to the maize crop.On P-limiting tropical soils, it is important to prevent soil drying to avoid soil drying induced P deficiency. In these conditions tree species that are able to mobilize P can prevent competition with the crop and may even increase crop performance.     

Stable high yields with zero tillage and permanent bed planting?

Subtropical highlands of the world have been densely populated and intensively cropped. Agricultural sustainability problems resulting from soil erosion and fertility decline have arisen throughout this agro-ecological zone. This article considers practices that would sustain higher and stable yields for wheat and maize in such region. A long-term field experiment under rainfed conditions was started at El Batán, Mexico (2240 m a.s.l.; 19.31°N, 98.50°W; fine, mixed, thermic, Cumulic Haplustoll) in 1991. It included treatments varying in: (1) rotation (continuous maize (Zea mays) or wheat (Triticum aestivum) and the rotation of both); (2) tillage (conventional, zero and permanent beds); (3) crop residue management (full, partial or no retention). Small-scale maize and wheat farmers may expect yield improvements through zero tillage, appropriate rotations and retention of sufficient residues (average maize and wheat yield of 5285 and 5591 kg ha⁻¹), compared to the common practices of heavy tillage before seeding, monocropping and crop residue removal (average maize and wheat yield of 3570 and 4414 kg ha⁻¹). Leaving residue on the field is critical for zero tillage practices. However, it can take some time—roughly 5 years—before the benefits are evident. After that, zero tillage with residue retention resulted in higher and more stable yields than alternative management. Conventional tillage with or without residue incorporation resulted in intermediate yields. Zero tillage without residue drastically reduced yields, except in the case of continuous wheat which, although not high yielding, still performed better than the other treatments with zero tillage and residue removal. Zero tillage treatments with partial residue removal gave yields equivalent to treatments with full residue retention (average maize and wheat yield of 5868 and 5250 kg ha⁻¹). There may be scope to remove part of the residues for fodder and still retain adequate amounts to provide the necessary ground cover. This could make the adoption of zero tillage more acceptable for the small-scale, subsistence farmer whose livelihood strategies include livestock as a key component. Raised-bed cultivation systems allow both dramatic reductions in tillage and opportunities to retain crop residues on the soil surface. Permanent bed treatments combined with rotation and residue retention yielded the same as the zero tillage treatments, with the advantage that more varied weeding and fertilizer application practices are possible. It is important small-scale farmers have access to, and are trained in the use of these technologies.     

Physiological determinants of maize and sunflower grain yield as affected by nitrogen supply

Utilisation of nitrogen (N) has been closely related to increases in crop productivity. However, not all crops respond similarly and the objective of this study is to identify physiological processes that determine responses to N supply for maize and sunflower. Grain yield in maize (range: 210–1255 g m⁻²) was greater and more responsive to N supply than in sunflower (106–555 g m⁻² in carbohydrate equivalents) over a wide range of total N uptake (3–>20 g N m⁻²). In maize, differences in grain yield among levels of N supply were associated more with variation in biomass than in harvest index. In sunflower, differences in grain yield (in carbohydrate equivalents) among levels of N supply were related similarly to variation in both biomass and harvest index. The decrease in biomass production with decreasing N supply was associated with decreases in both radiation interception and radiation use efficiency (RUE). Decreased interception was due to effects of N supply on reducing canopy leaf area, whereas the reduced RUE was associated with decreased SLN. Total biomass production in maize was more responsive to N supply than in sunflower. The major determinants of the differences in response of biomass accumulation to N supply found between maize and sunflower are: (i) sunflower tends to maintain SLN with increase in partitioning of N to leaves under N limitation whereas maize tends to maintain leaf area with increase in partitioning of biomass to leaves and (ii) the ability of maize to maintain N uptake following cessation of leaf production.     

Productivity and resource use of direct-(drum)-seeded and transplanted rice in puddled soils in rice–rice and rice–wheat ecosystems

Conventional tilled transplanting, a widely practiced method of rice (Oryza sativa L.) establishment in puddled soils in rice–rice and rice–wheat (Triticum aestivum L.) systems in Asia, requires a large amount of labor and water, which are becoming scarce and expensive. Growing more food with the same production costs or even reduced costs and sustaining the quality of the natural resource base are a major concern. On-farm trials were conducted in Chuadanga District of Bangladesh during the wet season as monsoon rice (aman) and during the dry season as winter rice (boro) in 2006–07 to evaluate the effects of establishment methods with improved crop management on productivity, resource (land, water, and labor) use, and economic return. Rice was established by sowing in line with a drum seeder on conventional tilled puddled soils (CT-DrumR) and by transplanting in line on the day of CT-DrumR (CT-TPR1) and 30 and 35 days after CT-DrumR (CT-TPR2) in aman and boro seasons, respectively. Farmers’ usual transplanting time corresponds to the day of CT-TPR2. Grain yields in CT-DrumR and CT-TPR2 were similar but the crop occupied the main field 22–24 days longer in CT-DrumR than in CT-TPR2, resulting in lower productivity (45 kg grain ha⁻¹ day⁻¹ vs. 55 kg grain ha⁻¹ day⁻¹) in both seasons. Drum-seeded rice matured earlier by 8 and 11 days, received 12% and 6% less irrigation water, saved 19 and 24 person-days ha⁻¹, and gave higher gross margins of 6% and 4% but input costs increased by 20% and 12% than CT-TPR2 in aman and boro seasons, respectively. There is a need to examine these benefits of drum-seeded rice in relation to the feasibility of adoption by farmers.     

Accumulation of cadmium by flax and linseed cultivars in field-simulated conditions: A potential for phytoremediation of Cd-contaminated soils

The possibility of use of two technological types of Linum usitatissimum L., namely flax (grown for fibre) and linseed (grown for seed), for phytoextraction of cadmium (Cd) from Cd-contaminated soil was studied. A four-year field-simulated experiment was carried out with 6 flax and 4 linseed cultivars in order to study organ accumulation of Cd by flax and linseed plants at artificial concentration range 10-1000 mg Cd kg⁻¹ soil. The most Cd was accumulated by roots, followed by shoots, while reproductive parts (capsules and seeds) played comparably smaller role. The increasing soil Cd concentration resulted in increasing Cd accumulation by roots, while transport to above-ground plant parts was progresivelly inhibited. Even high soil Cd concentrations (1000 mg Cd kg⁻¹ soil) had not dramatic negative effect on plant growth and development. Cultivar differences as well as the differences between both technological Linum types have been found in Cd accumulation (flax being better Cd accumulator than linseed). Nevertheless, the recorded variation between technological types and within cultivars is in multiples of Cd values (units of mg Cd kg⁻¹ DW), not in orders of magnitude as needed for practical phytoextraction. A significant year-to-year effect on plant growth/development resulting in high variation in Cd accumulation was observed. Flax cv. Jitka exhibited good transport of Cd from roots to above-ground parts, while flax cv. Merkur showed high retention of Cd in roots. Further, the contrasting cultivars in total Cd accumulation (high accumulating flax cv. Jitka versus low accumulating linseed cv. Jupiter) were selected for future experiments. The uptake of Cd by flax/ linseed from ha per season was calculated and the strategy for flax/linseed growing on heavy metal polluted soils with subsequent utilization of heavy metal-contaminated biomass is discussed.     

Mineral element distributions in milling fractions of Chinese wheats

Malnutrition related to micronutrient deficiency can create immense economic and societal problems. The objective of this study was to quantify the mineral element concentration distribution in milled fractions, using 43 common wheat (Triticum aestivum L.) cultivars sown in Jinan, China during the 2005–2006 crop season. All 43 cultivars had low Fe (average 28.2 mg Kg⁻¹) and Zn (28.6 mg Kg⁻¹) concentrations, and wide ranges of variation for mineral element concentrations. Highly significant effects among milling fractions and cultivars on all traits were observed, with fraction effect being the larger. There was an uneven distribution of mineral element concentrations in wheat grain. Shorts and bran fractions had the highest mineral element concentrations, whereas flours from break and reduction had low concentrations. Compared with those in the central endosperm, the concentration of inorganic phosphorus (Pi) decreased the most with decreasing flour yield, whereas the concentration of phytic acid P (PAP), phytase activity, and Ca decreased the least. Pi was the most concentrated element in the aleurone, whereas PAP, phytase activity, and Ca were the least, compared to those in the central endosperm. Milling technique through adjusting flour yield can be used to improve the element composition of flour.     

Pig slurry applications to alfalfa: Productivity,solar radiation utilization,N and P removal

A field study was carried out over 4 years at one site in the Low Po Valley, Northern Italy, to examine the effect of various levels of pig slurry applications on alfalfa (Medicago sativa L.) productivity, solar radiation utilization, and nutrient removal. Treatments consisted of three liquid pig manure rates, estimated to provide in total 300, 450 and 600 kg N ha⁻¹ year⁻¹ (PS300, PS450, PS600, respectively), and one unfertilized control (named as Control). Treatments were applied on the second and third year of crop stand (1994 and 1995), whilst during the subsequent fourth and fifth years of crop stand (1996 and 1997) the residual effects of previous treatments were investigated. Regardless of crop age and year-to-year variability, pig slurry tended to increase annual forage production during the 2 years of fertilization and the subsequent biennium of stand duration. Overall, the forage dry matter production, accumulated over four growing seasons and 17 cuts, was 39 000 kg ha⁻¹ for the Control, 44 500 kg ha⁻¹ (+14%) for PS300, to 49 800 kg ha⁻¹ (+28%) for PS450 and 45 800 kg ha⁻¹ (+17%) for PS600. Nitrogen concentration in shoot dry matter was not influenced by the treatment applied. P concentration, on the other hand, was substantially increased by all three rates of pig slurry application, with an evident residual effect observed during the last 2 years of crop stand. However, the evident increase of P availability, assured by pig slurry fertilization, resulted in most of cases in luxury consumption of P by the crop plant. A strong linear relationship was found between cumulative forage dry matter and accumulated incident global solar radiation. Pig slurry fertilization increased significantly the slope of the regressions with respect to the Control. Since enhanced N and P availability may reduce the carbon costs for sustaining root nodules and symbiotic organisms, it seems likely that the crop plant must gain advantage in terms of dry matter produced per unit of radiation intercepted. However, further research is needed to clarify whether the effect of manure is attributable to improved alfalfa efficiency in converting intercepted solar energy into forage dry matter, to enhanced canopy cover thus higher radiation capture per unit of soil area, or to a combination of both mechanisms.     

Nutrient and assimilate partitioning in two tropical maize cultivars in relation to their tolerance to soil acidity

The use of Al-tolerant and P-efficient maize cultivars is an important component of a successful production system on tropical acid soils with limited lime and P inputs. Grain yield and secondary plant traits, including root and aboveground biomass, nutrient content and leaf development, were evaluated from 1996 to 2002 in field experiments on an Oxisol in order to identify maize characteristics useful in genetic improvement. Here we present the results of the 2002 trial and compare them with previous results. The aim of this experiment was to assess the effect of assimilate and nutrient partitioning on the growth and grain yield of two tropical cultivars having different Al tolerance (CMS36, tolerant, Spectral, moderately tolerant). The soil had an Al saturation of 36% in topsoil (pH 4.5) and >45% below 0.3 m depth (pH 4.2). Measurements made from emergence to grain filling included: root, stem and leaf biomass, P and N content, leaf area index (LAI), radiation use efficiency (RUE), soil available N and root profiles at anthesis. The experiments consisted of two P treatments, zero applied or 45 kg P ha⁻¹ (−P and +P). All the treatments received N and K fertilizers. In −P, root biomass and LAI at anthesis were twice as great in CMS36 as in Spectral. In +P the differences between cultivars were negligible. Roots were deeper in CMS36 due to its higher Al tolerance. Total biomass and grain yield were not strongly related to root biomass and LAI. Other factors such as the leaf biomass and the amount of nutrients per unit leaf area were highly correlated with RUE and biomass. In −P, Spectral had the same total biomass but a higher grain yield than CMS36 (2.1 Mg ha⁻¹ versus 1.5 Mg ha⁻¹). This was due to a higher leaf P content (+40%), a greater RUE (+74%), and a lower number of sterile plants. In +P, CMS36 had higher total biomass and grain yield (4.1 Mg ha⁻¹ versus 3.1 Mg ha⁻¹). This was due to its higher leaf P (+25%) and leaf N (+43%) contents, and an increased RUE (+130%) that were associated with higher P and N uptake. Our results indicated that although root tolerance to Al toxicity is necessary for good crop performance on acid soils, assimilate and nutrient partitioning in the aboveground organs play a major role in plant adaptation and may partially compensate for a lower root tolerance.     

Influence of crop rotation on selected chemical and physical soil properties in potato cropping systems

Crop yields are often increased through crop rotation. This study examined selected soil chemical and physical properties that may constitute the N and non-N related effects of crop rotation in potato cropping systems. Potato (Solanum tuberosum L. Norwis) was grown continuously and in two-year rotations with annual alfalfa (Medicago sativa L. Nitro), hairy vetch (Vicia villosa Roth), white lupin (Lupinus albus L. Ultra), and oat (Avena sativa Astro). Hairy vetch contributed more residue N than any other crop rotation, ranging from 110 to 119 kg N ha^?1. Inorganic N concentrations in potato soils were related to the previous crop’s residue N contents, and were highest following vetch and alfalfa and lowest following oat and potato. The highest mineralizable N concentration was found following vetch (46.6 mg N kg^?1). Saturated soil hydraulic conductivity in potato following all rotations ranged from 9.88 to 11.28 cm h^?1 compared to 5.71 cm h^?1 for continuous potato. Higher soil water contents were maintained in the 30 to 45 cm depth for all rotations compared to continuous potato. Thus several parameters indicate substantial N effects associated with particular crop rotations. Soil hydraulic conductivity and soil water status may also represent significant components of the rotation effect not directly related to N for these cropping systems.     

Satellite images as a tool to identify accelerated atrazine mineralization in soils

Microflora adaptation to atrazine (6-chloro-N²-ethyl-N⁴-isopropyl-1,3,5-triazine-2,4-diamine) mineralization due to its frequent use on the same soil has been clearly demonstrated. Studies show accelerated herbicide mineralization with mineralization percentages reaching up to 60% of the applied atrazine in a few days, which results in decreased weed control efficiency. Frequently, atrazine doses are increased to circumvent low efficiency, although this solution does not solve accelerated atrazine mineralization. The identification of soils with accelerated atrazine mineralization to guide selection of adequate management strategies and achieve good atrazine performance in adapted soils is critical. The present research assessed accelerated atrazine mineralization recognition on the basis of previous years maize (Zea mays L.) cropping as an indicator of atrazine use identified using satellite images. Three years of crop sequences were monitored by visual interpretation of Landsat satellite images. Bands 3, 4, and 5 were evaluated and corresponded, respectively, to red, near infrared, and mid-infrared. Vegetation was distinguished by selecting the R:4 G:5 B:3 color composition. Prior to assessment, atrazine behavior was evaluated in soils with high (S_H) and low (S_L) atrazine mineralization capacity. ¹⁴C-ring-labeled atrazine distribution between extractable, non-extractable, and mineralized soil culture fractions was subject to monitoring. Atrazine mineralization was determined by soil laboratory incubation. These included some soils of known past use and others with history predicted by satellite imagery. Topsoil (0-10 cm) samples were extracted according to two soil sampling strategies: Type A sampling (designated site A) consisted of 25 topsoil samples with known history, and type B sampling (designated site B) comprised 20 topsoil samples from history inferred via satellite imagery.Atrazine mineralization was monitored for 23 days under laboratory conditions. Soil ¹⁴C applied mineralization ranged from 0.3-73.0% and 0.2-30.0% in sites A and B, respectively. These broad ranges were closely related to maize presence/absence in the crop rotation at both sites. Following three straight growing seasons of maize, atrazine mineralization capacity reached a plateau in site A soils, with similar results observed in site B soils. This pattern suggests that satellite image information will be of utility to soil managers in selecting strategies to improve atrazine efficiency, including simultaneous fertilization, post-emergence atrazine applications, and choice of maize hybrids based on canopy architecture and weed competitiveness.     

Efficacy of Rheum officinale liquid formulation on cucumber powdery mildew

Rheum officinale liquid formulation, the ethanol extract from roots of R. officinale Baill., formulated as physcion 5 g l⁻¹ aqueous solution (AS), has been commercialized in China for controlling cucumber powdery mildew (Podosphaera xanthii (Castagne) U. Braun & Shishkoff). The efficacy of the product was evaluated in pot tests under controlled conditions and in open and protected fields in China over 2 years. In most trials, the efficacy reached above 80% at the rates of 10–50 mg a.i l⁻¹ water after three applications and at the rates of 20–50 mg a.i l⁻¹ water after two applications. The cucumber fruit yield in the product treatment was as many or more as triadimefon treatment, and over 53.1% compared to the untreated control. These results showed that Chinese rhubarb extract could be an effective alternative plant protecting agent in the integrated and biological management of cucumber powdery mildew.     

Termite prevalence and crop lodging under conservation agriculture in sub-humid Zimbabwe

Provision of permanent soil cover using crop residues in conservation agriculture (CA) is constrained by livestock grazing and termite consumption in smallholder farming systems of sub Saharan Africa. This study evaluated the effects of surface applied maize (Zea mays L.) crop residues on termite prevalence, crop damage due to termite attack and maize yield over two seasons, 2008/9 and 2009/10. Treatments with residue application rates of 0, 2, 4 and 6 t ha⁻¹ under CA and a conventional mouldboard ploughing (CMP) control were laid out in a randomized complete block design with four replicates on three farm sites in Kadoma, Zimbabwe. Maize residues increased (P < 0.05) termite numbers compared to CMP treatment. Crop lodging at harvest increased (P < 0.05) from 30 to 34% in CMP to 42–48% in CA systems. However, no significant difference was found in crop lodging with increasing residue rates within CA treatments. Significantly higher crop yields were observed under CA (P < 0.05) ranging from 2900 - 3348 kg ha⁻¹ in 2008/9 season compared to CMP with 2117 kg ha⁻¹. Nevertheless, increasing residue cover in CA did not necessarily increase maize crop yield. Thus, increasing crop residue application rates under CA increased termite prevalence while crop lodging was influenced more by soil tillage system than by crop residue application rates.     

Biomass yield and energy balance of three perennial crops for energy use in the semi-arid Mediterranean environment

Three different lignocellulosic energy crops (a local clone of Arundo donax L., Miscanthus x giganteus Greef et Deu. and Cynara cardunculus L. var. altilis D.C. cv. “Cardo gigante inerme”) were compared over 5 years (2002–2007) for crop yield, net energy yield and energy ratio. In a hilly interior area of Sicily (Italy), two different irrigation treatments (75 and 25% of ETm restoration) and two nitrogen fertilization levels (100 and 50 kg ha⁻¹) were evaluated in a split-plot experiment. In the fourth and fifth years of the field experiment (2005–2007) no fertilizer or irrigation was used.From crop establishment to the third year, above ground dry matter yield increased over all studied factors, in A. donax from 6.1 to 38.8 t ha⁻¹ and in M. x giganteus from 2.5 to 26.9 t ha⁻¹. Fifteen months after sowing, C. cardunculus yielded 24.7 t ha⁻¹ of d.m. decreasing to 8.0 t ha⁻¹ in the third year. In the fourth and fifth years, above ground dry matter yields of all crops decreased, but A. donax and M. x giganteus still maintained high productivity levels in both years. By contrast the yield of C. cardunculus yield fell to less than 1 t ha⁻¹ of d.m. by the fourth year.Energy inputs of A. donax and M. x giganteus were higher in the year of establishment than that of C. cardunculus (34 GJ ha⁻¹ for A. donax and M. x giganteus and 12 GJ ha⁻¹ for C. cardunculus), mainly due to irrigation.Net energy yield showed low or negative values in the establishment year in A. donax and M. x giganteus. In the second and third year, net energy yield of A. donax was exceptionally high (487.2 and 611.5 GJ ha⁻¹, respectively), whilst M x giganteus had lower values (232.2 and 425.9 GJ ha⁻¹, respectively). M x giganteus attained its highest net energy yield in the fourth year (447.2 GJ ha⁻¹). Net energy yield of C. cardunculus reflected energy output of the crop, being high in the first compared to subsequent years (364.7, 277.0 and 119.2 GJ ha⁻¹, respectively for the first, second and third years).A significant effect of the different irrigation treatments was noted on all the studied parameters in all species. Conversely, only A. donax was affected by nitrogen fertilization.