Crop Residue Application Research Articles

A 3‐year field measurement of methane and nitrous oxide emissions from rice paddies in China: Effects of water regime, crop residue, and fertilizer application

A 3‐year field experiment was conducted to simultaneously measure methane (CH4) and nitrous oxide (N2O) emissions from rice paddies under various agricultural managements including water regime, crop residue incorporation, and synthetic fertilizer application. In contrast with continuous flooding, midseason drainage incurred a drop in CH4 fluxes while triggering substantial N2O emission. Moreover, N2O emissions after midseason drainage depended strongly on whether or not fields were waterlogged due to intermittent irrigation. Urea application tended to reduce CH4 emissions but significantly increased N2O emissions. Under a water regime of flooding‐midseason drainage‐reflooding‐moist intermittent irrigation but without water logging (F‐D‐F‐M), both wheat straw and rapeseed cake incorporation increased CH4 emissions by 252%, and rapeseed cake increased N2O by 17% while wheat straw reduced N2O by 19% compared to controls. Seasonal average fluxes of CH4 ranged from 25.4 mg m−2 d−1 when no additional residue was applied under the water regime of flooding‐midseason drainage‐reflooding to 116.9 mg m−2 d−1 when wheat straw was applied at 2.25 t ha−1 under continuous irrigation flooding. Seasonal average fluxes of N2O varied between 0.03 mg N2O‐N m−2 d−1 under continuous flooding and 5.23 mg N2O‐N m−2 d−1 under the water regime of F‐D‐F‐M. Both crop residue‐induced CH4, ranging from 9 to 15% of the incorporated residue C, and N2O, ranging from 0.01 to 1.78% of the applied N, were dependent on water regime in rice paddies. Estimations of net global warming potentials (GWPs) indicate that water management by flooding with midseason drainage and frequent water logging without the use of organic amendments is an effective option for mitigating the combined climatic impacts from CH4 and N2O in paddy rice production.

Changes in P fractions and sorption in an Alfisol following crop residues application

AbstractWith the emphasis on sustainable agriculture, attention has been increasingly turning to recycling of crop residues as a component of fertility management strategies for tropical soils. We assessed the effects of soybean residue (SR) and wheat residue (WR) applied either alone or in combination with fertilizer P (FP) on dynamics of labile P, distribution of P fractions, and P sorption in a semiarid tropical Alfisol by conducting a 16 w long incubation experiment. The amount of P added through crop residues, FP or their combinations was kept constant at 10 mg P (kg soil)–1. Addition of SR or WR resulted in net increase of labile inorganic (Pi) and organic P (Po) and microbial P throughout the incubation period, except that the WR decreased labile Pi during first 2 w due to Pi immobilization. The P immobilization associated with WR addition was, however, offset when fertilizer P was combined with WR. Generally, the increases in labile‐P fractions were larger with the SR and SR+FP than with the WR and WR+FP. The sequential fractionation of soil P at the end of 16 w indicated that a major part of added fertilizer P transformed into moderately labile and stable P fractions as evident from the increased NaOH‐Pi and HCl‐P in the FP treatment. In contrast, the addition of SR and WR alone or in combination with FP favored a build‐up in NaHCO3‐Pi and ‐Po and NaOH‐Po fractions while causing a decrease in NaOH‐Pi and HCl‐P fractions. The addition of these crop residues also effectively decreased the P‐sorption capacity and hence reduced the standard P requirement of the soil (i.e., the amount of P required to maintain optimum solution P concentration of 0.2 mg P l–1) by 24%–43%. Results of the study, thus, imply that soybean and wheat crop residues have the potential to improve P fertility of Alfisols by decreasing P‐sorption capacity and by redistributing soil P in favor of labile‐P fractions and promoting accretion of organic P.

Nitrogen use efficiency by maize as affected by a mucuna short fallow and P application in the coastal savanna of West Africa

Maize is the primary food crop grown by farmers in the coastal savanna region of Togo and Benin on degraded (rhodic ferralsols), low in soil K-supplying capacity, and non-degraded (plinthic acrisols) soils. Agronomic trials were conducted during 1999–2002 in southern Togo on both soil types to investigate the impact of N and P fertilization and the introduction of a mucuna short fallow (MSF) on yield, indigenous N supply of the soil, N recovery fraction and internal efficiency of maize. In all plots, an annual basal dose of 100 kg K ha−1 was applied to the maize crop. Maize and mucuna crop residues were incorporated into the soil during land preparation. Treatment yields were primarily below 80% of CERES-MAIZE simulated weather-defined maize yield potentials, indicating that nutrients were more limiting than weather conditions. On degraded soil (DS), maize yields increased from 0.4 t ha−1 to 2.8 t ha−1 from 1999 to 2001, without N or P application, in the absence of MSF, with annual K application and incorporation of maize crop residues. Application of N and P mineral fertilizer resulted in yield gains of 1–1.5 t ha−1. With MSF, additional yield gains of between 0.5 and 1.0 t ha−1 were obtained at low N application rates. N supply of the soil increased from 10 to 42 kg ha−1 from 1999 to 2001 and to 58 kg N ha−1 with MSF. Application of P resulted in significant improvements in N recovery fraction, and greatest gains were obtained with MSF and P application. MSF did not significantly affect internal N efficiency, which averaged 45 kg grain (kg N uptake)−1. On non-degraded soils (NDS) and without N or P application, in the absence of MSF, maize yields were about 3 t ha−1 from 1999 to 2001, with N supply of the soil ranging from 55 to 110 kg N ha−1. Application of 40 kg P ha−1 alone resulted in significant maize yield gains of between 1.0 (1999) and 1.5 (2001) t ha−1. Inclusion of MSF did not significantly improve maize yields and even reduced N recovery fraction as determined in the third cropping year (2001). Results illustrate the importance of site-specific integrated soil fertility management recommendations for the southern regions of Togo and Benin that consider indigenous soil nutrient-supplying capacity and yield potential. On DS, the main nutrients limiting maize growth were N and probably K. On NDS, nutrients limiting growth were mainly N and P. Even on DS rapid gains in productivity can be obtained, with MSF serving as a means to allow farmers with limited financial means to restore the fertility of such soils. MSF cannot be recommended on relatively fertile NDS.

Carbon dioxide, methane, and nitrous oxide emissions from a rice-wheat rotation as affected by crop residue incorporation and temperature

Field measurements were made from June 2001 to May 2002 to evaluate the effect of crop residue application and temperature on CO2, CH4, and N2O emissions within an entire rice-wheat rotation season. Rapeseed cake and wheat straw were incorporated into the soil at a rate of 2.25 t hm−2 when the rice crop was transplanted in June 2001. Compared with the control, the incorporation of rapeseed cake enhanced the emissions of CO2, CH4, and N2O in the rice-growing season by 12.3%, 252.3%, and 17.5%, respectively, while no further effect was held on the emissions of CO2 and N2O in the following wheatgrowing season. The incorporation of wheat straw enhanced the emissions of CO2 and CH4 by 7.1% and 249.6%, respectively, but reduced the N2O emission by 18.8% in the rice-growing season. Significant reductions of 17.8% for the CO2 and of 12.9% for the N2O emission were observed in the following wheatgrowing season. A positive correlation existed between the emissions of N2O and CO2 (R 2 = 0.445,n = 73,p < 0.001) from the rice-growing season when N2O was emitted. A trade-off relationship between the emissions of CH4 and N2O was found in the rice-growing season. The CH4 emission was significantly correlated with the CO2 emission for the period from rice transplantation to field drainage, but not for the entire rice-growing season. In addition, air temperature was found to regulate the CO2 emissions from the non-waterlogged period over the entire rice-wheat rotation season and the N2O emissions from the nonwaterlogged period of the rice-growing season, which can be quantitatively described by an exponential function. The temperature coefficient (Q 10) was then evaluated to be 2.3±0.2 for the CO2 emission and 3.9±0.4 for the N2O emission, respectively.

Effect of Incorporation of Crop Residues on a Maize–Groundnut Sequence in the Humid Tropics. II. Soil Physical and Chemical Properties

A two‐year study (1997–1999) was conducted on a sandy clay loam (Typic Paleudult) at the experimental farm of the Universiti Putra to determine the effects of application of crop residues on changes of some soil properties in a maize (Zea mays L.)–groundnut (Arachis hypogaea) crop rotation system. Five crops of a rotation of sweet corn–groundnut–sweet corn–groundnut–sweet corn were sown with three treatments: recommended inorganic fertilizer [nitrogen (N), phosphorus (P), and potassium (K)] with crop residue (T1), recommended inorganic fertilizer without crop residues (T2) or one‐half of the recommended inorganic fertilizer with crop residues combined with 10 t ha−1 of chicken manure (T3). Soil organic carbon (OC), soil water content and soil bulk density were not significantly changed. Application of crop residues for two years increased cation exchange capacity (CEC) whereas supplementing crop residues with CM had significantly increased soil pH of the topsoil. Phosphorous in manure treatment had moved down the soil profile, which might cause eutriphication of under ground water, particularly during the rainy season. Based on this work, incorporation of crop residues could be a beneficial practice for improving the fertility of acid soils.

Recovery of Nitrogen from Maize Residue and Inorganic Fertilizer in a Maize‐Groundnut Rotation System in Humid Tropics of Malaysia

Incorporation of crop residues after harvest may improve nitrogen (N) retention of tropical soils. A maize‐groundnut rotation experiment was established in an Ultisol to study the recovery by the crop‐soil system of N from mineral fertilizer and from the first maize residue. Out of the recommended N fertilizer for maize (150 kg N ha− 1), 60 kg N ha− 1 was applied in the form of ammonium sulphate (9.82 atom percent 15N excess) to the first maize crop and traced (for four crops) in the subsequent cropping system, with or without incorporation of crop residues. Similarly, N in the labelled residues of the first crop (maize) was also traced in the soil‐crop system with incorporation of unlabelled crop residues. Recovery of fertilizer 15N by the first crop ranged from 20 to 22%. In the subsequent four crops, this value averaged 2% (but ranged from 0.4 to 6%). The proportion of fertilizer N retained in the soil (0–50 cm) after harvest of the first crop was 35 to 44% whereas after harvest of the subsequent crops, this proportion was 30 (but ranged from 24 to 34%) in crop residue treated plots and 22% (but ranged from 18 to 27%) in plots where crop residues were removed. Maize residue‐N recovery in the subsequent three crops averaged only 5% (but ranged from 1 to 11%), being highest in the crop after crop residue incorporation. The corresponding recovery in the soil (0–50 cm) averaged across crops was 46% (but ranged from 40 to 52%). In tropical regions with high rainfall, conserving and decreasing soil N losses from mineral fertilizers could be achieved (in the long term) by the combined application of crop residues with mineral fertilizer.

Soil Organic Matter Fractions in Humid Tropics as Influenced by Application of Crop Residues

The contribution of crop residues to soil organic matter (SOM) in the sand size (particulate organic matter, POM) and sodium (Na) Iodide light (NAL) fractions were determined from soil samples (0–20 cm) collected from an experiment (April 1997–August 1999) studying the contribution of crop residues in sustaining yields of maize (Zea mays L.) and groundnut (Arachis hypogaea L.) in a crop rotation system. The treatments were: recommended inorganic fertilizer (NPK) with crop residues (T1), recommended inorganic fertilizer without crop residues (T2), and half dose of the recommended inorganic fertilizer with crop residues and combined with 10 t ha−1 chicken manure (T3). Soil organic matter size fractionation was carried out for samples collected after harvest of the second (1998) and fourth (1999) crop whereas density fractionation was carried out for samples collected after harvest of the fourth crop. Results showed that dry matter content of the POM, organic carbon (C) and nitrogen (N) relative to total soil dry weight, total soil C and total soil N in T1 and t3 plots were statistically similar to T2 plots. For all treatments, these values were found to be 1.8–3.3%, 8.5–18.1% and 4.1–7.8% for total dry matter, content of C and N, respectively. After two years, 67% of the POM dry matter weight was recovered in the small size (0.125–0.053 mm) compared to 13% in the 2.0–0.25 mm size particles. Also for all treatments, C and N in the light fractions (LF) were 0.5–0.7%, 0.6–2.1%, 0.4–1.0% (in the free LF) and 0.03–0.08%, 0.02–0.09%, 0.04–0.09% (in the occluded LF). Dry matter content of the occluded organic matter was significantly (P≤0.05) lower in T3 plots (0.93%) compared to T1 and T2 (0.13–0.2%). It was concluded that during application of organic inputs in the humid tropics, two years study was not sufficient for positive accumulation of labile SOM.

Effect of Incorporation of Crop Residues on a Maize–Groundnut Sequence in the Humid Tropics. I. Yield and Nutrient Uptake

Low soil organic matter (OM) characterizes most soils of the humid tropics because crop residues are not returned to the field. A two‐year (1997–1999) field experiment was carried out in an Ultisol to determine the contribution of crop residue application in sustaining yields of maize (Zea mays L.) and groundnut (Arachis hypogaea) in a crop rotation system. Three management practices were compared, inorganic fertilizer with crop residues (T1), inorganic fertilizer without crop residue (T2) and half dose of inorganic fertilizer with crop residues combined with chicken manure (CM) (T3), in a randomized block design. During five crops cycle of continuous application of crop residues with inorganic fertilizers or combined with CM, 43% of the observed maximum yield of the maize was sustained compared to 21% in plots where crop residues were removed. Nitrogen (N) and potassium (K) uptake by the subsequent crops were significantly higher in crop residue treatments whereas phosphorus (P), calcium (Ca), and magnesium (Mg) were not significantly affected by application of crop residues. In the highly weathered soils of the tropics, incorporation of crop residues appeared to be a beneficial management practice for sustaining crop yields.

Interactions between crop residues application and mycorrhizal developments and some soil-root interface properties and mineral acquisition by plants in an acidic soil

The addition of plant residues and the appropriate management of arbuscular mycorrhizal (AM) symbioses have been tested in an acidic soil, an Andisol from Southern Chile, to ascertain whether these agro-technologies help plants to withstand potential mineral deficiency and the toxicities inherent to the low pH conditions. Firstly, the effects of legume (lupine) and non-legume (wheat) crop residues on some key root-soil interface activities (including AM development), on mineral acquisition by the plants, and on the yield of wheat growing in the test Andisol were investigated in a pot experiment under greenhouse conditions. Both lupine and wheat residues were added at a rate equivalent to 300 g m–2 to the natural soil. These organic amendments increased soil pH (wheat more than lupine), P availability and AM development (lupine more than wheat), plant performance and mineral acquisition (wheat more than lupine). Because of an increase in mycorrhizal activity, which appeared to be involved in the effect of the added crop (particularly lupine) residues, the role of the AM symbiosis was further investigated in a tailored inoculation assay, using a selected AM fungus (Glomus etunicatum), in interaction with lupine and wheat residues. A significant effect of AM inoculation on the reduction of Zn and Cu, and Mn and Al acquisition was demonstrated, which could be of interest in acid soils with regard to potential toxicity problems.

Effect of rates and sources of phosphorus on productivity and economics of rice (Oryza sativa) as influenced by crop-residue incorporation

A field experiment was conducted at New Delhi for 3 years during rainy season ( kharif) of 2001 to 2003 to study the effect of crop-residue incorporation on the relative efficiency of di-ammonium phosphate (DAP) and Mussoorie rock phosphate (MRP) in rice ( Oryza sativa L.). Phosphorus application generally increased the growth and yield parameters, yields as well as gross and net returns of rice. The increase of these parameters was however signifi- cant when the rate of P application was increased from 0 to 35 kg P/ha. At 35 kg P/ha MRP in conjunction with phosphate solubilizing bacteria (PSB) was statistically on a par with DAP, increasing the grain yield by 10-17%, P uptake by 26-54%, available P content in soil by 12-99% and net profit by 15-37% over the control. Agronomic effi- ciency and apparent recovery of DAP were higher than those of MRP at 17.5 kg P/ha, but on a par with those at 35 kg P/ha. Crop-residue incorporation had no significant effect on grain yield but it significantly increased the appar- ent recovery of applied P and available P content of soil. Thus, the combined application of MRP, PSB and crop residue proved a good practice that can be used as P fertilizer for rice.

Effect of conservation agriculture practices and irrigation scheduling on productivity and water-use efficiency of maize (Zea mays)wheat (Triticum aestivum) cropping system

A field experiment was carried out during 201112 and 201213 at the research farm of IGAR-lndian Agricul- tural Research Institute, New Delhi, India, in sandy-loam soil, to study effect of conservation agriculture practices and irrigation scheduling on productivity and water-use effi0ienoy of maize (Zea mays L.)wheat [Triticum aestivum (L) emend. Fiori &amp; Paol.l cropping system. The grain yield of maize was significantly higher under raised bed (RB) planting to the tune of 13.3% over conventional tillage (CT) during both the years. The increase in irriga- tion water-use efficiency (IWUE) of maize was 4046% and higher with RB and zero tillage (ZT) over CT respectively. Residue retention was more beneficial under RB than residue incorporation in CT. In wheat, 613% higher grain yield under RB was found in comparison to GT. The increase in IWI-JE of wheat was found higher in RB (3240%) compared to ZT (812%) over CT, as the grain yield was more with per unit of water applied under RB- The highest system productivity was recorded under RB (9.92 and 9.80 t/ha) followed by ZT (9.08 and 9.04 t/ ha) and the minimum under GT (8.63 and 8.84 t/ha during 201112 and 201213 respectively) during both the years. The yield of crops and system productivity improved owing to application of crop residue. The results also revealed that system productivity of maizewheat cropping system was significantly influenced because of ditfer- ent irrigation scheduling during both the years. Adoption of RB with crop residue along with 40% available soil- moisture depletion (ASMD) can be recommended for improving resource-use efficiency and productivity of maize wheat cropping system.

Destructive and non-destructive measurements of residual crop residue and phosphorus effects on growth and composition of herbaceous fallow species in the Sahel

Little is known about the residual effects of crop residue (CR) and phosphorus (P) application on the fallow vegetation following repeated cultivation of pearl millet [Pennisetum glaucum (L.) R. Br.] in the Sahel. The objective of this study, therefore, was (i) to measure residual effects of CR, mulched at annual rates of 0, 500, 1000 and 2000 kg CR ha−1, broadcast P at 0 and 13 kg P ha−1 and P placement at 0, 1, 3, 5 and 7 kg P ha−1 on the herbaceous dry matter (HDM) 2 years after the end of the experiment and (ii) to test a remote sensing method for the quantitative estimation of HDM. Compared with unmulched plots, a doubling of HDM was measured in plots that had received at least 500 kg CR ha−1. Previous broadcast P application led to HDM increases of 14% compared with unfertilised control plots, whereas no residual effects of P placement were detected. Crop residue and P treatments caused significant shifts in flora composition. Digital analysis of colour photographs taken of the fallow vegetation and the bare soil revealed that the number of normalised green band pixels averaged per plot was highly correlated with HDM (r = 0.86) and that red band pixels were related to differences in soil surface crusting. Given the traditional use of fallow vegetation as fodder, the results strongly suggest that for the integrated farming systems of the West African Sahel, residual effects of soil amendments on the fallow vegetation should be included in any comprehensive analysis of treatment effects on the agro-pastoral system.

Soil carbon dynamics of conventional tillage and no-till agroecosystems at Georgia Piedmont — HSB-C models

This model was designed to simulate the dynamics of soil organic matter (SOM) and biomass change of detritus soil food webs after the application of crop residue in agroecosystems. Background data and literature parameters were used to initialize the model and a short-term field experiment was conducted to calibrate the model. Our model is a synthesis and integration of many others’ previous studies because many others’ ideas on food web or SOM modeling were incorporated into our model. In our model, soil microorganisms were considered to be the major decomposers of organic matter with soil animals playing an important role in decomposing organic matter by controlling the population of soil microorganisms through trophic interactions. Though we did not model the soil food web into species or functional groups, we attempted to represent the hierarchical structure and trophic interactions of soil food webs as complete as possible. The whole soil food web was conceptualized as a ‘super organism’ to process organic matter in the model diagram. State variables of our model were categorized into soil organic matter pools, inorganic carbon pool, and soil organism pools. Flows were modeled based on first order kinetics. A tillage effect was introduced in our model by assuming that soil microorganisms, microarthropods and earthworms decrease temporarily immediately after the tillage operation. We also introduced a ‘minimum population’ protection mechanism for each group of soil organisms by assuming that predation ceases when energy obtained can not offset the energy expended in prey-searching and feeding. We found that the simulation outputs fitted the measured data very well, the simulation outputs were in the range of field measurements in most cases. However, there was a significant discrepancy in respiration between simulation output and field measurement in both conventional tillage (CT) and no-till (NT), particularly in NT agroecosystems. We hypothesized that plant roots should be responsible for this discrepancy. The sensitivity analysis of our model showed that the population of soil microorganisms was controlled by resources rather than predators. However, the populations of soil protozoa, nematodes and microarthropods were controlled by both resources and predators.

Crop residue and tillage effects on carbon sequestration in a Luvisol in central Ohio

Soils play a key role in the global carbon cycle. They can be a source or a sink of carbon and influence CO 2 concentrations in the atmosphere. In order to calculate the carbon budget of a region, the effect of soil management practices on carbon sequestration in soils needs to be quantified. Objectives of this experiment were to determine: (i) the effects of ridge till, plow till and no-till on the soil organic carbon (SOC) pool; (ii) the SOC loss or sequestration for mulch rates of 0–16 Mg ha −1 year −1 wheat ( Triticum aestivum L.) straw applied in combination with each tillage method, and (iii) impacts of tillage and crop residue treatments on soil physical quality, including aggregation and porosity. The experiment was initiated in 1989 on a Crosby silt loam (Stagnic Luvisol) in Central Ohio. Seven years after initiation of the experiment, there was a positive, linear effect of residue application rate on SOC contents in all tillage treatments. In the eighth year of the experiment these trends were confirmed for plow and no-till, but not for ridge till. Linear-regression equations, relating SOC content for the 0–10 cm soil depth to mulch rate, were: for no-till: SOC (Mg ha −1) = 15.21 + 0.32 [Residue (Mg ha −1 year −1)] ( r = 0.68) and for plow till: SOC = 11.95 + 0.27 [Residue] ( p = 0.72). The carbon conversion efficiencies were 8% per year for plow till and 10% per year for no-till. Detailed sampling at different depths revealed that increases in SOC content were only significant for the 0–5 cm depths of plow and no-till treatments. Effects of crop residue application on water stable aggregation in the 0–10 cm layer were most pronounced with plow till and ridge till but not with no-till. Water retention characteristics, a measure of pore size distribution, was not influenced by tillage system, but crop residue application had a significant effect on water retention in the 0–10 cm layer at matric suctions of 30–300 kPa. This means that residue application increased macropores of diameters 1–10 μm. It is concluded that, depending on the amount of crop residue returned to the soil, the large numbers of farmers converting from plow to no-till cultivation in the Corn Belt may create an important sink for atmospheric CO 2.

Yield response of maize (Zea mays L.) to crop residue management on two major soil types Of Alemaya, Eastern Ethiopia: I. Effects of varying rates of applied and residual N and P fertilizers

Field trials were conducted on two soil types for seven years (1988–1994) to investigate grain yield response of maize to crop residue application as influenced by varying rates of applied and residual N and P fertilizers. Yearly application of N and P fertilizers at both one-half and full recommended rates resulted in grain yield increases of more than 500 and 1100 kg ha-1, respectively over application of only crop residue. Moreover, grain yield responses due to residual N and P fertilizers applied only during the first year were found to be comparable to the yearly applications of these fertilizers. Rainfall and soil type have exerted considerable influences on the grain yield response obtained in this study. Grain yield exhibited a corresponding decrease with decreasing rainfall. Grain yield increases on Typic Pellustert were relatively higher than on Typic Ustorthent.

Phosphorus application affects the nutritional quality of millet grain in the Sahel

The application of phosphorus (P) and crop residues (CR) to acid sandy soils of the Sahel has been shown to increase yields of pearl millet ( Pennisetum glaucum L.) several-fold. Information is lacking, however, about possible detrimental effects of such yield-enhancing amendments on grain quality, in particular the bioavailability of zinc (Zn) as defined by the phytate:zinc molar ratio (PZMR) and the concentrations of calcium, micronutrients, and protein. To determine the effects of CR and P on grain quality, millet seeds taken from the grain stores of 14 farmers and from a 2-yr on-station fertilizer experiment were analyzed for macronutrients, Zn, copper, iron, and phytate-P. The on-station experiment comprised four millet lines, P applied at 0 and 13 kg ha −1, and CR applied at 500 and 2000 kg ha −1 as surface mulch or ash. Grain from farmers' unfertilized millet had PZMRs ranging from 15 to 30. Application of P increased the concentrations of phytic acid in the grain between 25 and 29% and decreased Zn concentrations between 6 and 11%. The reasons for this were greater P uptake and a dilution of Zn by the large yield increases after P application. Phosphorus application decreased protein concentrations in both years, and increased the PZMRs from 20 to 28 in 1992 and from 21 to 29 in 1993. Although CR markedly increased millet yield, their application had little effect on PZMRs. While PZMRs above 15 are generally considered critical for Zn nutrition of humans, meat consumption and traditional practices of millet processing may increase Zn bioavailability in local dishes. Further studies of full diets are therefore needed, particularly among rural groups at particularly high risk of Zn deficiency such as nursing women and small children before definitive conclusions can be drawn about the effects of P fertilizer application to millet on the nutritional status of farmers in the Sahel.

Effect of tied ridges on grain yield response of Maize (Zea mays L.) to application of crop residue and residual N and P on two soil types at Alemaya, Ethiopia

Field experiments were conducted on two soil types over a period of five years (1986–1990) to investigate the effects of tied ridges and planting systems on the grain yield response of maize to applications of crop residue and residual N and P fertilizers. Grain yields were increased by the use of tied ridges. Further increases in grain yields resulted from residual N and P and crop residue applied separately or together. Under all fertilization practices, planting in the furrow of tied ridges resulted in higher grain yields than planting on top of tied ridges. The effect of the tied ridges in increasing grain yields was generally better in the drier periods and the more so when the ends of the ridges were tied. In wetter seasons the open end tied ridges gave higher yields than the closed end tied ridges. The effect of tied ridges on grain yield response of maize to application of crop residue and residual N and P fertilizers was influenced by rainfall and by soil type.

PHOSPHORUS AND MILLET CROP RESIDUE APPLICATION AFFECT THE QUANTITY AND QUALITY OF MILLET LEAVES AND FODDER WEEDS FOR RUMINANTS IN AGRO-PASTORAL SYSTEMS OF THE SAHEL

Low levels of phosphorus limit the yield of pearl millet (Pennisetum glaucum) grown on acid sandy soils of the West African Sahel. The application of phosphorus and the recycling of millet residues produces large increases in the total dry matter and grain yields of millet but little is known about the effects of these amendments on the by-products of millet fields which include weeds and millet leaves at harvest. Phosphorus applied at 13 kg ha−1 as single superphosphate and millet residues applied at 500 or 2000 kg ha−1 as a mulch or as the ash from 2000 kg millet residues ha−1 that had been burned, increased dry matter yields of millet leaves and weeds leading to large increments in the total in vitro metabolizable energy harvested per unit area. These increases in dry matter production were only accompanied by minor decreases in the concentration of crude protein. The increased availability of millet by-products should be taken into account when evaluating the effects of phosphorus and crop residue application on the economy and sustainability of agro-pastoral farming systems in the West African Sahel.

Energy-use patterns in sub-tropical rice-wheat cropping under short term application of crop residue and fertilizer

Rice-wheat cropping in the sub-tropics is energy intensive, requiring a major input from fossil fuel. These crops produce lots of residue, part of which is often wasted in burning, the incorporation of which is beneficial when applied with fertilizer. Reserves of fossil fuel is decreasing at an increasing rate. Therefore, it is more important to know the effect of application of residue production from these crops in the light of recycling of energy and its output. Keeping this in view in a field experiment between 1990 and 1992, three levels of residue incorporation: (i) nil, (ii) half, (iii) full of residue production from one crop to the other were combined with two levels of mineral fertilizer: (i) no fertilizer, (ii) standard level of 120, 60, 60 kg N, P 2O 5 and K 2O per hectare as treatments. The trade-off studies showed that applications of half the crop residue with fertilizer consistently produced the highest grain yield of rice and wheat. Addition of residue without fertilizer had little benefit while application of fertilizer without residue had moderate effects. The combined application of half the residue with fertilizer proved to be the best combination providing the maximum production of crop per unit use of fossil fuel. The highest labour productivity (crop production/hour of labour) was also found under the same treatment. But further addition of residue with fertilizer declined the crop production per unit area, per unit of fossil fuel or per hour of labour. So keeping in view the fast depleting commercial energy sources, incorporating half the residue production of the crop with recommended fertilizer in a rice-wheat cropping may be a wise practice in solving the energy problem for higher production in this part of the subtropics.

Effects of Crop Residue and Phosphorus Application on the Spatial Variability of Non-destructively Measured Millet Growth in the Sahel

SUMMARYSpatial variability in soil parameters and plant growth in the Sahel are still poorly understood and may hamper the interpretation of experimental results. This paper examines whether or not soil amendments such as phosphorus and crop residues affect the variability of final dry matter production in pearl millet (Pennisetum glaucum). Within- and between-plot variation in millet growth was studied in a three-year experiment with three levels of crop residues and four levels of phosphorus. The effects of different rates of application on within-plot variation in number of tillers, number of heads, maximum tiller height, and total above-ground dry matter of single mature millet plant stands (pockets) were calculated. Above-ground dry matter, estimated non-destructively using an equation derived from numbers of tillers and heads and from maximum plant height, gave good predictions of total dry matter for a range of genotypes across the 12 treatments. Crop residue and phosphorus application reduced the number of missing pockets, leading to a more uniform stand with fewer pockets which did not produce grain. With amendments, pockets were also taller and of more uniform height but a decrease in variability of total dry matter production only became evident after standardization of the data. The results show the need for a clear definition of ‘growth variability’ in millet and indicate that both chemical and non-chemical factors govern its expression in the Sahel.Efectos de los residuos de las cosechas y del fósforo en la variabilidad del mijo