Reducing the emissions of greenhouse gases (GHG) from paddy fields is crucial both for the sustainability of rice production and mitigation of global climatic warming. The effects of applying industrial and agricultural wastes as fertilizer on the reduction of GHG emissions in cropland areas, however, remain poorly known. We studied the effects of the application of 8 Mg ha−1 of diverse wastes on GHG emission and rice yield in a subtropical paddy in southeastern China. Plots fertilized with steel slag, biochar, shell slag, gypsum slag and silicate and calcium fertilizer had lower total global-warming potentials (GWP, including CO2, CH4 and N2O emissions) per unit area than control plots without waste application despite non-significant differences among these treatments. Structural equation models showed that the effects of these fertilization treatments on gas emissions were partially due to their effects on soil variables, such as soil water content or soil salinity. Steel slag, biochar and shell slag increased rice yield by 7.1%, 15.5% and 6.5%, respectively. The biochar amendment had a 40% lower GWP by Mg−1 yield production, relative to the control. These results thus encourage further studies of the suitability of the use waste materials as fertilizers in other different types of paddy field as a way to mitigate GHG emissions and increase crop yield.

Permanent tree crop agriculture and multi-strata agroforestry are among the most promising options for the agricultural use of the mostly nutrient-poor and physically fragile soils of central Amazonia. In general, though, information on the optimum management of local tree crops under these conditions is inadequate. Annatto (Bixa orellana) is a small tree of tropical American origin whose seeds contain a non-toxic, carotenoid dye that is used widely in food and cosmetic products. The authors studied seed yields at ages four to seven years, biomass at seven years, nutrient accumulation and mineral nutrition of annatto trees growing in multi-strata agroforestry with different inputs of fertilizer and lime on a xanthic Ferralsol in central Amazonia. Leaf samples of three age classes were collected four times during one year, and nutrient concentrations were related to soil nutrient status, growth and yield of the trees in order to develop an optimum sampling scheme for foliar analysis. Growth and yields of the trees showed a pronounced response to increased fertilizer and lime input, which seemed to be due mainly to improved availability of phosphorus. Nitrogen fertilizer had no effect and may not be necessary for well-established trees on this soil. High litter quality and substantial nutrient recycling with annual pruning make annatto a valuable component for agroforestry systems. In this experiment, however, yields were low and decreased after the fifth year, presumably as an effect of infertile soil, shading by larger trees and, possibly, a negative effect of the drastic annual pruning with removal of the entire leaf and small-branch biomass on the vitality of the trees. Annatto is probably best suited for associations with small tree crops. Less drastic pruning treatments than those practiced in this experiment may be preferable.

A participatory on-farm research project was started at Tah village, 100 km south of Aleppo, Syria in 1984. The objective was to introduce annual medics (Medicago spp.) as a replacement for fallow in dryland wheat (Triticum durum)/fallow farming systems. About 50 farmers were directly involved in the project while an equal number were passive participants, receiving seed but no technical advice. The project did not attain its original intention of introducing a ley-farming system into Syria. The Syrian Government decided to eliminate fallow – which was to receive medics – in the agricultural planning for 1989–90. An array of profitable crops such as lentil (Lens culinaris), cumin (Cuminum cyminum), sesame (Sesamum indicum) and watermelon (Citrullus lanatus), together with price supports on wheat presented formidable economic competition to the use of pasture on cultivated land. Technical constraints include insufficient farm size, lack of a medic phase in every year, deep ploughing, overgrazing and uncontrolled grazing. The Tah project experience also suggests that feed production projects must include an assessment of how the feed benefits animals and be designed to demonstrate the economic advantages of integrating livestock and crops in dryland farming systems.

Most previous studies focused on intercropping systems involving two-crop associations. However, there is much scope to improve existing cropping systems by devising and evaluating modifications that allow more effective use of the season. To this effect, experiments were conducted to quantify efficiency of sequential intercropping consisting of maize (Zea mays L.), common bean (Phaseolus vulgaris L.) and mung bean (Vigna radiata (L.) Wilczek) during 2007 and 2009 cropping seasons, in southern Ethiopia. Treatments included three- and two-crop associations and equivalent sole crops of components. Land equivalent ratio (LER) and area time equivalency ratio (ATER) were used to estimate intercropping advantage. Maize had the highest partial LER, 0.95, whenever mung bean comes first in the sequence. Comparable partial LERs were observed in common bean irrespective of planting times while mung bean had greater partial LERs from simultaneous rather than sequential planting. Maize had the highest competitive ratio (1.56) followed by common bean (0.67) and mung bean (0.53). The three-crop association involving simultaneous planting of maize with mung bean followed by common bean (MZ + MB − CB) gave the highest mean total LER of 1.66. This combination also had the highest combined productivity and maximum monetary gain, which is above the minimum acceptable marginal rate of return. It exceeded advantages from intercrops of maize–common bean by 41% and maize–mung bean by 23%. Thus, farmers would get greater advantage from practicing sequential intercropping in areas where the season is sufficient to grow long-duration maize.

The partitioning of dry matter between vegetative and reproductive yield components was analysed for four diverse peanut cultivars at a range of sowing dates and plant populations in sub-tropical Queensland, Australia. Rates of accumulation of pods (pod addition) varied significantly with both cultivar and sowing date. Within cultivars, much of this variation could be attributed to variation in crop growth rate during the critical pod addition period. The proportion of current assimilate distributed to pods depended on inherent cultivar characteristics and also correlated well with the current crop growth rate relative to the crop growth rate during pod addition (that is, with relative source activity). Neither plant density nor spatial arrangement had any significant effects on patterns of assimilate distribution. All cultivars appeared capable of remobilizing stored assimilate to maintain constant rates of pod yield increase despite fluctuations in crop growth rate which might be expected to produce short term source limitations to pod yield accumulation. The harvest index (HI) increased linearly during the entire pod fill period in all cultivars except the very early maturing Spanish cultivar Chico. Neither density nor spatial arrangement affected rate of increase in HI except in Chico, where increased density produced increased rates of increase in HI. Variation in the rate of HI increase among sowing dates was small.

Distributión de la materia seca en el maní

The effect of soil salinity on growth and yield of broad bean was investigated, using correlation analysis. The salinity level at which 50% reduction in bean yield occurred was 9 mmho/cm. The negative correlation between dry matter production and yield and ECe, together with the field observations, indicated that soil salinity may be responsible for the different growth and yield of broad bean fields in the salt-affected areas of northern Sudan.

Grain yields of cowpea [Vigna unguiculata (L.) Walp.] in the Nigerian savannas are low even with the cultivation of improved varieties. The recommended spacing for cowpea is 75 × 20 cm with two seeds planted per stand. This corresponds to plant population of 133333 plants ha−1, which may not be sufficient for optimal cowpea yield. Field experiments were conducted to determine plant density effects on cowpea performance in the Northern Guinea and the Sudan savannas of Nigeria and also to determine if genotypes varied in their response to plant density. Four cowpea varieties with contrasting maturity duration were planted in single, double and triple rows on ridges spaced 75 cm apart to achieve corresponding densities of 133333, 266666 and 400000 plants ha−1, respectively. Plant densities of 266666 and 400000 plants ha−1 gave higher crop performance in terms of light interception, biomass production, yield and yield components for all cowpea varieties. Yield increases were related largely to increased pod and seed production but the effect of seed size on yield was relatively minor. Our results provide evidence that the current density of 133333 plants ha−1 used by farmers is not optimum for cowpea production. Smallholder farmers can increase cowpea grain and fodder yields if they use a density of 266666 plants ha−1 in cowpea cultivation. Further yield increases when cowpea is planted at 400000 plants ha−1 may not be sufficient to offset the cost of seed.

Soil acidity, incipient potassium deficiency, and a deficiency of one or more trace elements were limiting factors in three trials of long-term soil fertility changes under continuous cultivation in the Sudan Savanna zone of Nigeria. The effectiveness of organic manures is explained largely or wholly in terms of these factors, since no evidence has yet been found to suggest that the addition of organic matter as such is of value.

Field experiments were conducted for 3 years covering 4 crop seasons at Lucknow to study the utility of pigeonpea (Cajanus cajan) as an intercrop in economizing N for maize (Zea mays) and to assess the residual fertility of kharif crops on autumn-planted sugarcane (Saccharum officinarum). Pigeonpea increased the soil N content due to substantial nodulation, but as an intercrop it did not increase the yield of maize at any level of nitrogen. Sugarcane grown after pigeonpea yielded 43% more than when grown after maize. Intercropping pigeonpea in maize would be more beneficial than growing a pure crop of maize before planting sugarcane.

The performance of promising genotypes of faba bean developed for areas with limited rainfall was compared with the local landrace, ILB 1814, at Tel Hadya in Syria during 1989–1988 using different row spacings and sowing densities. In the last two years of the trials the performance of the improved genotypes and ILB 1814 was compared with and without supplemental irrigation. Yields of ILB 1814 were better than the highest yielding genotypes in some years and similar to them in others. In seasons with limited rainfall the best yields were obtained by using a narrow row spacing and dense sowing, and yields were significantly improved by irrigation. Grain yield was correlated with biomass and the number of pods per unit area. The percentage of radiation intercepted was highest in ILB 1814, particularly when sown with a narrow row spacing and at a high plant density. Soil water extraction, evapotranspiration and water use efficiency were improved by sowing at a narrowrow spacing and high plant density.

Los nemátodos de las plantas y la agricultura continua

In order to identify factors that constrain or favour adoption of five crop or forage related and six animal husbandry technologies promoted by government to small-scale dairy farmers, a field survey was conducted with 115 farmers. A binary logistic regression model was fitted to identify socioeconomic and farm variables explaining the technology adoption. Factors that favoured technology adoption were based on perceived usefulness, productivity and benefits to the farm, farmer's skills and farm characteristics; moreover farmers were more willing to use technologies which required low levels of investment such as de-worming, vaccines, and data recording. Constraints were related to economic restrictions, lack of knowledge, lack of land, herd size, lack of extension advice, lack of information about government programmes, requirements associated with applying for government financial support, and technologies considered to be of little or no importance to the farm such as herbicides, artificial insemination (AI) and milking machines. Adoption of crop or forage related and animal husbandry technologies was significantly associated (p < 0.05) with socioeconomic (farmer's education, farmer's experience, farmer's wealth status) and farm characteristics (herd size, cows in production, milk yield, total hectares and technological level). It is concluded that the approach implemented in this study enables identification of key factors together with the communication approaches that have been successful.

The effect of boron nutrition on the susceptibility of young tenera oil palm seedlings to red spider mite attack was studied. Highest concentrations of mites were recorded in seedlings which had received little or no boron in the growing media. Injuries by mites were greatest when the leaves had the highest number of mites per unit area, the lowest boron concentration and the lowest concentration of cyanidin.

Advanced genotypes of common bean (Phaseolus vulgaris L.) were tested on-station and on-farm to evaluate their performance and acceptability under farmers' circumstances. Farmers were given seed of the genotypes to plant a minimum area of 100 m2 to be grown as a sole crop or intercropped with sorghum according to their preference. Yield, seed colour, taste, maturity time, disease reaction, growth habit and many other bean characteristics were assessed by farmers. The promising genotypes were higher yielding than the farmers' genotypes in most testing sites. Pairwise ranking of the genotypes showed that in export-oriented western Hararghe, white pea bean (navy bean) type Awash-1 and food bean G-2816 were preferred. In eastern Hararghe GLP ×92 and G-2816 were highly preferred but white pea beans were not preferred. Genotypes in advanced observation nurseries were also evaluated by the farmers and some of the genotypes have been promoted for further testing in yield trials. Selection criteria have been proposed by the farmers in each region. Future breeding and selection of genotypes will incorporate the proposed selection criteria and priorities of the two regions.

This paper concludes the series with comments on regression, covariance analysis, and correlation. The importance of choosing a regression function, whether linear or non-linear, appropriate to problem and data is emphasized and the nature of parameter estimation is outlined. The merits of transformation of variates and the importance of introducing a proper number of parameters are briefly discussed. Common misunderstandings of the meaning of ‘the regression of y on x’ for experimental data are related to the analysis of covariance.

Regression with two or more regressors increases the computations but does not alter principles. Adjustment of means by use of covariance analysis is a much under-exploited technique in its direct sense; it also offers a computationally convenient way of handling missing observations and related problems. An attempt is made to overcome the confusions of interpretation between the regression equations of y on x and of x on y. A final section warns against misuses of correlation coefficients; the opportunities for misuse are too many for brief summary, yet such coefficients can be helpful when interpreted with care.

The fifth leaf of tomato plants sampled at the early flowering stage (seventh to eighth week after sowing) gave good assessments of N, P and K requirements of the tomato crop growing in the field but total N was less useful than nitrate-nitrogen for diagnosing nitrogen needs. The levels of critical N, P and K in the crop were 0·4 per cent NO3-N, 0·4 per cent P and 4 per cent K, with severe deficiencies when levels were less than 0·1, 0·15 and 2 per cent respectively.

In rainfed lowland rice-based systems, increasing labour scarcity due to off-farm employment is encouraging farmers to switch from transplanting to dry direct seeding (DDS). To assure stable productivity at a level comparable with or superior to transplanting, DDS management must ensure rice seedlings have access to nutrients in order to be competitive with weeds, which must also be suppressed. This paper examined farmer perceptions of DDS using a farmer survey, and used on-farm experiments to examine responses of rainfed lowland rice to integrated nutrient–weed management, based around mechanised DDS. In the survey, weeds were the biggest problem faced by farmers in using DDS (61%). In 90% of cases, farmers reported that weeds had increased under DDS, with most farmers (78%) controlling weeds by hand. All farmers said they would use DDS in the following season (100%), due to labour savings (47%), timeliness of operations, improved productivity, low investment or a combination of these (44%). In on-farm experiments, banding nutrients with the seed at sowing enhanced early dry matter of rice, while early weed dry matter was reduced. Early weed control using ducklings or hand weeding reduced weed competition and increased rice growth, with ducklings providing additional yield benefits over hand weeding. Early increases in seedling vigour of rice, and in weed suppression, carried through to greater dry matter and yield of rice at maturity. Integrated nutrient–weed management in mechanised DDS increased DDS yields, reduced DDS yield variability and contributed to sustainability of DDS rice systems.

Soil quality indicators (SQI) can be used as a synthetic tool for the assessment of the sustainability of agricultural systems. In this study, we developed SQI using minimum data set (MDS) and determined the response of SQI to long-term tillage systems. Field pea (Pisum sativum L.) and spring wheat (Triticum aestivum L.) were grown in alternate years at northwestern China, and soil attributes and crop productivity were measured 6 years after the initiation of the experiment. The MDS used to develop the SQI included soil physical (aggregate, bulk density, capillary porosity, field capacity), chemical (soil organic matter, total nitrogen, available phosphorus, available potassium) and biological (microbial count, microbial biomass, and the activities of catalase, urease, alkaline phosphatase, and invertase) properties. All the property variables were measured in each of the 0–5, 5–10 and 10–30 cm depths and those variables that contributed significantly to the SQI were selected to be included in the MDS. Amongst the measured variables, bulk density and microbial counts occurred in the MDS of all the three depths, suggesting that these two properties are highly affected by the tillage treatments. In the long-term field experiment, the no-till with stubble covering the soil surface treatment received the greatest SQI score and achieved the highest crop yield. Soil quality under tillage systems can be assessed adequately using MDS measured at the top soil (0–5 cm) layer in rainfed agro-ecosystems.

Mesquite (Prosopis spp) is a nitrogen-fixing and drought-resistant leguminous tree which exists in many of the semi-arid regions of the world but little has been done to develop its potential for wood, nitrogen fixation or pod yield. We report field and greenhouse cultural practices for mesquite and the results of a field screening trial for biomass production of 32 accessions, representing North and South American and African germplasm. Non-destructive biomass estimates, derived from height and stem diameter measurements, had a 180-fold range; the preponderance of slow-growing accessions were from the rangelands of southwestern USA.