Water stress induces some physiological changes in plants and has cumulative effects on crop growth and yield. Field experiments were conducted to study the effect of deficit irrigation (DI) on yield and some physiological parameters in cotton and maize in a sequential cropping system. Creation of soil moisture gradient is indispensable to explore the beneficial effects of partial root zone drying (PRD) irrigation and it could be possible only through alternate deficit irrigation (ADI) practice in paired row system of drip layout that is commonly practiced in India. In the present study, PRD and DI concepts (creation of soil moisture gradient) were implemented through ADI at two levels of irrigation using drip system. Maize was sown after cotton under no till condition without disturbing the raised bed and drip layout. Relative leaf water content (RLWC) and chlorophyll stability index (CSI) of cotton and maize were reduced under water stress. A higher level of leaf proline content was observed under severe water-stressed treatments in cotton and maize. RLWC and CSI were highest and leaf proline content was lowest in mild water deficit (ADI at 100% crop evapotranspiration once in three days) irrigation in cotton and maize. The same treatments registered higher values for crop yields, net income and benefit cost ratio for both the crops.

Chicken manure is a potential source of plant available phosphorous (P) and this field study explored its use for dry land maize production in a soil with very low inherent P levels. The treatments consisted of applying 0, 20, 40 and 80 kg P ha−1 each from chicken manure (2.3% P), inorganic fertilizer (single super phosphate, 10.5% P) and a combination of manure and fertilizer. The treatments were replicated four times in a randomized complete block design over two crop seasons. The results revealed that maize growth and yield responded to the P from both manure and fertilizer compared to the control. There were significantly (p < 0.05) taller plants and yield (grain and biomass) in maize supplied with P than control. At each level of P application however, the response was higher for fertilizer than manure. The combination of manure and inorganic fertilizer produced results that were in the middle. There were strong indications that application of chicken manure was associated with increased lodging possibly due to the additional N in the manure, attack by stalk borer (Buseola fusca) and reduced seedling emergence. The application of chicken manure on the other hand led to increased pH and greater residual P content of the soil than fertilizer. It is concluded that chicken manure presents a viable option for supplying P to sustain maize crops in the smallholder farming sector of South Africa and its management warrants further investigation in view of the potential adverse impacts on soil and water resources that can accrue when large amounts are used for a long period.

A serious problem in long-term field experiments is that soil is moved from plot to plot as a result of cultivations. The problem is often overlooked and very few attempts have been made to quantify this movement under varying conditions.

A simple, mathematical model for approximating the movement of soil in one horizontal dimension by repeated tillage with one or more tillage implements is presented. The model describes the development with time of a concentration gradient of substance, by means of the solution of a diffusion equation. The model is in agreement with ‘the central limit theorem’, when it is used for the situation where the same cultivations are repeated many times in alternating directions.

The model fitted well to data taken from the literature.

Commercial cassava production from true cassava seeds (TCS) appears to be a promising option for reducing or eliminating several of the production constraints associated with vegetative propagation. The most important contribution of TCS would be to reduce virus build-up in vegetative material and to resolve the problems of stake storage, low multiplication rate and the long growth cycle. Preliminary results suggest that the root yield potential of TCS is comparable with that of traditional vegetative propagation. Improvements in the capacity of true seed progenies to germinate and establish in the field can be achieved either genetically or through pre-planting seed treatments such as coating the seed with rock phosphate. Development of a successful TCS technology will require a multidisciplinary approach, involving basic studies in cassava breeding, physiology, agronomy, socio-economics and other fields.

In symbiotically-dependent chickpea, nodule mass and rates of nitrogenase activity increased when vegetative growth increased rapidly, but declined during fruiting. The specific activity of nodules declined as their mass rapidly increased. Nodule mass and rates of nitrogenase activity varied between genotypes, as did the point of maximum activity, which in some genotypes occurred before fruit growth dominated shoot growth. Current N2-fixation supplied most of the nitrogen for pod and seed growth, but in some genotypes mobilization of nitrogen from vegetative parts was evident. Seed attracted up to 50% of assimilated nitrogen; residual nitrogen was contained mainly in leaf and pod tissue, though in one genotype stem nitrogen was plentiful.

Arbuscular mycorrhizal fungi (AMF) may have a major role in phosphorus nutrition of crops in Lombok, where fertilizer use is low. As a start to understanding this role, AMF dynamics were monitored from the 1999 non-rice season to the end of the 1999/2000 rice season at 32 sites including dryland systems with no rice, upland rice and flooded systems with one or two rice crops per year in the rotation. Over all four systems, root colonization was greater in vertisol (22.3 % of roots) than in regosol (9.5 %) soil, possibly due to lower Bray-1 P content of the vertisol (6.2 v. 13.7 mg kg−1). Colonization was poor in flooded rice (3.1–5.1 %); at the same sampling times it was better in upland rice (10.6–13.4 %) and in non-rice crops growing in dryland systems (13.8–17.0 %). Therefore, the low colonization in flooded rice appeared to be the result of flooding, rather than the rice itself. Flooding also reduced transparent spore numbers, but sufficient inoculum appeared to survive flooding for plants in the following non-rice season to be well colonized (19–33 %) regardless of system. These non-flooded crops appear to replenish depleted AMF propagules.

Nitrogen was lost through leaching, both as and , even after application of the ammoniacal form in a reduced soil zone. Under saturation the loss was more through , and under submergence through nitrogen. The loss was accelerated when all the nitrogen was applied at one time at the early stage of crop growth. Application at transplanting proved unproductive. Three split application at active vegetative, reproductive and ripening phases helped to give maximum responses in both alluvial clay and lateritic sandy clay loam soil.

Whole branches were removed from trees in the field, at regular intervals, to follow the increase in dry weight of fruits and new vegetative growth. Information on the partition of carbohydrates was gained by comparing the growth of untreated, defoliated, de-blossomed and ring-barked branches. Untreated branches increased in weight rapidly when their fruits began to expand, probably because they imported carbohydrates, and their net photosynthetic capacity increased. More young fruits were shed from defoliated than from untreated branches, thus partially compensating for loss of leaf. Non-fruiting, and sometimes fruiting, branches exported a considerable amount of assimilate during the dry seasons, when the trunk-root system was a relatively important dry matter sink. When there were many fruitless branches on fruiting trees, the fruiting branches imported carbohydrates from them during the whole period of fruit growth, whereas fruitless branches imported carbohydrates only when there was a ‘flush’ of shoot growth.

Alternate row mixtures of millet, maize and sorghum were compared with equivalent areas of sole crops. Yield of mixtures were rarely reduced but there was a gain when components differed by a certain margin in height or age at maturity, or both. Approximately 75% of variation in yield gain from mixing was attributable to these two factors. Subsistence farmers who mix a fast-growing early-maturing cereal with a slower-growing, later-maturing one thus reduce interference between neighbouring plants during the reproductive phase of growth, and obtain grain harvest spread in time and heavier than from equivalent areas of the component sole crops.

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.

The relation between current yield and future yield components in the oil palm (Elaeis guineensis Jacq.) was investigated by removing a proportion of inflorescences before anthesis. This disbudding caused mean fruit bunch weight to increase by over 60%, with corresponding increases in the components of bunch weight. The total number of inflorescences produced increased by 10%, the sex ratio increased from 72 to 91% females, and inflorescence abortion and bunch failure rates were halved. As a result, the number of bunches harvested was reduced by less than the level of disbudding, and removal of 75% of inflorescences only reduced yield by 42%. Disbudded palms also grew more vigorously. The time intervals between a change in the level of fruiting activity and the resulting changes in yield components were determined by recording the yield components during the period after disbudding was stopped.

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.

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

Use of biochar (B) and poultry manure (PM) as soil amendments can improve the productivity and sustainability of tropical agriculture. Our fieldwork is the first research on the agronomic use of B and PM for the growth of cocoyam in sandy soil of the humid tropics. In this study, the effects of B, PM and their mixture were investigated on soil properties, mineral and nutrient concentrations, growth, and corm and cormel yields of cocoyam during the 2017 and 2018 cropping seasons. The experiment consisted of 4 × 2 factorial combinations of B (0, 10, 20, and 30 Mg ha−1) and PM (0 and 7.5 Mg ha−1). In both years, the application of B and PM either alone or in combination improved soil physical and chemical properties, plant nutritional status, growth, and corm and cormel yields of cocoyam. The combination of 30 Mg ha−1 B and 7.5 Mg ha−1 PM (B30 + PM7.5) gave the highest corm and cormel yields of cocoyam. Pooled over the 2 years, application of B at 30 Mg ha−1 and PM at 7.5 Mg ha−1 (B30 + PM7.5) significantly increased corm yield of cocoyam by 47 and 66%, respectively, when compared with sole PM at 7.5 Mg ha−1 and B at 30 Mg ha−1. Lowest corm and cormel yields were obtained for the unmanure control. The combination of 30 Mg ha−1 B and 7.5 Mg ha−1 PM is recommended for soil fertility management and cocoyam production in the rainforest agroecology of SW Nigeria.

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.

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.

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.