Data from 94 experiments on sorghum/pigeonpea intercropping were examined for evidence that the stability of yield is greater with intercropping than sole cropping. Stability of the major component (sorghum) was examined by calculating the distribution of yields; stability of the overall intercropping system was examined by calculating coefficients of variation, by computing regressions of yield against an environmental index, and by estimating the probability of monetary returns falling below given ‘disaster’ levels. All these approaches have some merit; taking the last as an example, it was found that for a particular ‘disaster’ level quoted, sole pigeonpea would fail one year in five, sole sorghum one year in eight, but intercropping only one year in thirty-six. Intercropping gave yield advantages under a wide range of environmental conditions and there was no significant evidence that advantages were greater under stress. This is discussed in relation to possible mechanisms contributing to greater yield stability.

A simple competitive ratio (CR) is proposed as a measure of intercrop competition, to indicate the number of times by which one component crop is more competitive than the other. Intercropping data show that this CR term could be useful in (i) comparing the competitive ability of different crops, (ii) measuring competitive changes within a given combination, (iii) identifying which plant characters are associated with competitive ability, and (iv) determining what competitive balance between components is most likely to give maximum yield advantages.

On the basis of a preliminary experiment with 20-day-old Cicer seedlings, wherein the values obtained by integrating the in vivo nitrate reductase (NR) activity with the duration closely approximated the actual reduced N, a field experiment was conducted with cv BG 203 (indeterminate type) to ascertain the extent to which the nitrate assimilated via the enzyme NR contributed to the total reduced N. Soil-derived N accounted for 15.1, 8.3 and 7.2% of the total reduced N at pre-flowering (I), profuse flowering (II) and seed filling (III) stages respectively. Out of the total soil-derived N, 10.1, 59.3 and 30.6% was reduced during stages I, II and III respectively.

Sesame was grown in four seasons in which differences in the distribution of the rains and treatments of pre-sowing flooding, irrigation during crop growth and surface drainage resulted in contrasts in soil water content and crop development. In wet years pre-sowing flooding, absence of surface drainage and premature irrigation gave 32–37% decreases in yield. In a season of low rainfall prevention of surface run-off and one later irrigation gave, in the absence of pre-sowing flooding, a 43% increase in yield over that from plots irrigated only at sowing and with surface drainage. Agronomic applications are discussed.

Leaf area index is an important parameter in many agronomic and physiological studies, but its determination in cowpea (Vigna unguiculata) and soyabean (Glycine max) is difficult and time consuming. A simple and rapid method is described in which dry weights of the middle leaflets were used to predict leaf areas of cowpea and soyabean. This method was based on results which indicated that leaf dry weights were highly correlated to leaf areas and that the ratio between leaf area of the terminal leaflet and total area of a trifoliate leaf was constant, at least in some cultivars, giving ratios of 0.37 for cowpea and 0.33 for soyabean.

Six products possessing suitable physical properties as fluid carriers for pre-germinated seed were assessed for their effects on seedling emergence. Both glasshouse and field experiments measured the carriers' performance on eight crop species at varying extrusion rates and under different environmental conditions. Synthetic clay or polyacrylate increased seedling emergence by 10% compared with the sodium alginate control. Seedling emergence was least affected by moisture stress when synthetic clay was used as the carrier.

Dry matter produced and allocated to the tuber and aerial portions of yam plants (Dioscorea spp) were studied over 3 cropping seasons in the moist forest region of Nigeria, in an attempt to relate dry matter accumulation to vegetative maturity in the crop. The effect of duration of growth of yam on post-harvest dormancy was also studied. Cultivars differed both in the total amount and period of growth when most dry matter was accumulated. A higher proportion of dry matter was allocated to tubers in lower-yielding than in higher-yielding cultivars. It appears that a yam tuber is ‘mature’ almost as soon as it is formed.

On unlimed Malaysian peat (pH 3.5), flue-cured tobacco produced negligible leaf yields and showed no response to urea. Liming up to pH 5.25 (32 t/ha lime) linearly increased leaf yield. Tobacco responded linearly without reduced leaf quality to 90 k/ha N at pH 4.01 (8 t/ha lime), but to 45 kg/ha N at pH 4.40–5.25 (16–32 t/ha lime), higher N rates at the respective liming levels producing leaves of lower quality. The optimum rates of P and K for flue-cured tobacco appeared to be 26 and 186 kg/ha respectively, with linear responses up to those rates.

Five field experiments studied the effects of high planting densities, ranging from 83,000 to 667,000 seeds/ha, on eleven soyabean cultivars. Germination rates ranging from 32 to 100% and averaging 76%, resulted in actual plant densities of 45,000 to 296,000 plants/ha. Bean yields of the four shortest and earliest-maturing (64–67 days) cvs (Wakashima, Shi-shi, Palmetto and Tai Tah Kaoh Siang 58) increased with increasing density, producing highest yields at the highest plant densities investigated (222,000–286,000/ha) but 7 taller cvs, maturing in 80–126 days (P2, C13, C21, P4, D5, T10 and C28), produced reduced yields with increasing density, the lowest densities investigated (45,000–83,000 plants/ha) giving the highest bean yields.

The yield and gross returns (Rs/ha) were studied over two years in three experiments on intercropping in corn and sorghum. Paired-row planting recorded 8 to 12% and 44% higher yield in corn and sorghum respectively over conventional equidistant planting at the same plant populations. Additional gross returns due to intercropping ranged from 24 to 76% in corn (1975–76 winter) and 4 to 56% in corn and 15 to 75% in sorghum (1976 rainy season) compared to pure crops. Intercropping was beneficial, particularly in the limited cropping periods of this semi-arid tropical zone.

Root development of maize (Zea mays), soyabean (Glycine max), cowpea (Vigna unguiculata), and pigeonpea (Cajanus cajan) was investigated with and without tillage. Observations were made at different growth stages by digging trenches normal to the rows, by core sampling, and by observing growth of roots against glass windows. There were more maize roots in the surface layer (0–10 cm) with no-tillage than in conventionally ploughed plots, but at 10–40 cm maize roots were more abundant and soyabean and pigeonpea roots less so in the no-tillage plots.

A field experiment to study weed and fertility management in rain-fed maize was undertaken at the Palampur Experimental Farm during the wet seasons of 1977 and 1978. Intercropping soya-bean in maize did not impose undue competition and significantly increased net profit per ha. Yields and net returns were significantly higher when weeds were controlled and 80 kg N/ha was applied. Increased application of fertilizer without weed control did not alter the yield of maize, and there was no response to phosphorus. Various yield attributes of maize were significantly affected by weeding and nitrogen treatments through their effects on grain and stover.

Cowpea cvs Ife Brown and New Era were sown at a wide range of densities in 1976 and 1977 (early season) at Ibadan in the rainforest zone of Nigeria. In 1977 (late season), the experiment was modified and Ife Brown and Vita 5 were used. All the cultivars were indeterminate. Grain yields were higher at lower densities, especially in 1977 (late season). Numbers of leaves, branches and pods were also inversely related to density, but there were differences between varieties in flowering, branching and leaf and pod production.

An experiment at the University of Queensland studied the response of Crotalaria juncea to a single cut above node 4 or 10 at 6, 8 or 10 weeks after planting under long or short (inductive) daylengths. Initial deleterious effects of cutting on plant parts were in the sequence nodules > roots > shoots. Subsequent greater regrowth from plants cut earliest and at the higher node was associated with higher residual leaf area and negative growth rates were inferred below 90 cm2 pot−1. Redistribution of assimilate from stem to leaf production followed cutting; in inductive daylengths of 11.4 hours, flowering was delayed and the proportion of leaf increased from 21.0 to 32.4%. The high nitrogen content of leaf (3.5–5.3%) compared to stem (0.6–1.7%) indicated that early cutting was important in producing good quality hay.

Experimental Agriculture, vol. 16, page 94:

EVALUATING TECHNICAL INNOVATIONS UNDER LOW-RESOURCE FARMER CONDITIONS

By J. C. FLINN and J. LAGEMANN

International Institute of Tropical Agriculture, Ibadan, Nigeria

The following corrections should be made to Table 3:

1. To be consistent with the text, the two column headings Bi should read bi.

2. The constant terms reported are log b0; the antilogs of these values – which are extremely close to 1.0 – should have been reported in the table as the estimated partial regression coefficients for the constant X0.