A fluorescent-dye technique has been developed to measure root length of field crops. Roots are washed from soil samples, stained for about 30 min in a solution of fluorescein diacetate in acetone, washed, spread out on a tension table and photographed under UV light. Lengths of fluorescent roots recorded on the photograph are estimated by line intersection. The method is quick, simple, inexpensive and largely eliminates the usual time-consuming, tedious process of hand-sorting live roots from organic debris. Whereas all the roots of young laboratory-grown plants take up the dye, some older roots of field-grown crops do not fluoresce. Data indicate that the method may also give information on root diameter.

Large yields and dry matter production rates have been recorded for tropical perennial crops, despite the fact that little research has been done on most of them. Considerable increases in productivity should still be possible, since the potential energy fixation rate for such crops is estimated to be about 1.2 TJ ha−1 a−1. The dry matter equivalent of this energy varies between species; the oil crops and rubber, in particular, have large energy contents in their respective economic products. Hot leaf temperatures appear to limit productivity in some crops, while unfavourable partitioning of assimilates limits yield at the large leaf area indices necessary to maximize dry matter production. Respiratory losses are large in these crops and selection for smaller respiration rates could lead to considerable improvements in their net productivity.

A two year study on ‘Pusa Sawani’ okra grown during the summer in Rampur, Nepal (228 m OD; 27° 37′ N) has shown that spacing did not affect days to first harvest or pod length but that pod number plant−1 was affected significantly. Although individual plant yields at each harvest were maximum viith plants spaced 45 cm apart (a population of about 50,000 plants ha−1) pod yields ha−1 were maximum with plants spaced only 15 cm apart (about 150,000 ha−1). Applications of nitrogen fertilizer hastened the first harvest by 4–6 days compared to the unfertilized control plots. The greatest pod yield (9.3 t ha−1) was obtained from plots given 60 kg N ha−1.

Glasshouse studies have shown that nodulation and dinitrogen fixation in groundnuts grown in a sand/vermiculite mixture increased with an increase in Rhizobium numbers inoculated onto each seed. Cultivars Robut 33-1 and TMV 2 required 106 rhizobia seed−1 for maximum nodulation and dinitrogen fixation, while cv. Kadiri 71-1 required larger numbers.

Experiments in Brazil have shown that a sorghum-pulse (cowpea or common bean) intercrop system yielded more grain than the monocrop system and produced a Land Equivalent Ratio (LER) greater than 1.00 even though rainfall was limited. Sorghum competed less than maize with the associated pulse when Competitive Ratios (CR) were considered. In cowpeas, CR values were correlated positively with the number of pods and seeds plant−1. The two crops in the intercrop systems were responsive to fertilizer application. Thus, improved management (i.e. fertilizer usage) was appropriate without the loss of the advantageous effects realized from intercropping.

Accumulation curves for N, P, K and Ca were determined for intercropped maize and cowpeas given different fertilizer combinations. Both species competed for these four elements, with cowpeas suffering relatively more than maize. A concept of a Nutrient Supplementation Index (NSI) was developed to aid studies on fertilization of crop mixtures. Using this index, it was estimated that an additional 9.7, 24.0, 9.7 and 30.6% of N, P, K and Ca, respectively (based on the requirement of sole-crop maize), might be needed to satisfy the combined needs of a 1:1 row maize–cowpea intercrop.