D. J. Greenwood

Shoot yield drives phosphorus use efficiency in Brassica oleracea and correlates with root architecture traits

The environmental and financial costs of using inorganic phosphate fertilizers to maintain crop yield and quality are high. Breeding crops that acquire and use phosphorus (P) more efficiently could reduce these costs. The variation in shoot P concentration (shoot-P) and various measures of P use efficiency (PUE) were quantified among 355 Brassica oleracea L. accessions, 74 current commercial cultivars, and 90 doubled haploid (DH) mapping lines from a reference genetic mapping population. Accessions were grown at two or more external P concentrations in glasshouse experiments; commercial and DH accessions were also grown in replicated field experiments. Within the substantial species-wide diversity observed for shoot-P and various measures of PUE in B. oleracea, current commercial cultivars have greater PUE than would be expected by chance. This may be a consequence of breeding for increased yield, which is a significant component of most measures of PUE, or early establishment. Root development and architecture correlate with PUE; in particular, lateral root number, length, and growth rate. Significant quantitative trait loci associated with shoot-P and PUE occur on chromosomes C3 and C7. These data provide information to initiate breeding programmes to improve PUE in B. oleracea.

The effect of oxygen concentration on the decomposition of organic materials in soil

Summary1. Techniques are described for relating the oxygen concentrations in the soil water on the surfaces of micro-organisms to their metabolizing activities.2. Studies were made on the decomposition of organic materials in water-saturated crumbs (mean radius 1.55 × 10−1 cm) of a loam soil.3. Respiration of water-saturated crumbs was not inhibited unless the oxygen concentration was less than about 10−6M. Evidence was obtained that above a similar low oxygen concentration there was no inhibition of respiration in soils of widely different type.4. Anaerobic decomposition of the soil organic matter was very slow. Anaerobic decomposition of casein digest was more rapid than that of any other material tested; the products were water soluble and included 83 µ-equivalents of volatile fatty acid per mg of α-amino-N decomposed.5. Casein digest percolation of soil crumbs under air resulted in the formation of micro-organisms that respired at 70 per cent of their maximum rate when the oxygen concentration was about 2.7 × 10−6M.6. No products of anaerobic casein digest decomposition could be detected on percolating casein digest through soil crumbs when 80 per cent of the soil contained no oxygen and the maximum concentration in any part of the soil was about 3 × 10−5M.7. The kinetics of oxygen uptake consequent on the decomposition of casein digest and of other simple organic compounds in soil crumbs were similar and were only slightly affected by reduction of oxygen partial pressure in the atmosphere from 15 to 1.7 cm of mercury.8. It is concluded that ‘change-over’ from aerobic to anaerobic metabolism of organic materials takes place in widely different soils at an oxygen concentration less than about 3 × 10−6M.

Root development of vegetable crops

SummaryMeasurements were made at intervals during the growth of seven different vegetable crops grown on the same soil to find how far root development and crop growth could be described by simply derived equations and to find how far the parameter values varied from crop to crop.For each crop K1 ln W+W, (where W is total plant dry weight, t ha−1 and K1 is equal to 1 t ha−1) was linearly related to time from emergence, as in past experiments.The derived equation % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaciiBaiaac6% gaieaacaWFmbGaa8xpaiaa-ngadaWgaaWcbaGaa8NAaaqabaGccqGH% RaWkcaWFIbWaaSbaaSqaaiaa-PgaaeqaaOGaciiBaiaac6gacaWFxb% acdiGaa4xlaiaa-1gacaWF0baaaa!43A9!

Response of potatoes to N fertilizer: Dynamic model

\ln L = c_j + b_j \ln W - mt

Response of potatoes to N fertilizer: Quantitative relations for components of growth

where L is total root length per unit area, t is time from emergence, cj and bj are coefficients that depend on the crop (j) and m is a coefficient having the same value for all crops, removed 89.4% of the total variance in ln L. The best fit was obtained with a value of m that implied that about 3% of the root carbon was mineralized each day.Generally the logarithm of root density declined linearly with increasing depth. Most of the variation between the gradients of these relations for the different crops was removed by a single regression against logarithm of total root length.The main discernible differences between species in their rooting patterns were that root length for a given top weight of legumes was about half that of non legumes, that the development of storage roots was associated with a less steep decline in root density with depth than for other crops and that onions were exceptional in that the depth to which their roots penetrated did not change appreciably during much of the growing season.A single linear relationship between root depth and top weight (r2=0.85) covered all non-leguminous crops except onions and another relationship (r2=0.80) covered the legumes.

Comparison of the effects of nitrogen fertilizer on the yield, nitrogen content and quality of 21 different vegetable and agricultural crops.

Quantitative relationships for growth rate and its dependence on plant nitrogen concentration are developed from the results of experiments on potatoes, cereals and vegetables. The relationships appear to be of general applicability and most coefficients in them are similar for widely different crops.

Opportunities for improving irrigation efficiency with quantitative models, soil water sensors and wireless technology

SummaryA simulation model is described to interpret N fertilizer experiments on potatoes. It calculates the total growth of dry matter, the N uptake, the partition of dry matter and of N between tuber and foliage and the distribution of inorganic N down the profile for each day during the growing season.The validity of the model was tested against measurements of these parameters made at approximately fortnightly intervals on plots that received N fertilizer and those that received none in 4 experiments on a sand, 4 on a sandy loam and 3 on a clay soil.Simulated values were in reasonably good agreement with the measured values in all experiments. Overall the sums of squares of the differences between the simulated and measured values of the %N in the total plant, and the total amount of inorganic N in the top metre of soil and the logarithms of the total weight of dry matter, tuber dry weight, N uptake in the entire plant and N uptake in the tubers were each less than 25% of the sum of squares of the measured values about the mean.Only 9 inputs were required for the model. It was found essential to take account of differences in spring and summer leaching but not of inter-site differences in mineralization rate.

Apparent recovery of fertilizer n by vegetable crops

BackgroundMean phosphorous:nitrogen (P:N) ratios and relationships of P:N ratios with the growth rate of organisms indicate a surprising similarity among and within microbial species, plants, and insect herbivores. To reveal the cellular mechanisms underling this similarity, the macromolecular composition of seven microorganisms and the effect of specific growth rate (SGR) on RNA:protein ratio, the number of ribosomes, and peptide elongation rate (PER) were analyzed under different conditions of exponential growth.ResultsIt was found that P:N ratios calculated from RNA and protein contents in these particular organisms were in the same range as the mean ratios reported for diverse organisms and had similar positive relationships with growth rate, consistent with the growth-rate hypothesis. The efficiency of protein synthesis in microorganisms is estimated as the number of active ribosomes required for the incorporation of one amino acid into the synthesized protein. This parameter is calculated as the SGR:PER ratio. Experimental and theoretical evidence indicated that the requirement of ribosomes for protein synthesis is proportional to the RNA:protein ratio. The constant of proportionality had the same values for all organisms, and was derived mechanistically from the characteristics of the protein-synthesis machinery of the cell (the number of nucleotides per ribosome, the average masses of nucleotides and amino acids, the fraction of ribosomal RNA in the total RNA, and the fraction of active ribosomes). Impairment of the growth conditions decreased the RNA:protein ratio and increased the overall efficiency of protein synthesis in the microorganisms.ConclusionOur results suggest that the decrease in RNA:protein and estimated P:N ratios with decrease in the growth rate of the microorganism is a consequence of an increased overall efficiency of protein synthesis in the cell resulting from activation of the general stress response and increased transcription of cellular maintenance genes at the expense of growth related genes. The strong link between P:N stoichiometry, RNA:protein ratio, ribosomal requirement for protein synthesis, and growth rate of microorganisms indicated by the study could be used to characterize the N and P economy of complex ecosystems such as soils and the oceans.